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Challenges and Opportunities for Urban Environmental Health and Sustainability: the HEALTHY-POLIS initiative

• Sotiris Vardoulakis 1 , 3 ,
• Keith Dear 2 &
• Paul Wilkinson 3  

Environmental Health volume  15 , Article number:  S30 ( 2016 ) Cite this article

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Cities around the world face many environmental health challenges including contamination of air, water and soil, traffic congestion and noise, and poor housing conditions exacerbated by unsustainable urban development and climate change. Integrated assessment of these risks offers opportunities for holistic, low carbon solutions in the urban environment that can bring multiple benefits for public health. The Healthy-Polis consortium aims to protect and promote urban health through multi-disciplinary, policy-relevant research on urban environmental health and sustainability. We are doing this by promoting improved methods of health risk assessment, facilitating international collaboration, contributing to the training of research scientists and students, and engaging with key stakeholders in government, local authorities, international organisations, industry and academia. A major focus of the consortium is to promote and support international research projects coordinated between two or more countries. The disciplinary areas represented in the consortium are many and varied, including environmental epidemiology, modelling and exposure assessment, system dynamics, health impact assessment, multi-criteria decision analysis, and other quantitative and qualitative approaches. This Healthy-Polis special issue presents a range of case studies and reviews that illustrate the need for a systems-based understanding of the urban environment.

Rapid urbanization, combined with rapid improvement in standards of living is stretching natural resources and threatening environmental quality in many countries. Population density has reached unprecedented levels in most parts of the high, medium and low income world. The urban population in 2014 was 54 % of the total global population, up from 30 % in 1950, and is projected to account for around 66 % of the global population by 2050 [ 1 ]. Urban areas are facing a range of environmental health challenges including contamination of air, water and soil. Sprawling urban areas contribute to traffic congestion, with associated air pollution, noise and long commuting times affecting public health and productivity across the world.

In addition, climate change is likely to aggravate certain urban health risks and inequalities by increasing the frequency and severity of extreme weather events (heatwaves, storms and floods), potentially contributing to air pollution episodes (ground-level ozone and pollen) and disturbing urban ecology [ 2 ], [ 3 ]. The urban heat island effect (i.e. the difference in temperatures between a city centre and the surrounding countryside) also exacerbates heat stress in built up areas [ 4 ]. This has knock-on effects on the indoor environment, energy demand (for ventilation and cooling) and public health [ 5 ], [ 6 ].

However, there is also an opportunity here: climate change mitigation and adaptation measures can deliver a range of health benefits. These health benefits are likely to result from “low carbon” policies aimed at lowering greenhouse gas emissions by improving energy efficiency in buildings (enhancing thermal comfort for occupants) [ 5 ], reducing dependency on private car use (improving physical activity levels and local air quality) [ 7 ], increasing renewable energy generation (improving ambient air quality) [ 8 ], and reducing meat and dairy consumption (reducing saturated fat intake) [ 9 ]. Accounting for the health co-benefits of climate change mitigation strengthens the case for reductions in greenhouse gas emissions from many sectors. However, attention should also be paid to the unintended harmful effects of certain carbon reduction policies. For example, home energy efficiency measures have the potential to worsen indoor air quality if steps are not taken to maintain good ventilation [ 10 ]; and the promotion of active travel has the potential to increase road injury risks without separation of cyclists and pedestrians from other road traffic [ 7 ].

Cities are complex systems. Research to elucidate pathways to better health and wellbeing demands systems-based, interdisciplinary methods involving epidemiologists, toxicologists, urban planners, environmental scientists, mathematical modellers, engineers, IT experts, social scientists, public health researchers and health care professionals. Importantly, local communities need to be involved in research projects aiming to inform local policies from an early stage. This can be achieved through genuine stakeholder engagement [ 11 ], citizen science and knowledge co-generation approaches [ 12 ], which raise awareness, provide valuable information and improve acceptability of interventions.

Methodological innovation in epidemiology, exposure assessment and risk analysis, and standardization of methods across countries, are needed to address complex environmental health challenges in the context of climate change and sustainable development. Relevant areas include the assessment and reduction of the health risks and impacts of weather extremes, air pollution, water contamination and other forms of environmental hazard, especially in the context of climate change, and evaluating mitigation and adaptation options [ 13 ]. These challenges highlight the need for integrated assessment methods that account for the complex interactions (including feedback loops) between climatic, environmental and behavioural factors, and the urban fabric [ 14 ]. This is particularly the case in global megacities where exposure to environmental stressors (such air pollution, congestion, heat and noise) can be substantially higher than in rural areas. Particular opportunities for influencing development pathways may arise in the multitude of rapidly developing cities in low and middle income countries. System dynamics approaches [ 15 ] and multi-criteria decision analysis methods [ 16 ] integrating quantitative and qualitative evidence can help characterise the likely overall impacts of policy options in urban environments.

This is the approach adopted by Healthy-Polis ( www.healthy-polis.org ), a new international consortium for urban environmental health and sustainability which aims to: (1) promote innovation and standardization in research methods (including exposure modelling, environmental epidemiology, risk analysis and integrated assessment methods), (2) facilitate international, multi-disciplinary research collaborations, (3) provide training and promote capacity building especially in rapidly urbanizing countries, and (4) evaluate and promote environmental interventions to improve public health in cities.

A particular emphasis of Healthy-Polis is on engendering and supporting a growing community of young researchers in the field of urban environmental health, climate change and sustainability, who will push the research agenda forward through global collaborations in the coming critical decades.

Methods and case studies

The disciplinary areas represented in Healthy-Polis are many and varied, including environmental epidemiology, modelling and exposure assessment, system dynamics, health impact assessment, multi-criteria decision analysis, and other quantitative and qualitative approaches. Key areas of interest (Fig.  1 ) were discussed at the 1 st Healthy-Polis workshop in Manchester, U.K. (6 March 2014).

Healthy-Polis. Key areas of scientific research and inter-linkages in the urban environment

In this special issue of Environmental Health, we present twelve contributions that address the aims of the Healthy-Polis consortium using methods from many disciplines. Perhaps the most familiar connection between climate change and health is the impact of extreme weather events such as heatwaves. A systematic review by Arbuthnott et al. [ 17 ] covers the important question of whether susceptibility to heat and cold has changed over time. It appears that various populations did become less susceptible to heat, although attribution to a specific cause is difficult. Heaviside et al. [ 18 ] consider the attribution of mortality to the Urban Heat Island effect during heatwaves, finding an appreciable contribution of this effect to the excess mortality experienced in the West Midlands region of England in the 2003 European heatwave. In regard to the co-benefits of climate change mitigation, Sabel et al. [ 19 ] report on the health benefits of several European and Chinese cities’ actual mitigation efforts, finding mixed results but with relatively modest health gains. The significant contribution of this study was in additionally considering climate change impacts on positive health outcomes, such as wellbeing.

We include a set of papers that address various aspects of disease in the urban environment. Asikainen et al. [ 20 ] focus on the calculation of the annual burden of disease caused by exposure to indoor air pollution in EU countries, and how best to ventilate with outdoor air, which may also be polluted. Considering various measures of urban form in 50 urban areas in England, Fecht et al. [ 21 ] intriguingly report higher rates of premature cardiovascular mortality in cities with higher densities of road junctions. Turning to infectious disease, Semenza et al. [ 22 ] present a predictive model of West Nile Virus infections based on ambient temperature and other environmental determinants. Higher rates are projected under climate change which has implications for the safety of the blood supply. Analysing the consequences of China’s massive ongoing migration and rapid urbanisation, Li et al. [ 23 ] show that action to protect and improve health in cities can be taken at multiple scales from national to individual.

Many of the Healthy-Polis papers address the broad area of urbanisation and planning. Macmillan et al. [ 24 ] report a project in which over 50 stakeholders collaboratively built causal diagrams to capture the complexities of housing, energy and wellbeing and developed criteria for assessing housing policy, while Nieuwenhuijsen [ 25 ] surveys new concepts and methods developed to address the complexity of urban environmental health in the wider context of urban and transport planning. Turning to specifics, Woods et al. [ 26 ] show how multi-criteria decision analysis can be used to prioritize environmental health hazards in a city. Salmond et al. [ 27 ] consider the ecosystem services and disservices provided by planting street trees as an urban planning tool, and argue that a holistic approach is necessary to ensure a net benefit. Finally, Rietveld et al. [ 28 ] argue for a systems approach to water and waste management in cities, illustrating their points with case studies from three continents.

Conclusions and vision

The range of risks and opportunities for urban environmental health explored in this special issue clearly demonstrates the complexity of the challenge cities are facing in the 21 st century in the context of climate, land use and demographic change. As the planet becomes increasingly urbanised, pressure on natural resources (air, water, soil), urban infrastructure (housing and transport) and health care systems increases, but so does our capacity to address risks though technological innovation, international co-operation, and participatory decision-making at city level. Solutions may involve advanced “smart” systems (e.g. controlling energy consumption, temperature and ventilation in houses) as well as more traditional approaches (e.g. urban greening, promoting walking and cycling) to improve health and wellbeing. Importantly, these solutions need to be assessed in a holistic way to maximise the benefits (“win-win”, e.g. reducing energy consumption and improving thermal comfort and air quality in buildings) and avoid unintended trade-offs (“win-lose”, e.g. planting tree species that are aesthetically appealing but require high energy input for maintenance). Methods such as multi-criteria decision analysis, participatory system dynamics modelling and quantitative health impacts assessment can help avoid pitfalls of the past and create healthier and more sustainable cities. Healthy-Polis is committed to capitalizing on these opportunities by supporting international collaboration, building research capacity, and promoting dialogue between researchers, policy-makers and local communities.

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Li X, Song J, Lin T, Dixon J, Zhang G, Ye H: Urbanization and health in China, thinking at the national, local and individual levels. Environ Health. 2016, 15 (Suppl 1): xx-

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Acknowledgements

We are grateful to the Healthy-Polis scientific advisory committee, and to all authors and reviewers who contributed to this special issue.

Declarations

Public Health England has provided funding for the publication fee of this article.

This article has been published as part of Environmental Health Volume 15 Suppl 1, 2016: Healthy-Polis: Challenges and Opportunities for Urban Environmental Health and Sustainability. The full contents of the supplement can be found at http://www.ehjournal.net/supplements/15/S1 .

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Vardoulakis, S., Dear, K. & Wilkinson, P. Challenges and Opportunities for Urban Environmental Health and Sustainability: the HEALTHY-POLIS initiative. Environ Health 15 (Suppl 1), S30 (2016). https://doi.org/10.1186/s12940-016-0096-1

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A cloak of smog gives Fresno, California, a hazy look. Smog, a hybrid of the words "smoke" and "fog," is caused when sunlight reacts with airborne pollution, including ash, dust, and ground-level ozone.

Urban Threats

Urbanization spurs a unique set of issues to both humans and animals.

The promise of jobs and prosperity, among other factors, pulls people to cities. Half of the global population already lives in cities, and by 2050 two-thirds of the world's people are expected to live in urban areas. But in cities two of the most pressing problems facing the world today also come together: poverty and environmental degradation.

Poor air and water quality, insufficient water availability, waste-disposal problems, and high energy consumption are exacerbated by the increasing population density and demands of urban environments. Strong city planning will be essential in managing these and other difficulties as the world's urban areas swell.

• Intensive urban growth can lead to greater poverty, with local governments unable to provide services for all people.
• Concentrated energy use leads to greater air pollution with significant impact on human health.
• Automobile exhaust produces elevated lead levels in urban air.
• Large volumes of uncollected waste create multiple health hazards.
• Urban development can magnify the risk of environmental hazards such as flash flooding .
• Pollution and physical barriers to root growth promote loss of urban tree cover.
• Animal populations are inhibited by toxic substances, vehicles, and the loss of habitat and food sources.
• Combat poverty by promoting economic development and job creation.
• Involve local community in local government.
• Reduce air pollution by upgrading energy use and alternative transport systems.
• Create private-public partnerships to provide services such as waste disposal and housing.
• Plant trees and incorporate the care of city green spaces as a key element in urban planning.

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• ENVIRONMENT AND CONSERVATION
• AIR POLLUTION
• URBAN PLANNING
• WASTE MANAGEMENT

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Urbanization and Air Pollution: Then and Now

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Since the beginning of the industrial revolution, people have increasingly congregated in urban areas so that as of 2005, more than half of us lived in cities [ Cohen , 2006], There are about 28  megacities , defined by populations greater than 10 million. Most projected future growth in the world’s population will occur in urban areas [ United Nations , 2014].

Air pollution often plagues industrialized cities, particularly during their early development. Episodes of high levels of sulfurous smog killed or sickened thousands in Donora, Penn., in 1948 , as well as in London in 1952 [ Bell and Davis, 2001; Helfand et al., 2001]. Other cities—primarily in the industrialized regions of the United States and Europe—also suffered from notoriously bad air quality. These events were the result of very high emissions of sulfur dioxide, smoke, and other particles during stagnant, foggy weather conditions.

As governments controlled more traditional pollution sources and urban vehicle fleets grew, a different type of air pollution also arose. Photochemical air pollution —a new phenomenon, distinct from sulfurous smog—clouded the skies over Los Angeles, first recognized in the 1950s. This type of air pollution results from photochemical reactions involving nitrogen oxides (NO x ) and volatile organic compounds ( VOCs; e.g., ethylene and benzene) that produce ozone (O 3 ) and particulate matter. Both cause lung problems, among other deleterious effects, and particulate matter reduces visibility.

In North America and Europe, the coupling of industrialization and air pollution required the creation of air quality standards and regulations for emission sources such as vehicles , electrical power generation , and industrial facilities . The success of these efforts has caused the most severe air pollution episodes to be distant memories in those regions. However, as industrialization spread, air quality concerns also spread to other areas of the globe. For example, recent news headlines warn of extreme air pollution episodes in many Chinese cities, including Beijing, Shanghai, and Guangzhou (Figure 1), showing that urban air pollution remains a major world health issue [ Chen et al ., 2013; Grahame et al. , 2014].

Cleaning up the world’s air is a daunting task. However, a broad review of about 6 decades of efforts in Los Angeles, including how scientists overcame societal and technical challenges, demonstrates that air quality in megacities can, in fact, be greatly improved. Several questions remain: Looking forward, what new challenges will megacities now developing throughout the world face? Are there limits to further improvement of air quality in more developed countries? Looking back, has the improved air quality in our cities been worth the large expense required?

Steps Taken to Recover Air Quality over Los Angeles

At its height in the 1950s and 1960s, air pollution got so bad in Los Angeles that reportedly “parents kept their kids out of school; athletes trained indoors; citrus growers and sugar-beet producers watched in dismay as their crops withered; the elderly and young crowded into doctors’ offices and hospital ERs with throbbing heads and short­ness of breath.” Motorcycle couriers even donned gas masks during particularly severe episodes . On rare occasions, ozone con­centrations exceeded 600 parts per billion by volume (ppbv, repre­sent­ing nanomoles per mole ambient air), and ­8-hour averages sometimes exceeded 300 ppbv (Figure 2a).

In Los Angeles, scientific and engineering advances com ­ bined with political and societal commitment sustained over decades resulted in remarkable air quality improvement . The city took a comprehensive approach that addressed all emission sources. Officials banned open burning and passed laws that curbed industrial pollution. They regulated emissions from electrical power generation; plants emitting in excess of certain thresholds closed. Companies built new power plants elsewhere and transmitted electricity into the city.

However, the most critical and effective efforts addressed motor vehicle emissions. Initial efforts controlled emissions of VOCs and included notably catalytic convertors , engine redesign, and fuel reformulation to minimize evaporation and optimize performance of emission controls.

Documenting Recovery

In Los Angeles, ambient concentrations of VOCs have decreased by a factor of 50 from 1960 to 2010 (solid purple line in Figure 2b), despite a threefold increase in fuel used [ Warneke et al ., 2012]. Compared with their counterparts in 1960, modern automobiles emit less than 1% as many VOCs per distance traveled. Motor vehicle emissions of NO x have decreased more slowly: Ambient concentrations of NO x have decreased by a factor of 4 from 1960 to 2010 (solid orange line in Figure 2b) [ Pollack et al ., 2013].

Photochemical modeling of the historical changes in pollutant concentrations in Los Angeles has not been accomplished in detail, mainly because of difficulties in reconstructing the emissions inventory. Modeling particulate matter, especially secondary organic aerosols, is particularly challenging. Measurements and modeling do show that the photochemistry of VOCs and NO x is nonlinear, and ambient concentrations of ozone, peroxyacetyl nitrate (PAN), and particulate matter have responded in a complex manner to emission changes.

Ozone has decreased at about the same rate as NO x (Figure 2b), but detailed chemical modeling shows that this is not a simple causal relationship. The ratio of ambient VOCs to NO x , which controls many aspects of the photochemistry, has decreased by a factor of about 12 over the period from 1960 to 2010 because of different reduction rates of VOCs and NO x emissions. Interestingly, PAN (which was responsible for severe eye irritation in Los Angeles several decades ago) has decreased by a factor of about 130, a decrease greater than that of either VOCs or NO x .

Challenges to Curbing Air Pollution

Why did the improvements shown in Figure 2 take so long to accomplish? Not only was development of the scientific understanding and engineering advances challenging, but protracted legal, social, and political processes also slowed implementation of the required emission controls.

Effective air pollution control efforts require concerted action over the entire airshed . This proved difficult—the Los Angeles region contains 3 counties and more than 50 separate cities. Progress proceeded slowly until officials formed the South Coast Air Quality Management District in 1976, which then regulated all stationary emission sources within the region in a consistent and comprehensive manner.

Government officials, industry managers, and the public have maintained these concerted pollution control efforts for more than 50 years in Los Angeles. Progress there and across the United States occurred over such a long period that many have forgotten how bad air pollution once was and have failed to notice the gains made. In fact, most people alive in the United States today never experienced the very poor air quality of Los Angeles that occurred in past decades. This fading societal memory poses another challenge: how to ensure that improved air quality is not compromised as communities focus on efforts to spur depressed economies and deal with other urgent societal problems.

Los Angeles: A Pollution Analogue for China?

Residents of Beijing now face problems from degraded air quality similar to those the residents of Los Angeles once faced. As the Guardian reports , “Chinese scientists have warned that the country’s toxic air pollution is now so bad that it resembles a nuclear winter, slowing photosynthesis in plants—and potentially wreaking havoc on the country’s food supply” [ Kaiman , 2014].

The comparison between cities in Figure 1 suggests that present urban visibility degradation in Beijing is similar to that in Los Angeles 65 years ago. Although measurement methods and data reporting procedures have changed, in situ atmospheric measurements of particulate matter suggest that the maximum concentrations in Beijing now may be higher than those ever experienced in Los Angeles, but on an annual average basis, Los Angeles may have had worse particulate matter air quality.

In contrast, reported O 3 concentrations in Beijing seldom exceed 200 ppbv [e.g., Zhang et al ., 2004], so O 3 in Los Angeles had been worse than what Beijing has experienced so far. Air pollution in cities such as Beijing is in transition from sulfurous smog to photochemical air pollution. The rapid increase in motor vehicles in Beijing and other developing cities may lead to greater photochemical O 3 production and higher future O 3 concentrations.

A Regional, If Not Global, Approach

As urbanization, global population, and economic development increase, long-range transport of pollution becomes an increasingly important factor for cities looking to improve air quality. Regardless of where we live, air flow brings pollution from our upwind neighbors to us, whether those neighbors are nearby urban areas, adjacent states or countries, or relatively distant continents. Similarly, transport of our own pollution affects our downwind neighbors.

The importance of regional transport of pollutants originally emerged in Europe (e.g., acid precipitation  [ Nordo , 1976]) and later in North America (e.g., Ozone Transport Assessment Group research in the eastern United States [ Parker and Blodgett , 1999]). In Houston—a city that recently rivaled Los Angeles for the worst U.S. air quality largely because it is home to a large fraction of the U.S. petrochemical industry—the contribution of O 3 transported into the city has been, on average, larger than the contribution of local photochemical production, even on days when O 3 exceeded the National Ambient Air Quality Standards (NAAQS) [ Berlin et al ., 2013].

Long-range transport of O 3 and particulate matter is an important issue to consider in all urban areas, not only in the more developed countries where local emissions have already been stringently controlled but also in densely populated developing countries, where large cities lie in close proximity to one another. In Asia, high population densities over a very broad region mean that the regional transport of pollution amplifies risks from poor Asian air quality in ways that have no analogue in the United States. For example, more than 800 million people live in eastern China, which includes Beijing and four other megacities. The air flowing into each of these cities will often carry a concentrated mix of aged pollution from an upwind city. The addition of fresh emissions from local sources to the transported pollution will likely present new challenges to scientific understanding of photochemical smog—challenges that must be surmounted in the effort to improve Chinese air quality.

Just as the establishment of the South Coast Air Quality Management District was required to effectively improve the air quality in Los Angeles, it is likely that the entire eastern China region, or at least the North China Plain, will need to be treated as a single air basin before improvement in air quality can be seen in Beijing, Shanghai, and the surrounding areas.

The modeling results shown in Figure 3 emphasize that, in effect, the entire eastern China region should be con­sidered to be one very large super megacity. Other areas in Asia (e.g., the ­Indo-​­Gangetic Plain) may face similar prob­lems and may need similar concerted mitigation efforts.

Limits to Air Quality Improvement

Despite the documented successes in the United States following implementation of the Clean Air Act , the United States’s ability to improve air quality has limits. Figure 2a shows that O 3 mixing ratios have now dropped much below those observed before 1970; however, this decrease cannot continue indefinitely. Air flowing into the United States contains background O 3 concentrations, and similar considerations exist for particulate matter.

An emerging challenge for American policies involves determining at what point air quality has been improved to an optimum extent. Even the background O 3 and particulate concentrations transported into the country may have adverse health effects; however, these con­cen­trations cannot be reduced solely by local and regional emission control efforts. Setting the U.S. NAAQS while considering only health impacts without regard to feasibility—as currently is required of the U.S. Environ­mental Protection Agency (EPA)—will likely lead to stan­dards that cannot be met in some areas.

Are Pollution Control Efforts Worth It?

Has the improvement of air quality in U.S. urban areas been worth the cost? EPA conducted a series of studies to specifically determine how the overall health, welfare, ecological, and economic benefits of Clean Air Act (CAA) programs com­pare to the costs of these programs.

The first report released in 1997 presented a retro­spective analysis of costs and benefits for the period spanning 1970 to 1990, and the later reports provided a prospective analysis for 1990 to 2020. These reports underwent extensive review by panels of outside experts and by the Department of Labor and Department of Commerce.

EPA found that improving air quality has been costly: Control efforts from 1970 to 1990 cost an estimated $0.52 trillion (inflation adjusted to 1990 dollars), whereas the central estimate of total monetized benefits of the CAA from 1970 to 1990 was $22 trillion. Thus, the air quality improvement that resulted from the CAA from 1970 to 1990 was quite ­cost-​­effective, with benefits exceeding costs by a ratio of approximately 42:1 (best estimate). Subsequent EPA reports found continuing large ­benefit-​to-​cost ratios.

In addition, as noted in the first report, “there are social and personal values furthered by the Clean Air Act, which have not been effectively captured by the ­dollar-​based measures” used in the studies. Reductions in adverse health and environmental effects enhance quality of life well beyond factors that can be monetized. How can one fairly value a morning walk while breathing fresh air and enjoying a view of the surroundings? Such an activity was seldom available to Los Angeles residents during the mid-20th century.

The EPA reports can assure developing megacities that investments in air quality improvement are rewarded by improved health and general ­well-​­being of the urban populations. Although the experience in the United States may not directly apply to other megacities, it is a guide to some of the scientific, technical, and policy approaches required elsewhere.

Bell, M. L., and D. L. Davis (2001), Reassessment of the lethal London fog of 1952: Novel indicators of acute and chronic consequences of acute exposure to air pollution, Environ. Health Perspect. , 109(3), 389–394.

Berlin, S. R., A. O. Langford, M. Estes, M. Dong, and D. D. Parrish (2013), Magnitude, decadal changes and impact of regional background ozone transported into the greater Houston, Texas area, Environ. Sci. Technol . , 47 (24), 13,985–13,992, doi:10.1021/es4037644.

Chen, Y., A. Ebenstein, M. Greenstone, and H. Lie (2013), Evidence on the impact of sustained exposure to air pollution on life expectancy from China’s Huai River policy, Proc. Natl. Acad. Sci. U. S. A., 110 (32), 12,936–12,941, doi:10.1073/pnas.1300018110.

Cohen, B. (2006), Urbanization in developing countries: Current trends, future projections, and key challenges for sustainability, Technol. Soc., 28 , 63–80, doi:10.1016/j.techsoc.2005.10.005.

Grahame, T. J., R. Klemm, and R. B. Schlesinger (2014), Public health and components of particulate matter: The changing assessment of black carbon, J. Air Waste Manage. Assoc., 64 (6), 620–660, doi:10.1080/10962247.2014.912692.

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Kaiman, J. (2014), China’s toxic air pollution resembles nuclear winter, say scientists, Guardian , 25 Feb. [Available at http://www.theguardian.com/world/2014/feb/25/china-toxic-air-pollution-nuclear-winter­scientists.]

Nordo, J. (1976), Long-range transport of ­air­pollutants in Europe and acid precipitation in Norway, Water Air Soil Pollut., 6 , 199–217.

Parker, L., and J. E. Blodgett (1999), Air quality: EPA’s ozone transport rule, OTAG, and Section 216 petitions—A hazy situation?, report, Congr. Res. Serv., Washington D. C [Available at http://­digital.­library.unt.edu/ark:/­67531/metacrs935/.]

Pollack, I. B., T. B. Ryerson, M. Trainer, J. A. Neuman, J. M. Roberts, and D. D. Parrish (2013), Trends in ozone, its precursors, and related secondary oxidation products in Los Angeles, California: A synthesis of measurements from 1960 to 2010, J. Geophys. Res. Atmos., 118 , 5893–5911, doi:10.1002/jgrd.50472.

United Nations (2014), World Urbanization Prospects: 2014 Revision Highlights, New York.

Warneke, C., J. A. de Gouw, J. S. Holloway, J. Peischl, T. B. Ryerson, E. Atlas, D. Blake, M. Trainer, and D. D. Parrish (2012), Multiyear trends in volatile organic compounds in Los Angeles, California: Five decades of decreasing emissions, J. Geophys. Res., 117 , D00V17, doi:10.1029/2012JD017899.

Zhang, Q., B. Yuan, M. Shao, X. Wang, S. Lu, K. Lu, M. Wang, L. Chen, ­C.-C. Chang, and S. C. Liu (2014), Variations of ­ground­level O3 and its precursors in Beijing in summertime between 2005 and 2011, Atmos. Chem. Phys., 14 , 6089–6101, doi:10.5194/acp-14-6089-2014.

Zhao, C., Y. Wang, and T. Zeng (2009), East China Plains: A “basin” of ozone pollution, Environ. Sci. Technol., 43 , 1911–1915.

Author Information

David D. Parrish, Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, and Chemical Sciences Division, Earth Science Research Laboratory, National Oceanic and Atmospheric Administration (NOAA), Boulder, Colo.; email: [email protected]; and William R. Stockwell, Department of Chemistry and the NOAA Center for Atmospheric Sciences, Howard University, Washington, D. C.

Citation: Parrish, D., and W. Stockwell (2015), Urbanization and air pollution: Then and now, Eos, 96, doi:10.1029/2015EO021803.

© 2015. American Geophysical Union. All rights reserved.

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• Pollution Due to Urbanisation Essay

Essay on Pollution Due to Urbanisation

Below, you will find an essay on pollution due to urbanisation (long) and also a short essay on pollution due to urbanisation. While urbanisation has its positives, it is imperative to look at every object according to its pros and cons. Here are two essays on pollution due to urbanisation of 400-500 words and 100-200 words, respectively. We will discuss the importance of urbanisation for countries, and how urbanisation is polluting the world.

Long Essay on Pollution Due to Urbanisation

Urbanisation is a great concept which is required to develop any country. It refers to the concept of urbanising remote areas by building infrastructure which then brings about development. Infrastructure refers to all the buildings and institutions which are necessary for economic development to take place in an area. For example, educational institutions like schools, colleges, vocational learning centres are part of the infrastructure. Healthcare facilities such as hospitals and clinics, employment opportunities, food security, etc. are also part of the infrastructure of a country.

It is seen very often that a big corporation sets up shop in a rural area, and around this, infrastructure is built, and development and urbanisation take place. Jamshedpur is an example of such a place, where Tata Industries set up shop many years ago and made the area highly developed. Thus, urbanisation definitely encourages the people of a place to have a better life by giving them more opportunities to achieve good life through education, jobs, etc.

On the other hand, it must be duly noted that urbanisation is one of the leading causes of pollution in today’s world. There are several different kinds of pollution, such as air pollution, water pollution, soil pollution and noise pollution. The facets of urbanisation contribute to each one of these types of pollution in one way or another. Factories and mines contribute to air pollution through the fumes that each of them emits into the air. The damage done to the water and soil around factories because of their flowing septic is harmful to both humans as well as aquatic life. Additionally, the noises that come from mines, the whirring of machinery in factories, etc. contribute to noise pollution.

Additionally, it is not only big industries that contribute to pollution due to urbanisation. Part of urbanisation is also the development of roads, which means more cars, buses, two-wheelers, three-wheelers, trucks, etc. on the road. These all contribute to noise pollution because of the incessant honking, and also to air pollution, because of the fumes that all motor vehicles emit. Even when we are stuck in traffic in an auto, it becomes difficult to breathe because of the fumes which surround us on the roads. If we are finding it difficult to breathe, imagine what so many fumes are doing to our planet.

Short Essay on Pollution Due to Urbanisation

150 Words Paragraph On Pollution Due to Urbanisation

Pollution takes place when air, water or soil becomes contaminated with unwanted substances. Air pollution takes place because of the fumes of factories and motor vehicles on th e road. Soil pollution and water pollution take place due to the septic waste being released into soil or water that surrounds a factory. Even oil spills are a major reason for water pollution, and all kinds of pollution can be very dangerous for living beings. Another type of pollution is noise pollution, which comes from the honking of cars, loud sounds in factories, the passing of aeroplanes and trains, etc.

Urbanisation is a result of the need to achieve economic development. It refers to when a relatively rural or remote area is made more urban by constructing roads, hospitals, schools, offices, etc. In this way, development is a result of urbanisation, which is extremely good for all countries.

However, all the great factors that urbanisation brings in, such as factories to work in, motor vehicles to drive, and so much more, all of these contribute to pollution more and more. Even though urbanisation is very important for a country, it is important to address all the kinds of pollution

Pollution is one of the most pressing concerns confronting our civilization today. When their environment deteriorates on a daily basis, humans face major challenges. The mixing of any toxic element or contaminants in our natural environment is referred to as pollution. Many contaminants are introduced into the natural environment as a result of human activities, contaminating it too dangerous proportions. Pollution is caused by a variety of factors, one of which is urbanisation.

The negative aspect of urbanisation is the manufacturers, which emit a great deal of pollution. Their equipment emits smoke into the environment, pollutes water streams and the surrounding land, and makes a lot of noise. As a result, there is a lot of pollution as a result of urbanisation, and it is extremely destructive to the environment when it first begins.

The majority of the pollution in our environment is due to urbanisation. It's because factories are springing up all over the place, there are a lot more cars on the road now, and so on.

Pollution Due to Urbanisation

Our mother planet is choking, and we are unable to do anything about it. Today, we confront several issues, one of which is pollution. Pollution occurs when a contaminating substance is introduced into our environment and pollutes our natural resources. There are numerous causes of pollution, most of which are caused by humans. Natural resources and habitats have been depleted as a result of our activities.

Urbanisation is one of the primary causes of human pollution. Pollution levels began to rise when humans began to construct cities and industrialization developed. Human needs continue to expand, and we loot our mother planet to meet them. As a result of development, many beautiful valleys, mountains, hilltop stations, and woods have become pollution carriers. Trees have been felled, rivers and lakes have been poisoned, and natural reserves have been exploited.

As a result, we now live in severely polluted cities where daily life has become increasingly challenging. As a result of urban pollution, we are experiencing a variety of health issues, the worst part of which is that we are fully unconscious of it. It is past time for us to take steps to reduce pollution and make the world a better place for future generations.

Urbanisation is a really great step forward for any country, and it is and should be the main aim of all countries. All people around the world should have access to proper healthcare, education, sanitation, nourishment and safety, and urbanisation is how we can help achieve this goal. However, in the process of meeting this goal, we cannot forget that pollution due to urbanisation does take place, and is very dangerous for the planet and, therefore, all species living on earth in the long run.

FAQs on Pollution Due to Urbanisation Essay

1. What are the pros and cons of urbanisation according to the essay on pollution due to urbanisation?

The essay on pollution due to urbanisation says that urbanisation is good and is vital for a country, but can also be harmful for the environment. Urbanisation brings in better education, better healthcare facilities, better roads, and better infrastructure in general. However, it improves the lifestyles of human beings at the cost of hurting the environment by putting more contaminants into air, water and soil in the form of toxic fumes and septic waste. Thus, urbanisation is important, but it has to be brought about in a more sustainable manner.

2. How can we reduce pollution due to urbanisation?

At the individual level, there are some very simple ways to reduce pollution due to urbanisation. To reduce air pollution, we can choose to walk, carpool, or use public transport instead of taking a taxi. Garbage should not be thrown on roads and in water bodies, in order for us to stop soil and water pollution. We should also not honk on roads unnecessarily, to curb noise pollution. Unless the big companies and industries do not decide to take a stand and do what’s good for the environment, we will have to keep relying only on individual measures.

3. What are the different types of pollution and their causes?

Pollution in Cities: Types and Causes

Air Pollution: The air in metropolitan places is constantly polluted with harmful compounds, making breathing increasingly dangerous. The air in cities is suffocating. The air is polluted by smoke from autos, factories, and power plants. There are also other contaminants in the air, such as chemical spills and other harmful substances.

Water Pollution: Natural water supplies are becoming increasingly scarce in metropolitan areas, and those that do exist are becoming progressively contaminated. There is a lot of waste dumping in lakes and rivers, such as residential and industrial waste. A lot of trash is washed into the rivers when it rains.

Soil Pollution: Toxic mixtures in the soil are causing ecosystem disruption.

Noise Pollution: Cities are among the noisiest places on the planet. Noise pollution is caused by a variety of sources, including traffic noises, loudspeakers, and other undesirable noises, which cause a variety of health problems.

Radioactive Pollution:   Nuclear power facilities' unintentional leaks represent a serious concern.

Visual Pollution: Signs, billboards, screens, high-intensity lights, and other forms of overexposure to sights in cities can also be highly unsettling.

There is also ' Thermal pollution ,' which is created by an excess of heat trapped in the earth's atmosphere.

4. How can pollution due to urbanisation be controlled?

One can implement the following methods to reduce pollution caused by urbanisation: 

Conserve Energy: People in urban areas always use more energy than people in rural areas. The use of energy results in numerous types of pollution. One of the most effective strategies to reduce pollution is to conserve energy wherever possible. When you are not using an electrical appliance, turn it off. This tiny step can make a tremendous difference.

Reduce water waste: We waste a lot of water on a daily basis, which might have negative implications. We must make every effort to utilize as little water as possible.

Plant more trees: Urban areas are the ones with the least amount of greenery. It's a good idea to have a kitchen garden and a little lawn near your house.

Green belts: The government can assist by declaring specific sections in each city as green belts, allowing trees and other plants to flourish freely.

Use fewer loudspeakers: Using fewer loudspeakers can significantly minimise noise pollution. It's also a good idea to turn down the music level at functions after a specific amount of time has passed.

Indoors: In cities, home interiors are likewise heavily contaminated. We must also have some plants inside our homes to filter the polluted indoor air.

Industrial trash: Factory owners must make every effort to avoid dumping industrial waste in lakes or rivers. The government can also enact legislation in this regard.

5.  What problems are caused due to Urbanization?

The necessity for open space to develop roads, buildings, and bridges, among other things, resulted in widespread deforestation. To accommodate the ever-increasing population, trees were cut down, fields were cleared, and built new space. It goes without saying that tree cutting is a major source of pollution. The high population density resulted in a scarcity of everything, including space and natural resources such as water and coal.

A number of serious challenges have arisen as a result of the interaction of the urban population with the environment. The spending habits and lifestyles of the urban people had a significant impact on the environment. Consumption of food, energy, and water is all higher in cities. Cities have much more filthy air than rural areas. This is mainly due to the increased use of automobiles and the expansion of industries and factories that pollute the air.  We utilise electricity to power almost all of our equipment.

6. What is urbanisation, and how is it caused?

The population shift from rural to urban regions, the resulting decline in the number of people living in rural areas, and the methods in which societies adjust to this transition are all referred to as urbanisation. It is basically the process by which towns and cities evolve and grow as more people choose to live and work in central locations.

Individual, community and state activity result in either organic or planned urbanisation. Living in a city can be culturally and economically advantageous since it can provide more options for access to the labour market, better education, housing, and safety conditions, as well as lower commute and transit time and costs. A healthy urban environment is characterised by density, proximity, diversity, and marketplace rivalry. However, there are also negative social consequences associated with urban living, such as alienation, stress, higher living costs, and mass marginalisation. Suburbanization, which is occurring in the greatest developing countries' cities, can be seen as an attempt to balance these negative aspects of city living while still giving access to a huge number of shared resources.

7. What is the Impact of Urbanisation in Indian Cities?

The following are the main effects of urbanisation on environmental quality in Indian cities:

According to the entire slum population in India in 1991, 41 per cent of the overall slum population lived in cities with populations of one million or more, which account for 27 percent of the country's total population.

According to the current situation of municipal solid trash creation and collection situation in Indian metropolitan cities, Maharashtra creates the most municipal solid garbage (11,000 tonnes per day), followed by Delhi (8700 tonnes per day) in 2019, both of which are expected to rise in the near future.

In India and other Metropolitan Cities, the number of automobiles on the road is increasing.

In India and other metropolitan cities, the number of automobiles on the road has increased. The usage of vehicles has increased by 10% or more on average, posing a significant threat to air pollution.

Water resources are dwindling day by day as a result of rising population, wasteful usage, and a lack of conservation. Huge amounts of wastewater enter rivers as cities and industries grow, contaminating river streams that are used for drinking and other reasons.

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Essay on Pollution Crisis in Urban Areas

August 29, 2021 by Sandeep

The presence of poisonous, contaminating substances in the environment around us creates havoc to the dwelling space and introduces harmful and non-biodegradable substances. These harmful chemical-laden toxic elements cause ‘pollution.’ Below, we have provided pollution crisis in urban areas essay, suitable for aspirants preparing for competitive exams.

Urbanisation and Pollution

Man and his ways have polluted the environment around us; it’s a phenomenon prevailing since many millions of years and has reached alarming levels today. The concern in the urban areas is more severe because the greenery belt in the metros cities is severely low, and pollution levels are very high. There is no control on pollution and no scientific checks that can solidly create a lasting impact to decrease pollution levels.

Urban areas have a higher density of vehicles, more emissions from factories and industries, a higher rate of food adulteration, etc. This has caused an overall rise in the average temperatures, created a way for global warming. Due to this, people are suffering from deadly diseases, like cancer and asthma, acid rains are becoming more common. Air, water, land pollution is fully contaminating the environment around us severely.

Burning of Farm Residues

Whenever we take a long drive towards the out suits of any city, we can find thick and thin piles of smoke swelling up from small or big farmlands. It could be paddy straws that are being burnt or any other agricultural leftovers. They cause major reasons for pollution . They can be detrimental to our health too. They have very high small micro-level particles that can choke our lungs and trouble the respiratory system. The concentration of these fine particles in the residue burning would be so high that the smoke can enter the nearby, immediate urban landscape and cause huge damage to the lungs.

Very high levels of toxic elements like nitrogen, phosphorus, etc., are found in this kind of smoke emitting residue burning. The levels of potassium and sulphur can act upon the neighbouring lands and destroy the top layers of the soil. Thus even fertile lands can become barren and unfit for cultivation. This issue could be circled under the group of soil pollution.

The Air Act of 1981 considers burning crops and farm residues an unacceptable and punishable act and can be tried under a judicial lens. But strict enforcement of laws by authorities at the grassroots level is almost absent, making it easy for farmers to continue with their unscientific acts. A simple remedy to this burning issue could be to find alternate rises of farm residues to avoid burning them.

Indian Transportation of Pollution

As chocolates are to children, so is motor pollution to vehicles plying on Indian roads, especially city and urban areas. The environment is degraded by pollutants emitted out from the fumes of exhausts fitted to vehicles. They have ill effects on plant life, animal life and destroy the delicate balance present in the ecosystem. The motor or vehicular pollutants include carbon monoxide, toxic nitrogen oxide, ammonia, high hydrogen, and sulphur dioxide levels. Economic liberation in urban areas has made people more outgoing in their choices of vehicles.

A small family of four now has all four members having four different vehicles to use. It is not about necessity; it is a question of luxury. So the amount of pollution previously caused by a family vehicle has proportionately increased to nearly four-fold. The term ‘car pollution’ is commonly used in urban areas for obvious reasons. The greenhouse emissions can cause a lot of destruction to our atmosphere.

Petrol and diesel, when burnt, release harmful by-products into the environment. The smoke released from cars contains a huge list of pollutants. Particulate matter can choke our lungs and lead to deadly diseases like cancer. The fuel that silently escapes fuel tanks in vehicles is very toxic. They can silently deplete the protective layers of the atmosphere and add to the greenhouse effect.

Better Management of Resources

The primary and most prominent form of pollution in urban areas that reduces the green belt and improves specific contamination is air pollution . We cannot just blame vehicles for pollution. In our day-to-day lives, we depend on plastic items for almost every other need.

We have plastic toothbrushes, plastic mugs, plastic pens, etc. Our whole life revolves around plastic usage! Plastic, after being thrown, does not decay and can cause major health hazards that can’t be cured. Every year along big seashores, we find whales falling dead on the shore with a stomach filled with tons of plastic. So plastic is not a good choice, and we can replace it with other alternatives.

When we step outside our rooms, we forget to turn off lights and fans, leading to energy wastage. Every house, be it in urban or rural background, churns out piles of waste from their homes every day. A scientific way of waste disposal could end soil pollution and attract better ways of handling and treating waste and disposed of resources.

Paper can be recycled, but plastic cannot be recycled. So we can replace our plastic bags and use paper bags in their place. We have to ensure the safe disposal of paints, varnishes, worn-out batteries. Not disposing of them could pollute the air in the immediate environment/neighbourhood and cause further pollution.

Pollution and Loss to National Income

As we begin to put more things into our wardrobe, we should also consciously understand that we are adding to the heap of pollutants around us. When we don’t recycle items and litter our places, we congest our environment and degrade the quality of life. We cause pollution to the air and water sources. Industrial pollution adds debris and creates more havoc than we think. For every such pollution activity, there are associated costs that escalate now and then.

The costs associated with pollution are not directly assessed when a country’s GDP is taken into account. Yet, if we go by relative figures, we can see the same reflected in our national income. Take a simple example: every tourist who visited the sacred Ganges at Varanasi polluted or contributed to pollution. It could be plastic wastes or contaminating water sources.

When all this piled up and was no longer tolerable, the action was essential, and thus it took thousands of crores to clean up the river. This comes from the taxpayer’s money. With every such source of pollution at various other points, national income is seriously affected by pollution factors. Environmental woes add to the problem of pollution plus eat up into the taxpayer’s money since huge sums of relief funds need to be necessitated for welfare activities. Citizens charters have risen to bring about awareness, and we as responsible citizens should stop tolerating this menace.

International Reputation

Pollution, filth, and dirt are common sights when we visit public places in urban areas. Be its railway stations, airports, or bus stands, awareness and consciousness regarding cleanliness are less. When international delegates visit our country to explore business possibilities, they fight for space and greenery in a contaminated and germ-laden atmosphere. So, often the name we achieve in an international scene gets clutched and results in poor remarks in international arenas due to pollution and environmental degradation.

Threat of Diseases

Paying a casual visit to a nearby slum area will give you glaring images of filth, uncleared garbage, poor sanitation facilities, and above all, the spring of diseases and the thriving of life risky viruses and bacteria. Pollution can cause many deadly diseases to both humans and animals. Bronchitis and asthma are becoming common ailments in cities. Not just the older people, even younger generations are falling prey to it.

Smoking is a very normal activity in public places in cities. Smoking can cause cancer of the lungs. The onset of respiratory disease is mainly due to high levels of pollution in cities. Water-borne contaminants can easily cause cholera and diphtheria. Dysentery is a common problem in children when accidentally fed with polluted water. The sewage water mixed with good, potable water can cause mutations to genes and alter the specific creation of progeny in human beings.

Not just that, the high levels of adulterants and toxic minerals and chemicals present in the food we eat can cause gastrointestinal disorders and give way to incurable diseases. Mutations causing cancer are one of the most common things we get to hear, and the loss of lives due to pollution is undoubtedly on a steady rise.

WHO Reports

Some of the recent reports cited, formulated, and land out to the Indian public have shortlisted cities with very high pollution levels and threaten the people living there. Gwalior is one of those prominent cities where levels of air pollution are just unacceptable. The WHO also prescribes safety levels and permissible levels of air pollution. Cities like Delhi are much higher than these permissible levels. The cause of such high levels of toxic pollution can be attributed to a rich concentration of particulate matter.

The Kashmir region and neighbouring Himalayan states are also slowly creeping into the list, given their shift from slow pollution to high contamination levels in air matter. Global reports published by WHO every year collect research data from nearly thousands of Indian cities, say around 3000 and more, and then come up with the final list of most polluted cities. The Indian government has also set up committees to act upon this data and monitor pollution.

Ranking of Indian Cities

It is strange to find many Indian cities making their way into the world’s most polluted cities. The numbers are not just ones or twos; they have a major share in terms of pollution. Gwalior leads the list, followed by Allahabad, Patna, and Raipur. Delhi comes a close next. The power plants and industries in these cities contribute maximum to pollution.

All three categories of pollution – air, water, and land were taken into account while listing cities for pollution. Severe health issues and more effective laws to curb pollution in these cities are called for to enforce norms. Environmental degradation and the eruption of health hazards are some of the other threats and risks that can be expected due to pollution.

Introduction to Urban Air Pollution

• First Online: 25 September 2020

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• S. M. Shiva Nagendra 6 ,
• Mukesh Khare 7 ,
• Uwe Schlink 8 &
• Anju Elizbath Peter 6  

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Urban air quality is highly dynamic and it is largely controlled by micrometeorological conditions as well as anthropogeinic emissions. The unprecedented growth of urban centres, industries and vehicles population have resulted in serious air quality problems in several countries. In this chapter we briefly discuss urban air pollution, types of air pollutants, sources of air pollution, air quality trends, current air pollution issues and air quality management options.

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S. M. Shiva Nagendra & Anju Elizbath Peter

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Shiva Nagendra, S.M., Khare, M., Schlink, U., Peter, A.E. (2021). Introduction to Urban Air Pollution. In: Shiva Nagendra, S.M., Schlink, U., Müller, A., Khare, M. (eds) Urban Air Quality Monitoring, Modelling and Human Exposure Assessment. Springer Transactions in Civil and Environmental Engineering. Springer, Singapore. https://doi.org/10.1007/978-981-15-5511-4_1

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Environmental and Health Impacts of Air Pollution: A Review

Ioannis manisalidis.

1 Delphis S.A., Kifisia, Greece

2 Laboratory of Hygiene and Environmental Protection, Faculty of Medicine, Democritus University of Thrace, Alexandroupolis, Greece

Elisavet Stavropoulou

3 Centre Hospitalier Universitaire Vaudois (CHUV), Service de Médicine Interne, Lausanne, Switzerland

Agathangelos Stavropoulos

4 School of Social and Political Sciences, University of Glasgow, Glasgow, United Kingdom

Eugenia Bezirtzoglou

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 ).

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 ).

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 ).

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.

Pollution is the introduction of harmful materials into the environment. These harmful materials are called pollutants.

Biology, Ecology, Health, Earth Science, Geography

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Pollution is the introduction of harmful materials into the environment . These harmful materials are called pollutants . Pollutants can be natural, such as volcanic ash . They can also be created by human activity, such as trash or runoff produced by factories. Pollutants damage the quality of air, water, and land. Many things that are useful to people produce pollution. Cars spew pollutants from their exhaust pipes. Burning coal to create electricity pollutes the air. Industries and homes generate garbage and sewage that can pollute the land and water. Pesticides —chemical poisons used to kill weeds and insects— seep into waterways and harm wildlife . All living things—from one-celled microbes to blue whales—depend on Earth ’s supply of air and water. When these resources are polluted, all forms of life are threatened. Pollution is a global problem. Although urban areas are usually more polluted than the countryside, pollution can spread to remote places where no people live. For example, pesticides and other chemicals have been found in the Antarctic ice sheet . In the middle of the northern Pacific Ocean, a huge collection of microscopic plastic particles forms what is known as the Great Pacific Garbage Patch . Air and water currents carry pollution. Ocean currents and migrating fish carry marine pollutants far and wide. Winds can pick up radioactive material accidentally released from a nuclear reactor and scatter it around the world. Smoke from a factory in one country drifts into another country. In the past, visitors to Big Bend National Park in the U.S. state of Texas could see 290 kilometers (180 miles) across the vast landscape . Now, coal-burning power plants in Texas and the neighboring state of Chihuahua, Mexico have spewed so much pollution into the air that visitors to Big Bend can sometimes see only 50 kilometers (30 miles). The three major types of pollution are air pollution , water pollution , and land pollution . Air Pollution Sometimes, air pollution is visible . A person can see dark smoke pour from the exhaust pipes of large trucks or factories, for example. More often, however, air pollution is invisible . Polluted air can be dangerous, even if the pollutants are invisible. It can make people’s eyes burn and make them have difficulty breathing. It can also increase the risk of lung cancer . Sometimes, air pollution kills quickly. In 1984, an accident at a pesticide plant in Bhopal, India, released a deadly gas into the air. At least 8,000 people died within days. Hundreds of thou sands more were permanently injured. Natural disasters can also cause air pollution to increase quickly. When volcanoes erupt , they eject volcanic ash and gases into the atmosphere . Volcanic ash can discolor the sky for months. After the eruption of the Indonesian volcano of Krakatoa in 1883, ash darkened the sky around the world. The dimmer sky caused fewer crops to be harvested as far away as Europe and North America. For years, meteorologists tracked what was known as the “equatorial smoke stream .” In fact, this smoke stream was a jet stream , a wind high in Earth’s atmosphere that Krakatoa’s air pollution made visible. Volcanic gases , such as sulfur dioxide , can kill nearby residents and make the soil infertile for years. Mount Vesuvius, a volcano in Italy, famously erupted in 79, killing hundreds of residents of the nearby towns of Pompeii and Herculaneum. Most victims of Vesuvius were not killed by lava or landslides caused by the eruption. They were choked, or asphyxiated , by deadly volcanic gases. In 1986, a toxic cloud developed over Lake Nyos, Cameroon. Lake Nyos sits in the crater of a volcano. Though the volcano did not erupt, it did eject volcanic gases into the lake. The heated gases passed through the water of the lake and collected as a cloud that descended the slopes of the volcano and into nearby valleys . As the toxic cloud moved across the landscape, it killed birds and other organisms in their natural habitat . This air pollution also killed thousands of cattle and as many as 1,700 people. Most air pollution is not natural, however. It comes from burning fossil fuels —coal, oil , and natural gas . When gasoline is burned to power cars and trucks, it produces carbon monoxide , a colorless, odorless gas. The gas is harmful in high concentrations , or amounts. City traffic produces highly concentrated carbon monoxide. Cars and factories produce other common pollutants, including nitrogen oxide , sulfur dioxide, and hydrocarbons . These chemicals react with sunlight to produce smog , a thick fog or haze of air pollution. The smog is so thick in Linfen, China, that people can seldom see the sun. Smog can be brown or grayish blue, depending on which pollutants are in it. Smog makes breathing difficult, especially for children and older adults. Some cities that suffer from extreme smog issue air pollution warnings. The government of Hong Kong, for example, will warn people not to go outside or engage in strenuous physical activity (such as running or swimming) when smog is very thick.

When air pollutants such as nitrogen oxide and sulfur dioxide mix with moisture, they change into acids . They then fall back to earth as acid rain . Wind often carries acid rain far from the pollution source. Pollutants produced by factories and power plants in Spain can fall as acid rain in Norway. Acid rain can kill all the trees in a forest . It can also devastate lakes, streams, and other waterways. When lakes become acidic, fish can’t survive . In Sweden, acid rain created thousands of “ dead lakes ,” where fish no longer live. Acid rain also wears away marble and other kinds of stone . It has erased the words on gravestones and damaged many historic buildings and monuments . The Taj Mahal , in Agra, India, was once gleaming white. Years of exposure to acid rain has left it pale. Governments have tried to prevent acid rain by limiting the amount of pollutants released into the air. In Europe and North America, they have had some success, but acid rain remains a major problem in the developing world , especially Asia. Greenhouse gases are another source of air pollution. Greenhouse gases such as carbon dioxide and methane occur naturally in the atmosphere. In fact, they are necessary for life on Earth. They absorb sunlight reflected from Earth, preventing it from escaping into space. By trapping heat in the atmosphere, they keep Earth warm enough for people to live. This is called the greenhouse effect . But human activities such as burning fossil fuels and destroying forests have increased the amount of greenhouse gases in the atmosphere. This has increased the greenhouse effect, and average temperatures across the globe are rising. The decade that began in the year 2000 was the warmest on record. This increase in worldwide average temperatures, caused in part by human activity, is called global warming . Global warming is causing ice sheets and glaciers to melt. The melting ice is causing sea levels to rise at a rate of two millimeters (0.09 inches) per year. The rising seas will eventually flood low-lying coastal regions . Entire nations, such as the islands of Maldives, are threatened by this climate change . Global warming also contributes to the phenomenon of ocean acidification . Ocean acidification is the process of ocean waters absorbing more carbon dioxide from the atmosphere. Fewer organisms can survive in warmer, less salty waters. The ocean food web is threatened as plants and animals such as coral fail to adapt to more acidic oceans. Scientists have predicted that global warming will cause an increase in severe storms . It will also cause more droughts in some regions and more flooding in others. The change in average temperatures is already shrinking some habitats, the regions where plants and animals naturally live. Polar bears hunt seals from sea ice in the Arctic. The melting ice is forcing polar bears to travel farther to find food , and their numbers are shrinking. People and governments can respond quickly and effectively to reduce air pollution. Chemicals called chlorofluorocarbons (CFCs) are a dangerous form of air pollution that governments worked to reduce in the 1980s and 1990s. CFCs are found in gases that cool refrigerators, in foam products, and in aerosol cans . CFCs damage the ozone layer , a region in Earth’s upper atmosphere. The ozone layer protects Earth by absorbing much of the sun’s harmful ultraviolet radiation . When people are exposed to more ultraviolet radiation, they are more likely to develop skin cancer, eye diseases, and other illnesses. In the 1980s, scientists noticed that the ozone layer over Antarctica was thinning. This is often called the “ ozone hole .” No one lives permanently in Antarctica. But Australia, the home of more than 22 million people, lies at the edge of the hole. In the 1990s, the Australian government began an effort to warn people of the dangers of too much sun. Many countries, including the United States, now severely limit the production of CFCs. Water Pollution Some polluted water looks muddy, smells bad, and has garbage floating in it. Some polluted water looks clean, but is filled with harmful chemicals you can’t see or smell. Polluted water is unsafe for drinking and swimming. Some people who drink polluted water are exposed to hazardous chemicals that may make them sick years later. Others consume bacteria and other tiny aquatic organisms that cause disease. The United Nations estimates that 4,000 children die every day from drinking dirty water. Sometimes, polluted water harms people indirectly. They get sick because the fish that live in polluted water are unsafe to eat. They have too many pollutants in their flesh. There are some natural sources of water pollution. Oil and natural gas, for example, can leak into oceans and lakes from natural underground sources. These sites are called petroleum seeps . The world’s largest petroleum seep is the Coal Oil Point Seep, off the coast of the U.S. state of California. The Coal Oil Point Seep releases so much oil that tar balls wash up on nearby beaches . Tar balls are small, sticky pieces of pollution that eventually decompose in the ocean.

Human activity also contributes to water pollution. Chemicals and oils from factories are sometimes dumped or seep into waterways. These chemicals are called runoff. Chemicals in runoff can create a toxic environment for aquatic life. Runoff can also help create a fertile environment for cyanobacteria , also called blue-green algae . Cyanobacteria reproduce rapidly, creating a harmful algal bloom (HAB) . Harmful algal blooms prevent organisms such as plants and fish from living in the ocean. They are associated with “ dead zones ” in the world’s lakes and rivers, places where little life exists below surface water. Mining and drilling can also contribute to water pollution. Acid mine drainage (AMD) is a major contributor to pollution of rivers and streams near coal mines . Acid helps miners remove coal from the surrounding rocks . The acid is washed into streams and rivers, where it reacts with rocks and sand. It releases chemical sulfur from the rocks and sand, creating a river rich in sulfuric acid . Sulfuric acid is toxic to plants, fish, and other aquatic organisms. Sulfuric acid is also toxic to people, making rivers polluted by AMD dangerous sources of water for drinking and hygiene . Oil spills are another source of water pollution. In April 2010, the Deepwater Horizon oil rig exploded in the Gulf of Mexico, causing oil to gush from the ocean floor. In the following months, hundreds of millions of gallons of oil spewed into the gulf waters. The spill produced large plumes of oil under the sea and an oil slick on the surface as large as 24,000 square kilometers (9,100 square miles). The oil slick coated wetlands in the U.S. states of Louisiana and Mississippi, killing marsh plants and aquatic organisms such as crabs and fish. Birds, such as pelicans , became coated in oil and were unable to fly or access food. More than two million animals died as a result of the Deepwater Horizon oil spill. Buried chemical waste can also pollute water supplies. For many years, people disposed of chemical wastes carelessly, not realizing its dangers. In the 1970s, people living in the Love Canal area in Niagara Falls, New York, suffered from extremely high rates of cancer and birth defects . It was discovered that a chemical waste dump had poisoned the area’s water. In 1978, 800 families living in Love Canal had to a bandon their homes. If not disposed of properly, radioactive waste from nuclear power plants can escape into the environment. Radioactive waste can harm living things and pollute the water. Sewage that has not been properly treated is a common source of water pollution. Many cities around the world have poor sewage systems and sewage treatment plants. Delhi, the capital of India, is home to more than 21 million people. More than half the sewage and other waste produced in the city are dumped into the Yamuna River. This pollution makes the river dangerous to use as a source of water for drinking or hygiene. It also reduces the river’s fishery , resulting in less food for the local community. A major source of water pollution is fertilizer used in agriculture . Fertilizer is material added to soil to make plants grow larger and faster. Fertilizers usually contain large amounts of the elements nitrogen and phosphorus , which help plants grow. Rainwater washes fertilizer into streams and lakes. There, the nitrogen and phosphorus cause cyanobacteria to form harmful algal blooms. Rain washes other pollutants into streams and lakes. It picks up animal waste from cattle ranches. Cars drip oil onto the street, and rain carries it into storm drains , which lead to waterways such as rivers and seas. Rain sometimes washes chemical pesticides off of plants and into streams. Pesticides can also seep into groundwater , the water beneath the surface of the Earth. Heat can pollute water. Power plants, for example, produce a huge amount of heat. Power plants are often located on rivers so they can use the water as a coolant . Cool water circulates through the plant, absorbing heat. The heated water is then returned to the river. Aquatic creatures are sensitive to changes in temperature. Some fish, for example, can only live in cold water. Warmer river temperatures prevent fish eggs from hatching. Warmer river water also contributes to harmful algal blooms. Another type of water pollution is simple garbage. The Citarum River in Indonesia, for example, has so much garbage floating in it that you cannot see the water. Floating trash makes the river difficult to fish in. Aquatic animals such as fish and turtles mistake trash, such as plastic bags, for food. Plastic bags and twine can kill many ocean creatures. Chemical pollutants in trash can also pollute the water, making it toxic for fish and people who use the river as a source of drinking water. The fish that are caught in a polluted river often have high levels of chemical toxins in their flesh. People absorb these toxins as they eat the fish. Garbage also fouls the ocean. Many plastic bottles and other pieces of trash are thrown overboard from boats. The wind blows trash out to sea. Ocean currents carry plastics and other floating trash to certain places on the globe, where it cannot escape. The largest of these areas, called the Great Pacific Garbage Patch, is in a remote part of the Pacific Ocean. According to some estimates, this garbage patch is the size of Texas. The trash is a threat to fish and seabirds, which mistake the plastic for food. Many of the plastics are covered with chemical pollutants. Land Pollution Many of the same pollutants that foul the water also harm the land. Mining sometimes leaves the soil contaminated with dangerous chemicals. Pesticides and fertilizers from agricultural fields are blown by the wind. They can harm plants, animals, and sometimes people. Some fruits and vegetables absorb the pesticides that help them grow. When people consume the fruits and vegetables, the pesticides enter their bodies. Some pesticides can cause cancer and other diseases. A pesticide called DDT (dichlorodiphenyltrichloroethane) was once commonly used to kill insects, especially mosquitoes. In many parts of the world, mosquitoes carry a disease called malaria , which kills a million people every year. Swiss chemist Paul Hermann Muller was awarded the Nobel Prize for his understanding of how DDT can control insects and other pests. DDT is responsible for reducing malaria in places such as Taiwan and Sri Lanka. In 1962, American biologist Rachel Carson wrote a book called Silent Spring , which discussed the dangers of DDT. She argued that it could contribute to cancer in humans. She also explained how it was destroying bird eggs, which caused the number of bald eagles, brown pelicans, and ospreys to drop. In 1972, the United States banned the use of DDT. Many other countries also banned it. But DDT didn’t disappear entirely. Today, many governments support the use of DDT because it remains the most effective way to combat malaria. Trash is another form of land pollution. Around the world, paper, cans, glass jars, plastic products, and junked cars and appliances mar the landscape. Litter makes it difficult for plants and other producers in the food web to create nutrients . Animals can die if they mistakenly eat plastic. Garbage often contains dangerous pollutants such as oils, chemicals, and ink. These pollutants can leech into the soil and harm plants, animals, and people. Inefficient garbage collection systems contribute to land pollution. Often, the garbage is picked up and brought to a dump, or landfill . Garbage is buried in landfills. Sometimes, communities produce so much garbage that their landfills are filling up. They are running out of places to dump their trash. A massive landfill near Quezon City, Philippines, was the site of a land pollution tragedy in 2000. Hundreds of people lived on the slopes of the Quezon City landfill. These people made their living from recycling and selling items found in the landfill. However, the landfill was not secure. Heavy rains caused a trash landslide, killing 218 people. Sometimes, landfills are not completely sealed off from the land around them. Pollutants from the landfill leak into the earth in which they are buried. Plants that grow in the earth may be contaminated, and the herbivores that eat the plants also become contaminated. So do the predators that consume the herbivores. This process, where a chemical builds up in each level of the food web, is called bioaccumulation . Pollutants leaked from landfills also leak into local groundwater supplies. There, the aquatic food web (from microscopic algae to fish to predators such as sharks or eagles) can suffer from bioaccumulation of toxic chemicals. Some communities do not have adequate garbage collection systems, and trash lines the side of roads. In other places, garbage washes up on beaches. Kamilo Beach, in the U.S. state of Hawai'i, is littered with plastic bags and bottles carried in by the tide . The trash is dangerous to ocean life and reduces economic activity in the area. Tourism is Hawai'i’s largest industry . Polluted beaches discourage tourists from investing in the area’s hotels, restaurants, and recreational activities. Some cities incinerate , or burn, their garbage. Incinerating trash gets rid of it, but it can release dangerous heavy metals and chemicals into the air. So while trash incinerators can help with the problem of land pollution, they sometimes add to the problem of air pollution. Reducing Pollution Around the world, people and governments are making efforts to combat pollution. Recycling, for instance, is becoming more common. In recycling, trash is processed so its useful materials can be used again. Glass, aluminum cans, and many types of plastic can be melted and reused . Paper can be broken down and turned into new paper. Recycling reduces the amount of garbage that ends up in landfills, incinerators, and waterways. Austria and Switzerland have the highest recycling rates. These nations recycle between 50 and 60 percent of their garbage. The United States recycles about 30 percent of its garbage. Governments can combat pollution by passing laws that limit the amount and types of chemicals factories and agribusinesses are allowed to use. The smoke from coal-burning power plants can be filtered. People and businesses that illegally dump pollutants into the land, water, and air can be fined for millions of dollars. Some government programs, such as the Superfund program in the United States, can force polluters to clean up the sites they polluted. International agreements can also reduce pollution. The Kyoto Protocol , a United Nations agreement to limit the emission of greenhouse gases, has been signed by 191 countries. The United States, the world’s second-largest producer of greenhouse gases, did not sign the agreement. Other countries, such as China, the world’s largest producer of greenhouse gases, have not met their goals. Still, many gains have been made. In 1969, the Cuyahoga River, in the U.S. state of Ohio, was so clogged with oil and trash that it caught on fire. The fire helped spur the Clean Water Act of 1972. This law limited what pollutants could be released into water and set standards for how clean water should be. Today, the Cuyahoga River is much cleaner. Fish have returned to regions of the river where they once could not survive. But even as some rivers are becoming cleaner, others are becoming more polluted. As countries around the world become wealthier, some forms of pollution increase. Countries with growing economies usually need more power plants, which produce more pollutants. Reducing pollution requires environmental, political, and economic leadership. Developed nations must work to reduce and recycle their materials, while developing nations must work to strengthen their economies without destroying the environment. Developed and developing countries must work together toward the common goal of protecting the environment for future use.

How Long Does It Last? Different materials decompose at different rates. How long does it take for these common types of trash to break down?

• Paper: 2-4 weeks
• Orange peel: 6 months
• Milk carton: 5 years
• Plastic bag: 15 years
• Tin can: 100 years
• Plastic bottle: 450 years
• Glass bottle: 500 years
• Styrofoam: Never

Indoor Air Pollution The air inside your house can be polluted. Air and carpet cleaners, insect sprays, and cigarettes are all sources of indoor air pollution.

Light Pollution Light pollution is the excess amount of light in the night sky. Light pollution, also called photopollution, is almost always found in urban areas. Light pollution can disrupt ecosystems by confusing the distinction between night and day. Nocturnal animals, those that are active at night, may venture out during the day, while diurnal animals, which are active during daylight hours, may remain active well into the night. Feeding and sleep patterns may be confused. Light pollution also indicates an excess use of energy. The dark-sky movement is a campaign by people to reduce light pollution. This would reduce energy use, allow ecosystems to function more normally, and allow scientists and stargazers to observe the atmosphere.

Noise Pollution Noise pollution is the constant presence of loud, disruptive noises in an area. Usually, noise pollution is caused by construction or nearby transportation facilities, such as airports. Noise pollution is unpleasant, and can be dangerous. Some songbirds, such as robins, are unable to communicate or find food in the presence of heavy noise pollution. The sound waves produced by some noise pollutants can disrupt the sonar used by marine animals to communicate or locate food.

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Focus on cities will boost benefits of air pollution action for most vulnerable

by Hayley Dunning, Imperial College London

Meeting UK air pollution targets by focusing on urban areas will maximize health benefits for the most deprived communities.

A study led by Imperial College London researchers shows that reducing typically urban sources of fine-particle air pollution like roads, wood burners, and machinery would also reduce inequalities in how different communities suffer the health impacts .

Air pollution can reach the lungs, causing short-term irritation and more harmful long-term impacts on heart and lung function. For people with existing conditions like heart failure and asthma, this can worsen already serious health problems. Residents or workers in more deprived areas are more likely to suffer these conditions, and as such are disproportionately impacted by air pollution.

The new study shows that while there are many ways to reduce the UK population's exposure to air pollution overall, focusing on these typically urban sources benefits deprived areas more, reducing the health inequalities across the country. The research is published in Environmental Advances .

Lead researcher Dr. Huw Woodward, from the Centre for Environmental Policy at Imperial College London, said, "People facing higher air pollution in deprived areas suffer health inequalities, which have a profound impact on their quality of life. Reducing air pollution will benefit everyone, but thinking more deeply about how we get there can also help us alleviate the impact on the most vulnerable in society."

Reducing bias

There are several types of air pollution, including nitrous dioxide and fine particles. This study focused on a type of fine-particle pollution called PM2.5 (pollution particles that are less than 2.5 microns across).

The UK Environment Act of 2021 set a target for cutting the population's exposure to PM2.5 by 35% by 2040, compared to 2018 levels. In practice, this means reducing the sources of the pollution, which include industry, road transport, energy production and agriculture.

Experts and policymakers use models to explore different ways of reaching the target by reducing pollution from these sources by different proportions. While all reductions in pollutant emissions will reduce the population's exposure, previous studies have not considered how different ways of reaching the target would influence the health inequality.

To track how different scenarios impact the inequality, the team created a new metric, called the Indicator of Exposure Bias (IoEB). They paired this with the UK Integrated Assessment Model, used to investigate the impact of future emissions scenarios on air quality in England.

The team modeled several of these scenarios, including two that meet the 2040 target, and used the IoEB to assess their impact on the exposure bias. The successful scenarios both achieved the target by reducing PM2.5 sources from all sectors, but one focused more on urban sources, including road transport and wood burners.

While both these scenarios reduced the exposure bias, the one focusing more on urban sources had a larger impact, reducing the bias by 59% (compared to 43% for the other scenario).

North-south divide

There is also a bias between Southern and Northern areas of England, with the former experiencing higher levels of PM2.5 air pollution. This bias is due to the south receiving a greater proportion of pollution from shipping channels and continental neighbors. The south of England has fewer deprived areas than the north, and as such this north-south divide in PM2.5 from non-UK sources reduces the overall bias towards deprived areas.

Despite this, deprived areas still experience higher levels of PM2.5 pollution. Of the sources under English control, the bias towards deprived areas is greater than that assessed by considering all sources including those from outside of the UK.

The study looked at pollution at the level of populations, as individual exposure is very difficult to estimate accurately.

The team believes their new measure can be applied to different countries or regions using models that estimate population exposure and socioeconomic status. This could allow policymakers to identify the sectors which contribute disproportionately to the bias in exposure and to identify effective strategies for reducing this bias .

Provided by Imperial College London

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• The impact of air pollution on your health

Associate Professor of Epidemiology and Global Public Health

May 31, 2024

I am fascinated with how the world around us—specifically the air we breathe—impacts our health. Growing up in the smog of Los Angeles, the haze was more than just a backdrop for my day-to-day activities; it was also an early lesson in environmental health that has become the focus of my career.

As a researcher and instructor, I use modern principles of epidemiology, environmental health, exposure science, and biostatistics to study the impacts of our environment, including air pollution, on our health. 

Air pollution is important to think about because we are all obligatory breathers. We all need air to live—from the day we are born to the day we die- and our air contains contaminants that are harmful to our health. When we are experiencing high levels of pollution, like during wildfire events, we may be able to see the poor quality of our air but pollution is also present when it is invisible to us. 

Exposures to air pollution, even at levels below our current regulatory standards, can have lasting effects on health. For example, in my research, I've seen how sustained exposure to dirty air can damage children's lungs and lead to plaque buildup in the arteries of adults. While this sometimes surprises people, it’s helpful to think about air pollution as being similar to smoking cigarettes. Although the exposure is much more diluted, we are still breathing in microscopic particles and gases that may originate from smoke from traffic or industry or other sources. When we inhale these pollutants, they can trigger a chain reaction in the body, similar to cigarette smoke. This may start with inflammation as a protective response but over time can lead to chronic illnesses as severe as heart disease. The smallest pollutants can pass into our bloodstream and travel to important organs in our bodies like our brains, leading to sometimes less expected outcomes like dementia. Notably, air pollution increases the risk of disease among all people but certain groups, like young children, older adults, and people with chronic diseases likely face even greater risks from these exposures. 

Listen to "Breathing Easy: Navigating the Invisible Impact of Air Pollution" on Spreaker.

Even though air pollution levels have declined in the last several decades in the United States, those declines have not been the same everywhere and some neighborhoods still have high levels. Similarly, breathing in outdoor air is not the only cause of exposure. For example, children can experience high levels of exposure during their commutes to school if they ride very old diesel school buses. 

Another area of my research examines the impact of school bus emissions on children’s health. Our findings present a clear message: Cleaner school buses equal healthier kids, who show up to school more and learn more. Therefore, I really must applaud the investments by the EPA and the government in helping school districts purchase newer and cleaner buses. Our findings suggest that their investments have improved the health of children, resulting in direct educational and economic benefits.

In addition to exposures from the transportation sector and other more traditional industrial sources of air pollution, we have recently seen the impact of wildfires on air quality. In some parts of the country, wildfires have emerged as a leading source of population exposure to air pollution. Our group recently demonstrated that the health impacts of these events may extend beyond the times when the air is thick with smoke and repeated exposures may increase the risk of dementia among older adults. 

We found similar relationships with air pollution from agricultural activities where the application of neurotoxic pesticides are common, suggesting a compelling argument for a broader consideration of what constitutes an important pollution source for health.

We're all breathing in air pollution no matter where we live or what side of the political divide we land on, and we all experience the health impacts of those exposures.

Although we are learning that there are many health impacts of air pollution from both traditional and non-traditional sources, the silver lining is found in regulatory successes such as the National Ambient Air Quality Standards , which have significantly reduced pollution levels and contributed to the increased life expectancy of Americans. 

As an eternal optimist, I often think about the many ways in which we can intervene to reduce population exposures and improve health. This will require a commitment to clean air, but the call to action is clear. Therefore, what I would love to see is that, as a society, we start to value clean air, and we approach this as a nonpartisan issue. We're all breathing in air pollution no matter where we live or what side of the political divide we land on, and we're all experiencing the health impacts of those exposures. In my dream world, our society would value clean air and protect health.

About the author

Sara Adar is an associate professor of epidemiology at the University of MichiganSchool of Public Health. Her research primarily focuses on the effects of air pollution and noise on healthy aging, with additional interestsin global health, extreme weather events, and intervention strategies to improve health.

• Listen to Adar on the Population Healthy podcast: The invisible impacts of air pollution
• READ: Sara Adar’s research informs the EPA and helps safeguard kids
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• Published: 03 March 2022

Sustainable strategies to treat urban runoff needed

• Mathieu Lapointe   ORCID: orcid.org/0000-0001-6582-9010 1 ,
• Chelsea M. Rochman 2 &
• Nathalie Tufenkji   ORCID: orcid.org/0000-0002-1546-3441 1  

Nature Sustainability volume  5 ,  pages 366–369 ( 2022 ) Cite this article

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Most cities lack holistic monitoring and green infrastructure to mitigate pollution in urban runoff. We call for systematic characterization of runoff and more widespread treatment to protect biodiversity and human health. This challenge requires data-driven, adapted, low-cost and sustainable solutions for dense urban centres.

Cities are epicentres for anthropogenic inputs into the environment across the globe. Specifically, urban runoff is a major pathway for pollution to contaminate aquatic ecosystems. As urban areas (mainly composed of impervious surfaces such as asphalt and concrete) increase, so does urban runoff — directly impacting surface water quality and storage 1 . In general, urban runoff is not treated, releasing several million tons of toxic, non-biodegradable and emerging contaminants — including plastic debris, hydrocarbons, detergents, solvents, pathogens, pesticides, heavy metals and engineered nanomaterials — to the environment. In this way, urban runoff is a complex mixture of anthropogenic stressors, some of which can induce acute toxicity to aquatic organisms 2 , while others (individually or as a mixture) could present a chronic risk to ecosystems and to humans via seafood and drinking water. Urban runoff mortality syndrome is a well-understood phenomenon that describes mass die-offs in salmon due to untreated stormwater 3 . International actions and policies could be implemented to control pollutant release 4 , preventing adverse ecological impacts and long-range transport. Akin to industrial or municipal treated wastewaters, we believe that cities, particularly those surrounded by a small hydrographic network where contaminant dilution is low after discharge into natural waters, should consider allocating more resources to characterize and treat urban runoff. Although several large cities have stormwater best management practices (BMPs) in place, they are mainly designed for water infiltration and/or storage and to address intense rainfall events. They do not target local anthropogenic stressors. Treatment of anthropogenic stressors could occur through the implementation of green infrastructure, such as modular (bio)retention cells, permeable pavements and more advanced sustainable processes. Treatment is particularly critical during intense precipitation events and for sewer systems that combine runoff waters and municipal or industrial wastewater (with overflows being sent to natural waters), or for municipalities with several cross-connected sewers. The local flow-buffering capacity of a stormwater treatment system is critical, with growing concerns regarding flooding associated with global climate change. Yet urban planners and water managers lack reliable tools to design urban stormwater management infrastructure that takes into account both flood and water-quality control. Here we discuss the need for routine characterization of urban runoff and new investments in infrastructure and instrumentation directed towards sustainable and improved stormwater management.

A complex cocktail

The cocktail in urban runoff released to natural waters (~110 billion gallons per year in New York City alone) 5 extends beyond the classical water-quality indicators routinely assessed (for example, total suspended solids, metals, phosphorus and nitrogen). Many other contaminants are released to natural waters via urban stormwater runoff and stormwater sewer systems every day, some of which cause acute toxicity to aquatic organisms (Fig. 1 ). For example, leachate from tyre rubber (6PPD-quinone) can exceed the acute toxicity threshold concentration in urban streams by more than 20 times 2 . Beyond tyre-wear debris, other plastic-based litter is common in stormwater runoff. In the San Francisco Bay, stormwater runoff is the largest pathway for microplastics 6 . Combined sewer overflow carrying untreated municipal wastewaters also contributes to this load. Moreover, the extensive utilization of single-use personal protective equipment due to the SARS-CoV-2 pandemic (estimated annually at ~15,50 billion masks and 780 billion gloves globally), contributes to the release of plastic litter 7 . Whole masks could reach natural waters via stormwater sewers without any treatment barrier, hence releasing millions of plastic fibres. Several other synthetic wastes, such as cigarette butts (4.5 trillion littered in the environment yearly) 8 and, for combined sewer systems, microfibres from textiles (for example, polyester and acrylic), are also discharged during rainfall events.

Audrey Desaulniers (Orceine).

Runoffs are not treated.

Gasoline and oil spills, heavy metals and petroleum-based compounds from asphalt-based surfaces such as rooftops and roads (for example, polycyclic aromatic hydrocarbons (PAHs)) also raise concerns. After a rainfall event, approximately 4,500 ng PAH l –1 was detected in a Colombian river, while some PAHs have a median lethal concentration (LC 50 ) below 2,000 ng l –1 (refs. 9 , 10 ). In some urban areas, fertilizers used for turf maintenance and pesticides or biocides used for parasite control or to protect building surfaces are systematically measured in natural waters (up to 1.8 μg l –1 during peak event) 11 . Persistent per- and polyfluoroalkyl substances present in paper, textiles, flame retardants, pesticides and oils could also be released in natural waters (up to 850 ng l –1 ) 12 . Finally, engineered nanomaterials can be released from outdoor surface coatings such as paints and stains.

Several other anthropogenic contaminants are released to natural waters after intense precipitation events; many of which are overlooked, such as salts and de-icing chemicals applied in winter, solvents and detergents (for example, windshield washer), and brominated flame retardants. Others are simply unknown. Moreover, the large populations of city-acclimated and domestic animals (for example, mustelids, birds, skunks, raccoons, squirrels and cats) could contribute to the release of pathogens, organic phosphorus and nitrogen (that is, urea) in natural waters.

A need for improved characterization

Importantly, the concentrations of these contaminants are not systematically measured, while their combined toxicity effects are ill-defined and potentially underestimated. A better understanding of the loadings of contaminants and any relevant toxicity is crucial to evaluate the risk to aquatic ecosystems and determine sites where mitigation strategies are needed. New innovative low-cost solutions are needed to monitor target contaminants, while simple indicators such as turbidity might be useful to estimate the load of colloidal contaminants (for example, microplastics) 13 . Moreover, whole effluent toxicity testing could be used to determine when urban runoff is a threat. Where toxicity is determined, effect-directed chemical analysis can be implemented to identify chemicals for future targeting. Furthermore, BMPs can be put in place to mitigate the pollution. This procedure can inform both hotspots for toxicity (and thus mitigation) and a targeted suite of chemicals to be monitored and/or regulated. The proposed monitoring of water quality could be combined with existing quantitative tools to monitor flow (for example, online turbidimeter combined with flowmeter). Strategically localized dual systems that are able to quantitatively and qualitatively monitor runoff could be more common in cities (in larger sewers) to better evaluate risk. Monitoring that is designed to provide information about both contamination and risk is crucial for governments and scientists to establish whether more active management is needed and whether urban runoff should be treated before being released into the environment.

Call for sustainable solutions

To simultaneously consider the complexity of hydrology (that is, the impact of rainfall intensity and local topography, which influence flooding) and water quality, urban runoff storage and treatment processes should be more common, especially for densely populated cities where natural landscape is insufficiently available to process, infiltrate and treat stormwater. New and strategically geolocalized infiltration areas, collection systems and/or modular treatment processes that provide certain flexibility for expansion can help mitigate floods and the load of contaminants during peak rainfall or snowmelt events. Large-scale viable and sustainable solutions are needed to store and passively treat urban runoff and deal with intense rainfall events that cannot be hydraulically supported by existing wastewater treatment plants designed to treat lower flow rates. Examples of such existing solutions, as well as more sustainable solutions to be adapted for runoff treatment, include retention ponds, bioretention cells or raingardens (~95% particle removal), coarse sand filters, bio-assisted aggregation and filtration systems, aerated ponds, underground tanks in dense urban areas, adsorption via functionalized media in a granular filter, passive aggregation and settling tanks and passive O 2 /ultraviolet (photo)oxidation. Such retention processes could act as onsite surge tanks while also removing several contaminants from runoff, combined sewer overflow, or cross-connected sewers before discharge into natural waters.

Examples of existing and new promising solutions are presented in Fig. 2 and include hydraulic buffers (solutions 2, 4, 5, 7, 8, 9 and 10), physicochemical filtration and adsorption systems (solution 6, for soluble and particulate matters), bioretention and biodegradation processes (solutions 4, 7, 9 and 10), underground separation units based on centripetal or gravitational force (solutions 3 and 5, for particulates), and (bio)flocculant-assisted bioretention and settling tank (solution 2; partially buried, for soluble and particulate matters). Simple process units can be implemented directly in stormwater sewers or manholes; for instance, vortex separators (solution 3) to remove denser particles from water, screens to trap larger debris (>10 mm), modular biofilters to remove nutrients, heavy metals and oils, and porous granular filters to trap smaller particles (<1 mm; solution 6). On a domestic scale, green roofs (solution 7, which can lead to considerable runoff reduction with only 10% of buildings having green roofs) 14 , infiltration areas (for example, grass and gardens, mulches and sand-capped lawns rather than concrete pavement; solutions 7 and 8) and small (underground) reservoirs (solution 5) — all acting as surge ‘tanks’ or a hydraulic buffer — could also be considered to reduce the load on larger municipal infrastructure. All of these solutions could be designed with a bypass when the system is at capacity, which is expected to occur during intense rainfall events and to be exacerbated due to climate change. Moreover, to reduce cost and facilitate integration of such solutions in dense cities, some systems could be designed to deal with the runoff ‘first flush’, as the initial rainfall usually releases higher contaminant loads 11 . Ideally, the proposed processes must be designed to require minimal maintenance between rainfall events.

Each number represents a different solution for runoff treatment, as shown in the corresponding key. In solution 2, contaminant aggregation or settling is improved with (bio)flocculants. Valve 2 is open to send settled sludge to 1 and clean water is sent back to the river. Valve 1 is open when turbidity is acceptable, or closed for longer settling. In solutions 3 and 5, centripetal and gravitational forces, respectively, separate large/dense solids from water. In solution 4, no chemical is added, colloids are removed via passive settling and bioretention. Longer residence times enable biofilm formation and biodegradation. In solution 6, recycled crushed glass grafted with metals improves colloid retention and adsorption of soluble contaminants via electrostatic interactions. In solutions 7–10, colloids and soluble contaminants are removed and the processes also act as hydraulic buffers. Arrows in dark and light blue indicate raw and treated waters, respectively.

Besides the positive impact on water quality and helping to preserve biodiversity and mitigate urban heat island effects, the amount of green space in dense urban areas has been correlated with human health and socioeconomic benefits 15 . As successfully reported in some cities (for example, Philadelphia, Singapore and Hong Kong), green (treatment) infrastructure could reduce runoff flows and floods, and recharge and maintain the quality of aquifer and groundwater to secure water supply in some developing and/or arid countries 16 , 17 . Green treatment infrastructure in the United States currently represents <10% (US$4.2 billion) of the total capital investments used (US$48.0 billion) to address combined sewer overflows and meet water-quality objectives of the Clean Water Act 18 . Yet, several cities report that green infrastructure itself is more cost-effective than conventional ‘grey infrastructure’ sewer systems (for example, Philadelphia and Milwaukee) 5 , in addition to reducing the load directed to wastewater treatment plants (that is, smaller sewer systems and plants are required). Moreover, with climate change and rapid urbanization, increasing green space in cities dedicated to water infiltration would reduce the risk of flooding — and its associated economic burden — caused by the growth of impervious surfaces in dense urban areas 19 . Existing green infrastructures are currently geolocalized and designed to manage floods and water accumulation. If cities are aiming for more versatile green infrastructure, the design should consider requirements for both water storage and treatment. Besides precipitation rates and intensities, the climate would also impact the design. For example, lower temperatures are known to impact adsorption kinetics in porous granular filters and increase water viscosity, which also impacts particle separation via settling. Hence, the required contact time in cold water during filtration and settling could also govern the size of the system. Moreover, the type of technology implemented (for example, granular filter versus adsorbent) will be largely influenced by local contamination patterns and water characteristics. For example, runoff with high concentrations of suspended solids (such as sand and tyre-wear particles) may require different technologies than runoffs with high levels of soluble phosphorus.

Cities have limited resources available for stormwater management. Hence, to maximize the cost-effectiveness of existing and future green infrastructures, and to reduce the risk of acute toxicity in natural waters, the proposed solutions could be coupled with more advanced process control or with data-driven machine-learning techniques 20 . Rainfall intensity–duration–frequency curves, storm water models, weather forecasts, sudden and planned events (for example, hydrocarbon spills and salts applied in winter), novel qualitative and quantitative tools, and river flows could all be included in the data stream. For example, by using such predictive analytics, the retention tanks proposed in Fig. 2 (solutions 2 and 4) could be deliberately purged to prioritize expected incoming acute contaminations; for instance, combined sewer overflows and perfluoroalkyl-substances-based flame retardants released during fire controls.

As few policies constrain the design of solutions, cities should benefit from a certain flexibility and be able to implement locally adapted, realistic, sustainable and low-cost processes. Despite the challenges to the implementation of new processes for runoff, we believe that such holistic solutions should be considered globally by cities when opportunities for infrastructure changes arise. This could mitigate and prevent the influx of contaminated runoff into aquatic ecosystems and protect animals, people and resources that are imperative to our global communities.

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Acknowledgements

N.T. acknowledges the Canada Research Chairs Program, the McGill Sustainability Systems Initiative and the Killam Research Fellowship. M.L. was supported by a FRQNT Postdoctoral Fellowship. We also acknowledge B. Barbeau from Polytechnique Montreal for his helpful comments.

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Lapointe, M., Rochman, C.M. & Tufenkji, N. Sustainable strategies to treat urban runoff needed. Nat Sustain 5 , 366–369 (2022). https://doi.org/10.1038/s41893-022-00853-4

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Passive ecosystem services, juxtaposed with engineered processes, can democratize wastewater treatment

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