research papers on environmental impact

2019 Best Papers published in the Environmental Science journals of the Royal Society of Chemistry

In 2019, the Royal Society of Chemistry published 180, 196 and 293 papers in Environmental Science: Processes & Impacts , Environmental Science: Water Research & Technology , and Environmental Science: Nano , respectively. These papers covered a wide range of topics in environmental science, from biogeochemical cycling to water reuse to nanomaterial toxicity. And, yes, we also published papers on the topic of the environmental fate, behavior, and inactivation of viruses. 1–10 We are extremely grateful that so many authors have chosen our journals as outlets for publishing their research and are equally delighted at the high quality of the papers that we have had the privilege to publish.

Our Associate Editors, Editorial Boards, and Advisory Boards were enlisted to nominate and select the best papers from 2019. From this list, the three Editors-in-Chief selected an overall best paper from the entire Environmental Science portfolio. It is our pleasure to present the winners of the Best Papers in 2019 to you, our readers.

Overall Best Paper

In this paper, Johansson et al. examine sea spray aerosol as a potential transport vehicle for perfluoroalkyl carboxylic and sulfonic acids. The surfactant properties of these compounds are well known and, in fact, key to many of the technical applications for which they are used. The fact that these compounds are enriched at the air–water interface makes enrichment in sea spray aerosols seem reasonable. Johansson et al. systematically tested various perfluoroalkyl acids enrichment in aerosols under conditions relevant to sea spray formation, finding that longer chain lengths lead to higher aerosol enrichment factors. They augmented their experimental work with a global model, which further bolstered the conclusion that global transport of perfluoroalkyl acids by sea spray aerosol is and will continue to be an important process in determining the global distribution of these compounds.

Journal Best Papers

Environmental Science: Processes & Impacts

First Runner-up Best Paper: Yamakawa, Takami, Takeda, Kato, Kajii, Emerging investigator series: investigation of mercury emission sources using Hg isotopic compositions of atmospheric mercury at the Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS), Japan , Environ. Sci.: Processes Impacts , 2019, 21 , 809–818, DOI: 10.1039/C8EM00590G .

Second Runner-up Best Paper: Avery, Waring, DeCarlo, Seasonal variation in aerosol composition and concentration upon transport from the outdoor to indoor environment , Environ. Sci.: Processes Impacts , 2019, 21 , 528–547, DOI: 10.1039/C8EM00471D .

Best Review Article: Cousins, Ng, Wang, Scheringer, Why is high persistence alone a major cause of concern? Environ. Sci.: Processes Impacts , 2019, 21 , 781–792, DOI: 10.1039/C8EM00515J .

Environmental Science: Water Research & Technology

First Runner-up Best Paper: Yang, Lin, Tse, Dong, Yu, Hoffmann, Membrane-separated electrochemical latrine wastewater treatment , Environ. Sci.: Water Res. Technol. , 2019, 5 , 51–59, DOI: 10.1039/C8EW00698A .

Second Runner-up Best Paper: Genter, Marks, Clair-Caliot, Mugume, Johnston, Bain, Julian, Evaluation of the novel substrate RUG™ for the detection of Escherichia coli in water from temperate (Zurich, Switzerland) and tropical (Bushenyi, Uganda) field sites , Environ. Sci.: Water Res. Technol. , 2019, 5 , 1082–1091, DOI: 10.1039/C9EW00138G .

Best Review Article: Okoffo, O’Brien, O’Brien, Tscharke, Thomas, Wastewater treatment plants as a source of plastics in the environment: a review of occurrence, methods for identification, quantification and fate , Environ. Sci.: Water Res. Technol. , 2019, 5 , 1908–1931, DOI: 10.1039/C9EW00428A .

Environmental Science: Nano

First Runner-up Best Paper: Janković, Plata, Engineered nanomaterials in the context of global element cycles , Environ. Sci.: Nano , 2019, 6 , 2697–2711, DOI: 10.1039/C9EN00322C .

Second Runner-up Best Paper: González-Pleiter, Tamayo-Belda, Pulido-Reyes, Amariei, Leganés, Rosal, Fernández-Piñas, Secondary nanoplastics released from a biodegradable microplastic severely impact freshwater environments , Environ. Sci.: Nano , 2019, 6 , 1382–1392, DOI: 10.1039/C8EN01427B .

Best Review Article: Lv, Christie, Zhang, Uptake, translocation, and transformation of metal-based nanoparticles in plants: recent advances and methodological challenges , Environ. Sci.: Nano , 2019, 6 , 41–59, DOI: 10.1039/C8EN00645H .

Congratulations to the authors of these papers and a hearty thanks to all of our authors. As one can clearly see from the papers listed above, environmental science is a global effort and we are thrilled to have contributions from around the world. In these challenging times, we are proud to publish research that is not only great science, but also relevant to the health of the environment and the public. Finally, we also wish to extend our thanks to our community of editors, reviewers, and readers. We look forward to another outstanding year of Environmental Science , reading the work generated not just from our offices at home, but also from back in our laboratories and the field.

Kris McNeill, Editor-in-Chief

Paige Novak, Editor-in-Chief

Peter Vikesland, Editor-in-Chief

• A. B Boehm, Risk-based water quality thresholds for coliphages in surface waters: effect of temperature and contamination aging, Environ. Sci.: Processes Impacts , 2019, 21 , 2031–2041,   10.1039/C9EM00376B .
• L. Cai, C. Liu, G. Fan, C Liu and X. Sun, Preventing viral disease by ZnONPs through directly deactivating TMV and activating plant immunity in Nicotiana benthamiana , Environ. Sci.: Nano , 2019, 6 , 3653–3669,   10.1039/C9EN00850K .
• L. W. Gassie, J. D. Englehardt, N. E. Brinkman, J. Garland and M. K. Perera, Ozone-UV net-zero water wash station for remote emergency response healthcare units: design, operation, and results, Environ. Sci.: Water Res. Technol. , 2019, 5 , 1971–1984,   10.1039/C9EW00126C .
• L. M. Hornstra, T. Rodrigues da Silva, B. Blankert, L. Heijnen, E. Beerendonk, E. R. Cornelissen and G. Medema, Monitoring the integrity of reverse osmosis membranes using novel indigenous freshwater viruses and bacteriophages, Environ. Sci.: Water Res. Technol. , 2019, 5 , 1535–1544,   10.1039/C9EW00318E .
• A. H. Hassaballah, J. Nyitrai, C. H. Hart, N. Dai and L. M. Sassoubre, A pilot-scale study of peracetic acid and ultraviolet light for wastewater disinfection, Environ. Sci.: Water Res. Technol. , 2019, 5 , 1453–1463,   10.1039/C9EW00341J .
• W. Khan, J.-Y. Nam, H. Woo, H. Ryu, S. Kim, S. K. Maeng and H.-C. Kim, A proof of concept study for wastewater reuse using bioelectrochemical processes combined with complementary post-treatment technologies, Environ. Sci.: Water Res. Technol. , 2019, 5 , 1489–1498,   10.1039/C9EW00358D .
• J. Heffron, B. McDermid and B. K. Mayer, Bacteriophage inactivation as a function of ferrous iron oxidation, Environ. Sci.: Water Res. Technol. , 2019, 5 , 1309–1317,   10.1039/C9EW00190E .
• S. Torii, T. Hashimoto, A. T. Do, H. Furumai and H. Katayama, Impact of repeated pressurization on virus removal by reverse osmosis membranes for household water treatment, Environ. Sci.: Water Res. Technol. , 2019, 5 , 910–919,   10.1039/C8EW00944A .
• J. Miao, H.-J. Jiang, Z.-W. Yang, D.-y. Shi, D. Yang, Z.-Q. Shen, J. Yin, Z.-G. Qiu, H.-R. Wang, J.-W. Li and M. Jin, Assessment of an electropositive granule media filter for concentrating viruses from large volumes of coastal water, Environ. Sci.: Water Res. Technol. , 2019, 5 , 325–333,   10.1039/C8EW00699G .
• K. L. Nelson, A. B. Boehm, R. J. Davies-Colley, M. C. Dodd, T. Kohn, K. G. Linden, Y. Liu, P. A. Maraccini, K. McNeill, W. A. Mitch, T. H. Nguyen, K. M. Parker, R. A. Rodriguez, L. M. Sassoubre, A. I. Silverman, K. R. Wigginton and R. G. Zepp, Sunlight mediated inactivation of health relevant microorganisms in water: a review of mechanisms and modeling approaches, Environ. Sci.: Processes Impacts , 2018, 20 , 1089–1122,   10.1039/C8EM00047F .

REVIEW article

Environmental and health impacts of air pollution: a review.

• 1 Delphis S.A., Kifisia, Greece
• 2 Laboratory of Hygiene and Environmental Protection, Faculty of Medicine, Democritus University of Thrace, Alexandroupolis, Greece
• 3 Centre Hospitalier Universitaire Vaudois (CHUV), Service de Médicine Interne, Lausanne, Switzerland
• 4 School of Social and Political Sciences, University of Glasgow, Glasgow, United Kingdom

One of our era's greatest scourges is air pollution, on account not only of its impact on climate change but also its impact on public and individual health due to increasing morbidity and mortality. There are many pollutants that are major factors in disease in humans. Among them, Particulate Matter (PM), particles of variable but very small diameter, penetrate the respiratory system via inhalation, causing respiratory and cardiovascular diseases, reproductive and central nervous system dysfunctions, and cancer. Despite the fact that ozone in the stratosphere plays a protective role against ultraviolet irradiation, it is harmful when in high concentration at ground level, also affecting the respiratory and cardiovascular system. Furthermore, nitrogen oxide, sulfur dioxide, Volatile Organic Compounds (VOCs), dioxins, and polycyclic aromatic hydrocarbons (PAHs) are all considered air pollutants that are harmful to humans. Carbon monoxide can even provoke direct poisoning when breathed in at high levels. Heavy metals such as lead, when absorbed into the human body, can lead to direct poisoning or chronic intoxication, depending on exposure. Diseases occurring from the aforementioned substances include principally respiratory problems such as Chronic Obstructive Pulmonary Disease (COPD), asthma, bronchiolitis, and also lung cancer, cardiovascular events, central nervous system dysfunctions, and cutaneous diseases. Last but not least, climate change resulting from environmental pollution affects the geographical distribution of many infectious diseases, as do natural disasters. The only way to tackle this problem is through public awareness coupled with a multidisciplinary approach by scientific experts; national and international organizations must address the emergence of this threat and propose sustainable solutions.

Approach to the Problem

The interactions between humans and their physical surroundings have been extensively studied, as multiple human activities influence the environment. The environment is a coupling of the biotic (living organisms and microorganisms) and the abiotic (hydrosphere, lithosphere, and atmosphere).

Pollution is defined as the introduction into the environment of substances harmful to humans and other living organisms. Pollutants are harmful solids, liquids, or gases produced in higher than usual concentrations that reduce the quality of our environment.

Human activities have an adverse effect on the environment by polluting the water we drink, the air we breathe, and the soil in which plants grow. Although the industrial revolution was a great success in terms of technology, society, and the provision of multiple services, it also introduced the production of huge quantities of pollutants emitted into the air that are harmful to human health. Without any doubt, the global environmental pollution is considered an international public health issue with multiple facets. Social, economic, and legislative concerns and lifestyle habits are related to this major problem. Clearly, urbanization and industrialization are reaching unprecedented and upsetting proportions worldwide in our era. Anthropogenic air pollution is one of the biggest public health hazards worldwide, given that it accounts for about 9 million deaths per year ( 1 ).

Without a doubt, all of the aforementioned are closely associated with climate change, and in the event of danger, the consequences can be severe for mankind ( 2 ). Climate changes and the effects of global planetary warming seriously affect multiple ecosystems, causing problems such as food safety issues, ice and iceberg melting, animal extinction, and damage to plants ( 3 , 4 ).

Air pollution has various health effects. The health of susceptible and sensitive individuals can be impacted even on low air pollution days. Short-term exposure to air pollutants is closely related to COPD (Chronic Obstructive Pulmonary Disease), cough, shortness of breath, wheezing, asthma, respiratory disease, and high rates of hospitalization (a measurement of morbidity).

The long-term effects associated with air pollution are chronic asthma, pulmonary insufficiency, cardiovascular diseases, and cardiovascular mortality. According to a Swedish cohort study, diabetes seems to be induced after long-term air pollution exposure ( 5 ). Moreover, air pollution seems to have various malign health effects in early human life, such as respiratory, cardiovascular, mental, and perinatal disorders ( 3 ), leading to infant mortality or chronic disease in adult age ( 6 ).

National reports have mentioned the increased risk of morbidity and mortality ( 1 ). These studies were conducted in many places around the world and show a correlation between daily ranges of particulate matter (PM) concentration and daily mortality. Climate shifts and global planetary warming ( 3 ) could aggravate the situation. Besides, increased hospitalization (an index of morbidity) has been registered among the elderly and susceptible individuals for specific reasons. Fine and ultrafine particulate matter seems to be associated with more serious illnesses ( 6 ), as it can invade the deepest parts of the airways and more easily reach the bloodstream.

Air pollution mainly affects those living in large urban areas, where road emissions contribute the most to the degradation of air quality. There is also a danger of industrial accidents, where the spread of a toxic fog can be fatal to the populations of the surrounding areas. The dispersion of pollutants is determined by many parameters, most notably atmospheric stability and wind ( 6 ).

In developing countries ( 7 ), the problem is more serious due to overpopulation and uncontrolled urbanization along with the development of industrialization. This leads to poor air quality, especially in countries with social disparities and a lack of information on sustainable management of the environment. The use of fuels such as wood fuel or solid fuel for domestic needs due to low incomes exposes people to bad-quality, polluted air at home. It is of note that three billion people around the world are using the above sources of energy for their daily heating and cooking needs ( 8 ). In developing countries, the women of the household seem to carry the highest risk for disease development due to their longer duration exposure to the indoor air pollution ( 8 , 9 ). Due to its fast industrial development and overpopulation, China is one of the Asian countries confronting serious air pollution problems ( 10 , 11 ). The lung cancer mortality observed in China is associated with fine particles ( 12 ). As stated already, long-term exposure is associated with deleterious effects on the cardiovascular system ( 3 , 5 ). However, it is interesting to note that cardiovascular diseases have mostly been observed in developed and high-income countries rather than in the developing low-income countries exposed highly to air pollution ( 13 ). Extreme air pollution is recorded in India, where the air quality reaches hazardous levels. New Delhi is one of the more polluted cities in India. Flights in and out of New Delhi International Airport are often canceled due to the reduced visibility associated with air pollution. Pollution is occurring both in urban and rural areas in India due to the fast industrialization, urbanization, and rise in use of motorcycle transportation. Nevertheless, biomass combustion associated with heating and cooking needs and practices is a major source of household air pollution in India and in Nepal ( 14 , 15 ). There is spatial heterogeneity in India, as areas with diverse climatological conditions and population and education levels generate different indoor air qualities, with higher PM 2.5 observed in North Indian states (557–601 μg/m 3 ) compared to the Southern States (183–214 μg/m 3 ) ( 16 , 17 ). The cold climate of the North Indian areas may be the main reason for this, as longer periods at home and more heating are necessary compared to in the tropical climate of Southern India. Household air pollution in India is associated with major health effects, especially in women and young children, who stay indoors for longer periods. Chronic obstructive respiratory disease (CORD) and lung cancer are mostly observed in women, while acute lower respiratory disease is seen in young children under 5 years of age ( 18 ).

Accumulation of air pollution, especially sulfur dioxide and smoke, reaching 1,500 mg/m3, resulted in an increase in the number of deaths (4,000 deaths) in December 1952 in London and in 1963 in New York City (400 deaths) ( 19 ). An association of pollution with mortality was reported on the basis of monitoring of outdoor pollution in six US metropolitan cities ( 20 ). In every case, it seems that mortality was closely related to the levels of fine, inhalable, and sulfate particles more than with the levels of total particulate pollution, aerosol acidity, sulfur dioxide, or nitrogen dioxide ( 20 ).

Furthermore, extremely high levels of pollution are reported in Mexico City and Rio de Janeiro, followed by Milan, Ankara, Melbourne, Tokyo, and Moscow ( 19 ).

Based on the magnitude of the public health impact, it is certain that different kinds of interventions should be taken into account. Success and effectiveness in controlling air pollution, specifically at the local level, have been reported. Adequate technological means are applied considering the source and the nature of the emission as well as its impact on health and the environment. The importance of point sources and non-point sources of air pollution control is reported by Schwela and Köth-Jahr ( 21 ). Without a doubt, a detailed emission inventory must record all sources in a given area. Beyond considering the above sources and their nature, topography and meteorology should also be considered, as stated previously. Assessment of the control policies and methods is often extrapolated from the local to the regional and then to the global scale. Air pollution may be dispersed and transported from one region to another area located far away. Air pollution management means the reduction to acceptable levels or possible elimination of air pollutants whose presence in the air affects our health or the environmental ecosystem. Private and governmental entities and authorities implement actions to ensure the air quality ( 22 ). Air quality standards and guidelines were adopted for the different pollutants by the WHO and EPA as a tool for the management of air quality ( 1 , 23 ). These standards have to be compared to the emissions inventory standards by causal analysis and dispersion modeling in order to reveal the problematic areas ( 24 ). Inventories are generally based on a combination of direct measurements and emissions modeling ( 24 ).

As an example, we state here the control measures at the source through the use of catalytic converters in cars. These are devices that turn the pollutants and toxic gases produced from combustion engines into less-toxic pollutants by catalysis through redox reactions ( 25 ). In Greece, the use of private cars was restricted by tracking their license plates in order to reduce traffic congestion during rush hour ( 25 ).

Concerning industrial emissions, collectors and closed systems can keep the air pollution to the minimal standards imposed by legislation ( 26 ).

Current strategies to improve air quality require an estimation of the economic value of the benefits gained from proposed programs. These proposed programs by public authorities, and directives are issued with guidelines to be respected.

In Europe, air quality limit values AQLVs (Air Quality Limit Values) are issued for setting off planning claims ( 27 ). In the USA, the NAAQS (National Ambient Air Quality Standards) establish the national air quality limit values ( 27 ). While both standards and directives are based on different mechanisms, significant success has been achieved in the reduction of overall emissions and associated health and environmental effects ( 27 ). The European Directive identifies geographical areas of risk exposure as monitoring/assessment zones to record the emission sources and levels of air pollution ( 27 ), whereas the USA establishes global geographical air quality criteria according to the severity of their air quality problem and records all sources of the pollutants and their precursors ( 27 ).

In this vein, funds have been financing, directly or indirectly, projects related to air quality along with the technical infrastructure to maintain good air quality. These plans focus on an inventory of databases from air quality environmental planning awareness campaigns. Moreover, pollution measures of air emissions may be taken for vehicles, machines, and industries in urban areas.

Technological innovation can only be successful if it is able to meet the needs of society. In this sense, technology must reflect the decision-making practices and procedures of those involved in risk assessment and evaluation and act as a facilitator in providing information and assessments to enable decision makers to make the best decisions possible. Summarizing the aforementioned in order to design an effective air quality control strategy, several aspects must be considered: environmental factors and ambient air quality conditions, engineering factors and air pollutant characteristics, and finally, economic operating costs for technological improvement and administrative and legal costs. Considering the economic factor, competitiveness through neoliberal concepts is offering a solution to environmental problems ( 22 ).

The development of environmental governance, along with technological progress, has initiated the deployment of a dialogue. Environmental politics has created objections and points of opposition between different political parties, scientists, media, and governmental and non-governmental organizations ( 22 ). Radical environmental activism actions and movements have been created ( 22 ). The rise of the new information and communication technologies (ICTs) are many times examined as to whether and in which way they have influenced means of communication and social movements such as activism ( 28 ). Since the 1990s, the term “digital activism” has been used increasingly and in many different disciplines ( 29 ). Nowadays, multiple digital technologies can be used to produce a digital activism outcome on environmental issues. More specifically, devices with online capabilities such as computers or mobile phones are being used as a way to pursue change in political and social affairs ( 30 ).

In the present paper, we focus on the sources of environmental pollution in relation to public health and propose some solutions and interventions that may be of interest to environmental legislators and decision makers.

Sources of Exposure

It is known that the majority of environmental pollutants are emitted through large-scale human activities such as the use of industrial machinery, power-producing stations, combustion engines, and cars. Because these activities are performed at such a large scale, they are by far the major contributors to air pollution, with cars estimated to be responsible for approximately 80% of today's pollution ( 31 ). Some other human activities are also influencing our environment to a lesser extent, such as field cultivation techniques, gas stations, fuel tanks heaters, and cleaning procedures ( 32 ), as well as several natural sources, such as volcanic and soil eruptions and forest fires.

The classification of air pollutants is based mainly on the sources producing pollution. Therefore, it is worth mentioning the four main sources, following the classification system: Major sources, Area sources, Mobile sources, and Natural sources.

Major sources include the emission of pollutants from power stations, refineries, and petrochemicals, the chemical and fertilizer industries, metallurgical and other industrial plants, and, finally, municipal incineration.

Indoor area sources include domestic cleaning activities, dry cleaners, printing shops, and petrol stations.

Mobile sources include automobiles, cars, railways, airways, and other types of vehicles.

Finally, natural sources include, as stated previously, physical disasters ( 33 ) such as forest fire, volcanic erosion, dust storms, and agricultural burning.

However, many classification systems have been proposed. Another type of classification is a grouping according to the recipient of the pollution, as follows:

Air pollution is determined as the presence of pollutants in the air in large quantities for long periods. Air pollutants are dispersed particles, hydrocarbons, CO, CO 2 , NO, NO 2 , SO 3 , etc.

Water pollution is organic and inorganic charge and biological charge ( 10 ) at high levels that affect the water quality ( 34 , 35 ).

Soil pollution occurs through the release of chemicals or the disposal of wastes, such as heavy metals, hydrocarbons, and pesticides.

Air pollution can influence the quality of soil and water bodies by polluting precipitation, falling into water and soil environments ( 34 , 36 ). Notably, the chemistry of the soil can be amended due to acid precipitation by affecting plants, cultures, and water quality ( 37 ). Moreover, movement of heavy metals is favored by soil acidity, and metals are so then moving into the watery environment. It is known that heavy metals such as aluminum are noxious to wildlife and fishes. Soil quality seems to be of importance, as soils with low calcium carbonate levels are at increased jeopardy from acid rain. Over and above rain, snow and particulate matter drip into watery ' bodies ( 36 , 38 ).

Lastly, pollution is classified following type of origin:

Radioactive and nuclear pollution , releasing radioactive and nuclear pollutants into water, air, and soil during nuclear explosions and accidents, from nuclear weapons, and through handling or disposal of radioactive sewage.

Radioactive materials can contaminate surface water bodies and, being noxious to the environment, plants, animals, and humans. It is known that several radioactive substances such as radium and uranium concentrate in the bones and can cause cancers ( 38 , 39 ).

Noise pollution is produced by machines, vehicles, traffic noises, and musical installations that are harmful to our hearing.

The World Health Organization introduced the term DALYs. The DALYs for a disease or health condition is defined as the sum of the Years of Life Lost (YLL) due to premature mortality in the population and the Years Lost due to Disability (YLD) for people living with the health condition or its consequences ( 39 ). In Europe, air pollution is the main cause of disability-adjusted life years lost (DALYs), followed by noise pollution. The potential relationships of noise and air pollution with health have been studied ( 40 ). The study found that DALYs related to noise were more important than those related to air pollution, as the effects of environmental noise on cardiovascular disease were independent of air pollution ( 40 ). Environmental noise should be counted as an independent public health risk ( 40 ).

Environmental pollution occurs when changes in the physical, chemical, or biological constituents of the environment (air masses, temperature, climate, etc.) are produced.

Pollutants harm our environment either by increasing levels above normal or by introducing harmful toxic substances. Primary pollutants are directly produced from the above sources, and secondary pollutants are emitted as by-products of the primary ones. Pollutants can be biodegradable or non-biodegradable and of natural origin or anthropogenic, as stated previously. Moreover, their origin can be a unique source (point-source) or dispersed sources.

Pollutants have differences in physical and chemical properties, explaining the discrepancy in their capacity for producing toxic effects. As an example, we state here that aerosol compounds ( 41 – 43 ) have a greater toxicity than gaseous compounds due to their tiny size (solid or liquid) in the atmosphere; they have a greater penetration capacity. Gaseous compounds are eliminated more easily by our respiratory system ( 41 ). These particles are able to damage lungs and can even enter the bloodstream ( 41 ), leading to the premature deaths of millions of people yearly. Moreover, the aerosol acidity ([H+]) seems to considerably enhance the production of secondary organic aerosols (SOA), but this last aspect is not supported by other scientific teams ( 38 ).

Climate and Pollution

Air pollution and climate change are closely related. Climate is the other side of the same coin that reduces the quality of our Earth ( 44 ). Pollutants such as black carbon, methane, tropospheric ozone, and aerosols affect the amount of incoming sunlight. As a result, the temperature of the Earth is increasing, resulting in the melting of ice, icebergs, and glaciers.

In this vein, climatic changes will affect the incidence and prevalence of both residual and imported infections in Europe. Climate and weather affect the duration, timing, and intensity of outbreaks strongly and change the map of infectious diseases in the globe ( 45 ). Mosquito-transmitted parasitic or viral diseases are extremely climate-sensitive, as warming firstly shortens the pathogen incubation period and secondly shifts the geographic map of the vector. Similarly, water-warming following climate changes leads to a high incidence of waterborne infections. Recently, in Europe, eradicated diseases seem to be emerging due to the migration of population, for example, cholera, poliomyelitis, tick-borne encephalitis, and malaria ( 46 ).

The spread of epidemics is associated with natural climate disasters and storms, which seem to occur more frequently nowadays ( 47 ). Malnutrition and disequilibration of the immune system are also associated with the emerging infections affecting public health ( 48 ).

The Chikungunya virus “took the airplane” from the Indian Ocean to Europe, as outbreaks of the disease were registered in Italy ( 49 ) as well as autochthonous cases in France ( 50 ).

An increase in cryptosporidiosis in the United Kingdom and in the Czech Republic seems to have occurred following flooding ( 36 , 51 ).

As stated previously, aerosols compounds are tiny in size and considerably affect the climate. They are able to dissipate sunlight (the albedo phenomenon) by dispersing a quarter of the sun's rays back to space and have cooled the global temperature over the last 30 years ( 52 ).

Air Pollutants

The World Health Organization (WHO) reports on six major air pollutants, namely particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. Air pollution can have a disastrous effect on all components of the environment, including groundwater, soil, and air. Additionally, it poses a serious threat to living organisms. In this vein, our interest is mainly to focus on these pollutants, as they are related to more extensive and severe problems in human health and environmental impact. Acid rain, global warming, the greenhouse effect, and climate changes have an important ecological impact on air pollution ( 53 ).

Particulate Matter (PM) and Health

Studies have shown a relationship between particulate matter (PM) and adverse health effects, focusing on either short-term (acute) or long-term (chronic) PM exposure.

Particulate matter (PM) is usually formed in the atmosphere as a result of chemical reactions between the different pollutants. The penetration of particles is closely dependent on their size ( 53 ). Particulate Matter (PM) was defined as a term for particles by the United States Environmental Protection Agency ( 54 ). Particulate matter (PM) pollution includes particles with diameters of 10 micrometers (μm) or smaller, called PM 10 , and extremely fine particles with diameters that are generally 2.5 micrometers (μm) and smaller.

Particulate matter contains tiny liquid or solid droplets that can be inhaled and cause serious health effects ( 55 ). Particles <10 μm in diameter (PM 10 ) after inhalation can invade the lungs and even reach the bloodstream. Fine particles, PM 2.5 , pose a greater risk to health ( 6 , 56 ) ( Table 1 ).

Table 1 . Penetrability according to particle size.

Multiple epidemiological studies have been performed on the health effects of PM. A positive relation was shown between both short-term and long-term exposures of PM 2.5 and acute nasopharyngitis ( 56 ). In addition, long-term exposure to PM for years was found to be related to cardiovascular diseases and infant mortality.

Those studies depend on PM 2.5 monitors and are restricted in terms of study area or city area due to a lack of spatially resolved daily PM 2.5 concentration data and, in this way, are not representative of the entire population. Following a recent epidemiological study by the Department of Environmental Health at Harvard School of Public Health (Boston, MA) ( 57 ), it was reported that, as PM 2.5 concentrations vary spatially, an exposure error (Berkson error) seems to be produced, and the relative magnitudes of the short- and long-term effects are not yet completely elucidated. The team developed a PM 2.5 exposure model based on remote sensing data for assessing short- and long-term human exposures ( 57 ). This model permits spatial resolution in short-term effects plus the assessment of long-term effects in the whole population.

Moreover, respiratory diseases and affection of the immune system are registered as long-term chronic effects ( 58 ). It is worth noting that people with asthma, pneumonia, diabetes, and respiratory and cardiovascular diseases are especially susceptible and vulnerable to the effects of PM. PM 2.5 , followed by PM 10 , are strongly associated with diverse respiratory system diseases ( 59 ), as their size permits them to pierce interior spaces ( 60 ). The particles produce toxic effects according to their chemical and physical properties. The components of PM 10 and PM 2.5 can be organic (polycyclic aromatic hydrocarbons, dioxins, benzene, 1-3 butadiene) or inorganic (carbon, chlorides, nitrates, sulfates, metals) in nature ( 55 ).

Particulate Matter (PM) is divided into four main categories according to type and size ( 61 ) ( Table 2 ).

Table 2 . Types and sizes of particulate Matter (PM).

Gas contaminants include PM in aerial masses.

Particulate contaminants include contaminants such as smog, soot, tobacco smoke, oil smoke, fly ash, and cement dust.

Biological Contaminants are microorganisms (bacteria, viruses, fungi, mold, and bacterial spores), cat allergens, house dust and allergens, and pollen.

Types of Dust include suspended atmospheric dust, settling dust, and heavy dust.

Finally, another fact is that the half-lives of PM 10 and PM 2.5 particles in the atmosphere is extended due to their tiny dimensions; this permits their long-lasting suspension in the atmosphere and even their transfer and spread to distant destinations where people and the environment may be exposed to the same magnitude of pollution ( 53 ). They are able to change the nutrient balance in watery ecosystems, damage forests and crops, and acidify water bodies.

As stated, PM 2.5 , due to their tiny size, are causing more serious health effects. These aforementioned fine particles are the main cause of the “haze” formation in different metropolitan areas ( 12 , 13 , 61 ).

Ozone Impact in the Atmosphere

Ozone (O 3 ) is a gas formed from oxygen under high voltage electric discharge ( 62 ). It is a strong oxidant, 52% stronger than chlorine. It arises in the stratosphere, but it could also arise following chain reactions of photochemical smog in the troposphere ( 63 ).

Ozone can travel to distant areas from its initial source, moving with air masses ( 64 ). It is surprising that ozone levels over cities are low in contrast to the increased amounts occuring in urban areas, which could become harmful for cultures, forests, and vegetation ( 65 ) as it is reducing carbon assimilation ( 66 ). Ozone reduces growth and yield ( 47 , 48 ) and affects the plant microflora due to its antimicrobial capacity ( 67 , 68 ). In this regard, ozone acts upon other natural ecosystems, with microflora ( 69 , 70 ) and animal species changing their species composition ( 71 ). Ozone increases DNA damage in epidermal keratinocytes and leads to impaired cellular function ( 72 ).

Ground-level ozone (GLO) is generated through a chemical reaction between oxides of nitrogen and VOCs emitted from natural sources and/or following anthropogenic activities.

Ozone uptake usually occurs by inhalation. Ozone affects the upper layers of the skin and the tear ducts ( 73 ). A study of short-term exposure of mice to high levels of ozone showed malondialdehyde formation in the upper skin (epidermis) but also depletion in vitamins C and E. It is likely that ozone levels are not interfering with the skin barrier function and integrity to predispose to skin disease ( 74 ).

Due to the low water-solubility of ozone, inhaled ozone has the capacity to penetrate deeply into the lungs ( 75 ).

Toxic effects induced by ozone are registered in urban areas all over the world, causing biochemical, morphologic, functional, and immunological disorders ( 76 ).

The European project (APHEA2) focuses on the acute effects of ambient ozone concentrations on mortality ( 77 ). Daily ozone concentrations compared to the daily number of deaths were reported from different European cities for a 3-year period. During the warm period of the year, an observed increase in ozone concentration was associated with an increase in the daily number of deaths (0.33%), in the number of respiratory deaths (1.13%), and in the number of cardiovascular deaths (0.45%). No effect was observed during wintertime.

Carbon Monoxide (CO)

Carbon monoxide is produced by fossil fuel when combustion is incomplete. The symptoms of poisoning due to inhaling carbon monoxide include headache, dizziness, weakness, nausea, vomiting, and, finally, loss of consciousness.

The affinity of carbon monoxide to hemoglobin is much greater than that of oxygen. In this vein, serious poisoning may occur in people exposed to high levels of carbon monoxide for a long period of time. Due to the loss of oxygen as a result of the competitive binding of carbon monoxide, hypoxia, ischemia, and cardiovascular disease are observed.

Carbon monoxide affects the greenhouses gases that are tightly connected to global warming and climate. This should lead to an increase in soil and water temperatures, and extreme weather conditions or storms may occur ( 68 ).

However, in laboratory and field experiments, it has been seen to produce increased plant growth ( 78 ).

Nitrogen Oxide (NO 2 )

Nitrogen oxide is a traffic-related pollutant, as it is emitted from automobile motor engines ( 79 , 80 ). It is an irritant of the respiratory system as it penetrates deep in the lung, inducing respiratory diseases, coughing, wheezing, dyspnea, bronchospasm, and even pulmonary edema when inhaled at high levels. It seems that concentrations over 0.2 ppm produce these adverse effects in humans, while concentrations higher than 2.0 ppm affect T-lymphocytes, particularly the CD8+ cells and NK cells that produce our immune response ( 81 ).It is reported that long-term exposure to high levels of nitrogen dioxide can be responsible for chronic lung disease. Long-term exposure to NO 2 can impair the sense of smell ( 81 ).

However, systems other than respiratory ones can be involved, as symptoms such as eye, throat, and nose irritation have been registered ( 81 ).

High levels of nitrogen dioxide are deleterious to crops and vegetation, as they have been observed to reduce crop yield and plant growth efficiency. Moreover, NO 2 can reduce visibility and discolor fabrics ( 81 ).

Sulfur Dioxide (SO 2 )

Sulfur dioxide is a harmful gas that is emitted mainly from fossil fuel consumption or industrial activities. The annual standard for SO 2 is 0.03 ppm ( 82 ). It affects human, animal, and plant life. Susceptible people as those with lung disease, old people, and children, who present a higher risk of damage. The major health problems associated with sulfur dioxide emissions in industrialized areas are respiratory irritation, bronchitis, mucus production, and bronchospasm, as it is a sensory irritant and penetrates deep into the lung converted into bisulfite and interacting with sensory receptors, causing bronchoconstriction. Moreover, skin redness, damage to the eyes (lacrimation and corneal opacity) and mucous membranes, and worsening of pre-existing cardiovascular disease have been observed ( 81 ).

Environmental adverse effects, such as acidification of soil and acid rain, seem to be associated with sulfur dioxide emissions ( 83 ).

Lead is a heavy metal used in different industrial plants and emitted from some petrol motor engines, batteries, radiators, waste incinerators, and waste waters ( 84 ).

Moreover, major sources of lead pollution in the air are metals, ore, and piston-engine aircraft. Lead poisoning is a threat to public health due to its deleterious effects upon humans, animals, and the environment, especially in the developing countries.

Exposure to lead can occur through inhalation, ingestion, and dermal absorption. Trans- placental transport of lead was also reported, as lead passes through the placenta unencumbered ( 85 ). The younger the fetus is, the more harmful the toxic effects. Lead toxicity affects the fetal nervous system; edema or swelling of the brain is observed ( 86 ). Lead, when inhaled, accumulates in the blood, soft tissue, liver, lung, bones, and cardiovascular, nervous, and reproductive systems. Moreover, loss of concentration and memory, as well as muscle and joint pain, were observed in adults ( 85 , 86 ).

Children and newborns ( 87 ) are extremely susceptible even to minimal doses of lead, as it is a neurotoxicant and causes learning disabilities, impairment of memory, hyperactivity, and even mental retardation.

Elevated amounts of lead in the environment are harmful to plants and crop growth. Neurological effects are observed in vertebrates and animals in association with high lead levels ( 88 ).

Polycyclic Aromatic Hydrocarbons(PAHs)

The distribution of PAHs is ubiquitous in the environment, as the atmosphere is the most important means of their dispersal. They are found in coal and in tar sediments. Moreover, they are generated through incomplete combustion of organic matter as in the cases of forest fires, incineration, and engines ( 89 ). PAH compounds, such as benzopyrene, acenaphthylene, anthracene, and fluoranthene are recognized as toxic, mutagenic, and carcinogenic substances. They are an important risk factor for lung cancer ( 89 ).

Volatile Organic Compounds(VOCs)

Volatile organic compounds (VOCs), such as toluene, benzene, ethylbenzene, and xylene ( 90 ), have been found to be associated with cancer in humans ( 91 ). The use of new products and materials has actually resulted in increased concentrations of VOCs. VOCs pollute indoor air ( 90 ) and may have adverse effects on human health ( 91 ). Short-term and long-term adverse effects on human health are observed. VOCs are responsible for indoor air smells. Short-term exposure is found to cause irritation of eyes, nose, throat, and mucosal membranes, while those of long duration exposure include toxic reactions ( 92 ). Predictable assessment of the toxic effects of complex VOC mixtures is difficult to estimate, as these pollutants can have synergic, antagonistic, or indifferent effects ( 91 , 93 ).

Dioxins originate from industrial processes but also come from natural processes, such as forest fires and volcanic eruptions. They accumulate in foods such as meat and dairy products, fish and shellfish, and especially in the fatty tissue of animals ( 94 ).

Short-period exhibition to high dioxin concentrations may result in dark spots and lesions on the skin ( 94 ). Long-term exposure to dioxins can cause developmental problems, impairment of the immune, endocrine and nervous systems, reproductive infertility, and cancer ( 94 ).

Without any doubt, fossil fuel consumption is responsible for a sizeable part of air contamination. This contamination may be anthropogenic, as in agricultural and industrial processes or transportation, while contamination from natural sources is also possible. Interestingly, it is of note that the air quality standards established through the European Air Quality Directive are somewhat looser than the WHO guidelines, which are stricter ( 95 ).

Effect of Air Pollution on Health

The most common air pollutants are ground-level ozone and Particulates Matter (PM). Air pollution is distinguished into two main types:

Outdoor pollution is the ambient air pollution.

Indoor pollution is the pollution generated by household combustion of fuels.

People exposed to high concentrations of air pollutants experience disease symptoms and states of greater and lesser seriousness. These effects are grouped into short- and long-term effects affecting health.

Susceptible populations that need to be aware of health protection measures include old people, children, and people with diabetes and predisposing heart or lung disease, especially asthma.

As extensively stated previously, according to a recent epidemiological study from Harvard School of Public Health, the relative magnitudes of the short- and long-term effects have not been completely clarified ( 57 ) due to the different epidemiological methodologies and to the exposure errors. New models are proposed for assessing short- and long-term human exposure data more successfully ( 57 ). Thus, in the present section, we report the more common short- and long-term health effects but also general concerns for both types of effects, as these effects are often dependent on environmental conditions, dose, and individual susceptibility.

Short-term effects are temporary and range from simple discomfort, such as irritation of the eyes, nose, skin, throat, wheezing, coughing and chest tightness, and breathing difficulties, to more serious states, such as asthma, pneumonia, bronchitis, and lung and heart problems. Short-term exposure to air pollution can also cause headaches, nausea, and dizziness.

These problems can be aggravated by extended long-term exposure to the pollutants, which is harmful to the neurological, reproductive, and respiratory systems and causes cancer and even, rarely, deaths.

The long-term effects are chronic, lasting for years or the whole life and can even lead to death. Furthermore, the toxicity of several air pollutants may also induce a variety of cancers in the long term ( 96 ).

As stated already, respiratory disorders are closely associated with the inhalation of air pollutants. These pollutants will invade through the airways and will accumulate at the cells. Damage to target cells should be related to the pollutant component involved and its source and dose. Health effects are also closely dependent on country, area, season, and time. An extended exposure duration to the pollutant should incline to long-term health effects in relation also to the above factors.

Particulate Matter (PMs), dust, benzene, and O 3 cause serious damage to the respiratory system ( 97 ). Moreover, there is a supplementary risk in case of existing respiratory disease such as asthma ( 98 ). Long-term effects are more frequent in people with a predisposing disease state. When the trachea is contaminated by pollutants, voice alterations may be remarked after acute exposure. Chronic obstructive pulmonary disease (COPD) may be induced following air pollution, increasing morbidity and mortality ( 99 ). Long-term effects from traffic, industrial air pollution, and combustion of fuels are the major factors for COPD risk ( 99 ).

Multiple cardiovascular effects have been observed after exposure to air pollutants ( 100 ). Changes occurred in blood cells after long-term exposure may affect cardiac functionality. Coronary arteriosclerosis was reported following long-term exposure to traffic emissions ( 101 ), while short-term exposure is related to hypertension, stroke, myocardial infracts, and heart insufficiency. Ventricle hypertrophy is reported to occur in humans after long-time exposure to nitrogen oxide (NO 2 ) ( 102 , 103 ).

Neurological effects have been observed in adults and children after extended-term exposure to air pollutants.

Psychological complications, autism, retinopathy, fetal growth, and low birth weight seem to be related to long-term air pollution ( 83 ). The etiologic agent of the neurodegenerative diseases (Alzheimer's and Parkinson's) is not yet known, although it is believed that extended exposure to air pollution seems to be a factor. Specifically, pesticides and metals are cited as etiological factors, together with diet. The mechanisms in the development of neurodegenerative disease include oxidative stress, protein aggregation, inflammation, and mitochondrial impairment in neurons ( 104 ) ( Figure 1 ).

Figure 1 . Impact of air pollutants on the brain.

Brain inflammation was observed in dogs living in a highly polluted area in Mexico for a long period ( 105 ). In human adults, markers of systemic inflammation (IL-6 and fibrinogen) were found to be increased as an immediate response to PNC on the IL-6 level, possibly leading to the production of acute-phase proteins ( 106 ). The progression of atherosclerosis and oxidative stress seem to be the mechanisms involved in the neurological disturbances caused by long-term air pollution. Inflammation comes secondary to the oxidative stress and seems to be involved in the impairment of developmental maturation, affecting multiple organs ( 105 , 107 ). Similarly, other factors seem to be involved in the developmental maturation, which define the vulnerability to long-term air pollution. These include birthweight, maternal smoking, genetic background and socioeconomic environment, as well as education level.

However, diet, starting from breast-feeding, is another determinant factor. Diet is the main source of antioxidants, which play a key role in our protection against air pollutants ( 108 ). Antioxidants are free radical scavengers and limit the interaction of free radicals in the brain ( 108 ). Similarly, genetic background may result in a differential susceptibility toward the oxidative stress pathway ( 60 ). For example, antioxidant supplementation with vitamins C and E appears to modulate the effect of ozone in asthmatic children homozygous for the GSTM1 null allele ( 61 ). Inflammatory cytokines released in the periphery (e.g., respiratory epithelia) upregulate the innate immune Toll-like receptor 2. Such activation and the subsequent events leading to neurodegeneration have recently been observed in lung lavage in mice exposed to ambient Los Angeles (CA, USA) particulate matter ( 61 ). In children, neurodevelopmental morbidities were observed after lead exposure. These children developed aggressive and delinquent behavior, reduced intelligence, learning difficulties, and hyperactivity ( 109 ). No level of lead exposure seems to be “safe,” and the scientific community has asked the Centers for Disease Control and Prevention (CDC) to reduce the current screening guideline of 10 μg/dl ( 109 ).

It is important to state that impact on the immune system, causing dysfunction and neuroinflammation ( 104 ), is related to poor air quality. Yet, increases in serum levels of immunoglobulins (IgA, IgM) and the complement component C3 are observed ( 106 ). Another issue is that antigen presentation is affected by air pollutants, as there is an upregulation of costimulatory molecules such as CD80 and CD86 on macrophages ( 110 ).

As is known, skin is our shield against ultraviolet radiation (UVR) and other pollutants, as it is the most exterior layer of our body. Traffic-related pollutants, such as PAHs, VOCs, oxides, and PM, may cause pigmented spots on our skin ( 111 ). On the one hand, as already stated, when pollutants penetrate through the skin or are inhaled, damage to the organs is observed, as some of these pollutants are mutagenic and carcinogenic, and, specifically, they affect the liver and lung. On the other hand, air pollutants (and those in the troposphere) reduce the adverse effects of ultraviolet radiation UVR in polluted urban areas ( 111 ). Air pollutants absorbed by the human skin may contribute to skin aging, psoriasis, acne, urticaria, eczema, and atopic dermatitis ( 111 ), usually caused by exposure to oxides and photochemical smoke ( 111 ). Exposure to PM and cigarette smoking act as skin-aging agents, causing spots, dyschromia, and wrinkles. Lastly, pollutants have been associated with skin cancer ( 111 ).

Higher morbidity is reported to fetuses and children when exposed to the above dangers. Impairment in fetal growth, low birth weight, and autism have been reported ( 112 ).

Another exterior organ that may be affected is the eye. Contamination usually comes from suspended pollutants and may result in asymptomatic eye outcomes, irritation ( 112 ), retinopathy, or dry eye syndrome ( 113 , 114 ).

Environmental Impact of Air Pollution

Air pollution is harming not only human health but also the environment ( 115 ) in which we live. The most important environmental effects are as follows.

Acid rain is wet (rain, fog, snow) or dry (particulates and gas) precipitation containing toxic amounts of nitric and sulfuric acids. They are able to acidify the water and soil environments, damage trees and plantations, and even damage buildings and outdoor sculptures, constructions, and statues.

Haze is produced when fine particles are dispersed in the air and reduce the transparency of the atmosphere. It is caused by gas emissions in the air coming from industrial facilities, power plants, automobiles, and trucks.

Ozone , as discussed previously, occurs both at ground level and in the upper level (stratosphere) of the Earth's atmosphere. Stratospheric ozone is protecting us from the Sun's harmful ultraviolet (UV) rays. In contrast, ground-level ozone is harmful to human health and is a pollutant. Unfortunately, stratospheric ozone is gradually damaged by ozone-depleting substances (i.e., chemicals, pesticides, and aerosols). If this protecting stratospheric ozone layer is thinned, then UV radiation can reach our Earth, with harmful effects for human life (skin cancer) ( 116 ) and crops ( 117 ). In plants, ozone penetrates through the stomata, inducing them to close, which blocks CO 2 transfer and induces a reduction in photosynthesis ( 118 ).

Global climate change is an important issue that concerns mankind. As is known, the “greenhouse effect” keeps the Earth's temperature stable. Unhappily, anthropogenic activities have destroyed this protecting temperature effect by producing large amounts of greenhouse gases, and global warming is mounting, with harmful effects on human health, animals, forests, wildlife, agriculture, and the water environment. A report states that global warming is adding to the health risks of poor people ( 119 ).

People living in poorly constructed buildings in warm-climate countries are at high risk for heat-related health problems as temperatures mount ( 119 ).

Wildlife is burdened by toxic pollutants coming from the air, soil, or the water ecosystem and, in this way, animals can develop health problems when exposed to high levels of pollutants. Reproductive failure and birth effects have been reported.

Eutrophication is occurring when elevated concentrations of nutrients (especially nitrogen) stimulate the blooming of aquatic algae, which can cause a disequilibration in the diversity of fish and their deaths.

Without a doubt, there is a critical concentration of pollution that an ecosystem can tolerate without being destroyed, which is associated with the ecosystem's capacity to neutralize acidity. The Canada Acid Rain Program established this load at 20 kg/ha/yr ( 120 ).

Hence, air pollution has deleterious effects on both soil and water ( 121 ). Concerning PM as an air pollutant, its impact on crop yield and food productivity has been reported. Its impact on watery bodies is associated with the survival of living organisms and fishes and their productivity potential ( 121 ).

An impairment in photosynthetic rhythm and metabolism is observed in plants exposed to the effects of ozone ( 121 ).

Sulfur and nitrogen oxides are involved in the formation of acid rain and are harmful to plants and marine organisms.

Last but not least, as mentioned above, the toxicity associated with lead and other metals is the main threat to our ecosystems (air, water, and soil) and living creatures ( 121 ).

In 2018, during the first WHO Global Conference on Air Pollution and Health, the WHO's General Director, Dr. Tedros Adhanom Ghebreyesus, called air pollution a “silent public health emergency” and “the new tobacco” ( 122 ).

Undoubtedly, children are particularly vulnerable to air pollution, especially during their development. Air pollution has adverse effects on our lives in many different respects.

Diseases associated with air pollution have not only an important economic impact but also a societal impact due to absences from productive work and school.

Despite the difficulty of eradicating the problem of anthropogenic environmental pollution, a successful solution could be envisaged as a tight collaboration of authorities, bodies, and doctors to regularize the situation. Governments should spread sufficient information and educate people and should involve professionals in these issues so as to control the emergence of the problem successfully.

Technologies to reduce air pollution at the source must be established and should be used in all industries and power plants. The Kyoto Protocol of 1997 set as a major target the reduction of GHG emissions to below 5% by 2012 ( 123 ). This was followed by the Copenhagen summit, 2009 ( 124 ), and then the Durban summit of 2011 ( 125 ), where it was decided to keep to the same line of action. The Kyoto protocol and the subsequent ones were ratified by many countries. Among the pioneers who adopted this important protocol for the world's environmental and climate “health” was China ( 3 ). As is known, China is a fast-developing economy and its GDP (Gross Domestic Product) is expected to be very high by 2050, which is defined as the year of dissolution of the protocol for the decrease in gas emissions.

A more recent international agreement of crucial importance for climate change is the Paris Agreement of 2015, issued by the UNFCCC (United Nations Climate Change Committee). This latest agreement was ratified by a plethora of UN (United Nations) countries as well as the countries of the European Union ( 126 ). In this vein, parties should promote actions and measures to enhance numerous aspects around the subject. Boosting education, training, public awareness, and public participation are some of the relevant actions for maximizing the opportunities to achieve the targets and goals on the crucial matter of climate change and environmental pollution ( 126 ). Without any doubt, technological improvements makes our world easier and it seems difficult to reduce the harmful impact caused by gas emissions, we could limit its use by seeking reliable approaches.

Synopsizing, a global prevention policy should be designed in order to combat anthropogenic air pollution as a complement to the correct handling of the adverse health effects associated with air pollution. Sustainable development practices should be applied, together with information coming from research in order to handle the problem effectively.

At this point, international cooperation in terms of research, development, administration policy, monitoring, and politics is vital for effective pollution control. Legislation concerning air pollution must be aligned and updated, and policy makers should propose the design of a powerful tool of environmental and health protection. As a result, the main proposal of this essay is that we should focus on fostering local structures to promote experience and practice and extrapolate these to the international level through developing effective policies for sustainable management of ecosystems.

Author Contributions

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Conflict of Interest

IM is employed by the company Delphis S.A.

The remaining authors declare that the present review paper was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords: air pollution, environment, health, public health, gas emission, policy

Citation: Manisalidis I, Stavropoulou E, Stavropoulos A and Bezirtzoglou E (2020) Environmental and Health Impacts of Air Pollution: A Review. Front. Public Health 8:14. doi: 10.3389/fpubh.2020.00014

Received: 17 October 2019; Accepted: 17 January 2020; Published: 20 February 2020.

Reviewed by:

Copyright © 2020 Manisalidis, Stavropoulou, Stavropoulos and Bezirtzoglou. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Ioannis Manisalidis, giannismanisal@gmail.com ; Elisavet Stavropoulou, elisabeth.stavropoulou@gmail.com

† These authors have contributed equally to this work

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• Published: 04 October 2019

Engaging with research impact assessment for an environmental science case study

• Kirstie A. Fryirs   ORCID: orcid.org/0000-0003-0541-3384 1 ,
• Gary J. Brierley   ORCID: orcid.org/0000-0002-1310-1105 2 &
• Thom Dixon   ORCID: orcid.org/0000-0003-4746-2301 3  

Nature Communications volume  10 , Article number:  4542 ( 2019 ) Cite this article

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• Environmental impact
• Research management

An Author Correction to this article was published on 08 November 2019

This article has been updated

Impact assessment is embedded in many national and international research rating systems. Most applications use the Research Impact Pathway to track inputs, activities, outputs and outcomes of an invention or initiative to assess impact beyond scholarly contributions to an academic research field (i.e., benefits to environment, society, economy and culture). Existing approaches emphasise easy to attribute ‘hard’ impacts, and fail to include a range of ‘soft’ impacts that are less easy to attribute, yet are often a dominant part of the impact mix. Here, we develop an inclusive 3-part impact mapping approach. We demonstrate its application using an environmental initiative.

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Introduction.

Universities around the World are increasingly required to demonstrate and measure the impact of their research beyond academia. The Times Higher Education (THE) World University Rankings now includes a measure of knowledge transfer and impact as an indicator of an institution’s quality and the THE World University Rankings released their inaugural University impact rankings in 2019. With the global rise of impact assessment, most nations adopt a variant of the Organisation for Economic Cooperation and Development (OECD) definition of impact 1 ; “the contribution that research makes to the economy, society, environment or culture, beyond the contribution to academic research.” Yet research impact mapping provides benefits beyond just meeting the requirements for assessment 1 . It provides an opportunity for academics to reflect on and consider the impact their research can, and should, have on the environment, our social networks and wellbeing, our economic prosperity and our cultural identities. If considered at the development stage of research practices, the design and implementation of impact mapping procedures and frameworks can provide an opportunity to better plan for impact and create an environment where impact is more likely to be achieved.

Almost all impact assessments use variants of the Research Impact Pathway (Fig. 1 ) as the conceptual framework and model with which to document, measure and assess environmental, social, economic and cultural impacts of research 1 . This Pathway starts with inputs, followed by activities. Outputs and outcomes are produced and these lead to impact. Writing for Nature Outlook: Assessing Science , Morgan 2 reported on how Australia’s Commonwealth Scientific and Research Organisation (CSIRO) mapped impact using this approach. However, the literature contains very few worked examples to guide academics and co-ordinators in the process of research impact mapping. This is particularly evident for environmental initiatives and innovations 3 , 4 .

Here we provide a new, 3-part impact mapping approach that can accommodate non-linearity in the impact pathway and can more broadly include and assess both ‘hard’ impacts, those that can be directly attributed to an initiative or invention, and ‘soft’ impacts, those that can be indirectly attributed to an initiative or invention. We then present a worked example for an environmental innovation called the River Styles Framework, developed at Macquarie University, Sydney, Australia. The River Styles Framework is an approach to analysis, interpretation and application of geomorphic insights into river landscapes as a tool to support management applications 5 , 6 . We document and map how this Framework has shaped, and continues to shape, river management practice in various parts of the world. Through mapping impact we demonstrate how the River Styles Framework has contributed to environmental, social and economic benefits at local, national and international scales. Cvitanovic and Hobday (2018) 3  in Nature Communications might consider this case study a ‘bright spot’ that sits at the environmental science-policy-practice interface and is representative of examples that are seldom documented.

The Research Impact Pathway (modified from ref. 2 )

This case study is presented from the perspective of the researchers who developed the River Styles Framework, and the University Impact co-ordinator who has worked with the researchers to document and measure the impact as part of ex post assessment 1 , 7 . We highlight challenges in planning for impact, as the research impact pathway evolves and entails significant lag times 8 . We discuss challenges that remain in the mapping process, particularly when trying to measure and attribute ‘soft’ impacts such as a change in practice or philosophy, an improvement in environmental condition, or a reduction in community conflict to a particular initiative or innovation 9 . We then provide a personal perspective of the challenges faced and lessons learnt in applying and mapping research impact so that others, particularly in the environmental sciences and related interdisciplinary fields, can undertake similar exercises for their own research impact assessments.

Brief background on research impact assessment and reporting

Historical reviews of research policy record long-term shifts towards incorporation of concerns for research impact within national funding agencies. In the 1970s the focus was on ‘research utilisation’ 10 , more recently it has been on ‘knowledge mobilisation’ 11 . The focus is always on seeking to understand the actual manner and pathways through which research becomes incorporated into policy, and through which research has an economic, social, cultural and environmental impact. Often these are far from linear circumstances, entailing multiple pathways.

Since the 1980s, higher education systems around the world have been transitioning to performance-based research funding systems (PRFS). The initial application of the PRFS in university contexts occurred as part of the first Research Assessment Exercise (RAE) in the United Kingdom in 1986 12 . PRFS systems have been designed to reward and perpetuate the highest quality research, presenting notionally rational criteria with which to support more intellectually competitive institutions 13 . The United Kingdom’s (UK) RAE was replicated in Australia as the Research Quality Framework (RQF), and more recently as the Excellence in Research for Australia (ERA) assessment. In 2010, 15 countries engaged in some form of PRFS 14 . These frameworks focus almost solely on academic research performance and productivity, rather than the contribution and impact that research makes to the economy, society, environment or culture.

In the last decade, research policy frameworks have increasingly focused on facilitating national prosperity through the transfer, translation and commercialisation of knowledge 15 , 16 , combined with the integration of research findings into government policy-making 17 . In 2009, the Higher Education Funding Council for England conducted a year-long review and consultation process regarding the structure of the Research Excellence Framework (REF) 18 . Following this review, in 2010 the Higher Education Funding Council for England (HEFCE) commissioned a series of impact pilot studies designed to produce narrative-style case studies by 29 higher education institutions. The pilot studies featured five units of assessment: clinical medicine, physics, earth systems and environmental sciences, social work and social policy, and English language and literature 12 . These pilot studies became the basis of the REF conducted in the UK in 2014 9 , 19 with research impact reporting comprising a 20% component of the overall assessment.

In Canada, in 2009 and from 2014 the Canadian Academy of Health Sciences and Manitoba Research, respectively, developed an impact framework and narrative outputs to evaluate the returns on investment in health research 20 , 21 . Similarly the UK National Institute for Health Research (NIHR) regularly produces impact synthesis case studies 22 . In Ireland, in 2012, the Science Foundation Ireland placed research impact assessment at the core of its scientific and engineering research vision, called Agenda 2020 23 . In the United States, in 2016, the National Science Foundation, National Institute of Health, US Department of Agriculture, and US Environmental Protection Authority developed a repository of data and tools for assessing the impact of federal research and development investments 24 . In 2016–2017, the European Union (EU) established a high-level group to advise on how to maximise the impact of the EU’s investment in research and innovation, focussing on the future of funding allocation and the implementation of the remaining years of Horizon 2020 25 . In New Zealand, in 2017, the Ministry of Business, Innovation and Employment released a discussion paper proposing the introduction of an impact ‘pillar’ into the science investment system 26 . In 2020, Hong Kong will include impact assessment in their Research Assessment Exercise (RAE) for the first time 27 . Other countries including Denmark, Finland and Israel have scoped the use of research impact assessments of their major research programs as part of the Small Advanced Economies Initiative 28 .

In 2017, the Australian Research Council (ARC) conducted an Engagement and Impact Assessment Pilot (EIAP) 7 . While engagement is not analogous to impact, it is an evidential mechanism that elucidates the potential beneficiaries, stakeholders, and partners of academic research 12 , 16 . In addition to piloting narrative-style impact case study reporting, the EIAP characterised and mapped patterns of academic engagement with end users that create and enable research impact. The 2017 EIAP assessed a selection of disciplines for engagement, and a selection of disciplines for impact. Environmental science was a discipline selected for the impact pilot. These pilots became the basis for the Australian Engagement and Impact (EI) assessment in 2018 7 that ran in parallel with the ERA, and from which the case study in this paper is drawn.

Research impact assessment does not just include ex post reporting that can feed into a national PRFS. A large component of academic impact assessment involves ex ante impact reporting in research funding applications. In both the UK and Australia, the perceived merit of a research funding application has been linked in part to its planning and potential for external research impact. In the UK this is labelled a ‘Pathways to Impact’ statement (used by the Research Council UK), in Australia this is an Impact statement (used by the ARC), with a national interest statement also implemented in 2018. These statements explicitly draw from the ‘pathway to impact’ model which simplifies a direct and linear relationship between research excellence, research engagement, and research impact 29 . These ex ante impact statements can be difficult for academics, especially early career researchers, if they do not understand the process, nature and timing of impact. This issue exists in ex post impact reporting and assessment as well, with many researchers finding it difficult to supply evidence that directly or indirectly links their research to impacts that may have taken decades to manifest 1 , 7 , 8 . Also, the simplified linearity of the Research Impact Pathway model makes it difficult to adequately represent the transformation of research into impact.

For research impact statements and assessments to be successful, researchers need to understand the patterns and pathways by which impact occurs prior to articulating how their own research project might achieve impact ex ante, or has had impact ex post. The quality of research impact assessment will improve if researchers and funding agencies understand the types and qualities of impact that can reasonably be expected to arise from a research project or initiative.

Given the plethora of interest in, and a growing global movement towards, both ex ante and ex post research impact assessment and reporting, it is surprising that very few published examples demonstrate how to map research impact. Even in the business, economics and corporate sectors where impact assessment and reporting is common practice 30 , 31 , 32 , very few published examples exist. This hinders prospects for researchers and co-ordinators to develop a more critical understanding of impact, inhibiting more nuanced understandings of the pathways to impact model. Mapping impact networks and recording a cartography of impact for research projects and initiatives provides an appropriate basis to conduct such tasks. This paper provides a new method by which this can be achieved.

The research impact pathway and impact mapping

Many impact assessment frameworks around the world have common characteristics, often structured around the Research Impact Pathway model (Fig. 1 ). This model can be identified in a series of 2009 and 2016 Organisation for Economic Cooperation and Development (OECD) reports that investigated the mechanisms of impact reporting 1 , 33 . The Research Impact Pathway is presented as a sequence of steps by which impact is realised. This pathway can be visualised for an innovation or initiative using an impact mapping approach. It starts with inputs that can include funding, staff, background intellectual property and support structures (e.g., administration, facilities). This is followed by activities or the ‘doing’ elements. This includes the work of discovery (i.e., research) and the translation—i.e., courses, workshops, conferences, and processes of community and stakeholder engagement.

Outputs are the results of inputs and activities. They includes publications, reports, databases, new intellectual property, patents and inventions, policy briefings, media, and new courses or teaching materials. Inputs, activities and outputs can be planned and somewhat controlled by the researcher, their collaborators and their organisations (universities). Outcomes then occur under direct influence of the researcher(s) with intended results. This may include commercial products and licences, job creation, new contracts, grants or programs, citations of work, new companies or spin-offs and new joint ventures and collaborations.

Impacts (sometimes called benefits) tend to occur via uptake and use of an innovation or initiative by independent parties under indirect (or no) influence from the original researcher(s). Impacts can be ‘hard’ or ‘soft’ and have intended and unintended consequences. They span four main areas outside of academia, including environmental, social, economic and cultural spaces. Impacts can include improvements in environmental health, quality of life, changes in industry or agency philosophy and practice, implementation or improvement in policy, improvements in monitoring and reporting, cost-savings to the economy or industry, generation of a higher quality workforce, job creation, improvements in community knowledge, better inter-personal relationships and collaborations, beneficial transfer and use of knowledge, technologies, methods or resources, and risk-reduction in decision making.

The challenge: applying the research impact pathway to map impact for a case study

The River Styles Framework 5 , 34 aligns with UN Sustainable Development Goals of Life on Land and Clean Water and Sanitation that have a 2020 target to “ensure the conservation, restoration and sustainable use of terrestrial and inland freshwater ecosystems and their services” and a 2030 target to urgently “implement integrated water resources management at all levels” 35 .

The River Styles Framework is a catchment-scale approach to analysis and interpretation of river geomorphology 36 . It is an open-ended, generic approach for use in any landscape or environmental setting. The Framework has four stages (see refs. 5 , 37 , 38 , 39 ); (1) Analysis of river types, behaviour and controls, (2) Assessment of river condition, (3) Forecasting of river recovery potential, and (4) Vision setting and prioritisation for decision making.

River Styles Framework development, uptake, extension and training courses have contributed to a global change in river management philosophy and practice, resulting in improved on-ground river condition, use of geomorphology in river management, and end-user professional development. Using the River Styles Framework has changed the way river management decisions are made and the level of intervention and resources required to reach environmental health targets. This has been achieved through the generation of catchment-scale and regional-level templates derived from use of the Framework 6 . These templates are integrated with other biophysical science tools and datasets to enhance planning, monitoring and forecasting of freshwater resources 6 . The Framework is based on foundation research on the form and function of streams and their interaction with the landscape through which they flow (fluvial geomorphology) 5 , 40 .

The Framework has a pioneering structure and coherence due to its open-ended and generic approach to river analysis and interpretation. Going well beyond off-the-shelf imported manuals for river management, the Framework has been adopted because of its innovative approach to geomorphic analysis of rivers. The Framework is tailored for the landscape and institutional context of any given place to produce scaffolded, coherent and consistent datasets for catchment-specific decision making. Through on-ground communication of place-based results, the application of the Framework spans local, state, national and international networks and initiatives. The quality of the underlying science has been key to generating the confidence required in industry and government to adopt geomorphology as a core scientific tool to support river management in a range of geographical, societal and scientific contexts 6 .

The impact of this case study spans conceptual use, instrumental use and capacity building 4 defined as ways of thinking and alerting policy makers and practitioners to an issue. Impact also includes direct use of research in policy and planning decisions, and education, training and development of end-users, respectively 4 , 41 , 42 . The River Styles Framework has led to establishment of new decision-making processes while also changing philosophy and practice so on-ground impacts can be realised.

Impact does not just occur at one point in time. Rather, it comes and goes or builds and is sustained. How this is represented and measured, particularly for an environmental case study, and especially for an initiative built around a Framework where a traditional ‘product’, ‘widget’, or ‘invention’ is not produced is challenging 4 . More traditional metrics-based indicators such as the number of lives saved or the amount of money generated cannot be deployed for these types of case studies 4 , 9 . It is particularly challenging to unravel the commercial value and benefits of adopting and using an initiative (or Framework) that is part of a much bigger, international paradigm shift in river management philosophy and practice.

Similarly, how do you measure environmental, social, economic or cultural impacts of an initiative where the benefits can take many years (and in the case of rivers, decades) to emerge, and how do you then link and attribute those impacts directly with the design, development, use and extension of that initiative in many different places at many different times? For the River Styles Framework, on-ground impacts in terms of improved river condition and recovery are occurring 43 , but other environmental, social and economic benefits may be years or decades away. Impactful initiatives in themselves often reshape the contextual setting that then frames the next phase of science and management practices which leads to further implications for policy and institutional settings, and for societal (socio-cultural) and environmental benefits. This is currently the case in assessing the impact of the River Styles Framework.

The method: a new, 3-part impact mapping approach

Using the River Styles framework as an environmental case study, Fig. 2 presents a 3-part impact mapping approach that contains (1) a context strip, (2) an impact map, and (3) soft impact intensity strips to capture the scope of the impact and the conditions under which it has been realised. This approach provides a template that can be used or replicated by others in their own impact mapping exercises 44 .

The research impact map for the River Styles Framework case study. This map contains 3 parts, a context strip, impact map and soft impact intensity strips

The cartographic approach to mapping impact shown in Fig. 2 provides a mechanism to display a large amount of complex information and interactions in a style that conveys and communicates an immediate snapshot of the research impact pathway, its components and associated impacts. The map can be analysed to identify patterns and interactions between components as part of ex post assessment, and as a basis for ex ante impact forecasting.

The 3-part impact map output is produced in an interactive online environment, acknowledging that impact maps are live, open-ended documents that evolve as new impacts emerge and inputs, activities, outputs and outcomes continue. The map changes when activities, outputs or outcomes that the developers had forgotten, or considered to be peripheral, later re-appear as having been influential to a stakeholder, community or network not originally considered as an end-user. Such activities, outputs and outcomes can be inserted into a live map to broaden its base and understand the impact. Also, by clicking on each icon on the map, pop-up bubbles contain details that are specific to each component of the case study. This functionality can also be used to journal or archive important information and evidence in the ‘back-end’ of the map. Such evidence is often required, or called upon, in research impact assessments. Figure 2 only provides a static reproduction of the map output for the River Styles Framework. The fully worked, interactive, River Styles Framework impact map can be viewed at https://indd.adobe.com/view/c9e2a270–4396–4fe3-afcb-be6dd9da7a36 .

Context is a key driver of research impact 1 , 45 . Context can provide goals for research agendas and impact that feeds into ex ante assessments, or provide a lens through which to analyse the conditions within which certain impacts emerged and occurred as part of ex post assessment. Part 1 of our mapping approach produces a context strip that situates the case study (Fig. 2 ). This strip is used to document settings occurring outside of academia before, during and throughout the case study. Context can be local, national or global and examples can be gathered from a range of sources such as reports, the media and personal experience. For the River Styles case study only key context moments are shown. Context for this case study is the constantly changing communities of practice in global river restoration that are driven by (or inhibited by) the environmental setting (coded with a leaf symbol), policy and institutional settings (coded with a building symbol), social and cultural settings (coded with a crowd symbol), and economic settings (coded with a dollar symbol). For most case studies, these extrinsic setting categories will be similar, but others can be added to this part of the map if needed.

Part 2 of our mapping approach produces an impact map using the Research Impact Pathway (Fig. 1 ). This impact map (Fig. 2 ) documents the time-series of inputs (coded with a blue hexagon), activities (coded with a green hexagon), outputs (coded with a yellow hexagon), outcomes (coded with a red hexagon) and impacts (coded with a purple hexagon) that occurred for the case study. Heavier bordered hexagons and intensity strips represent international aspects and uptake. To start, only the primary inputs, activities, outputs and outcomes are mapped. A hexagon appears when there is evidence that an input, activity, output or outcome has occurred. Evidence includes event advertisements, reports, publications, website mentions, funding applications, awards, personnel appointments and communications products.

However, in conducting this standard mapping exercise it soon became evident that it is difficult to map and attribute impacts, particularly for an initiative that has a wide range of both direct and indirect impacts. To address this, our approach distinguishes between ‘hard’ impacts and ‘soft’ impacts. Hard impacts can be directly attributed to an initiative or invention, whereas soft impacts can be indirectly attributed to an initiative or invention. The inclusion of soft impacts is critical as they are often an important and sometimes dominant part of the impact mix. Both quantitative and qualitative measures and evidence can be used to attribute hard or soft impacts. There is not a direct one-to-one relationship between quantitative measurement of hard impacts and qualitative appraisal of soft impacts.

Hard impacts are represented as purple hexagons in the body of the impact map. For the River Styles Framework we have only placed a purple hexagon on the impact map where the impact can be ‘named’ and for which there is ‘hard’ evidence (in the form of a report, policy, strategic plan or citation) that directly mentions and therefore attributes the impact to River Styles. Most of these are multi-year impacts and the position of the hexagons on the map is noted at the first mention.

For many case studies, particularly those that impact on the environment, society and culture, attributing impact directly to an initiative or invention is not necessarily easy or straighforward. To address this our approach contains a third element, soft impact intensity strips (Fig. 2 ) to recognise, document, capture and map the extent and influence of impact created by an initiative or invention. This is represented as a heat intensity chart (coded as a purple bar of varying intenstiy) and organised under the environmental, social and economic categories that are often used to measure Triple-Bottom-Line (TBL) benefits in sustainability and research and development (R&D) reporting (e.g., refs. 7 , 46 ). Within these broad categories, soft impacts are categorised according to the dimensions of impacts of science used by the OECD 1 . These include environmental, societal, cultural, economic, policy, organisational, scientific, symbolic and training impacts. Each impact strip for soft impacts uses different levels of purple shading (to match the purple hexagon colour in the impact map) to visualise the timing and intensity of soft impacts. For the River Styles Framework, the intensity of the purple colour is used to show those impacts that have been most impactful (darker purple), the timing of initiation, growth or step-change in intensity of each impact, the rise and wane of some impacts and the longevity of others. A heavy black border is used to note the timing of internationalisation of some impacts. This heat intensity chart was constructed by quantitatively representing qualitative sentiment in testimonials, interviews, course evaluations and feedback, surveys and questionnaires, acknowledgements and recognitions, documentation of collaborations and networks, use of River Styles concepts, and reports on the development of spin-off frameworks. Quantitative representations of qualitative sentiment was achieved through using the methods of time-series keyword searches and expert judgement. These are just two methods by which the level of heat intensity can be measured and assigned 9 .

The outcome: impact of the River Styles Framework case study

Figure 2 , and its interactive online version, present the impact map for the River Styles Framework initiative and Table 1 documents the detail of the River Styles impact story from pre-1996 to post-2020. The distribution of colour-coded hexagons and the intensity of purple on the soft impact intensity strips on Fig. 2 demonstrates the development and maturation of the initiative and the emergence of the impact.

In the first phase (pre-1996–2002), blue inputs, green activities and yellow output hexagons dominate. The next phase (2002–2005) was an intensive phase of output production (yellow hexagons). It is during this phase that red outcome hexagons appear and intensify. From 2006, purple impact hexagons appear for the first time, representing hard impact outside of academia. Soft impacts also start to emerge more intensely (Fig. 2 ). 2008–2015 represents a phase of domestic consolidation of yellow outputs, red outcomes and purple impacts, and the start of international uptake. Some of this impact is under direct influence and some is independent of the developers of the River Styles Framework (Fig. 1 ). The number of purple impact hexagons is more intense during the 2008–2015 period and soft impacts intensify further. 2016–2018 (and beyond) represents a phase of extension into international markets, collaborations and impact (heavier bordered hexagons and intensity strips; Fig. 2 ). The domestic impacts that emerged most intensively post-2006 continue in the background. Green activity hexagons re-appear during this period, much like the 1996–2002 phase, but in an international context. Foundational science (green activity hexagons) re-emerge, particularly internationally with new collaborations. At the same time, yellow outputs and red outcomes continue.

For the River Styles case study the challenge still remains one of how to adequately attribute, measure and provide evidence for soft impacts 4 that include:

a change in river management philosophy and practice

an improvement in river health and conservation of threatened species

the provision of an operational Framework that provides a common and consistent approach to analysis

the value of knowledge generation and databases for monitoring river health and informing river management decision-making for years to come

the integration into, and improvement in, river management policy

a change in prioritisation that reduces risk in decision-making and cost savings on-the-ground

professional development to produce a better trained, higher quality workforce and increased graduate employability

the creation of stronger networks of river professionals and a common suite of concepts that enable communication

more confident and appropriate use of geomorphic principles by river management practitioners

an improvement in citizen knowledge and reduced community conflict in river management practice

Lessons learnt by applying research impact mapping to a real case study

When applying the Research Impact Pathway and undertaking impact mapping for a case study it becomes obvious that generating and realising impact is not a linear process and it is never complete, and in many aspects it cannot be planned 8 , 9 , 29 . Rather, the pathway has many highways, secondary roads, intersections, some dead ends or cul-de-sacs and many unexpected detours of interest along the way.

Cycles of input, activity, outputs, outcomes and impact occur throughout the process. There are phases where greater emphasis is placed on inputs and activities, or phases of productivity that produce outputs and outcomes, and there are phases where the innovation or initiative gains momentum and produces a flurry of benefits and impacts. However, throughout the journey, inputs, activities, outputs and outcomes are always occurring, and the impact pathway never ends. Some impacts come and go while others are sustained.

The saying “being in the right place at the right time with the right people” has some truth. Impact can be probabilistically generated ex ante by the researcher(s) regularly placing themselves and their outputs in key locations or ‘rooms’ and in ‘moments’ where the chance of non-academic translation is high 47 . Context is also critical 45 . Economic, political, institutional, social and environmental conditions need to come together if an innovation or initiative is to ‘get off the ground’, gain traction and lead to impact (e.g., Fig. 2 ). Ongoing and sustained support is vital. An innovation funded 10 years ago may not receive funding today, or an innovation funded today may not lead to impact unless the right sets of circumstances and support are in place. This is, in part, a serendipitous process that involves the calculated creation of circumstances aligned to evoke the ‘black swan’ event of impact 48 . The ‘black swan’ effect, coined by Nassem Nicholas Taleb, is a metaphor for an unanticipated event that becomes reinterpreted through the benefit of hindsight, or alternatively, an event that exists ‘outside the model’. For example, black swans were presumed not to exist by Europeans until they were encountered in Australia and scientifically described in 1790. Such ‘black swan’ events are a useful device in ex post assessment for characterising those pivotal moments when a research program translates into research impact. While the exact nature of such events cannot be anticipated, by understanding the ways in which ‘black swan’ events take place in the context of research impact, researchers can manufacture scenarios that optimise their probability of provoking a ‘black swan’ event and therefore translating their research project into research impact, albeit in an unexpected way. One ‘black swan’ event for the River Styles Framework occurred between 1996–2002 (Table 1 ). Initial motivations for developing the Framework reflected inappropriate use of geomorphic principles derived elsewhere to address management concerns for distinctive river landscapes and ecosystems in Australia. Although initial applications and testing of the Framework were local (regional-scale), advice by senior-level personnel in the original funding agency, Land and Water Australia (blue input hexagon in 1997; Fig. 2 ), suggested we make principles generic such that the Framework can be used in any landscape setting. The impact of this ‘moment’ was only apparent much later on, when the Framework was adopted to inform place-based, catchment-specific river management applications in various parts of the world.

What is often not recognised is the time lag in the research impact process 9 . Depending on the innovation or initiative, this is, at best, a decadal process. Of critical importance is setting the foundations for impact. The ‘gem of an idea’ needs to be translated into a sound program of research, testing (proof of concept), peer-review and demonstration. These foundations must generate a level of confidence in the innovation or initiative before uptake. A level of branding may be required to make the innovation or initiative stand out from the crowd. Drivers are required to incentivise academics, both internal and external to their University setting, encouraging them to go outside their comfort zone to apply and translate their research in ‘real-world’ settings. Maintaining passion, patience and persistence throughout the journey are some of the most hidden and unrecognised parts of this process.

Some impacts are not foreseeable and surprises are inevitable. Activities, outputs and outcomes that may initially have seemed like a dead end, often re-appear in a different context or in a different network. Other outputs or outcomes take off very quickly and are implemented with immediate impact. Catalytic moments are sometimes required for uptake and impact to be realised 8 . These surprises are particularly obvious when an innovation or initiative enters the independent uptake stage, called impact under indirect influence on Fig. 1 . In this phase the originating researchers, developers or inventors are often absent or peripheral to the impact process. Other people or organisations have the confidence to use the innovation or initiative (as intended, or in some cases not as intended), and find new ways of taking the impact further. The innovation or initiative generates a life of its own in a snowball effect. Independent uptake is not easily measured, but it is a critical indicator of impact. Unless the foundations are solid and sound, prospects for sustained impact are diminished.

The maturity and type of impact also vary in different places at different times. This is particularly the case for innovations and initiatives where local and domestic uptake is strong, but international impact lags. Some places may be well advanced on the uptake part of the impact journey, firmly embedding the benefits while developing new extensions, add-ons and spin-offs with inputs and activities. Elsewhere, the uptake will only have just begun, such that outputs and outcomes are the primary focus for now, with the aim of generating impact soon. In some instances, authorities and practitioners are either unaware or are yet to be convinced that the innovation or initiative is relevant and useful for their circumstances. In these places the focus is on the inputs and activity phases necessary to generating outputs and outcomes relevant to their situation and context. Managing this variability while maintaining momentum is critical to creating impact.

Future directions for the practice of impact mapping and assessment

The process of engaging with impact and undertaking impact mapping for an environmental case study has been a reflective, positive but challenging experience. Our example is typical of many of the issues that must be addressed when undertaking research impact mapping and assessments where both ‘hard’ and ‘soft’ impacts are generated. Our 3-part impact mapping approach helps deal with these challenges and provides a mechanism to visualise and enhance communication of research impact to a broad range of scientists and policy practitioners from many fields, including industry and government agencies, as well as citizens who are interested in learning about the tangible and intangible benefits that arise from investing in research.

Such impact mapping work cannot be undertaken quickly 44 , 45 . Lateral thinking is required about what research impact really means, moving beyond the perception in academia that outputs and outcomes equals impact 4 , 9 , 12 . This is not the case. The research impact journey does not end at outcomes. The real measure of research impact is when an initiative gains a ‘life of its own’ and is independently picked-up and used for environmental, social or economic benefit in the ‘real-world’. This is when an initiative exits from the original researcher(s) owning the entirety of the impact, to one where the researcher(s) have an ongoing contribution to vastly scaled-up sets of collective impacts that are no longer controlled by any one actor, community or network. Penfield et al. 9 relates this to ‘knowledge creep’ where new data, information or frameworks become accepted and get absorbed over time.

Careful consideration of how an initiative is developed, emerges, is used, and the resulting benefits is needed to map impact. This process, in its own regard, provides solid foundations for future planning and consideration of possible (or maybe unforeseen) opportunities to develop the impact further as part of ex ante impact forecasting 1 , 44 . It’s value also lies in communicating and teaching others, using worked case studies, about what impact can mean, to demonstrate how it can evolve and mature, and outline the possible pathways of impact as part of ex post impact assessment 1 , 44 .

With greater emphasis being placed on impact in research policy and reporting in many parts of the world, it is timely to consider the level of ongoing support required to genuinely capture and assess impact over yearly and decadal timeframes 20 . Creation of environments and cultures in which impact can be incubated, nourished and supported aids effective planning, knowledge translation and engagement. Ongoing research is required to consider, more broadly and laterally, what is measured, what indicators are used, and the evidence required to assign attribution. This remains a challenge not just for the case study documented here, but for the process of impact assessment more generally 1 , 9 . Continuous monitoring of impacts (both intended and unintended) is needed. To do this requires support and systems to gather, archive and track data, whether quantitative or qualitative, and adequately build evidence portfolios 20 . A keen eye is needed to identify, document and archive evidence that may seem insignificant at the time, but can lead to a step-change in impact, or a re-appearance elsewhere on the pathway.

Impact reporting extends beyond traditional outreach and service roles in academia 16 , 19 . Despite the increasing recognition of the importance of impact and its permeation into academic lives, it is yet to be formally built into many academic and professional roles 9 . To date, the rewards are implicit rather than explicit 44 . Support is required if impact planning and reporting for assessment is to become a new practice for academics.

Managing the research impact process is vital, but it is also important to be open to new ideas and avenues for creating impact at different stages of the process. It is important to listen and to be attuned to developments outside of academia, and learn to live with the creative spark of uncertainty as we expect the unexpected!

Change history

08 november 2019.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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Acknowledgements

We thank Simon Mould for building the online interactive version of the impact map for River Styles and Dr Faith Welch, Research Impact Manager at the University of Auckland for comments on the paper. The case study documented in this paper builds on over 20 years of foundation research in fluvial geomorphology and strong and lasting collaboration between researchers, scientists and managers at various universities and government agencies in many parts of the world.

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K.F. conceived, developed and wrote this paper. G.B., T.D. contributed to, and edited, the paper. K.F., T.D. conceived, developed and produced the impact mapping toolbox.

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K.F. and G.B. are co-developers of the River Styles Framework. River Styles foundation research has been supported through competitive grant schemes and university grants. Consultancy-based River Styles short courses taught by K.F. and G.B. are administered by Macquarie University. River Styles contract research is administered by Macquarie University and University of Auckland. River Styles as a trade mark expires in May 2020. T.D. declares no conflict of interest.

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Fryirs, K.A., Brierley, G.J. & Dixon, T. Engaging with research impact assessment for an environmental science case study. Nat Commun 10 , 4542 (2019). https://doi.org/10.1038/s41467-019-12020-z

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Airports and environmental sustainability: a comprehensive review

Fiona Greer 1,2 , Jasenka Rakas 1 and Arpad Horvath 1

Published 8 October 2020 • © 2020 The Author(s). Published by IOP Publishing Ltd Environmental Research Letters , Volume 15 , Number 10 Citation Fiona Greer et al 2020 Environ. Res. Lett. 15 103007 DOI 10.1088/1748-9326/abb42a

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Jasenka Rakas https://orcid.org/0000-0001-9694-3588

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Over 2500 airports worldwide provide critical infrastructure that supports 4 billion annual passengers. To meet changes in capacity and post-COVID-19 passenger processing, airport infrastructure such as terminal buildings, airfields, and ground service equipment require substantial upgrades. Aviation accounts for 2.5% of global greenhouse gas (GHG) emissions, but that estimate excludes airport construction and operation. Metrics that assess an airport's sustainability, in addition to environmental impacts that are sometimes unaccounted for (e.g. water consumption), are necessary for a more complete environmental accounting of the entire aviation sector. This review synthesizes the current state of environmental sustainability metrics and methods (e.g. life-cycle assessment, Scope GHG emissions) for airports as identified in 108 peer-reviewed journal articles and technical reports. Articles are grouped according to six categories (Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, Material and Resources, Multidimensional) of an existing airport sustainability assessment framework. A case study application of the framework is evaluated for its efficacy in yielding performance objectives. Research interest in airport environmental sustainability is steadily increasing, but there is ample need for more systematic assessment that accounts for a variety of emissions and regional variation. Prominent research themes include analyzing the GHG emissions from airfield pavements and energy management strategies for airport buildings. Research on water conservation, climate change resilience, and waste management is more limited, indicating that airport environmental accounting requires more analysis. A disconnect exists between research efforts and practices implemented by airports. Effective practices such as sourcing low-emission electricity and electrifying ground transportation and gate equipment can in the short term aid airports in moving towards sustainability goals. Future research must emphasize stakeholder involvement, life-cycle assessment, linking environmental impacts with operational outcomes, and global challenges (e.g. resilience, climate change adaptation, mitigation of infectious diseases).

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List of acronyms

1. introduction.

Airport infrastructure is a vital component of society's transportation network. There are more than 40 000 airports worldwide (CIA 2016 ). Around 2500 airports processed over 4 billion passengers in 2018 (IATA 2018 ). The onset of COVID-19 has drastically decreased air traffic levels (IATA 2020 ). It is likely that air travel will recover over the next couple of years and continue to rise. In the United States, massive investment is required (ASCE 2017 , ACC 2020 ) to modernize and retrofit aged, inadequate airport infrastructure (e.g. terminals, airfields, service equipment). Similar expansion projects and necessary reconfiguration projects for post COVID-19 processing of passengers are occurring worldwide. Airports are not solely transport nodes. The onset of 'airport cities' make this critical infrastructure a catalyst for economic, logistical, and social development (Appold and Kasarda 2013 ).

The environmental impacts attributed to airport construction and operational activities (e.g. building operation, ground service equipment (GSE)) are significant to consider, especially in light of the fact that as other transport sectors go 'green,' the air transport sector will face more challenges in reducing their environmental impacts. It is estimated that the aviation industry accounts for approximately 2.5% of global greenhouse gas (GHG) emissions in 2018 (IEA 2019 ), but that estimate excludes the impacts from airport construction and operation. An analysis of 2019 data for San Francisco International Airport (SFO 2018 , 2020 ) reveals an approximate annual breakdown of 85% for aviation GHG emissions and 15% for airport GHG emissions. Although not accounting for life-cycle impacts and not representative of every airport, this breakdown offers a sense of scope of how GHG impacts are divided between aviation (i.e. flights) and airport activities. The environmental impact of airport infrastructure/operations is not just limited to their GHG emissions. Airport construction and operation also results in emissions of air pollutants such as carbon monoxide (CO), nitrogen oxides (NO x ), and particulate matter (PM), displacement of and damage to natural ecosystems, generation of waste, and consumption of resources such as water.

In the public policy sphere, airport sustainability is an emerging area of interest. The aviation and airport communities recognize the important role that airport infrastructure plays in promoting beneficial environmental and human health outcomes. However, how the public sector addresses airport sustainability is fragmented and lacks rigorous appraisal of suggested best practices. Oftentimes, airport operators rely on other airports' existing sustainability guidelines for selecting 'green' practices that are not explicitly defined and quantified (Setiawan and Sadewa 2018 ). This review offers the public aviation sector, in particular, a much-needed overview of relevant sustainability indicators and methods for airport infrastructure and guidance in pursuing future research and implementation of sustainable practices and projects.

The expected increase in demand for air travel and the necessary upgrades for airport infrastructure compound the environmental impacts of airport construction and operation. In designing and operating the next generation of airport infrastructure (e.g. terminal buildings) there must be a systematic way for evaluating the resulting environmental impacts. Measures that assess the sustainability of the design, construction, and operation of airport infrastructure offer a potential solution for airport operators to consider.

1.1. History and background

Sustainability, as defined in the United Nations' Brundtland Report, states that present society must manage and consume resources so as not to compromise future society's needs (Brundtland et al 1987 ). While the Brundtland definition acknowledges human activity's environmental impact, it does not offer concrete guidance for achieving sustainability. A less abstract framework is the 'triple bottom line' approach, which aims to identify solutions that balance environmental, social, and economic interests (Elkington 1994 ).

Sustainability indicators, or metrics, can be used to measure the 'sustainability performance' of an airport. Metrics are critical because they allow for:

• Comparing the sustainability of one airport (or one type of airport) against another;
• Identifying the weak points or opportunities for improvement in airport infrastructure;
• Measuring progress towards meeting targeted goals.

A standardized, empirical metric is also crucial for making decisions about sustainable design and operation of airport infrastructure (Longhurst et al 1996 ). Stakeholder involvement in developing these indicators is necessary (Upham and Mills 2005 ). Sustainability metrics are a component of a larger-scale sustainability plan. Ideally, formalized sustainability plans developed by airports should incorporate metrics for tracking progress towards goals.

Airport sustainability, as defined by the aviation industry, incorporates the 'triple bottom line' concept with a fourth pillar focused on operational efficiency. Airport Council International (ACI) refers to this approach to sustainability as EONS (Martin-Nagle and Klauber 2015 , Prather 2016 ). Common subcategories of EONS are shown in table 1 . An important research dimension of the airport industry is the U.S. National Academies of Sciences' Airport Cooperative Research Program (ACRP), which researches and publishes synthesis reports and guidance for current sustainability practices at airports. ACRP reports are largely compiled through literature reviews of airports' published sustainability reports and through interviews, surveys, and questionnaires with airport operators. Recent topics of ACRP reports include:

• overall sustainability (Brown 2012 , Delaney and Thomson 2013 , Lurie et al 2014 , Prather 2016 , Malik 2017 );
• feasibility of on-site energy provision (Lau et al 2010 , Barrett et al 2014 ) and microgrids (Heard and Mannarino 2018 );
• GHG emission reduction strategies (ACRP, FAA, Camp, Dresser, & McKee et al 2011 , Barrett 2019 );
• air quality impacts (ACRP, FAA, CDM Federal Programs Corporation et al 2012a , ACRP 2012b , Lobo et al 2013 , Kim et al 2014 , 2015 )
• water efficiency (Krop et al 2016 ) and stormwater management (Jolley et al 2017 );
• habitat management (Belant and Ayers 2014 );
• sustainable ground transport (Kolpakov et al 2018 );
• sustainable construction practices (ACRP, FAA, Ricondo & Associates et al 2011 );
• waste management (Turner 2018 );
• climate change adaptation of airports (Marchi 2015 ).

Table 1.  Airport industry concept of sustainability or EONS, as defined by Prather, 2016.

The definition of environmental airport sustainability in the academic literature varies with some defining it according to multiple categories of environmental impacts (Chao et al 2017 , Ferrulli 2016 , Gomez Comendador et al 2019 ; Kilkis and Kilkis 2016 ) and others limiting that definition to traditional environmental aviation impacts such as emissions and noise (Lu et al 2018 ). Environmental sustainability is assessed using both quantitative and qualitative metrics/measures, and using both generalized, average airports (Chester and Horvath 2009 ) and data from operating airports (Chao et al 2017 ; Kilkis and Kilkis 2016 , Li and Loo 2016 ).

In both industry and academic research, environmental impacts are often disaggregated according to the airside and landside components of the airport system boundary. Figure 1 shows a plan view schematic of the typical features included in the airport system boundary. It should be noted that energy generation, water/wastewater (WW) treatment, and waste management infrastructure can be located within airport-owned property (i.e. decentralized) or within the surrounding community of the airport (i.e. centralized). Table 2 identifies the purpose and primary stakeholders for each airport component. Understanding the scope of airport infrastructure aids in identifying the most relevant environmental impacts and the stakeholders best equipped to mitigate those impacts.

Figure 1.  Plan view of airport system boundary. Key infrastructure features are identified.

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Table 2.  Purpose and primary stakeholders of key airport infrastructure.

1.2. Research objectives and goals

While previous studies have examined sustainability practices of individual airports (Berry et al 2008 , Prather 2016 ), this work represents the first comprehensive systematic review of academic and industry literature on airport environmental sustainability. The five objectives of this research are: (1) synthesize the existing literature on environmental sustainability indicators and metrics for airports; (2) review the application of sustainability indicators developed for the construction of terminals and other airport facilities at a case study airport (San Francisco International Airport also known as SFO); (3) identify gaps in the literature; (4) recommend what sustainability indicators/metrics should be employed at airports based upon the results of the literature review; (5) provide recommendations for future directions of research. Sustainability indicators are grouped according to the SFO framework: Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, Materials and Resources. These five categories provide a framework for stakeholders to begin exploring the scope of relevant environmental impacts. The breadth of the five categories also highlights that sustainability encompasses more than one type of impact (e.g. GHG emissions) and underscores that airports have multiple priorities in addressing their environmental impacts. The expected outcome from this review is the identification of gaps in the existing literature and practice as it pertains to evaluating the sustainability of airport infrastructure. Recommendations for future research directions will provide those in the academic realm, as well as in the public aviation sector, a robust assessment of what metrics, practices, and methods should be applied to achieve optimal performance outcomes.

1.3. Overview of article

Section 2 presents the methodology for conducting the systematic review. Section 3 follows with a characterization, trend analysis, and synthesis of the reviewed literature, along with a review of the sustainability indicators used at a current SFO infrastructure project. Section 4 discusses the limitations and gaps of the existing literature, analyzes the efficacy of SFO's sustainability assessment framework, and provides guidance for future research directions. Section 5 concludes with a summary of the overall work and a recommendation for practices that airports should implement in the short term.

2.1. Systematic literature review

2.1.1. criteria for selecting research papers.

The foremost criterion in selecting peer-reviewed research articles and technical reports is that they pertain to indicators (i.e. metrics or measurements) for environmental sustainability. Although the concept of sustainability also includes economic and social factors, they are outside the scope of this review. We excluded corporate sustainability reports published by individual airports as data from these reports often appear in non-standard formats. However, individual airport sustainability practices were explored as part of the review of academic and ACRP literature. We iteratively searched for peer-reviewed research articles and technical reports in Web of Science, Google Scholar, and the National Academies of Science' ACRP database that were relevant to 'airport sustainability,' using the key terms of 'airport' and variations of 'sustainability' including 'environmental sustainability,' 'sustainable development,' and 'environmental impact.'

Searches were conducted with key terms related to the five categories of the SFO framework (i.e. Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, Materials and Resources). Additional searches also included articles that incorporated life-cycle assessment (LCA), a method for assessing the 'cradle-to-grave' environmental impacts of a product, process, or project. We elected to also include search terms for Scope 1, Scope 2, and Scope 3 GHG emissions. Table 3 summarizes the definitions and examples of Scope GHG emissions.

Table 3.  Summary of GHG scope emissions for airports.

Characterizing GHG emissions according to the three Scopes aligns with airport industry practice of allocating responsibility for GHG emissions among airport stakeholders (ACA 2020 ). Exact search terms for all criteria are provided in table A1 in appendix A (available online at https://stacks.iop.org/ERL/15/103007/mmedia ). Articles that were relevant to at least more than one of the five sustainability categories were considered as part of a Multidimensional category.

Articles that focused on sustainability indicators for the construction and operation of physical airport infrastructure were prioritized. Articles were excluded if they concentrated on aircraft, aircraft fuel, or on aircraft operations within the airport boundary such as taxiing, queuing, and the landing and take-off (LTO) cycle. The rational for this exclusion is that aircraft-related sustainability is an already extensively reviewed subject (Agarwal 2010 , Blakey et al 2011 , Sarlioglu and Morris 2015 ). However, articles pertaining to aircraft servicing operations at airports (e.g. ground service equipment or GSE, de-icing) were included. All screening criteria are listed in table A2 in appendix A. Note that the time period of 2009 to 2019 is selected to provide a meaningful analysis of the academic literature, as interest in airport environmental sustainability as a research field began in earnest at the end of the 2000s.

The searches yielded a total of 108 articles grouped according to Energy and Atmosphere ( n = 22), Comfort and Health ( n = 25), Water and Wastewater ( n = 14), Site and Habitat ( n = 16), Materials and Resources ( n = 18), Multidimensional ( n = 13). Common themes of sustainability indicators for each category are depicted in figure 2 . A bibliography for all articles included in this systematic review is provided in appendix A (table A3). Section 3 provides a trend analysis of the articles included in the systematic review.

Figure 2.  Themes for each of the five sustainability categories.

3.1. Characterization of systematic literature review

A trend analysis of the reviewed articles indicates that interest in airport environmental sustainability has steadily increased over the period of 2009 to 2019 (figure 3 ). Article counts in each category theme (figure 4 ) reveal that research among the various categories is relatively balanced, with some prominent exceptions. Article counts for 'Ambient Air Quality,' 'Airfield Materials,' and 'Multidimensional' research themes are the highest. The high article counts for 'Ambient Air Quality' and 'Airfield Materials' suggests that research in the field of airport environmental sustainability largely focuses on the characteristics of an airport that are most prominent and apparent (i.e. the runway, taxiway, and apron). The high article count for the 'Multidimensional' category indicates that the research community is beginning to recognize that airport sustainability is comprised of multiple environmental impacts across multiple airport functions. In categories such as 'Waste Management' and 'Building Materials,' the small article counts imply that these specific subjects are still emerging as relevant research areas.

Figure 3.  Cumulative articles by year (dotted line = moving average).

Figure 4.  Cumulative articles by theme.

3.1.1. Synthesis of research by category

3.1.1.1. energy and atmosphere.

Common themes among the articles featured in the Energy and Atmosphere category include energy management of airport infrastructure, use of renewable energy on-site, and energy-related air emissions.

3.1.1.1.1. Energy management

Energy management refers to a process by which airports can characterize and monitor their energy consumption and enact measures to reduce it. Airports use fossil fuels (natural gas, petroleum) and electricity to perform various operational requirements such as controlling the thermal environment of buildings, lighting runways and buildings, and fueling airport ground equipment and vehicles. Using Seve Ballesteros-Santander Airport in Spain as a case study, it is estimated that most of the energy consumption at an airport is attributable to the terminal building with heating, ventilation, air conditioning (HVAC) and lighting being the most energy-intensive practices (Ortega Alba and Manana 2017 ). A best practice for energy management is implementation of an energy monitoring system (Lau et al 2010 ). Although not analyzed from an environmental perspective, airports represent an opportunity for exploring the implementation of microgrids, which allow for on-site energy generation and storage (Heard and Mannarino 2018 ).

Some literature indicates that if an airport has implemented specific energy management practices, then those practices are a marker of sustainability. A sample of practices that are considered sustainable and have been implemented at two case study airports (Baxter et al 2018a , 2018c ) is provided in table 4 . An airport that implements a standardized energy management system is considered to be sustainable (Uysal and Sogut 2017 ). Implementation of specific practices depends upon site characteristics including climate, occupancy level, and operating hours (Malik 2017 ). An analysis of energy related to the lighting of a Turkish airport terminal indicates that indoor lighting is a critical energy consumer (Kiyak and Bayraktar 2015 ).

Table 4.  Example energy conservation practices at airports as reported in Baxter et al ( 2018a , 2018c ).

3.1.1.1.2. Renewable energy

Implementation of on-site renewable energy is another typical indicator of sustainability as discussed in the literature. There are safety concerns (e.g. glare, radar interference) with some forms of renewable energy such as solar and wind (Barrett et al 2014 ), but airports are ideal candidates for employing on-site renewables because of their expansive land areas (Lau et al 2010 ). Metrics for evaluating the efficacy of on-site renewable energy such as solar photovoltaic (PV) systems include percentage of energy demand met by on-site renewables (Dehkordi et al 2019 ) and exergy (Kilkis and Kilkis 2017 , Sukumaran and Sudhakar 2018 ). Exergy, as it relates to provision of on-site solar PV, refers to the quality of the energy delivered; solar power tends to have high thermal losses unless cooling intervention is taken. In assessing the emissions impact from different energy sources in a district heating system at Schiphol Airport in the Netherlands, it is argued that GHG emissions should be estimated by accounting for both the first and second laws of thermodynamics (Kilkis and Kilkis 2017 ). Accounting for GHG emissions from both the quantity (first law) and quality (second law) of energy provides a more realistic analysis of the feasibility for achieving practices that are considered sustainable (e.g. net zero-carbon airport terminal buildings). Another metric for assessing environmental impacts from renewable energy at airports is absolute reduction of fossil fuel consumption, which is applied to evaluate a solar PV and battery storage project at Cornwall Airport Newquay in the United Kingdom (Murrant and Radcliffe 2018 ). Modeling of a solar PV farm at a rural U.S. airport indicates that this form of renewable energy can meet both the airport's and local community's electricity needs without compromising pilot or airspace safety (Anurag et al 2017 ). A groundwater source heat pump was found to meet indoor thermal requirements in a more energy-efficient manner (i.e. a higher coefficient of performance) than conventional heat pumps for a Tibetan airport (Zhen et al 2017 ). LCA is used to inventory the GHG emissions from using a biomass-fired combined heat and power plant at London Heathrow Airport to meet terminal building heating needs (Tagliaferri et al 2018 ).

3.1.1.1.3. Energy-related emissions

Recommended GHG emission reduction strategies related to energy use at airports pertain to designing building envelopes to be more energy efficient, using energy efficient equipment and fuels, relying on renewable energy, and managing use of refrigerants (ACRP, FAA, McKee, Dresser Camp, & Synergy Consulting Services 2011 , Barrett 2019 ). GHG emissions from annual airport energy consumption are a typical sustainability evaluation metric (Monsalud et al 2015 , Baxter et al 2018a , 2018c ). In practice, GHG emissions are often inventoried according to a framework developed by ACI, which recognizes that an airport is under direct control of GHG emissions from Scope 1 sources (e.g. on-site power generation) and Scope 2 sources (e.g. purchase from grid electricity), and only able to influence Scope 3 sources (e.g. emissions from an airline's GSE) (ACRP, FAA, Camp, Dresser, & McKee et al 2011 , Ozdemir and Filibeli 2014 ). The ACI framework accounts for the annual amount of electricity and natural gas consumed and the amount of fuel used to power airport ground vehicles. A similar method allocates emissions to each macro unit (e.g. GSE) at an Italian airport (Postorino and Mantecchini 2014 ). A more holistic approach for measuring an airport's energy consumption accounts for the loss of a carbon sink from the deforestation of the site on which Istanbul International Airport was built (Kılkış 2014 ).

3.1.1.2. Comfort and health

The Comfort and Health themes in the literature include building occupant comfort and health impacts related to ambient and indoor air quality.

3.1.1.2.1. Building occupant comfort

Passengers and airport/airline employees spend a considerable amount of time inside airport buildings such as terminals, maintenance facilities, and control towers. Occupant comfort in these buildings is relevant for environmental sustainability because aspects of comfort (i.e. thermal, ventilation, lighting) are directly related to metrics such as energy consumption. Research into novel air conditioning and heating systems in terminals at Chinese airports indicates that thermal and ventilation comfort can be satisfied while saving energy (Meng et al 2009 , Zhang et al 2013 , Zhao et al 2014 ; Liu et al 2019). An investigation of preferences at airports in the U.K. demonstrates that occupants tolerate higher thermal levels and prefer natural lighting, which have energy-saving implications (Kotopouleas and Nikolopoulou 2018 ). Designing airport buildings to emphasize natural lighting should incorporate the functional operational characteristics of air travel (i.e. operational peaks occur in the early morning and early to late evening) (Clevenger and Rogers 2017 ).

3.1.1.2.2. Indoor air quality

Exposure to air pollutants is known to cause negative human health impacts including increased risk of respiratory illness, cardiovascular disease, and death (Apte et al 2012 , Kim et al 2015 ). Indoor air quality (IAQ) research focuses on the pollutants and factors (e.g. ventilation systems, building design) that contribute to occupant exposure while inside facilities such as terminals and control towers. Research on exposure in indoor settings at airports has been limited to the concentrations of nitrogen dioxide (NO 2 ) and volatile organic compounds (VOCs) in a maintenance room at a Lebanon airport (Mokalled et al 2019 ), PM in a terminal building at a Chinese airport (Ren et al 2018 ), VOCs, PM, odorous gases, and carbon dioxide (CO 2 ) at an Italian airport terminal (Zanni et al 2018 ), and CO, VOCs, and PM in a control tower at a Greek airport (Helmis et al 2009 , Tsakas and Siskos 2011 ). One study linked IAQ at eight large Chinese airports with passenger satisfaction, finding that IAQ satisfaction is correlated with CO 2 concentration (Wang et al 2015 ).

3.1.1.2.3. Ambient air quality

Ambient, or outdoor, air quality at airports is a function of both aircraft and non-aircraft operations. Sources of non-aircraft emissions include the equipment used to clean, load, or reposition parked aircraft (i.e. GSE) or used to provide power to parked aircraft (i.e. ground power units or GPUs). Another source of emissions from parked aircraft is the auxiliary power unit (APU), an external rear engine on the aircraft which provides electrical power and thermal conditioning (ACRP , 2012b , Lobo et al 2013 ). Other outdoor sources include emissions from construction (Kim et al 2014 ) and operation of airport ground access vehicles (e.g. maintenance trucks, firetrucks). Much of the exposure to pollutants such as black carbon (a component of PM) occurs on the airfield's apron where aircraft are often positioned for passenger boarding and luggage loading (Targino et al 2017 ). Outdoor exposure to VOCs near a U.S. airport revealed higher-than-expected concentrations of toluene (Jung et al 2011 ). Construction of a terminal building at a major airport in Spain was a critical contributor to ambient levels of PM (Amato et al 2010 ).

A review of airport contributions to ambient air pollution suggests that research on emissions related to GSE, GPU, and APU operations is more limited relative to research on emissions from aircraft (Masiol and Harrison 2014 ). Concentrations of CO 2 , CO, PM, hydrocarbons, NO x , sulfur dioxide, sulfate, and black and organic carbon are estimated for APU and GSE use at 20 U. K. airports (Yim et al 2013 ), emissions of CO, hydrocarbons, and NO x from APUs and GSE are calculated for turnaround operations at major European airports (Padhra 2018 ), and concentrations of NO x and PM for APUs and GSE at Copenhagen Airport are calculated (Winther et al 2015 ). Provision of fixed electrical power and external air conditioning units is considered a sustainable solution for mitigating PM and NO x emissions from APU, GPU, and GSE operation (ACRP, 2012a , Yim et al 2013 , Winther et al 2015 , Padhra 2018 , Preston et al 2019 ). Use of alternative fuel (hydrogen) for powering GSE is considered another sustainable measure to improve ambient air quality on the airport apron (Testa et al 2014 ).

3.1.1.3. Water and wastewater

The major themes related to Water and Wastewater in the reviewed articles include water conservation strategies at airports and water quality concerns related to airport activities.

3.1.1.3.1. Water conservation

Airports consume water for indoor operations such as toilet-flushing, food preparation, and HVAC systems and for outdoor operations including irrigation and aircraft/infrastructure washing and maintenance (Krop et al 2016 ). The amount of water that major airports consume is not insignificant, and is on par with consumption patterns of small and medium-sized cities (de Castro Carvalho et al 2013 ). A typical metric for assessing airport water consumption is volume per day (Baxter et al 2019 ), but this metric fails to offer a broader picture of what sources of water are consumed and what management practices yield the best results (Couto et al 2013 ). The water conservation techniques proposed for airports include monitoring of water consumption, use of water efficient fixtures/fittings, reducing irrigation demand, and use of alternative water sources (e.g. rainwater, greywater, recycled wastewater).

An important point in the literature is that much of airport water consumption is for activities that do not require potable water. There is an opportunity for airports to rely upon alternative sources of water which have been studied for: rainwater harvesting at an Australian airport (Somerville et al 2015 ); wastewater reclamation for a Brazilian airport (Ribeiro et al 2013 ); greywater usage at a Brazilian airport (Couto et al 2013 , 2015 ); seawater and greywater use at an airport in Hong Kong (Leung et al 2012 ). These studies assess the efficacy of alternative sources in terms of demand met.

3.1.1.3.2. Water quality

Water quality concerns related to airport activity can be categorized as persistent, seasonal (e.g. from de-icing operations), and accidental (e.g. fuel spills) (Baxter et al 2019 ). Airports make efforts to prevent hazardous pollutants and fluids from entering groundwater or surface water bodies. Stormwater management strategies include use of bioretention basins, green roofs, harvesting, porous pavement, sand filters, and wetland treatment systems (Jolley et al 2017 ). The academic literature focuses on water quality issues stemming from de-icing activities, a necessary operation for aircraft and runways in cold-weather climates. De-icing fluid runoff can create negative surface water quality effects that impact aquatic flora and fauna by causing higher levels of chemical oxygen demand and lower levels of dissolved oxygen (Fan et al 2011 , Mohiley et al 2015 ). Potential mitigation measures for managing aircraft de-icing include utilization of novel soil filters (Pressl et al 2019 ) and treatment with constructed wetlands (Higgins et al 2011 ). Most studies assess the water quality impact of de-icing fluid, but one article examined the GHG impact from forgoing collection and treatment of de-icing fluid at a wastewater treatment plant and instead using on-site recycling (Johnson 2012 ).

3.1.1.4. Site and habitat

Major themes of the Site and Habitat category in the literature refer to the impact airport construction and operation have on existing natural ecosystems, the effects from on-site and public transportation options, and the implications of airport resilience to climate change.

3.1.1.4.1. Site

Airport development and operation requires suitable land area. In regions where existing land is not suitable, land reclamation is used to create a suitable airport environment. Research into the effects of land reclamation on existing ecosystems focus on impacts to soil, water, air, and animal species (Yan et al 2017 ; Zhao et al 2019 ). Another indicator in the literature refers to efficiency of airport land utilization, or how many aircraft operations occur per given unit area (Janic 2016 ). Airport operation and its impacts on wildlife populations is another area of research, with the goal of finding specific strategies to discourage and accommodate wildlife populations on airfields, airport water resources, terminal buildings, and control towers (Belant and Ayers 2014 ). Work done in the academic literature focuses on identifying the factors that attract avian species to green roofs (Washburn et al 2016 ), on the impacts of solar arrays on avian species (Devault et al 2014 ), and on the effects of airport expansion on bat populations (Divoll and O'Keefe 2018 ).

3.1.1.4.2. Transportation

Sustainable transportation, as it relates to airports, refers to the modes of transportation for shuttling passengers from terminals to parked aircraft and for bringing passengers to airports. Common sustainability practices for on-site transportation include: use of alternative vehicles (e.g. electric vehicles); restriction of vehicle idling; and reducing the number of empty trips (Kolpakov et al 2018 ). One study examined the use of an underground rapid transport system (URTS) for transporting airport passengers the long distances from main terminal buildings to satellite and midfield concourse terminals (Liu and Liao 2018 ). This study did not include specific environmental indicators, but noted that use of URTS is sustainable because it frees up congestion from passenger transport on the airfield concourse. Sustainable public transport options might include using automated vehicles (Wang and Zhang 2019 ), encouraging passengers to use existing public transport options by enhancing their capacity, discouraging private vehicle use, integrating with other transport hubs (Budd et al 2016 ), or installing dedicated electric vehicle charging infrastructure (Silvester et al 2013 ).

3.1.1.4.3. Resilience

The resilience of airports to climate change impacts is a significantly under-researched subject. Relevant risks that airports in coastal locations will face include impacts from sea-level rise and increased frequency of flooding events (Marchi 2015 , Burbidge 2016 , Poo et al 2018 ). Another site implication related to climate change is that increased mean air temperatures will make it harder for aircraft to generate lift, thereby necessitating the construction of longer runways (Coffel et al 2017 ).

3.1.1.5. Materials and resources

Themes from the literature for Materials and Resources center around selection of materials for the construction of airfield (e.g. runway, taxiway, apron) and terminal building infrastructure, as well as management of waste from airport construction and operation.

3.1.1.5.1. Airfield materials

Estimation of environmental effects of airfield pavements is a fairly well-researched subject area, relative to other airport infrastructure. Airfields are either made from asphalt or concrete, which are known major sources of GHGs (Horvath 2004 , Santero et al 2011 , Miller et al 2016 ). The sustainability of airfield pavements is constrained by structural integrity requirements and safety standards (Pittenger 2011 ).

Evaluation metrics for sustainable airport pavement can be general, such as implementing suggested best practices, including: using recycled aggregate in pavement mixes; using locally sourced construction materials; reducing idling times of construction equipment (Hubbard and Hubbard 2019 ). More specific critical factors of a sustainable airport pavement relate to its construction (i.e. the raw materials and equipment used, transportation, waste management) and its operation, which is a function of the pavement's structural characteristics (Babashamsi et al 2016 ). Table A4 in appendix A highlights the specific sustainable practices and assessment methods/metrics found in the literature as they pertain to different parts of the airfield. Example sustainable practices include use of supplementary cementitious materials (SCM) in concrete runways and use of recycled aggregates in taxiway and apron construction. LCA is frequently used in measuring the environmental sustainability of airfield pavements. The scope of most of the LCAs is limited to impacts from the raw material and construction phases of the airfield.

3.1.1.5.2. Building materials

Relative to the airfield, environmental impact analysis of other airport infrastructure (e.g. terminal buildings) is much more limited. LCAs have been performed to determine the optimum level of thermal insulation for terminal buildings at two Turkish airports with a focus on selecting a design that reduces GHG emissions (Akyuez et al 2017 , Kon and Caner 2019 ). An extensive overview of construction methods and building materials that are standard practice (e.g. using locally sourced materials) among the green building community is applied for airports (ACRP, FAA, Ricondo & Associates, R. &, Center for Transportation, C. for, & Ardmore Associates 2011 ). It is common practice, as mentioned in the ACRP literature, for airports to aim for green building certification from groups such as the U.S. Green Building Council's Leadership and Energy in Environmental Design (LEED) like LEED provides a checklist framework where building owners (municipalities in the case of airports) earn points for choosing 'green' building materials and design attributes, among other criteria. There are over 200 LEED certified airport buildings worldwide (USGBC 2020 ), with SFO's Terminal 2 the first LEED Gold airport terminal in the U.S. (SFO 2011 ).

3.1.1.5.3. Waste management

Analysis of waste management at airports is another emerging research area. Waste sources at airports include food waste from retailers/concessionaires, construction waste, and aircraft-related waste (Turner 2018 ). Metrics applied for analyzing waste at a major international airport include quantity of waste, waste source fraction, and waste amount per operation (Baxter et al 2018b ). One article assessed the life-cycle impact, in terms of air emissions, of six waste management scenarios at Hong Kong International Airport determining that on-site incineration with heat recovery yielded optimal results (Lam et al 2018 ).

3.1.1.6. Multidimensional studies

Sustainability, as expressed in ACRP reports (Brown 2012 , Delaney and Thomson 2013 , Lurie et al 2014 , Prather 2016 , Malik 2017 ), encompasses many categories including energy and climate, water, waste, natural resources, human well-being, transportation, and building design and materials. Many of the metrics that the ACRP literature use to assess the specific categories of sustainability mirror those described in the academic literature. A theme among the ACRP work is the evaluation of sustainability practices from an economic and practical perspective, recognizing that implementation can yield economic benefit but takes concerted, coordinated effort.

Table 5 identifies metrics used for quantifying impacts and strategies used to reduce impacts. These metrics and strategies are extracted from the multidimensional journal articles included in the systematic review. Each metric or strategy is prioritized to the one of the five categories of interest. While the focus of this review paper pertains to metrics/strategies that evaluate the sustainability of physical airport infrastructure, and not does focus on environmental impacts related to the aircraft LTO cycle, some of the multidimensional papers include indicators for evaluating those specific environmental impacts (e.g. noise from near-airport aircraft operations). The indicators in table 5 range from explicit, quantifiable metrics (e.g. tonnes CO 2 per passenger) to more vague best practices (e.g. conserve energy in airport buildings). The metrics and strategies that are explicit and quantifiable are more informative for enacting policy measures than are vague strategies such as 'conserve energy' or 'reduce emissions.' It is also more effective for metrics and strategies that connect environmental impacts to operational outcomes and level of service (e.g. number of passenger-miles traveled). Connecting impacts to level of service allows for airports to track how efficiently they are managing their impacts as numbers of operations increase.

Table 5.  Sustainability indicators from multidimensional papers.

a ISO 50 001 Certification = International Standard Organization's Energy Management System. b Airport Carbon Accreditation = ACI certification that recognizes an airport's efforts to manage CO 2 emissions. c ISO 40 001 Certification = International Standard Organization's Environmental Management System. d WLU = Work Load Unit, a standardized metric for airport operations in terms of number of passengers processed or mass of freight handled.

Indicators from each multidimensional paper do not always span all five categories of environmental sustainability, suggesting that consensus building on the definition of environmental sustainability needs to occur. The Energy and Atmosphere category dominates with metrics often related to reducing airport building and airfield energy consumption and air pollutant emissions. Of the eight journal articles included in table 5 , all include metrics for addressing noise pollution in the Comfort and Health category, but none provide explicit metrics for assessing indoor air quality for airport buildings. The indicators in the remaining three categories vary in level of specificity. As an example, in the Materials and Resources category, four of the articles suggest airports use 'green building materials' but only one article (Ferrulli 2016 ) identifies in some detail what that means.

A theme that emerges from the multidimensional papers are the different methods utilized in determining the overall sustainability of an airport. Utility-based methodologies are utilized in two of the multidimensional articles (Chao et al 2017 , Lu et al 2018 ) in the ranking of the most critical indicators by weights applied from expert opinion. Another method for assessing an airport's environmental sustainability is the application of a checklist-based point system where the most sustainable airport implements the most indicators with the highest level of points (Gomez Comendador et al 2019 ). One method incorporates cost-benefit analysis where each environmental indicator for an airport development project is transformed into a financial amount and the highest benefit-cost ratio yields the most sustainable outcome (Li and Loo 2016 ). A composite ranking indicator is created by normalizing indicators across all categories to compare the environmental sustainability of multiple airports (S. Kilkis and Kilkis 2016 ). Only one method applies life-cycle assessment in inventorying the environmental impact from the LTO cycle, APU and GSE operation, de-icing activities, lighting, and construction of an airport terminal, airfield, and parking lot (Chester and Horvath 2009 ).

The multidimensional articles that include case study airports are listed in table 6 , along with each airport's location. All of the case study airports are considered major international hubs, averaging millions of passengers per year. Their locations span the primary airport markets including Asia, Europe, and the United States, but do not reflect the emerging markets of Latin America and Southeast Asia. By comparing airports of a similar operational capacity, the multidimensional papers offer some insight into how varying regions influence environmental impact. However, more case study airports are necessary to capture local impacts. Insight is lacking on whether the sustainability indicators developed in these multidimensional articles result in distinct environmental outcomes for disparate levels of airport service (e.g. small, regional airports; medium hub airports). Modeling environmental impacts from an average airport (Chester and Horvath 2009 ) allows for generalization of results, which might yield more far-reaching outcomes (i.e. sustainability indicators can be applied to a greater range of airports).

Table 6.  Case study airports/locations from multidimensional papers.

3.1.2. Summary of trends in existing research

Figure 5 shows a word cloud diagram of the article titles included in each of five sustainability categories and the multidimensional category. Frequently used words appear larger relative to less frequently used words. Figure 5 provides a visual representation of the key themes for each category. A summary of key trends in the five sustainability categories and the multidimensional category include:

• Energy and atmosphere: Articles focus on investigating the efficacy of on-site renewable energy at various case study airports. Common sustainability indicators are total energy consumed and mass of GHG emissions from energy consumption. Best practices are considered as: monitoring of energy consumption; utilization of energy efficient HVAC equipment and lighting; installation of on-site renewable energy. There is some effort, particularly in the ACRP literature, to evaluate best practices from a practical perspective (e.g. addressing the safety implications of PV installations). Use of LCA in this category is limited.
• Comfort and health: Most of the research is focused on indoor comfort and health indicators like preferences for thermal and lighting conditions and concentrations of PM, VOCs, CO, and CO 2 . Studies on exposure to ambient air pollutants from non-aircraft sources are limited. Most of the research on ambient air quality aggregates emissions from all sources. There is recent effort to investigate the impact from non-aircraft sources such as APUs, GSE, and GPUs and to identify possible solutions for these equipment (e.g. use of external electrical power and air conditioning units).
• Water and wastewater: Articles focusing on estimating the potential utilization of alternative water sources at airports dominate. Water quality research pertains to impacts from stormwater and de-icing fluids. A typical article in the Water and Wastewater category includes annual water consumption per passenger or flight operation. There is discussion in the literature on whether a disaggregated metric (e.g. indoor water consumption per passenger, outdoor water consumption per passenger) might be a more effective performance indicator.
• Site and habitat: This category is the least explored in the literature. Few articles offer measurable indicators, with most of the quantifiable metrics relating to land use efficiency and destruction of wildlife habitat. There is need for quantifiable indicators for research in on-site, public/private transport and for climate change adaptation practices.
• Materials and resources: Research on the environmental sustainability of airfield pavements dominates this category. LCA is the most frequently used assessment methodology, with life-cycle GHG emissions and energy consumption the most common assessment metrics.
• Multidimensional: Research that investigates airport sustainability from a multidimensional perspective is grouped according to efforts by ACRP and by the academic community. ACRP largely defines environmental sustainability across the five categories (i.e. energy and atmosphere, comfort and health, water and wastewater, site and habitat, materials and resources), but often focuses on economic and practical factors of implementing sustainability best practices. These best practices are often identified through interviewing and surveying U.S. airports. Sustainability indicators in the academic literature predominantly focus on energy consumption and GHG emissions. Sustainability is assessed with a number of methodologies (e.g. utility-based theories, cost-benefit analysis, LCA), suggesting that within the academic community there is a lack of consensus on what attributes and indicators make an airport sustainable.

Figure 5.  Word cloud diagram of article titles included in systematic review. Frequently used terms appear larger relative to less frequently used terms.

3.2. Application of an airport sustainability assessment

This section reviews the application of the SFO environmental sustainability framework on an existing infrastructure project at the airport.

3.2.1. Selection of case study airport

San Francisco International Airport (SFO) is one of the United States' large hub airports and it serves major domestic and international routes. The airport ranked seventh among busiest airports in 2018, with enplanements totaling close to 28 million (FAA 2020b ). The airport was an early adopter in implementing sustainability efforts and in developing metrics to assess the sustainability of construction and operation of airport infrastructure projects (SFO 2020 , FAA 2020a ). A review of the implementation of SFO's sustainability framework answers two critical questions: (1) how sustainability efforts practically get implemented at airports, and (2) how their implementation is or is not effective in yielding measurable benefits. Featuring SFO as a case study offers stakeholders (e.g. regulators, airport operators, the public) insight into what is considered best practices, or acceptable methods, for managing environmental impacts for major international airports. Additionally, it provides some understanding of how sustainability measures at an airport like SFO might not work as well for other airport types (e.g. small hub, regional, general aviation, etc.).

3.2.2. Development of sustainability indicators

SFO is redeveloping their Terminal 1 as part of a capacity-enhancement upgrade for the entire airport; the upgrade will increase the terminal's total number of annual enplanements to 8.8 million. Sustainability indicators were developed in conjunction with SFO's planning, design, and construction guidelines as a measurable index for determining whether the Terminal 1 project will comply with the airport's overarching environmental goals (e.g. achieving GHG emission reductions relative to a baseline year). Each sustainability indicator is grouped according to relevant themes in the five categories of Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, and Materials and Resources. Indicators are either considered 'Mandatory Requirements' or 'Expanded Requirements.' 'Mandatory Requirements' outline metrics and practices that must be achieved according to applicable federal, state, regional building codes and city-wide mandates (e.g. meeting LEED requirements). 'Expanded Requirements' are voluntary metrics and practices that project participants (i.e. contractors) are obligated to implement where feasible. For example, a city-wide 'Mandatory Requirement' in the Energy and Atmosphere category mandates 40% reductions below 1990 GHG emissions by 2025. An example 'Expanded Requirement' calls for reduced GHG emissions from natural gas consumption by using automated HVAC systems.

3.2.3. Implementation of indicators

The indicators are intended to be used for the planning, design, construction, and operation/maintenance phases of airport facilities. An additional level of evaluation is applied to each 'Expanded Requirement.' Requirements are rated as 'Baseline,' 'Baseline Plus,' or 'Exceptional Project Outcome.' Per the previous 'Expanded Requirement' example, 'Baseline,' 'Baseline Plus,' or 'Exceptional Project Outcome' ratings would be given to 10%, 20%, and 30% reductions in GHG emissions, respectively. Such a rating system allows SFO to discern between project outcomes that are more 'sustainable' than others.

The results of an analysis of the projected reduction in annual GHG emissions per square meter from implementing Energy and Atmosphere 'Expanded Requirements' in SFO's Terminal 1 project are shown in figure 6 . The specific 'Expanded Requirements' include practices that rely on reduced natural gas and electricity consumption in terminal buildings (e.g. energy-efficient escalators, dynamic glazing, radiant heating and cooling). It is projected that these 'Expanded Requirements' will reduce Terminal 1's energy use intensity (EUI). The EUI indicates how much natural gas and electricity is consumed by buildings. By converting the EUI to an equivalent amount of GHG emissions per square meter, it can be shown that the GHG intensity of the Terminal 1 project will be less than the average of other SFO buildings. The blue bars in figure 6 show the amount of GHG emissions per square meter, while the dotted outline indicates the amount of annual GHG savings per square meter in the Terminal 1 project. The GHG emissions account for the upstream processes related to natural gas provision and electricity generation. See appendix B for the complete methodology in producing figure 6 . The savings represent an approximate 57% reduction relative to the average GHG intensity for all SFO airport building infrastructure.

Figure 6.  Reductions in GHG Intensity associated with implementing energy reducing 'Expanded Requirements' in Terminal 1 (T1) project relative to the SFO average. Savings are relative to 2018 data.

4. Discussion

4.1. limitations and gaps of existing research.

With few exceptions on airport energy (Kilkis and Kilkis 2017 , Tagliaferri et al 2018 ), overall sustainability (Chester and Horvath 2009 , 2012 , Taptich et al 2016 ), and airfield pavements, much of the research fails to holistically analyze the environmental impacts through supply chains and regional variations. While the ACRP literature provides a sample representation of current best practices at airports, its analysis is sometimes limited by the responses it receives from case-study airports. For both the ACRP and academic literature, analysis of sustainability indicators is often limited by the scope of a case-study airport, so it is difficult to link research results with suggested practice or policy outcomes.

The literature in the Energy and Atmosphere category lacks a broader understanding of how much energy is used at different airports, what it is used for, and where it comes from. Current estimates are limited by the number of existing case-study airports. With an exception (Ozdemir and Filibeli 2014 ), the academic literature limits its characterization of GHG emissions according to Scope 1, Scope 2, and Scope 3. This limitation in the literature indicates that there is a slight disconnect between the academic research community and the airport industry and stakeholders as the Scope characterization is how the industry thinks about and manages GHG emissions. Research that investigates different energy sources (e.g. solar; bioenergy) and energy provision strategies (e.g. grid versus on-site storage) is just beginning, and more effort in this area is needed. Additional gaps in the research include:

• Environmental impacts of energy consumption in terms of other pollutants besides GHG emissions;
• Environmental assessment of airports and supply chains using local and regional models and data (Cicas et al 2007 );
• Characterization and environmental impact assessment of energy consumption patterns for specific airport infrastructure and equipment by region (e.g. U.S. airport terminals are focused on food consumption; European/Asian airports serve as retail/recreational centers);
• Energy consumption impacts from construction of new airport expansion/retrofitting projects.

As with the Energy and Atmosphere category, research in the Comfort and Health category could be broadened to include more research and innovative and exploratory case studies. In light of COVID-19, more research is urgently needed to investigate how terminal building design and ventilation equipment might influence spread of infectious diseases. Ambient air quality research tends to aggregate sources, which makes it difficult to determine if mitigation policies are effective. Additional gaps in the research include:

• More human health-focused exposure studies related to operation of non-aircraft equipment, such as GSE, GPUs, APUs, and ground access vehicles;
• Investigation of air pollutant concentrations related to landside operations, such as passenger pick-up and drop-off;
• Research on human health impacts from airfield and terminal building maintenance, retrofit, and construction;
• Air quality impacts related to selection of different building materials and cleaning/daily maintenance procedures.

As suggested in the Water and Wastewater literature, assessing an airport's water consumption in terms of volume per day provides minimal insight. More research should be conducted to provide a thorough overview of disaggregated water consumption at the airport level so that sustainable practices can be implemented appropriately. A major gap in the literature is the complete lack of research into the linkage between water consumption, water quality, energy needed to convey, treat and heat water, and the resulting GHG and other environmental emissions and impacts. This water-energy nexus is particularly relevant in examining the environmental sustainability of using alternative sources of water at airports, especially with respect to potable versus non-potable demands and options.

Much of the literature in the Site and Habitat category lacks explicit, quantifiable sustainability indicators and there is vast room for investigation into the following gaps:

• Energy and environmental implications of constructing resilience infrastructure, such as sea walls and stormwater systems;
• Environmental impacts of onsite transportation systems, such as underground rapid transit systems;
• Overview of the types of suitable, environmentally efficient transportation modes within and outside of the airport boundary, which is dictated by airport configuration and location;
• Environmental trade-offs between site selection and terminal building orientation and layout of runways.

Research in the Materials and Resources category is predominantly focused on environmental impacts of airfield pavement construction and maintenance, with life-cycle energy consumption and GHG emissions as common metrics. Within the theme of airfield pavements, more research regarding innovative designs and maintenance techniques are warranted. There is a lack of understanding on what sustainable pavement practices can be implemented at airports of different operational capacities. Small and medium-sized airports might be good candidates for testing out innovative practices because their load or volume requirements tend to be smaller than those of larger airports. In terms of sustainable materials and design for airport buildings, research results are limited. In practice, it is more common for airports to strive for LEED certification of airport buildings. LEED, for practical purposes, is a relatively easy standard to implement, but is not sufficient for meeting quantified performance goals throughout the life cycle of airports. Additional gaps in the research include:

• Environmental impact of conventional and alternative construction materials in terminal building infrastructure;
• Sustainability impacts of supply chains and sourcing of airport construction materials;
• Deeper understanding leading to defensible actions on waste generation and waste management techniques at airports, especially in the context of waste-management policies such as 'zero-waste' and bans of single-use plastics.

A review of articles in the Multidimensional category indicates that there is no cohesive, agreed-upon definition of airport environmental sustainability. Gaps in the research include:

• Determining optimal methods for achieving overall environmental sustainability at an airport, also integrated with achieving specified city, regional-level, airline, or civil aviation targets;
• Integration of life-cycle, or holistic, thinking within a specified time horizon into decision making (e.g. should an airport implement an electricity-based strategy if the electricity is generated from fossil fuels?);
• Specifying environmental sustainability indicators in the context of airport operational safety;
• Investigating the overlap between environmental sustainability and airport resilience;
• Rigorous analysis of environmental sustainability and operational parameters;
• Integration of actions in achieving societal sustainable development (economic, environmental, social) with airport, airline, air traffic control, and in general, civil aviation goals.

4.2. Efficacy of case study application

A projected 57% reduction in annual GHG emissions per square meter from consuming natural gas and electricity on-site within the airport terminal buildings suggests that SFO's sustainability assessment indicators have the potential to be effective. A more meaningful expression of results would relate saved GHG emissions to the airport's level of service (e.g. GHG emissions per passenger or per revenue dollar). There are limitations to stating one airport's efforts as 'best practice.' It should be emphasized that applicability from the results of the case study are dependent upon local factors. For SFO, implementing energy-efficient strategies saves more GHG emissions because SFO's electricity is supplied from hydropower, which is less carbon-intensive relative to the state average. Utilizing low carbon-intensive energy is a key sustainability performance indicator. While post-facto analysis would be able to confirm actual GHG reductions from implementing 'Expanded Requirements,' the project is still ongoing. Some important observations can still be made regarding SFO's sustainability indicators.

In discussions with parties involved with the Terminal 1 reconstruction projects, having sustainability criteria at the outset of project development is crucial. All involved parties must be aware of their specific commitments. It is a good practice going forward for project contracts to incorporate strong sustainability performance indicators. SFO plans to integrate language more thoroughly into the Architectural and Engineering standards and guidelines that specifically align with two of SFO's guiding environmental priorities, namely climate change and human and ecological health. Regarding the former, the new contract language will explicitly require that decarbonization be reflected in project design and procurement. For example, instead of a voluntary consideration as part of an 'Expanded Requirement,' low-carbon structural steel would have to be selected as a building material.

The voluntary aspect of the framework (i.e. the 'Expanded Requirements') and the evaluation of 'Expanded Requirements' as baseline, baseline plus, and exceptional project outcome are rather subjective. Such subjectivity does not necessarily result in a completed project with the best environmental performance. Additionally, the SFO framework relies upon building codes that while they are 'state of the art' compared to building codes outside of California, represent a minimum standard. If interested in attaining a facility or project that meets a specified, quantifiable environmental outcome, the subjectivity of a rating system or checklist is not the most effective approach.

SFO's sustainability indicators do not explicitly consider the tradeoffs that potentially occur with prioritizing one criteria over the other; it is a rather static framework that could benefit from incorporating spatial and temporal factors. For example, electing to use a decentralized recycled water source (which is an 'Expanded Requirement' in the Water and Wastewater category) is sometimes an energy-intensive process which can result in increased GHG emissions while enhancing resilience. In this anecdotal example, there is a potential tradeoff between achieving water conservation and reducing GHG emissions. While the SFO framework might work well for an airport that explicitly prioritizes overarching goals (e.g. reducing GHG emissions and climate change impact), it might need to be reevaluated for airports that must equally consider sometimes conflicting environmental priorities.

4.3. Suggestions for direction of future research

The roadmap for future research of airport environmental sustainability emphasizes increased stakeholder involvement, more life cycle-based analysis, linkage of environmental impacts with operational outcomes, and addressing major challenges such as adaptation to climate change and mitigation of infectious diseases like COVID-19.

Airport environmental sustainability is often addressed at project scale. There is a need for investigating the larger role that airports have in impacting the environment, especially in the context of achieving city- and regional-level environmental outcomes that lead most directly to higher environmental quality of people and ecosystems. This ties in with stakeholder involvement because for sustainability indicators including GHG emissions, an airport only claims responsibility for Scope 1 and Scope 2 emissions. Airports often exclude ownership of Scope 3 emissions (e.g. emissions from an airline's GSE, without which there are no airports). The outcome of an airport excluding ownership of Scope 3 emissions is twofold: (1) it is more difficult to manage Scope 3 emissions, and (2) it is difficult to understand an airport's total GHG impact at the city/regional/state/national level, which is important for meeting larger-scale climate performance targets. Therefore, a broader analysis of how different stakeholders should be included in addressing environmental sustainability efforts is necessary.

Society faces important challenges such as adapting to climate change, mitigating the spread of pandemic-causing diseases, and enhancing environmental quality of people and ecosystems. An airport's role in addressing these challenges is largely undefined, but sure to be a significant one. It is imperative that thorough research on an airport's role in managing these challenges gets organized.

5. Conclusion

A comprehensive, systematic review of 108 peer-reviewed articles and technical reports related to assessing and measuring aspects of airports' environmental sustainability has been conducted. Articles have been characterized according to the following categories: Energy and Atmosphere, Comfort and Health, Water and Wastewater, Site and Habitat, Materials and Resources, Multidimensional. Along with a systematic review of academic literature, a review has been undertaken of the application of an existing airport sustainability assessment framework for a case study airport, SFO.

A broad conclusion from the systematic review is that interest in airport environmental sustainability as a research topic is steadily increasing, but that there is ample need for more investigation. Prominent research themes within the scope of airport environmental sustainability include analyzing the environmental impacts (namely GHG emissions) from airfield pavements and energy management strategies for airport buildings, but not from other components of airports and for other environmental emissions and impacts. There is a dearth of research on the impacts of indoor air quality at airports. In the research community, there appears to be a lack of consensus about the scope of environmental impacts that should be included when evaluating the overall sustainability of airports. GHG emissions from energy consumption are one of the most commonly used metrics in research focused on overall airport sustainability.

Methods for evaluating environmental impacts vary. Systems like the World Resource Institute's Scope 1, 2, and 3 designation for GHG emissions and the LEED system for buildings are well-represented in airport-industry practice. The Scope designation primarily divides responsibility for mitigating emissions between airports and airlines, creating a gap whereby airports cannot directly control all emission sources. LEED is a minimum standard that is not sufficient for meeting quantified performance goals throughout the life cycle and supply chains of airports.

Moving forward, the increased use of assessment methodologies such as LCA will be useful in guiding decision-makers and policy outcomes in a more robust, granular direction. In the academic literature, LCA is primarily used for evaluating the environmental impact of airfield pavement construction. However, LCA can and should be applied to evaluate all components of airport construction and operational activities and to guide decision-making as to what practices will yield optimal results. LCA is the only comprehensive, systematic methodology (defined in ISO 14040 and 14044) that estimates the entirety of life-cycle environmental impacts of a product, process, or service. This method is very useful for accounting for regional differences in impacts, for comparing among alternative strategies, and for identifying weak points or activities that result in the greatest environmental burdens. There are also economic and social aspects of LCA that are helpful for decision-makers. One LCA approach, Economic Input-Output LCA, can be used to evaluate the resources, energy, and emissions resulting from economic activity throughout a product's supply chain (Hendrickson et al 1998 ). There are efforts to use a life-cycle approach to focus on the social aspects of a product's impacts (Grubert 2018 ). While addressing the economic and social impacts from airports is beyond the scope of this review, the economic and social implications of airports are likewise very important and demand thorough investigations and actions.

In conjunction with LCA, future research should apply analysis that connects environmental impacts with operational parameters for specific airport occupant groups (e.g. ground handlers), airport infrastructure (e.g. apron), and airport scale (e.g. small, medium, large hubs). Accounting for operational parameters at different scales will provide a better understanding of how environmental sustainability efforts impact different stakeholders and the airport's primary function (i.e. processing passengers and cargo).

A key aspect of addressing the environmental sustainability of airports is the involvement of different stakeholders. As identified in figure 1 , the airport is comprised of airside and landside components. Historically, these components have been managed by distinct stakeholders. Understanding the relationship among the airport components, their respective environmental impacts, and their ways of managing stakeholder groups is critical because it leads to identifying who must act to mitigate environmental impacts. Figure 7 depicts an annotated version of the airport system boundary with suggested best practices for major airport components. Based on the literature review and the application of the SFO case study, effective sustainability practices that airports can implement in the short term are: (1) supply electricity from renewable, low-carbon sources whether on-site or from local utilities; (2) electrify transportation vehicles (e.g. shuttles, maintenance trucks) within the airport system boundary; (3) electrify all gate and ground service equipment; (4) implement water conservation practices like installation of water-efficient faucets and toilets; (5) install energy-efficient fixtures like LED lighting in all airport infrastructure; (6) select durable interior building materials for improved maintainability and reduced waste production.

Figure 7.  Suggested best practices for improving airport environmental sustainability.

These six suggested sustainability practices can result in prompt, substantive environmental benefits without significant tradeoffs. For example, relying on low-carbon electricity reduces GHG as well as other emissions. Electrifying ground service equipment and other airport vehicles results in reductions of air pollutants (NO x , PM) within the airport vicinity, which is a human health benefit. These practices are considered implementable in the 'short term' as opposed to longer-term projects such as changing the material composition of the airfield or installing on-site, decentralized wastewater treatment. These measures cover activities and operations that essentially occur at all airports, but to varying degrees of scale (e.g. all airports consume electricity). In that vein, ease of strategy implementation depends upon airport type, the resources (e.g. cost, accessibility, expertise) available to the airport for successful implementation and the controlling stakeholder. Further analysis of those distinctions is needed in future research.

One common tendency is for airports to adopt a perceived 'best practice' based upon another airport's successful implementation. But progress is needed to ensure that every airport considers all relevant environmental sustainability indicators systematically to account for regional and supply-chain effects rather than simply follow others' actions. This ties in with the further need to connect all relevant environmental impacts with local human health and ecosystem effects as communities living in proximity of airports bare a greater burden of airport operations. Future research should concentrate on the development of quantifiable indicators or performance metrics. Research and practice that increase stakeholder involvement, incorporates life-cycle assessment, and links environmental impacts with operational outcomes will help airports as well as the aviation industry to address their roles in major global challenges (e.g. climate change adaptation, mitigation of infectious diseases).

Acknowledgments

FG and JR acknowledge the financial support of the Sustainability Office at Groupe ADP.

Data availability statement

All data that support the findings of this study are included within the article (and any supplementary information files).

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The research environmental impact disclosure

• Published: 29 November 2021
• Volume 33 , pages 3–5, ( 2022 )

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Just in the past 12 months, we have witnessed significant devastating environmental events including, fires in southeast Mediterranean and Balkan countries, in the US and elsewhere, floods in Europe and Asia, and extreme temperatures including their odd fluctuation. We are also aware of the amount of waste we generate and its impact on land and seas and the destruction of parts of our natural resources. We definitely need to work together towards changing the course of events.

If we wanted, as researchers, not as other citizens, to contribute to sustainability or to address environmental challenges, what should we do?

The usual answer of the scientific or technological community would be: do more research on sustainability, life-cycle impact, and promote the publication and dissemination of such research hoping it will contribute to our stated cause. This is the classic response of these communities: observe an issue, study it, propose technical solutions, and implement them. Solutions could be: electric cars to replace gasoline cars; or recycling plastic to prevent its becoming waste, or lightweighting or renewables. There are, however, limitations to this approach. for example, do we really consider the long-term effects of a “sustainable” technology? How do we actually define a “sustainable” technology? Do we consider all sustainability aspects and technology’s side effects? There is not always a silver bullet and there could be many consequences and trade-offs: take the example of a study comparing vehicle concepts in China that found that electric or hybrid cars reduce global warming but at the same time increase mineral resource scarcity, and ecological and human toxicity (Zeng et al. 2021 ). Following this, mineral scarcity has significant implications for the environment (Rebello et al. 2021 ). In the same context, another study confirmed, that the environmental impact of an electric vehicle in China on eutrophication and acidification is significantly higher than from internal combustion engines (Sun et al. 2021 ). Another example is the trade-off between carbon and water footprint for biofuels (Berger et al. 2015 ). There is also more specific criticism about the concept of sustainability and its impact on addressing environmental challenges (e.g., Benson and Craig 2014 ; Fiala 2008 ). There is also an increasing need to address the social and economic sustainability dimension (Finkbeiner et al. 2010 ). Besides the sustainability-driven research, that explicitly deals with an assessment of these aspects, the vast amount of research studies do not deal with the environmental or sustainability implications at all. The question about their impacts on the environment remains unresolved. Technology development is definitely needed for human welfare and well-being, but it may need some regulation and a kind of instruction or information leaflet; just like any medicine has a package insert that provides warnings and informs about adverse effects.

For all types of research, we have to address two issues: what is the impact of the research activities themselves on the environment, and what is the impact of the outcome of the research? The former topic is receiving more attention lately (e.g., Fardet et al. 2020 ; Ligozat et al. 2020 ; Williams et al. 2021 ). Ligozat et al. ( 2020 ) rules include recommendations that are included in this editorial. Specifically, rule 7 “Evaluate the impact of your research practices,” is one that we adopt in this editorial: reflecting on the impact of our own research through a Research Environmental Impact Disclosure (REID) Footnote 1 to be discussed later. Moving a step further, we could claim that following the principle of reflexive practice (Reich 2017 ), if we designed our research to be more effective and efficient, it would also be more sustainable; we do think that those working on sustainability research should try to make their research sustainable. This is not only a moral obligation but will serve our self-interests.

Going back to the two issues related to research sustainability, there could be all four combinations including sustainable research that develops some sustainable solutions or research with zero impact on the environment that has a significant damaging effect on the environment. Let us consider some examples. If we develop a method for additive manufacturing (AM), it may save material used in traditional manufacturing but lead to waste more due to excessive use of prototyping or it may use toxic materials (Gao et al. 2015 ). Specific research on AM could identify where it stands and what are its long-term goals concerning this landscape (Bours et al. 2017 ). Another example is research on modularity that may allow reducing environmental impact because it allows for upgrading systems hence increasing their life but initially, it might harm the environment because it requires developing and manufacturing unnecessary interfaces and casings (Engel and Reich 2015 ). Some research such as on design theory or selection methods may find it more difficult to state environmental impact but perhaps this could be done depending on the particular topic. For example, research on axiomatic design might improve the ability to create functionality independent modules, making the aforementioned issues related to modularity applicable here.

Note that we are not making any judgment about the quality of research or its review outcome based on the REID. The goal is to increase awareness and allow the community to reflect on its activities. To illustrate, we could work on polluting products (such as gasoline cars) trying to improve them without attention to sustainability. The REID of such research might state that this research does not try to improve the environmental impact but that the outcome may be harming or improving it as a side effect. One complaint might be that if we consider sustainability as critical, we should abandon the desire to improve such cars and move to research products that have a much better positive environmental impact. Such discussion could be part of the REID but is outside the scope of the review decision.

We anticipate that if we, researchers, start to think about these issues proactively, our research activities would, and perhaps their outcome, be more sustainable.

As a scholarly journal, we want to contribute to addressing the environmental crisis. We can contribute in at least two ways along the lines mentioned above. One way is to encourage research papers on design for sustainability or design to reduce environmental impact. Such research may contribute to addressing environmental challenges. It could be realized by creating special issues and forming a dedicated team of experts that will review papers quickly. These ideas belong to the traditional approach of doing science: we provide better service to authors and attract them to work and publish on these topics.

But we want to go a step further. We want to increase the awareness of all the community of design researchers on this topic and make sure the community considers these issues in its work. One approach to foster this is to ask of every submission, a statement regarding its impact on the environment—the Research Environmental Impact Disclosure (REID). We are not aware of such initiative elsewhere but disclosures regarding ethical issues of conducting research are common. We are requested to disclose any conflict of interests when we submit a paper and we are requested to provide information regarding approval of studies on people or animals by some board of the authors’ institution. These, however, are quite simple statements. Reflecting on the environmental impact of research is more involved. We need to strike a balance between simple, insignificant, without review statement to elaborated, meaningful and reviewed REID.

We do not have expertise in judging what the best way is. We have not tried it and observed its outcome. This seems to be the first initiative of its kind in a journal. We do not attempt, therefore, to create a template such as the one shown in Table 1 to be filled by all researchers and coerce each submission into this template. We understand that there are very different types of papers submitted to the journal and different types of REID would fit them.

One approach may be to request with any paper a short statement, in which authors discuss their sustainability contribution. Of course, authors can write something there even though their project might be a bit mediocre in terms of sustainability, but at least it would make authors think and they would have to provide some information proactively. Initially, authors can design their statements taking into account this editorial, reflecting on their research and its relation to sustainability. Reviewers and editors could read it and provide feedback to the authors. We would make it clear to reviewers that the REID does not impact the editorial decision regarding the paper because some reviewers’ decisions might be influenced negatively by research that has negative environmental impacts.

The REID will appear with the paper before the references section and readers could reflect on it. It is within the interest of authors to make this REID as best reflecting their research impact on the environment.

We intend to start requesting a REID in a separate file or fill information through the submission process as we do with the conflict of interest statement. Authors can use the template in Table 1 or create their own template or format. Diversity will allow us to experiment, learn, and develop different types of REIDs for different types of research. We also envision that the REID initiative will drive deeper discussion on sustainability and ecological impact as these will be related to any research now. Indeed, these concepts already create debate in the community (e.g., Fiala 2008 ; Marcuse 1998 ).

Authors wishing to include discussion on these items in the REID are more than welcome.

Not to be confused with the journal name acronym RIED – Research in Enigneering Design.

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Reich, Y., Finkbeiner, M. The research environmental impact disclosure. Res Eng Design 33 , 3–5 (2022). https://doi.org/10.1007/s00163-021-00379-4

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Enhancing environmental research: web scraping and sustainability.

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Climate change, pollution, environmental degradation and resource depletion are just a few of the greatest challenges facing the world in the 21st century. Tackling these challenges means carrying out thorough research involving a huge pool of world data from sources such as satellite imagery, environmental monitoring stations and local field studies, providing an array of information on human interaction with nature.

But the real challenge comes in capturing massive amounts of real-time data so wise decisions can be made within the shortest time possible. To do this, we must better understand the role of modern data collection technologies in environmental research and how we can adapt our strategies to leverage these technologies more effectively.

Introduction To Environmental Research

Historical records show that concern for the environment goes back thousands of years. In fact, in 2700 BC, some of the first known laws were implemented to protect trees from continued deforestation in Ur, Mesopotamia. Centuries later, the establishment of Scotland's Coal Smoke Abatement Society in 1898 marked a significant community-driven response to environmental issues.

These movements have been fueled in the 21st century by advancements in technology—particularly in computing and data analysis—that have significantly impacted the research industry as a whole, beyond just the environmental sector. This then begs the question: With large-scale, global environmental data collection, how do we integrate and put such information to use to address environmental challenges?

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The 82 best memorial day sales to shop now before they re gone, reacher season 3 set photo shows alan ritchson s hulking new nemesis, worldwide data collection for environmental insights.

Environmental monitoring is critical for evaluating vital factors such as air and water quality. Across the globe, various organizations and research groups deploy sophisticated data collection techniques to track environmental health.

For instance, the World Air Quality Index project collects data from over 12,000 stations in more than 1,000 cities worldwide. This project aggregates real-time data on air pollution levels, which is crucial for assessing health risks, informing the public and shaping policy decisions. Most of this data is publicly available, allowing analysts and researchers to utilize it for further studies and environmental assessments.

In the U.S., the National Weather Service gathers data from weather stations nationwide. This data, essential for generating accurate weather forecasts, plays a crucial role in emergency preparedness, particularly in areas susceptible to extreme weather events. This information is also generally accessible to the public, supporting a variety of applications from academic research to commercial use in weather-related industries.

Furthermore, conservation organizations like the World Wildlife Fund monitor deforestation, wildlife trafficking and illegal fishing activities. Public access to this data can vary, with some information available for open use to aid in raising awareness and promoting conservation efforts.

This transparency not only promotes accountability but also fosters a collaborative approach to tackling environmental challenges.

The Impact Of Web Scraping On Environmental Policy And Advocacy

In the context of environmental research and policymaking, the ability to access information without source limitations can be a significant advantage. Web scraping can be a useful tool in this scenario, enabling researchers, policymakers and advocates to gather and analyze data from virtually any online source, irrespective of geographical and linguistic boundaries. This capability is particularly helpful in environmental science, in which the global nature of challenges like climate change, pollution and biodiversity loss demands a comprehensive understanding that spans across nations.

Considerations When Using Web Scraping For Environmental Purposes

Ensure data integrity..

Credibility checking of sources is important to confirm the dependability of data collected using web scraping. If the data that web scraping provides is incorrect, it could lead to misguided decisions and policymaking; hence, data accuracy is the top-most priority. The data needs to be updated regularly to keep it relevant, and using as many sources as possible for cross-verification will add strength to your dataset.

Use data effectively.

Data can be used to track changes in the environment, monitor ecosystem health and inform policymakers. Actively participate in the collection and data analysis processes to ensure optimal environmental management.

Use high-level analytic tools.

Integrate advanced analytical tools and technologies to further enhance the value of the data collected through web scraping. Tools like AI and machine learning can help identify patterns and predictions that might not be evident through traditional analysis methods. Incorporating these technologies can provide deeper insights into environmental data, leading to more effective strategies and solutions.

Looking Ahead: The Evolving Role Of Data In Environmental Advocacy

Web scraping has emerged as one important tool in environmental research, offering a method to rapidly collect and analyze data from a multitude of sources. As technology advances, the capabilities of data collection technology will expand, offering even more sophisticated tools for data extraction and analysis. These advancements will not only enhance the accuracy and depth of environmental research but also open new avenues for public engagement and policy influence.

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Environmental Sustainability Impacts of Solid Waste Management Practices in the Global South

Ismaila rimi abubakar.

1 College of Architecture and Planning, Imam Abdulrahman Bin Faisal University, Dammam 31441, Saudi Arabia

Khandoker M. Maniruzzaman

2 Department of Urban and Regional Planning, College of Architecture and Planning, Imam Abdulrahman Bin Faisal University, Dammam 31441, Saudi Arabia

Umar Lawal Dano

Faez s. alshihri, maher s. alshammari, sayed mohammed s. ahmed, wadee ahmed ghanem al-gehlani.

3 Department of Architecture, College of Architecture and Planning, Imam Abdulrahman Bin Faisal University, Dammam 32141, Saudi Arabia

Tareq I. Alrawaf

4 Department of Landscape Architecture, College of Architecture and Planning, Imam Abdulrahman Bin Faisal University, Dammam 31441, Saudi Arabia

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No data were reported in this review article.

Solid waste management (SWM) is one of the key responsibilities of city administrators and one of the effective proxies for good governance. Effective SWM mitigates adverse health and environmental impacts, conserves resources, and improves the livability of cities. However, unsustainable SWM practices, exacerbated by rapid urbanization and financial and institutional limitations, negatively impact public health and environmental sustainability. This review article assesses the human and environmental health impacts of SWM practices in the Global South cities that are the future of global urbanization. The study employs desktop research methodology based on in-depth analysis of secondary data and literature, including official documents and published articles. It finds that the commonplace SWM practices include mixing household and commercial garbage with hazardous waste during storage and handling. While waste storage is largely in old or poorly managed facilities such as storage containers, the transportation system is often deficient and informal. The disposal methods are predominantly via uncontrolled dumping, open-air incinerators, and landfills. The negative impacts of such practices include air and water pollution, land degradation, emissions of methane and hazardous leachate, and climate change. These impacts impose significant environmental and public health costs on residents with marginalized social groups mostly affected. The paper concludes with recommendations for mitigating the public and environmental health risks associated with the existing SWM practices in the Global South.

1. Introduction

Solid waste management (SWM) continues to dominate as a major societal and governance challenge, especially in urban areas overwhelmed by the high rate of population growth and garbage generation. The role of SWM in achieving sustainable development is emphasized in several international development agendas, charters, and visions. For example, sustainable SWM can help meet several United Nations’ Sustainable Development Goals (SDG), such as ensuring clean water and sanitation (SDG6), creating sustainable cities and inclusive communities (SDG11), mitigating climate change (SDG13), protecting life on land (SDG15), and demonstrating sustainable consumption and production patterns (SDG12) ( https://sdgs.un.org/goals , accessed on 26 September 2022). It also fosters a circular urban economy that promotes reductions in the consumption of finite resources, materials reuse and recycling for waste elimination, pollution reduction, cost saving, and green growth

However, coupled with economic growth, improved lifestyle, and consumerism, cities across the globe will continue to face an overwhelming challenge of SWM as the world population is expected to rise to 8 billion by 2025 and to 9.3 billion by 2050, out of which around 70% will be living in urban areas [ 1 , 2 ]. In developing countries, most cities collect only 50–80% of generated waste after spending 20–50% of their budgets, of which 80–95% are spent on collecting and transporting waste [ 3 , 4 ]. Moreover, many low-income countries collect as low as 10% of the garbage generated in suburban areas, which contributes to public health and environmental risks, including higher incidents of diarrhea and acute respiratory infections among people, particularly children, living near garbage dumps [ 5 ]. Obstacles to effective municipal SWM include lack of awareness, technologies, finances, and good governance [ 6 , 7 , 8 ].

Removing garbage from homes and businesses without greater attention to what was then carried out with it has also been the priority of municipal SWM in several cities of developing countries [ 9 ]. In most developing countries, garbage collected from households is disposed of in landfills or dumpsites, the majority of which are projected to reach their capacities within a decade. The unsustainable approach of dumping or burning waste in an open space, usually near poor communities on the city edge, or throwing garbage into water bodies was an acceptable garbage disposal strategy. Similarly, several cities still use old-generation or poorly managed facilities and informal uncontrolled dumping or open-air waste burning. Often, these practices affect marginalized social groups near the disposal sites [ 10 ]. Moreover, this approach poses several sustainability problems, including resource depletion, environmental pollution, and public health problems, such as the spread of communicable diseases.

However, ever since the advent of the environmental movement in the 1960s, there has been a far-reaching appreciation of environmental and public health risks of unsustainable SWM practices. In the 1970s and onward, SWM was a technical issue to be resolved using technology; hence, the emphasis and investments were placed on garbage collection equipment [ 5 ]. Although modern technology can significantly reduce emissions of hazardous substances, by the 1990s, that viewpoint changed when municipalities become unable to evacuate and dispose of garbage effectively without the active involvement of service users and other stakeholders [ 5 ]. The inability of the public sector in the global South to deliver sufficient improvement of SWM, coupled with the pressure from the financial institutions and other donor agencies, led to privatization policies at the end of the decade. However, as privatization failed to provide municipal SWM services to the poor and marginalized communities, the current global thinking on addressing municipal SWM problems is changing.

A more sustainable waste management approach prioritizes practices such as reduced production, waste classifications, reuse, recycling, and energy recovery over the common practices of landfilling, open dumps, and open incineration [ 11 , 12 , 13 ]. This approach, which is still at an early stage but getting increased attention in the Global South, is more inclusive and environment-friendly and has less negative impact on human health and the environment than the common practices [ 14 , 15 , 16 ]. As such, there is a need to assess SWM practices in the Global South and their impacts on environmental and human health because 90% of the expected growth in the urban population by 2050 is expected to happen here. So far, there are a few studies on the impacts of SWM practices on human health and the environment in the global regions.

Therefore, this review article addresses this knowledge gap by assessing the negative impacts of the dominant SWM practices on human and environmental health. Section 2 presents the research methodology. Section 3 reviews the major SWM practices in the Global South and assesses the environmental and public health implications of SWM practices in the Global South cities. While Section 4 discusses the implications of the findings and proffers recommendations that could help authorities to deal with SWM challenges and mitigate public and environmental health risks associated with unsustainable SWM practices, Section 5 concludes the paper.

2. Materials and Methods

The present paper utilizes a desktop research method of collecting and analyzing relevant data from the existing literature, as utilized in some previous studies [ 17 , 18 ]. The method consists of three iterative stages shown in Figure 1 : (a) scoping, (b) collecting relevant literature, and (c) data analysis. Firstly, the scoping stage involves defining and understanding the research problem under investigation and setting the study scope and boundary. The scope of the paper is to explore human and environmental impacts of SWM practices toward policy and practical recommendations for a more sustainable SWM system, with the Global South as the study boundary. This stage also helped identify relevant keywords to search for during the literature review in the second stage.

The flow chart of the research method (Source: [ 18 ] (p. 4)).

The second stage involved identifying and collecting relevant literature from online sources. The researchers utilized Google Scholar and Scopus databases to identify peer-reviewed academic works (peer-reviewed articles, conference proceedings, and books) as well as the gray literature. The literature that satisfied the following three inclusion criteria was identified and downloaded: (1) It is related to the study’s objective; (2) it is in the English language; and (3) it was published within the last twenty years, although some old documents about established concepts and approaches were also accessed. The downloaded gray literature includes newspaper articles, statistics, technical reports, and website contents from international development organizations such as the World Health Organization (WHO), the United Nations, and the World Bank.

In the last stage, the authors organized, analyzed, and synthesized the data collected from the literature. The downloaded works were organized according to the similarity of topics, even though some fit in more than one category. Then, each document was thoroughly examined, and themes concerned with SWM practices and their human and environmental impacts were collated, synthesized, and harmonized. Finally, the themes were summarized in Table A1 , Table A2 and Table A3 (see Appendix A ) and discussed. Implications and recommendations of the findings are then highlighted.

3. Results and Discussion

3.1. solid waste management practices in the global south.

Global municipal solid waste (MSW) generation rose from 1.3 billion tons in 2012 to 2.1 billion tons (0.74 kg/capita/day) as of 2016, which by 2050 is expected to increase by 70% to reach a total of 3.40 billion tons or 1.42 kg/capita/day [ 19 ]. The per capita MSW generation varies among regions and countries. In the EU (European Union), it ranges from 0.3–1.4 kg/capita/day [ 20 ], and in some African cities, the average is 0.78 kg/capita/day [ 21 ]. In Asia, urban areas generate about 760,000 tons of MSW per day, which is expected to increase to 1.8 million tons per day or 26% of the world’s total by 2025, despite the continent housing 53% of the world’s population [ 22 , 23 ]. In China, the total MSW generation was around 212 million tons (0.98 kg/capita/day) in 2006, out of which 91.4%, 6.4%, and 2.2% were disposed of via landfilling, incineration, and composting [ 24 ]. In 2010, only 660 Chinese cities produced about 190 million tons of MSW, accounting for 29% of the world’s total, while the total amount of solid waste in China could reach at least 480 million tons in 2030 [ 25 ]. In China, industrial waste (more than one billion tons) was five times the amount of MSW generated in 2002, which is expected to generate approximately twice as much MSW as the USA, while India will overtake the USA in MSW generation by 2030 [ 26 ].

In Malaysia, while the average rate of MSW generation was about 0.5–0.8 kg/person/day, Kuala Lumpur’s daily per capita generation rate was 1.62 kg in 2008 [ 27 ], which is expected to reach 2.23 kg in 2024 [ 28 ]. About 64% of Malaysia’s waste consists of household and office waste, 25% industrial waste, 8% commercial waste, and 3% construction waste [ 29 ]. In Sri Lanka, the assessed mean waste generation in 1999 was 6500 tons/day or 0.89 kg/cap/day, which is estimated to reach 1.0 kg/cap/day by 2025 [ 30 ]. With a 1.2% population growth rate, the total MSW generation in 2009 was approximately 7250 tons/day [ 31 ]. In Ghana, the solid waste generation rate was 0.47 kg/person/day, or about 12,710 tons per annum, consisting of biodegradable waste (0.318), non-biodegradable (0.096), and inert and miscellaneous waste (0.055) kg/person/day, respectively [ 32 ].

Moreover, global SWM costs are anticipated to increase to about $375.5 billion in 2025, with more than four-fold increases in lower- to middle-income countries and five-fold increases in low-income countries [ 33 ]. Globally, garbage collection, transportation, and disposal pose a major cost component in SWM systems [ 19 ]. Inadequate funding militates against the optimization of MSW disposal services. Table 1 compares the everyday SWM practices in low-, middle- and high-income countries according to major waste management steps. The literature indicates that waste generation rates and practices depend on the culture, socioeconomic status, population density, and level of commercial and industrial activities of a city or region.

Common MSW management practices by country’s level of economic development (adapted from [ 34 ]).

3.2. Environmental and Public Health Impacts of SWM Practices in the Global South

• (a)  Weak and Inadequate SWM System

Many problems in the cities of the global South are often associated with a weak or inadequate SWM system, which leads to severe direct and indirect environmental and public health issues at every stage of waste collection, handling, treatment, and disposal [ 30 , 31 , 32 , 33 , 34 ]. Inadequate and weak SWM results in indiscriminate dumping of waste on the streets, open spaces, and water bodies. Such practices were observed in, for example, Pakistan [ 35 , 36 ], India [ 37 ], Nepal [ 38 ], Peru [ 39 ], Guatemala [ 40 ], Brazil [ 41 ], Kenya [ 42 ], Rwanda [ 43 ], South Africa [ 44 , 45 ], Nigeria [ 46 ], Zimbabwe [ 47 ], etc.

The problems associated with such practices are GHG emissions [ 37 , 48 ], leachates [ 40 , 44 , 49 ], the spread of diseases such as malaria and dengue [ 36 ], odor [ 35 , 38 , 50 , 51 ], blocking of drains and sewers and subsequent flooding [ 52 ], suffocation of animals in plastic bags [ 52 ], and indiscriminate littering [ 38 , 39 , 53 ].

• (b)  Irregular Waste Collection and Handling

Uncollected and untreated waste has socioeconomic and environmental costs extending beyond city boundaries. Environmental sustainability impacts of this practice include methane (CH 4 ) emissions, foul odor, air pollution, land and water contamination, and the breeding of rodents, insects, and flies that transmit diseases to humans. Decomposition of biodegradable waste under anaerobic conditions contributes to about 18% and 2.9% of global methane and GHG emissions, respectively [ 54 ], with the global warming effect of about 25 times higher than carbon dioxide (CO 2 ) emissions [ 55 ]. Methane also causes fires and explosions [ 56 ]. Emissions from SWM in developing countries are increasing due to rapid economic growth and improved living standards [ 57 ].

Irregular waste collection also contributes to marine pollution. In 2010, 192 coastal countries generated 275 million metric tons of plastic waste out of which up to 12.7 million metric tons (4.4%) entered ocean ecosystems [ 58 ]. Moreover, plastic waste collects and stagnates water, proving a mosquito breeding habitat and raising the risks of dengue, malaria, and West Nile fever [ 56 ]. In addition, uncollected waste creates serious safety, health, and environmental consequences such as promoting urban violence and supporting breeding and feeding grounds for flies, mosquitoes, rodents, dogs, and cats, which carry diseases to nearby homesteads [ 4 , 19 , 59 , 60 ].

In the global South, scavengers often throw the remaining unwanted garbage on the street. Waste collectors are rarely protected from direct contact and injury, thereby facing serious health threats. Because garbage trucks are often derelict and uncovered, exhaust fumes and dust stemming from waste collection and transportation contribute to environmental pollution and widespread health problems [ 61 ]. In India’s megacities, for example, irregular MSW management is one of the major problems affecting air and marine quality [ 62 ]. Thus, irregular waste collection and handling contribute to public health hazards and environmental degradation [ 63 ].

• (c)  Landfilling and Open Dumping

Most municipal solid waste in the Global South goes into unsanitary landfills or open dumps. Even during the economic downturn during the COVID-19 pandemic, the amount of waste heading to landfill sites in Brazil, for example, increased due to lower recycling rates [ 64 ]. In Johor, Malaysia, landfilling destroys natural habitats and depletes the flora and fauna [ 65 ]. Moreover, landfilling with untreated, unsorted waste led to severe public health issues in South America [ 66 ]. Based on a study on 30 Brazilian cities, Urban and Nakada [ 64 ] report that 35% of medical waste was not properly treated before disposal, which poses a threat to public health, including the spread of COVID-19. Landfills and open dumps are also associated with high emissions of methane (CH 4 ), a major GHG [ 67 , 68 ]. Landfills and wastewater release 17% of the global methane emission [ 25 ]. About 29 metric tons of methane are emitted annually from landfills globally, accounting for about 8% of estimated global emissions, with 1.3 metric tons released from landfills in Africa [ 7 ]. The rate of landfill gas production steadily rises while MSW accumulates in the landfill emissions. Released methane and ammonia gases can cause health hazards such as respiratory diseases [ 37 , 69 , 70 , 71 ]. Since methane is highly combustible, it can cause fire and explosion hazards [ 72 ].

Open dumping sites with organic waste create the environment for the breeding of disease-carrying vectors, including rodents, flies, and mosquitoes [ 40 , 45 , 51 , 73 , 74 , 75 , 76 , 77 , 78 , 79 ]. Associated vector-borne diseases include zika virus, dengue, and malaria fever [ 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 ]. In addition, there are risks of water-borne illnesses such as leptospirosis, intestinal worms, diarrhea, and hepatitis A [ 80 , 81 ].

Odors from landfill sites, and their physical appearance, affect the lives of nearby residents by threatening their health and undermining their livelihoods, lowering their property values [ 37 , 38 , 68 , 82 , 83 , 84 ]. Moreover, the emission of ammonia (NH 3 ) from landfill sites can damage species’ composition and plant leaves [ 85 ]. In addition, the pollutants from landfill sites damage soil quality [ 73 , 84 ]. Landfill sites also generate dust and are sources of noise pollution [ 86 ].

Air and water pollution are intense in the hot and rainy seasons due to the emission of offensive odor, disease-carrying leachates, and runoff. Considerable amounts of methane and CO 2 from landfill sites produce adverse health effects such as skin, eyes, nose, and respiratory diseases [ 69 , 87 , 88 ]. The emission of ammonia can lead to similar problems and even blindness [ 85 , 89 ]. Other toxic gaseous pollutants from landfill sites include Sulphur oxides [ 89 ]. While less than 20% of methane is recovered from landfills in China, Western nations recover up to 60% [ 90 ].

Several studies report leachate from landfill sites contaminating water sources used for drinking and other household applications, which pose significant risks to public health [ 36 , 43 , 53 , 72 , 75 , 83 , 91 , 92 , 93 , 94 , 95 ]. For example, Hong et al. [ 95 ] estimated that, in 2006, the amount of leachates escaping from landfill sites in Pudong (China) was 160–180 m 3 per day. On the other hand, a properly engineered facility for waste disposal can protect public health, preserve important environmental resources, prevent clogging of drainages, and prevent the migration of leachates to contaminate ground and surface water, farmlands, animals, and air from which they enter the human body [ 61 , 96 ]. Moreover, heat in summer can speed up the rate of bacterial action on biodegradable organic material and produce a pungent odor [ 60 , 97 , 98 ]. In China, for example, leachates were not treated in 47% of landfills [ 99 ].

Co-mingled disposal of industrial and medical waste alongside municipal waste endangers people with chemical and radioactive hazards, Hepatitis B and C, tetanus, human immune deficiency, HIV infections, and other related diseases [ 59 , 60 , 100 ]. Moreover, indiscriminate disposal of solid waste can cause infectious diseases such as gastrointestinal, dermatological, respiratory, and genetic diseases, chest pains, diarrhea, cholera, psychological disorders, skin, eyes, and nose irritations, and allergies [ 10 , 36 , 60 , 61 ].

• (d)  Open Burning and Incineration

Open burning of MSW is a main cause of smog and respiratory diseases, including nose, throat, chest infections and inflammation, breathing difficulty, anemia, low immunity, allergies, and asthma. Similar health effects were reported from Nepal [ 101 ], India [ 87 ], Mexico, [ 69 ], Pakistan [ 52 , 73 , 84 ], Indonesia [ 88 ], Liberia [ 50 ], and Chile [ 102 ]. In Mumbai, for example, open incineration emits about 22,000 tons of pollutants annually [ 56 ]. Mongkolchaiarunya [ 103 ] reported air pollution and odors from burning waste in Thailand. In addition, plastic waste incineration produces hydrochloric acid and dioxins in quantities that are detrimental to human health and may cause allergies, hemoglobin deficiency, and cancer [ 95 , 104 ]. In addition, smoke from open incineration and dumpsites is a significant contributor to air pollution even for persons staying far from dumpsites.

• (e)  Composting

Composting is a biological method of waste disposal that entails the decomposing or breaking down of organic wastes into simpler forms by naturally occurring microorganisms, such as bacteria and fungi. However, despite its advantage of reducing organic waste by at least half and using compost in agriculture, the composting method has much higher CO 2 emissions than other disposal approaches. In Korea, for example, composting has the highest environmental impact than incineration and anaerobic digestion methods [ 105 ]. The authors found that the environmental impact of composting was found to be 2.4 times higher than that of incineration [ 105 ]. Some reviews linked composting with several health issues, including congested nose, sore throat and dry cough, bronchial asthma, allergic rhinitis, and extrinsic allergic alveolitis [ 36 , 106 ].

4. Implications and Recommendations

As discussed in the section above, there are many negative impacts of unsustainable SWM practices on the people and the environment. Although all waste treatment methods have their respective negative impacts, some have fewer debilitating impacts on people and the environment than others. The following is the summary of key implications of such unsustainable SWM practices.

• Uncollected organic waste from bins, containers and open dumps harbors rodents, insects, and reptiles that transmit diseases to humans. It also produces odor due to the decomposition of organic wastes, especially in the summer, and leachates that migrate and contaminate receiving underground and surface waters.
• Open dumps and non-engineered landfills release methane from decomposing biodegradable waste under anaerobiotic conditions. Methane is a key contributor to global warming, and it can cause fires and explosions.
• Non-biodegradable waste, such as discarded tires, plastics, bottles, and tins, pollutes the ground and collects water, thus creating breeding grounds for mosquitoes and increasing the risk of diseases such as malaria, dengue, and West Nile fever.
• Open burning of MSW emits pollutants into the atmosphere thereby increasing the incidences of nose and throat infections and inflammation, inhalation difficulties, bacterial infections, anemia, reduced immunity, allergies, and asthma.
• Uncontrolled incineration causes smog and releases fine particles, which are a major cause of respiratory disease. It also contributes to urban air pollution and GHG emissions significantly.
• Incineration and landfilling are associated with reproductive defects in women, developmental defects in children, cancer, hepatitis C, psychosocial impacts, poisoning, biomarkers, injuries, and mortality.

Therefore, measures toward more sustainable SWM that can mitigate such impacts must be worked out and followed. The growing complexity, costs, and coordination of SWM require multi-stakeholder involvement at each process stage [ 7 ]. Earmarking resources, providing technical assistance, good governance, and collaboration, and protecting environmental and human health are SWM critical success factors [ 47 , 79 ]. As such, local governments, the private sector, donor agencies, non-governmental organizations (NGOs), the residents, and informal garbage collectors and scavengers have their respective roles to play collaboratively in effective and sustainable SWM [ 40 , 103 , 107 , 108 ]. The following are key practical recommendations for mitigating the negative impacts of unsustainable SWM practices enumerated above.

First, cities should plan and implement an integrated SWM approach that emphasizes improving the operation of municipalities to manage all stages of SWM sustainably: generation, separation, transportation, transfer/sorting, treatment, and disposal [ 36 , 46 , 71 , 77 , 86 ]. The success of this approach requires the involvement of all stakeholders listed above [ 109 ] while recognizing the environmental, financial, legal, institutional, and technical aspects appropriate to each local setting [ 77 , 86 ]. Life Cycle Assessment (LCA) can likewise aid in selecting the method and preparing the waste management plan [ 88 , 110 ]. Thus, the SWM approach should be carefully selected to spare residents from negative health and environmental impacts [ 36 , 39 , 83 , 98 , 111 ].

Second, local governments should strictly enforce environmental regulations and better monitor civic responsibilities for sustainable waste storage, collection, and disposal, as well as health hazards of poor SWM, reflected in garbage littering observable throughout most cities of the Global South [ 64 , 84 ]. In addition, violations of waste regulations should be punished to discourage unsustainable behaviors [ 112 ]. Moreover, local governments must ensure that waste collection services have adequate geographical coverage, including poor and minority communities [ 113 ]. Local governments should also devise better SWM policies focusing on waste reduction, reuse, and recycling to achieve a circular economy and sustainable development [ 114 , 115 ].

Third, effective SWM requires promoting positive public attitudes toward sustainable waste management [ 97 , 116 , 117 , 118 ]. Therefore, public awareness campaigns through print, electronic, and social media are required to encourage people to desist from littering and follow proper waste dropping and sorting practices [ 36 , 64 , 77 , 79 , 80 , 82 , 91 , 92 , 119 ]. There is also the need for a particular focus on providing sorting bins and public awareness about waste sorting at the source, which can streamline and optimize subsequent SWM processes and mitigate their negative impacts [ 35 , 45 , 46 , 64 , 69 , 89 , 93 ]. Similarly, non-governmental and community-based organizations can help promote waste reduction, separation, and sorting at the source, and material reuse/recycling [ 103 , 120 , 121 , 122 ]. In Vietnam, for example, Tsai et al. [ 123 ] found that coordination among stakeholders and appropriate legal and policy frameworks are crucial in achieving sustainable SWM.

Fourth, there is the need to use environmentally friendly technologies or upgrade existing facilities. Some researchers prefer incineration over other methods, particularly for non-recyclable waste [ 44 , 65 ]. For example, Xin et al. [ 124 ] found that incineration, recycling, and composting resulted in a 70.82% reduction in GHG emissions from solid waste in Beijing. In Tehran city, Iran, Maghmoumi et al. [ 125 ] revealed that the best scenario for reducing GHG emissions is incinerating 50% of the waste, landfilling 30%, and recycling 20%. For organic waste, several studies indicate a preference for composting [ 45 , 51 , 75 ] and biogas generation [ 15 , 42 , 68 ]. Although some researchers have advocated a complete ban on landfilling [ 13 , 42 ], it should be controlled with improved techniques for leak detection and leachate and biogas collection [ 126 , 127 ]. Many researchers also suggested an integrated biological and mechanical treatment (BMT) of solid waste [ 66 , 74 , 95 , 119 ]. In Kenya, the waste-to-biogas scheme and ban on landfill and open burning initiatives are estimated to reduce the emissions of over 1.1 million tons of GHG and PM2.5 emissions from the waste by more than 30% by 2035 [ 42 ]. An appropriately designed waste disposal facility helps protect vital environmental resources, including flora, fauna, surface and underground water, air, and soil [ 128 , 129 ].

Fifth, extraction and reuse of materials, energy, and nutrients are essential to effective SWM, which provides livelihoods for many people, improves their health, and protects the environment [ 130 , 131 , 132 , 133 , 134 , 135 , 136 ]. For example, recycling 24% of MSW in Thailand lessened negative health, social, environmental, and economic impacts from landfill sites [ 89 ]. Waste pickers play a key role in waste circularity and should be integrated into the SWM system [ 65 , 89 , 101 , 137 ], even to the extent of taking part in decision-making [ 138 ]. In addition, workers involved in waste collection should be better trained and equipped to handle hazardous waste [ 87 , 128 ]. Moreover, green consumption, using bioplastics, can help reduce the negative impacts of solid waste on the environment [ 139 ].

Lastly, for effective SWM, local authorities should comprehensively address SWM challenges, such as lack of strategic SWM plans, inefficient waste collection/segregation and recycling, insufficient budgets, shortage of qualified waste management professionals, and weak governance, and then form a financial regulatory framework in an integrated manner [ 140 , 141 , 142 ]. Effective SWM system also depends on other factors such as the waste generation rate, population density, economic status, level of commercial activity, culture, and city/region [ 37 , 143 ]. A sustainable SWM strives to protect public health and the environment [ 144 , 145 ].

5. Conclusions

As global solid waste generation rates increase faster than urbanization, coupled with inadequate SWM systems, local governments and urban residents often resort to unsustainable SWM practices. These practices include mixing household and commercial garbage with hazardous waste during storage and handling, storing garbage in old or poorly managed facilities, deficient transportation practices, open-air incinerators, informal/uncontrolled dumping, and non-engineered landfills. The implications of such practices include air and water pollution, land degradation, climate change, and methane and hazardous leachate emissions. In addition, these impacts impose significant environmental and public health costs on residents with marginalized social groups affected mostly.

Inadequate SWM is associated with poor public health, and it is one of the major problems affecting environmental quality and cities’ sustainable development. Effective community involvement in the SWM requires promoting positive public attitudes. Public awareness campaigns through print, electronic, and social media are required to encourage people to desist from littering and follow proper waste-dropping practices. Improper SWM also resulted in water pollution and unhealthy air in cities. Future research is needed to investigate how the peculiarity of each Global South country can influence selecting the SWM approach, elements, aspects, technology, and legal/institutional frameworks appropriate to each locality.

Reviewed literature on the impacts of SWM practices in Asia (compiled by authors).

Reviewed literature on the impacts of SWM practices in South America (compiled by authors).

Reviewed literature on the impacts of SWM practices in Africa (compiled by authors).

Funding Statement

This research received no external funding.

Author Contributions

Conceptualization, I.R.A. and K.M.M.; methodology, I.R.A., K.M.M. and U.L.D.; validation, I.R.A., K.M.M. and U.L.D.; formal analysis, I.R.A. and K.M.M.; investigation, I.R.A., K.M.M., U.L.D., F.S.A., M.S.A., S.M.S.A. and W.A.G.A.-G.; resources, I.R.A., K.M.M., U.L.D., F.S.A., M.S.A., S.M.S.A., W.A.G.A.-G. and T.I.A.; data curation, U.L.D., F.S.A., M.S.A., S.M.S.A. and W.A.G.A.-G.; writing—original draft preparation, I.R.A., K.M.M., U.L.D., F.S.A., M.S.A., S.M.S.A. and W.A.G.A.-G.; writing—review and editing, I.R.A., K.M.M. and U.L.D.; supervision, F.S.A. and T.I.A.; project administration, I.R.A.; funding acquisition, I.R.A., K.M.M., U.L.D., F.S.A., M.S.A., S.M.S.A., W.A.G.A.-G. and T.I.A. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Data availability statement, conflicts of interest.

The authors declare no conflict of interest in conducting this study.

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