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• Published: 17 June 2020

Half the world’s population are exposed to increasing air pollution

• G. Shaddick   ORCID: orcid.org/0000-0002-4117-4264 1 ,
• M. L. Thomas 2 ,
• P. Mudu 3 ,
• G. Ruggeri 3 &
• S. Gumy 3  

npj Climate and Atmospheric Science volume  3 , Article number:  23 ( 2020 ) Cite this article

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Air pollution is high on the global agenda and is widely recognised as a threat to both public health and economic progress. The World Health Organization (WHO) estimates that 4.2 million deaths annually can be attributed to outdoor air pollution. Recently, there have been major advances in methods that allow the quantification of air pollution-related indicators to track progress towards the Sustainable Development Goals and that expand the evidence base of the impacts of air pollution on health. Despite efforts to reduce air pollution in many countries there are regions, notably Central and Southern Asia and Sub-Saharan Africa, in which populations continue to be exposed to increasing levels of air pollution. The majority of the world’s population continue to be exposed to levels of air pollution substantially above WHO Air Quality Guidelines and, as such, air pollution constitutes a major, and in many areas, increasing threat to public health.

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Introduction.

In 2016, the WHO estimated that 4.2 million deaths annually could be attributed to ambient (outdoor) fine particulate matter air pollution, or PM 2.5 (particles smaller than 2.5 μm in diameter) 1 . PM 2.5 comes from a wide range of sources, including energy production, households, industry, transport, waste, agriculture, desert dust and forest fires and particles can travel in the atmosphere for hundreds of kilometres and their chemical and physical characteristics may vary greatly over time and space. The WHO developed Air Quality Guidelines (AQG) to offer guidance for reducing the health impacts of air pollution. The first edition, the WHO AQG for Europe, was published in 1987 with a global update (in 2005) reflecting the increased scientific evidence of the health risks of air pollution worldwide and the growing appreciation of the global scale of the problem 2 . The current WHO AQG states that annual mean concentration should not exceed 10 μg/m 3  2 .

The adoption and implementation of policy interventions have proved to be effective in improving air quality 3 , 4 , 5 , 6 , 7 . There are at least three examples of enforcement of long-term policies that have reduced concentration of air pollutants in Europe and North America: (i) the Clean Air Act in 1963 and its subsequent amendments in the USA; (ii) the Convention on Long-range Transboundary Air Pollution (LRTAP) with protocols enforced since the beginning of the 1980s in Europe and North America 8 ; and (iii) the European emission standards passed in the European Union in the early 1990s 9 . However, between 1960 and 2009 concentrations of PM 2.5 globally increased by 38%, due in large part to increases in China and India, with deaths attributable to air pollution increasing by 124% between 1960 and 2009 10 .

The momentum behind the air pollution and climate change agendas, and the synergies between them, together with the Sustainable Development Goals (SDGs) provide an opportunity to address air pollution and the related burden of disease. Here, trends in global air quality between 2010 and 2016 are examined in the context of attempts to reduce air pollution, both through long-term policies and more recent attempts to reduce levels of air pollution. Particular focus is given to providing comprehensive coverage of estimated concentrations and obtaining (national-level) distributions of population exposures for health impact assessment. Traditionally, the primary source of information has been measurements from ground monitoring networks but, although coverage is increasing, there remain regions in which monitoring is sparse, or even non-existent (see Supplementary Information) 11 . The Data Integration Model for Air Quality (DIMAQ) was developed by the WHO Data Integration Task Force (see Acknowledgements for details) to respond to the need for improved estimates of exposures to PM 2.5 at high spatial resolution (0.1° × 0.1°) globally 11 . DIMAQ calibrates ground monitoring data with information from satellite retrievals of aerosol optical depth, chemical transport models and other sources to provide yearly air quality profiles for individual countries, regions and globally 11 . Estimates of PM 2.5 concentrations have been compared with previous studies and a good quantitative agreement in the direction and magnitude of trends has been found. This is especially valid in data rich settings (North America, Western Europe and China) where trends results are consistent with what has been found from the analysis of ground level PM 2.5 measurements.

Figure 1a shows average annual concentrations of PM 2.5 for 2016, estimated using DIMAQ,; and Fig. 1b the differences in concentrations between 2010 and 2016. Although air pollution affects high and low-income countries alike, low- and middle-income countries experience the highest burden, with the highest concentrations being seen in Central, Eastern Southern and South-Eastern Asia 12 .

a Concentrations in 2016. b Changes in concentrations between 2010 and 2016.

The high concentrations observed across parts of the Middle East, parts of Asia and Sub-Saharan regions of Africa are associated with sand and desert dust. Desert dust has received increasing attention due to the magnitude of its concentration and the capacity to be transported over very long distances in particular areas of the world 13 , 14 . The Sahara is one of the biggest global source of desert dust 15 and the increase of PM 2.5 in this region is consistent with the prediction of an increase of desert dust due to climate change 16 , 17 .

Globally, 55.3% of the world’s population were exposed to increased levels of PM 2.5 , between 2010 and 2016, however there are marked differences in the direction and magnitude of trends across the world. For example, in North America and Europe annual average population-weighted concentrations decreased from 12.4 to 9.8 μg/m 3 while in Central and Southern Asia they rose from 54.8 to 61.5 μg/m 3 . Reductions in concentrations observed in North America and Europe align with those reported by the US Environmental Protection Agency and European Environmental Agency (EEA) 18 , 19 . The lower values observed in these regions reflect substantial regulatory processes that were implemented thirty years ago that have led to substantial decreases in air pollution over previous decades 18 , 20 , 21 . In high-income countries, the extent of air pollution from widespread coal and other solid-fuel burning, together with other toxic emissions from largely unregulated industrial processes, declined markedly with Clean Air Acts and similar ‘smoke control’ legislation introduced from the mid-20th century. However, these remain important sources of air pollution in other parts of the world 22 . In North America and Europe, the rates of improvements are small reflecting the difficulties in reducing concentrations at lower levels.

Assessing the health impacts of air pollution requires detailed information of the levels to which specific populations are exposed. Specifically, it is important to identify whether areas where there are high concentrations are co-located with high populations within a country or region. Population-weighted concentrations, often referred to as population-weighted exposures, are calculated by spatially aligning concentrations of PM 2.5 with population estimates (see Supplementary Information).

Figure 2 shows global trends in estimated concentrations and population-weighted concentrations of PM 2.5 for 2010–2016, together with trends for SDG regions (see Supplementary Fig. 1.1 ). Where population-weighted exposures are higher than concentrations, as seen in Central Asia and Southern Asia, this indicates that higher levels of air pollution coincide with highly populated areas. Globally, whilst concentrations have reduced slightly (from 12.8 μg/m 3 in 2010 to 11.7 in 2016), population-weighted concentrations have increased slightly (33.5 μg/m 3 in 2010, 34.6 μg/m 3 in 2016). In North America and Europe both concentrations and population-weighted concentrations have decreased (6.1–4.9 and 12.4–9.8 μg/m 3 , respectively). The association between concentrations and population can be clearly seen for Central Asia and Southern Asia where concentrations increased from 29.6 to 31.7 μg/m 3 (a 7% increase) while population-weighted concentrations were higher both in magnitude and in percentage of increase, increasing from 54.8 to 61.5 μg/m 3 (a 12% increase).

a Concentrations. b Population-weighted concentrations.

For the Eastern Asia and South Eastern Asia concentrations increase from 2010 to 2013 and then decrease from 2013 to 2016, a result of the implementation of the ‘Air Pollution Prevention and Control Action Plan’ 21 and the transition to cleaner energy mix due to increased urbanization in China 23 , 24 , 25 . Population-weighted concentrations for urban areas in this region are strongly influenced by China, which comprises 62.6% of the population in the region. Population-weighted concentrations are higher than the concentrations and the decrease is more marked (in the population-weighted concentrations), indicating that the implementation of policies has been successful in terms of the number of people affected. The opposite effect of population-weighting is observed in areas within Western Asia and Northern Africa where an increasing trend in population-weighted concentrations (from 42.0 to 43.1. μg/m 3 ) contains lower values than for concentrations (from 50.7 to 52.6 μg/m 3 ). In this region, concentrations are inversely correlated with population, reflecting the high concentrations associated with desert dust in areas of lower population density.

Long-term policies to reduce air pollution have been shown to be effective and have been implemented in many countries, notably in Europe and the United States. However, even in countries with the cleanest air there are large numbers of people exposed to harmful levels of air pollution. Although precise quantification of the outcomes of specific policies is difficult, coupling the evidence for effective interventions with global, regional and local trends in air pollution can provide essential information for the evidence base that is key in informing and monitoring future policies. There have been major advances in methods that expand the knowledge base about impacts of air pollution on health, from evidence on the health effects 26 , modelling levels of air pollution 1 , 11 and quantification of health impacts that can be used to monitor and report on progress towards the air pollution-related indicators of the Sustainable Development Goals: SDG 3.9.1 (mortality rate attributed to household and ambient air pollution); SDG 7.1.2 (proportion of population with primary reliance on clean fuels and technology); and SDG 11.6.2 (annual mean levels of fine particulate matter (e.g., PM 2.5 and PM 10 ) in cities (population weighted)) 1 . There is a continuing need for further research, collaboration and sharing of good practice between scientists and international organisations, for example the WHO and the World Meteorological Organization, to improve modelling of global air pollution and the assessment of its impact on health. This will include developing models that address specific questions, including for example the effects of transboundary air pollution and desert dust, and to produce tools that provide policy makers with the ability to assess the effects of interventions and to accurately predict the potential effects of proposed policies.

Globally, the population exposed to PM 2.5 levels above the current WHO AQG (annual average of 10 μg/m 3 ) has fallen from 94.2% in 2010 to 90.0% in 2016, driven largely by decreases in North America and Europe (from 71.0% in 2010 to 48.6% in 2016). However, no such improvements are seen in other regions where the proportion has remained virtually constant and extremely high (e.g., greater than 99% in Central, Southern, Eastern and South-Eastern Asia Sustainable Development Goal (SDG) regions. See Supplementary Information for more details).

The problem, and the need for solutions, is not confined to cities: across much of the world the vast majority of people living in rural areas are also exposed to levels above the guidelines. Although there are differences when considering urban and rural areas in North America and Europe, in the vast majority of the world populations living in both urban and rural areas are exposed to levels that are above the AQGs. However, in other regions the story is very different (see Supplementary Information Fig. 7.1 and Supplementary Information Sections 7 and 8), for example population-weighted concentrations in rural areas in the Central and Southern Asia (55.5 μg/m 3 ), Sub-Saharan Africa (39.1 μg/m 3 ), Western Asia and Northern Africa (42.7 μg/m 3 ) and Eastern Asia and South-Eastern Asia (34.3 μg/m 3 ) regions (in 2016) were all considerably above the AQG. From 2010 to 2016 population-weighted concentrations in rural areas in the Central and Southern Asia region rose by approximately 11% (from 49.8 to 55.5 μg/m 3 ; see Supplementary Information Fig. 7.1 and Supplementary Information Sections 7 and 8). This is largely driven by large rural populations in India where 67.2% of the population live in rural areas 27 . Addressing air pollution in both rural and urban settings should therefore be a key priority in effectively reducing the burden of disease associated with air pollution.

Attempts to mitigate the effects of air pollution have varied according to its source and local conditions, but in all cases cooperation across sectors and at different levels, urban, regional, national and international, is crucial 28 . Policies and investments supporting affordable and sustainable access to clean energy, cleaner transport and power generation, as well as energy-efficient housing and municipal waste management can reduce key sources of outdoor air pollution. Interventions would not only improve health but also reduce climate pollutants and serve as a catalyst for local economic development and the promotion of healthy lifestyles.

Assessment of trends in global air pollution requires comprehensive information on concentrations over time for every country. This information is primarily based on ground monitoring (GM) from 9690 monitoring locations around the world from the WHO cities database for 2010–2016. However, there are regions in this may be limited if not completely unavailable, particularly for earlier years (see Supplementary Information). Even in countries where GM networks are well established, there will still be gaps in spatial coverage and missing data over time. The Data Integration Model for Air Quality (DIMAQ) supplements GM with information from other sources including estimates of PM2.5 from satellite retrievals and chemical transport models, population estimates and topography (e.g., elevation). Specifically, satellite-based estimates that combine aerosol optical depth retrievals with information from the GEOS-Chem chemical transport model 29 were used, together with estimates of sulfate, nitrate, ammonium, organic carbon and mineral dust 30 .

The most recent release of the WHO ambient air quality database, for the first time, contains data from GM for multiple years, where available The version of DIMAQ used here builds on the original version 11 , 30 by allowing data from multiple years to be modelled simultaneously, with the relationship between GMs and satellite-based estimates allowed to vary (smoothly) over time. The result is a comprehensive set of high-resolution (10 km × 10 km) estimates of PM2.5 for each year (2010–2016) for every country.

In order to produce population-weighted concentrations, a comprehensive set of population data on a high-resolution grid (Gridded Population of the World (GPW v4) database 31 ) was combined with estimates from DIMAQ. In addition, the Global Human Settlement Layer 32 was used to define areas as either urban, sub-urban or rural (based on land-use, derived from satellite images, and population estimates). A further dichotomous classification of whether grid-cells within a particular country were urban or rural (allocating sub-urban as either urban or rural) was based on providing the best alignment (at the country-level) to the estimates of urban-rural populations produced by the United Nations 27 .

It is noted that the estimates from DIMAQ used in this article may differ slightly from those used in the WHO estimates of the global burden of disease associated with ambient air pollution 1 , and the associated estimates of air pollution related SDG indicators, due to recent updates in the database and further quality assurance procedures.

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Acknowledgements

The authors would like to thank the WHO Data Integration Task Force, a multi-disciplinary group of experts established as part of the recommendations from the first meeting of the WHO Global Platform for Air Quality, Geneva, January 2014. The Task Force developed the Data Integration Model for Air Quality and consists of the first author, Michael Brauer, Aaron van Donkelaar, Rick Burnett, Howard H. Chang, Aaron Cohen, Rita Van Dingenen, Yang Liu, Randall Martin, Lance A. Waller, Jason West, James V. Zidek and Annette Pruss-Ustun. The authors would like to give particular thanks to Michael Brauer who provided specialist expertise, together with data on ground measurements, and Aaron van Donkelaar and the Atmospheric Composition Analysis Group at Dalhousie University for providing estimates from satellite remote sensing. The authors would also like to thank Dan Simpson for technical expertise on implementing extensions to DIMAQ. Matthew L Thomas is supported by a scholarship from the EPSRC Centre for Doctoral Training in Statistical Applied Mathematics at Bath (SAMBa), under the project EP/L015684/1. The views expressed in this article are those of the authors and they do not necessarily represent the views, decisions or policies to institutions with which they are affiliated.

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GS, PM, and SG conceived the project and led the writing of the manuscript. MLT and GR performed the data analysis. GS and MLT developed the statistical model used to produce the estimates. All authors contributed to the writing of the manuscript.

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Correspondence to G. Shaddick .

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Shaddick, G., Thomas, M.L., Mudu, P. et al. Half the world’s population are exposed to increasing air pollution. npj Clim Atmos Sci 3 , 23 (2020). https://doi.org/10.1038/s41612-020-0124-2

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From Fog to Smog: the Value of Pollution Information

In 2013, China launched a landmark program to monitor air quality and disclose real-time data, significantly increasing the public’s access to and awareness of pollution information. The program triggered cascading behavioral changes such as stronger avoidance of outdoor pollution exposure and increased spending on protective products. These behavioral responses mitigated the mortality impact of air pollution. Conservative estimates indicate that the program’s health benefits outweigh the costs by an order of magnitude. The findings highlight the benefits of improving public access to pollution information in developing countries which often experience severe air pollution but lack pollution data collection and dissemination.

We thank the editor and three anonymous referees whose detailed comments have greatly improved the paper. We also thank Doug Almond, Antonio Bento, Fiona Burlig, Trudy Cameron, Lucas Davis, Todd Gerarden, Jiming Hao, Guojun He, Zhiguo He, Joshua Graff Zivin, Matt Khan, Jessica Leight, Cynthia Lin Lowell, Grant McDermott, Francesca Molinari, Ed Rubin, Ivan Rudik, Joe Shapiro, Jeff Shrader, Jörg Stoye, Jeffrey Zabel, Shuang Zhang, and seminar participants at the 2019 NBER Chinese Economy Working Group Meeting, the 2019 NBER EEE Spring Meeting, the 2019 Northeast Workshop on Energy Policy and Environmental Economics, MIT, Resources for the Future, University of Alberta, University of Chicago, Cornell University, GRIPS Japan, Indiana University, Shanghai University of Finance and Economics, University of Kentucky, University of Maryland, University of Oregon, University of Texas at Austin, and Xiamen University for helpful comments. We thank Jing Wu and Ziye Zhang for their generous help with data, and Luming Chen, Deyu Rao, Binglin Wang, and Tianli Xia for outstanding research assistance. Barwick gratefully acknowledges the generous support by the National University of Singapore during her sabbatical visit. The views expressed herein are those of the authors and do not necessarily reflect the views of the National Bureau of Economic Research.

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Non-Technical Summaries

• Behavioral Changes Triggered by Information about Pollution Author(s): Panle Jia Barwick Shanjun Li Liguo Lin Eric Zou In China, an air-quality monitoring and disclosure program focused on fine particulate matter pollution led residents to buy air...

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Panle Jia Barwick & Shanjun Li & Liguo Lin & Eric Yongchen Zou, 2024. " From Fog to Smog: The Value of Pollution Information, " American Economic Review, vol 114(5), pages 1338-1381.

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REVIEW article

Environmental and health impacts of air pollution: a review.

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

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

Approach to the Problem

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Sources of Exposure

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

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

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

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

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

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

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

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

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

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

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

Lastly, pollution is classified following type of origin:

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

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

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

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

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

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

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

Climate and Pollution

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

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

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

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

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

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

Air Pollutants

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

Particulate Matter (PM) and Health

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

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

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

Table 1 . Penetrability according to particle size.

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

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

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

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

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

Gas contaminants include PM in aerial masses.

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

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

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

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

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

Ozone Impact in the Atmosphere

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

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

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

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

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

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

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

Carbon Monoxide (CO)

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

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

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

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

Nitrogen Oxide (NO 2 )

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

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

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

Sulfur Dioxide (SO 2 )

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

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

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

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

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

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

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

Polycyclic Aromatic Hydrocarbons(PAHs)

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

Volatile Organic Compounds(VOCs)

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

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

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

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

Effect of Air Pollution on Health

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

Outdoor pollution is the ambient air pollution.

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

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

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

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

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

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

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

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

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

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

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

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

Figure 1 . Impact of air pollutants on the brain.

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

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

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

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

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

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

Environmental Impact of Air Pollution

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Author Contributions

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

Conflict of Interest

IM is employed by the company Delphis S.A.

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

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

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

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

Reviewed by:

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

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

† These authors have contributed equally to this work

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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Open Access

Peer-reviewed

Research Article

A growing plastic smog, now estimated to be over 170 trillion plastic particles afloat in the world’s oceans—Urgent solutions required

Roles Conceptualization, Data curation, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Visualization, Writing – original draft, Writing – review & editing

* E-mail: [email protected] (ME); [email protected] (LME)

Affiliation 5 Gyres Institute, Los Angeles, California, United States of America

Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing – original draft, Writing – review & editing

Affiliations University of California Riverside, Riverside, California, United States of America, Moore Institute for Plastic Pollution Research, Long Beach, California, United States of America

Roles Investigation, Writing – original draft, Writing – review & editing

Affiliation California State Water Resources Control Board, Sacramento, California, United States of America

Roles Conceptualization, Writing – original draft, Writing – review & editing

Affiliation Stockholm Resilience Centre, Stockholm University, Stockholm, Sweden

Roles Data curation, Writing – original draft, Writing – review & editing

Affiliations Moore Institute for Plastic Pollution Research, Long Beach, California, United States of America, Algalita Marine Research and Education, Long Beach, California, United States of America

Affiliation EOS Center, San Francisco State University, Tiburon, California, United States of America

Affiliation ABR, Inc.--Environmental Research & Services, Fairbanks, Alaska, United States of America

Roles Conceptualization, Investigation, Methodology, Visualization, Writing – original draft, Writing – review & editing

Affiliations Facultad Ciencias del Mar, Universidad Católica del Norte (UCN), Coquimbo, Chile, Center for Ecology and Sustainable Management of Oceanic Islands (ESMOI), Coquimbo, Chile, Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Coquimbo, Chile

Affiliation Minderoo Foundation, Perth, Western Australia, Australia

• Marcus Eriksen, 
• Win Cowger, 
• Lisa M. Erdle, 
• Scott Coffin, 
• Patricia Villarrubia-Gómez, 
• Charles J. Moore, 
• Edward J. Carpenter, 
• Robert H. Day, 
• Martin Thiel, 
• Chris Wilcox

• Published: March 8, 2023
• https://doi.org/10.1371/journal.pone.0281596
• Reader Comments

As global awareness, science, and policy interventions for plastic escalate, institutions around the world are seeking preventative strategies. Central to this is the need for precise global time series of plastic pollution with which we can assess whether implemented policies are effective, but at present we lack these data. To address this need, we used previously published and new data on floating ocean plastics (n = 11,777 stations) to create a global time-series that estimates the average counts and mass of small plastics in the ocean surface layer from 1979 to 2019. Today’s global abundance is estimated at approximately 82–358 trillion plastic particles weighing 1.1–4.9 million tonnes. We observed no clear detectable trend until 1990, a fluctuating but stagnant trend from then until 2005, and a rapid increase until the present. This observed acceleration of plastic densities in the world’s oceans, also reported for beaches around the globe, demands urgent international policy interventions.

Citation: Eriksen M, Cowger W, Erdle LM, Coffin S, Villarrubia-Gómez P, Moore CJ, et al. (2023) A growing plastic smog, now estimated to be over 170 trillion plastic particles afloat in the world’s oceans—Urgent solutions required. PLoS ONE 18(3): e0281596. https://doi.org/10.1371/journal.pone.0281596

Editor: Judi Hewitt, The University of Auckland - City Campus: University of Auckland, NEW ZEALAND

Received: January 12, 2022; Accepted: January 26, 2023; Published: March 8, 2023

Copyright: © 2023 Eriksen et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All data from the Plastic Marine Pollution Global Dataset, Modeling code, and Trend Reversal data are available open source at github.com. https://github.com/wincowgerDEV/ocean_plastic_modeling .

Funding: ME received funding from the Baum Foundation to support expeditions and sample collection ( http://thebaumfoundation.org/ ). MT was supported by the European Union’s H2020 research and innovation programme MINKE project (under Grant Agreement No 101008724). These funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing interests: The authors have declared that no competing interests exist.

Introduction

Understanding the occurrence and trends of plastic abundance in the world are foundational to assessing current and potential future risks to humans and ecosystems [ 1 ]. Modeling plastic pollution’s fate and transport in the ocean surface layer (OSL) is complicated by complex mechanisms of degradation, fouling, and turbulent transport [ 2 ]. Fragmentation of large plastic results in micro- and nanoplastics leaving the OSL to shoreline and seafloor compartments, where they may cause harm to organisms through ingestion [ 3 ]. While recent modeling efforts suggest rapid export of plastic pollution away from the OSL [ 4 ], inputs are likely to continue [ 5 , 6 ]. Therefore, understanding trends in regional and global plastic pollution mass and abundance is essential to evaluating and mitigating the risks.

While challenging, quantifying the global mass of plastics has previously been estimated for the OSL at 93,000 to 578,000 tonnes [ 7 – 9 ]. Spatial and temporal data gaps and variability in station-selection, sample-collection, and analysis make interpreting snapshots in time challenging and make establishing a trend even more difficult for the OSL [ 10 ]. Edelson et al. [ 11 ] suggested that the wide variability in reported inputs reveals an urgent need for improved monitoring frameworks to facilitate global governance.

A few earlier trends offer a perspective of plastic accumulation in the oceans. Archived Continuous Plankton Recorder (CPR) samples show an increasing trend of microfibers since the 1960s [ 12 ] and an increasing trend of macroplastic entanglement since the late 1950s [ 13 ]. Day and Shaw [ 14 ] reported an increase of microplastics in the North Pacific between 1976 and 1985, and Wilcox et al. [ 15 ] observed an increasing trend in the western North Atlantic from 1986 to 2015, with a rate of increase paralleling global cumulative plastic production. Although these studies suggest long-term increases, they are only from northern oceans surrounded by the most industrialized countries. In contrast, other studies have found no evidence of a rise in plastic pollution over time [see references in [ 10 ]].

Here, we evaluate a global dataset with all available historical data to provide an estimate of the temporal tendencies of plastic concentrations in the global OSL. We also offer a historic overview of international policy measures to reduce plastic inputs; based on that evaluation we call for urgent and effective solutions.

Materials and methods

Data sets: net-tow sample collection and analysis.

We compiled data on OSL plastic abundance and distribution from published literature and unpublished sources, totaling 11,777 stations used in this trend analysis ( Fig 1 ; S1 Dataset and on GitHub https://github.com/wincowgerDEV/ocean_plastic_modeling ). Data were aggregated primarily from peer-reviewed manuscripts and previously unpublished data from 5 Gyres Institute expeditions. The data were collected with multiple methods of sea-surface sampling: manta trawl [ 8 , 16 ], AVANI trawl [ 17 ], or a rectangular neuston net [ 7 , 18 ]. We filtered the data to include samples with a lower mesh size range between 53μm and 505μm. Of the 11,777 samples in this study, 0.2% of samples were collected with a 53μm mesh (n = 27), 2.5% used 200μm (n = 303), 2.5% used 500–505μm (n = 293), and 94.7% used a 320–350μm (n = 11,154). The upper range of net openings was between 0.5m and 1m ( S1 Table ).

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A total of 11,777 stations were used to model a global time trend.

https://doi.org/10.1371/journal.pone.0281596.g001

Although there was some variability in the methodology for each dataset, the methods typically were as follows: with the aid of a dissecting microscope, microplastics were manually separated from natural debris after being sorted through sieves [ 19 , 20 ], then counted individually, before all microplastics from each size category were weighed together. To compute count data (in pieces km -2 ) we divided the total count of plastics collected by the surface area of water that the trawl went through. If this metric was not provided, we computed it using trawl dimensions and distance sampled as reported in the corresponding literature. If only the month and year were provided for the date, we used the 15th of the month specified as the day. Mass was estimated with a common conversion rate reported in the literature (1.36 x 10 −2 g particle -1 ) by Morét-Ferguson et al. [ 21 ].

Ocean surface-layer basins and currents

To improve estimates of OSL plastic abundance and distribution in different ocean basins, we assigned each station to one of six basins: North Atlantic, South Atlantic, North Pacific, South Pacific, Indian, and Mediterranean. The number of stations in each basin for each year is shown in Fig 2 . We used model estimates for OSL plastic concentrations from Van Sebille et al. [ 9 ] and centered and scaled them within each ocean basin as a stable time reference to correct spatial sampling biases.

Some ocean basins are overrepresented (e.g., North Atlantic and North Pacific), whereas others have very few observations at a minority of time points (e.g., Indian, South Atlantic, South Pacific, and Mediterranean).

https://doi.org/10.1371/journal.pone.0281596.g002

Wind and waves cause downward mixing of plastic particles at the OSL, decreasing the observed concentration when winds are strong [ 22 ]. This effect can be corrected by various process-based techniques when wind velocity is known [ 9 , 15 ]. We corrected all data on ocean-surface concentrations by using the ERA-Interim Project [ 23 ] wind dataset, which provides average monthly surface wind speeds at (256 height x 512 width approximately 80 km) planet-wide spatial resolution and the Kukulka et al. [ 22 ] equation. We chose to use the Kukulka et al. [ 22 ] equation from 2012 instead of the refined Kukulka and Brunner [ 24 ] equation from 2015 because we incorporated previously published datasets that utilized the earlier 2012 equation [ 22 ], and we chose to be consistent in wind-corrected data. In cases where previous published data had been corrected, we acquired raw data and utilized the Kukulka et al. equation to standardize wind-corrected concentrations. The average expected effect of the wind correction is ~2.5 times the observed concentrations [ 22 ]. The expected ocean concentrations were derived by Lagrangian modeling of surface drifters for the year 2016 with a spatial resolution of 1° [ 9 ]. The concentrations in each basin were scaled and centered so that the expected concentration values would facilitate a regression analysis.

We modeled OSL temporal trends in plastic abundance and distribution with the above datasets corrected for wind and basin over time. Although there are many examples of global and regional plastic abundance and distribution estimates at a single point in time, temporal trends proved more challenging to produce.

Here, we used a model that removed the effects of site-bias and non-detects from the observed concentrations. We corrected for non-detects by treating zeros in the data as censored observations, in which the actual observation is below the detection level (1/volume of water sampled), instead of being considered a true zero value. We estimated the likely values of the zero records with the cenros function in the NADA package [ 25 ]; this function is a regression on ordered statistics that fits a model to the observed data and their quantiles to extrapolate the left-censored values. After correcting for non-detects with the cenros function, we estimated the actual values of the zeros to include in the model ( S1 Fig ). Plotting log-transformed observed concentration and expected concentration from an oceanographic transport model revealed an ocean-basin and concentration bias (quantile–quantile (qq) plot) ( S2 Fig ). To correct the collinear effect of expected concentration, we first fit a generalized additive model (GAM) model (gamma distribution) between log-transformed observed concentration and expected concentration from the van Sebille model [ 9 ]. We fit the model (concentration = expected concentration + basin) to the observed concentrations to get the residuals. Here the predicted density has no temporal component, only a spatial one, so the residuals from this relationship give a measure of how much an observation diverges from the relative concentration across space that we would expect. We then explored support for a time trend by modeling the residuals from the model above using a smooth function on time in a generalized additive model ( S3 Fig ). This approach is similar to adding all variables to a single model but allows us to interpret more precisely the effect of time by itself without influence from the other variables due to collinearity. We then estimated the average concentration change through time by multiplying the mean concentration observed by the reverse log-transformed residual fit. This approach allowed us to predict global plastic quantity weighted by observed mean plastic concentrations without influence from spatial effects.

Modeled results of floating microplastic item count (trillion of particles) and mass (millions of tonnes) globally for each year were calculated by averaging daily model results. Daily model results for particle counts were calculated by multiplying model results (particles km -2 ) x 361,900,000 km 2 (ocean surface-area). Daily model results for mass were calculated by multiplying 1.36 x 10 −2 g (average particle mass and weight from [ 21 ] x the number of particles.

After accounting for wind, site selection, and biases due to under-sampling, a significant trend was observed with ocean plastic through time ( Fig 3 ). Plastic concentrations in the OSL varied over time, with a dramatic increase soon after the turn of the century. There are few samples before 1990, which is reflected in the width of the confidence intervals for the left-hand side of the temporal trend; however, during the last decade of the previous century the number of samples increased, resulting in reliable trends between 1990 and 2015 ( Fig 3 ).

Change in the abundance of ocean plastic through time in trillions of particles or tens of thousands of metric tonnes using a smoothing spline and a generalized additive model. Central line is the model fit; confidence intervals are 2 times the standard error of the model.

https://doi.org/10.1371/journal.pone.0281596.g003

For the period with extensive sample coverage (1990–2015), there is substantial variability until 2004, which could be interpreted as stagnation or a decreasing trend; however, from 2005 onward, there is a consistent and rapid increase in plastic abundance ( Fig 3 ). Based on our model results, we estimate that 82–358 trillion plastic particles (mean = 171 trillion plastic particles, primarily microplastics, weighing 1.1–4.9 million tonnes (mean = 2.3 million tonnes) were afloat in 2019 ( Table 1 ).

https://doi.org/10.1371/journal.pone.0281596.t001

Previous estimates of total ocean plastic concentrations distributed the model estimates back to ocean model grids [ 7 – 9 ]. The current estimate uses an oceanographic model to estimate concentrations by location, allowing us to extract a time trend without having to build a full spatio-temporal model. Then the model mean concentration prediction multiplied by the size of the ocean is used to predict the global ocean abundance; extrapolating the model predictions to ocean basins with few samples would have incorrectly estimated our certainty in the model grids.

Our study shows a significant increase since the turn of the century for the global ocean abundance and distribution of plastics in the OSL. The wide confidence intervals from 1979 to 1990 leave no clear detectable trend. From 1990 to 2005, concentrations of plastic fluctuate during this trendless period, followed by a dramatic increasing trend from 2006 onward. These observations may have been influenced by policy interventions, plastic production, fragmentation of existing floating plastic, and/or waste management and trade.

Temporal trend

The stagnating trend observed prior to 2006 may have benefitted from important policy measures that were implemented during and just before that period ( Fig 4 ). In 1988, MARPOL added Annex V, which established legally-binding agreements among 154 countries to end the discharge of plastics from naval, fishing, and shipping fleets. These interventions were preceded by the United Nations Convention on the Law of the Sea in 1982 and the Convention on the Prevention of Marine Plastic by Dumping of Wastes and other Matter in 1972 [ 26 ]. In 1991, the Plastic Industry Trade Association launched “Operation Clean Sweep” with a goal of zero loss of plastic pellets, powders, and flakes from factories [ 26 ], with decreasing pellet ingestion in biota observed [ 27 ]; however, these and others were voluntary agreements.

A cluster of binding international policy and maritime-law interventions preceding the millennium may have played a role in slowing the increasing trend of plastic waste in the OSL.

https://doi.org/10.1371/journal.pone.0281596.g004

The rapid increase from 2005 onwards may reflect exponential growth of plastic production as it relates to inputs [ 15 ] or changes in terrestrial waste generation and management [ 28 ]. Older macroplastics adrift or stranded on shorelines or in rivers [ 4 ] continue to degrade and fragment and contribute to increases in the abundance of microplastics [ 15 ].

Despite the observed trends, there is uncertainty in collating data at a global scale. However, the dramatic increase observed herein for oceanic microplastics after 2005 parallels trends estimated for global beaches [ 29 ], which are based on completely independent observations. These parallel trends strongly suggest that plastic pollution in the world’s oceans during the past 15 years has reached unprecedented levels. Considerable data exist for the North Pacific and North Atlantic basins, although we lack information for the other ocean basins. More samples are needed in the South Atlantic, South Pacific, Mediterranean, and Indian oceans, all of which remain data-poor regions (see also [ 29 ]). In the future, if greater attention is given to the southern hemisphere, and sampling occurs at more-even intervals, models can provide outputs with higher resolution that can better identify spatial and temporal trends.

The globalization of raw plastic materials accelerated at the turn of the century [ 30 ] leading to rapid increases in import, export, and domestic production of plastic products and packaging and to increases in the amount of plastic waste generated. Simultaneously, plastic recycling, even in countries with highly developed waste-management infrastructure, has historically been low [ 6 ]. This lack of recycling has resulted in a flood of plastic products and packaging with dead-end material flows, largely due to the international trade of low-value waste plastics that remain as mismanaged waste in the receiving country [ 31 ]. The turn of the century also marked increased emissions of plastic waste from large fishing fleets and artisanal fisheries [ 32 ].

Increased international economic activity and the fragmentation and resuspension of degraded macroplastics probably drive the observed increasing trend. These factors have overwhelmed both the natural export mechanisms that transport plastic out of the OSL and any positive impact of those early binding interventions that may have driven the observed decrease toward the end of last century.

Limitations

The study results are limited by sampling distribution and the unequal distribution of observations ( Fig 2 and S4 Fig ). The vast majority of samples was collected in the North Pacific and North Atlantic Oceans ( Fig 2 ). Therefore, our results will be biased to observed trends in those ocean basins. The coefficient of variation ( S4 Fig ) had a wide spread (min = 0.447, max = 10.558, mean = 2.602), which underscores the challenge in modeling time-trends of ocean plastic concentrations accurately. The South Atlantic, Mediterranean, and Indian oceans had the lowest coefficient of variations, but that may be more due to the small number of samples and limited spatial distributions there than having smaller spatial variations.

In addition, we recognize limitations in our estimates of particle counts and mass. Particle counts may vary considerably when considering the lower size limit for particles. In terms of mass, and while we used a simple conversion of count to mass [ 12 ], new techniques are being developed (e.g., machine learning) to estimate mas and count conversions more accurately [ 33 ].

Policy implications

The accelerating abundance of plastic in the OSL demands urgent international policy intervention to minimize ecological, social, and economic harm [ 5 ]. Without substantial widespread policy changes, the rate at which plastics enter aquatic environments will increase approximately 2.6-fold from 2016 to 2040 [ 6 ].

Existing international policies on plastic are fragmented, favor business-oriented solutions [ 34 ], lack specificity, and do not include measurable targets [ 35 ], with the exception of the 2019 Plastic Waste Amendments to the Basel Convention on the Control of Transboundary Movements of Hazardous Wastes and Their Disposal [ 36 ]. Although legally binding, this Convention regulates plastic trade only at the very end of its life cycle, once it becomes waste. International policy interventions after 2005 generally lack robust monitoring frameworks and enforcement mechanisms [ 34 – 37 ]. Because they also are non-binding and voluntary, they are not stemming the tide [ 38 ].

For example, the New Global Economy Commitment [ 39 ] promotes a set of circular economic principles to ensure the economic viability and meaningful reduction in the production of plastic waste: restrictions on certain products, extended producer responsibility for new and existing products, and waste-reduction targets. They invite stakeholders voluntarily to adopt the goal of making 100% of plastic packaging reusable, recyclable, or compostable by 2025, yet these measures advocate for private-sector self-regulation [ 34 ]. Economic barriers to recycled plastic continue to place virgin plastics at a lower cost, as the industries that produce and use plastics resist binding commitments to use recycled plastic and design standards for efficient recyclability, leaving recycling overall to fail expectations [ 40 ]. This increased production of virgin plastics will increasingly undermine circular economic principles, including the reuse economy and global policy interventions intended to reduce the most polluting plastic products and packaging [ 41 ].

Conclusions

Although scientists continue to understand better the environmental fate of plastic pollution, there is consensus that global increases in plastic production result in dramatic increases in plastic pollution as shown herein, underscoring the urgent need for effective global governance. Currently, we are at a turning point in history. Early in 2022, at the United Nations Environmental Assembly 5.2. in Nairobi, all Member States adopted a resolution to end plastic pollution, committing to establish a legally binding global agreement that addresses the full life-cycle of plastic, including its production, design, and disposal, by 2024 [ 42 ]. The final outcome of this agreement will be a treaty, but its strength will depend on commitments by the member states and on whether measures are focused on the full life cycle of plastics, from extraction and manufacturing to its end of life [ 43 ]. Environmental recovery of plastic has limited merit, so solution strategies must address those systems that restrict emissions of plastic pollution in the first place. Therefore, establishing standardized monitoring frameworks to track global trends and creating binding and enforceable international agreements to prevent the emissions of plastic pollution are the best long-term global solutions.

Supporting information

S1 dataset. these data are available at figshare.com..

Plastic Marine Pollution Global Dataset, Modeling code, and Trend Reversal data are available open source On GitHub. The following dataset includes all data points used in our model: https://github.com/wincowgerDEV/ocean_plastic_modeling .

https://doi.org/10.1371/journal.pone.0281596.s001

S1 Fig. Correcting for non-detects.

Correcting for non-detects using the cenros function, we estimated the actual values of the zeros to include in the model (A) observed concentration histogram log+1 transformed. Shows that there is a large gap between the zero observations and the nonzeros which indicates a need to correct non-detects. (B) corrected concentrations are normally distributed in log space.

https://doi.org/10.1371/journal.pone.0281596.s002

S2 Fig. QQ plots.

(A) QQ plots for the initial model fit and (B) the residual model fit.

https://doi.org/10.1371/journal.pone.0281596.s003

S3 Fig. Global trend based on residuals.

Annual global estimates of floating microplastic particles based on residuals from 1979 to 2019 show a period slow decreasing abundance and a steady increase from 2005 onward. Residuals are in log transformed space. The shaded grey area reflects confidence intervals. The “rugplot” at the bottom of the figure provides a line for each sample to show the density of stations. The low number of stations on either end of the figure results in wide confidence intervals.

https://doi.org/10.1371/journal.pone.0281596.s004

S4 Fig. Coefficient of variation for the datasets for each year.

Sampling from year to year and basin to basin has a similar about of relative variability, which is a good thing in terms of fitting models to it.

https://doi.org/10.1371/journal.pone.0281596.s005

S1 Table. Summary of datasets used in model.

The datasets used in the model (126 total). The year (of sample collection), data source, mesh size of net, the ocean basin, and the number of observations in that dataset are summarized.

https://doi.org/10.1371/journal.pone.0281596.s006

Acknowledgments

We thank Ocean Missions for data from Iceland and Greenland and thank Ocean Research Project for data from across the Arctic. We also thank the anonymous reviewers for their highly constructive suggestions, which helped to improve this manuscript.

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Smog, media attention, and corporate social responsibility—empirical evidence from Chinese polluting listed companies

• Environmental Concerns and Pollution control in the Context of Developing Countries
• Published: 06 January 2021
• Volume 28 , pages 46116–46129, ( 2021 )

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• Guobao Xiong 1 , 2 &
• Yuanda Luo 2  

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In recent years, the frequent occurrence of smog in Chinese cities has prompted great changes in the policy environment faced by enterprises. In this study, we address the question whether the decision-making behavior of enterprises will be affected by smog. This paper studied the 2010–2018 data of 218 listed Chinese polluting companies to investigate the impact of smog on corporate social responsibility (CSR). The subjects of this study were all listed on China’s A-share market on either the Shenzhen or Shanghai Stock Exchange. The empirical results indicate the following: (1) the more serious the smog, the more likely enterprises are to perform CSR; (2) smog exerts a higher impact on the social responsibility of enterprises that receive more media attention. Further research determined that media attention, whether positive, negative, or neutral, plays the same role in moderating the relationship between smog and CSR; and (3) compared to private enterprises, the function of smog in promoting the CSR fulfillment of state-owned enterprises (SOEs) is more obvious. Based on the reality of Chinese polluting industries, this research combined smog and media attention in the exploration of CSR, which not only enriches CSR research but also provides positive guidance for the sustainable development of polluting enterprises.

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Acknowledgments

We thank East China University of Technology for providing a platform and support for writing the paper.

This research was financially supported by the Humanities and Social Sciences Research Project of Jiangxi Universities (Project No: JD17002, JD17004) and The Young Marxist Theoretical Research and Innovation Project Funding Project of Jiangxi Province (Project No:20QM99).

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Xiong, G., Luo, Y. Smog, media attention, and corporate social responsibility—empirical evidence from Chinese polluting listed companies. Environ Sci Pollut Res 28 , 46116–46129 (2021). https://doi.org/10.1007/s11356-020-11978-4

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“Air pollution in Delhi: Its Magnitude and Effects on Health”

Centre for Community Medicine, All India Institute of Medical Sciences, New Delhi, India

Baridalyne Nongkynrih

Sanjeev kumar gupta.

Air pollution is responsible for many health problems in the urban areas. Of late, the air pollution status in Delhi has undergone many changes in terms of the levels of pollutants and the control measures taken to reduce them. This paper provides an evidence-based insight into the status of air pollution in Delhi and its effects on health and control measures instituted. The urban air database released by the World Health Organization in September 2011 reported that Delhi has exceeded the maximum PM10 limit by almost 10-times at 198 μ g/m3. Vehicular emissions and industrial activities were found to be associated with indoor as well as outdoor air pollution in Delhi. Studies on air pollution and mortality from Delhi found that all-natural-cause mortality and morbidity increased with increased air pollution. Delhi has taken several steps to reduce the level of air pollution in the city during the last 10 years. However, more still needs to be done to further reduce the levels of air pollution.

Pollution refers to the contamination of the earth's environment with materials that interfere with human health, quality of life or the natural functioning of the ecosystems. The major forms of pollution include water pollution, air pollution, noise pollution and soil contamination. Other less-recognised forms include thermal pollution and radioactive hazards. It is difficult to hold any one particular form responsible for maximum risk to health; however, air and water pollution appear to be responsible for a large proportion of pollution related health problems.

Of late, the air pollution status in Delhi has undergone many changes in terms of the levels of pollutants and the control measures taken to reduce them. This paper provides an evidence-based insight into the status of air pollution in Delhi and its effects on health and control measures instituted.

Status of Air Pollution in Delhi

Delhi (or the National Capital Territory of Delhi), is jointly administered by the central and state governments. It accommodates nearly 167.5 lakh people (2011 Census of India).( 1 )

Metros across the world bear the major brunt of environmental pollution; likewise, Delhi is at the receiving end in India.

A study funded by the World Bank Development Research Group was carried out in 1991-1994 to study the effects of air pollution.( 2 ) During the study period, the average total suspended particulate (TSP) level in Delhi was approximately five-times the World Health Organization's annual average standard. Furthermore, the total suspended particulate levels in Delhi during this time period exceeded the World Health Organization's 24-h standard on 97% of all days on which readings were taken. The study concluded that the impact of particulate matter on total non-trauma deaths in Delhi was smaller than the effects found in the United States of America, but found that a death associated with air pollution in Delhi caused more life-years to be lost because these deaths were occurring at a younger age.

A report by the Ministry of Environment and Forests, India, in 1997 reviewed the environmental situation in Delhi over concerns of deteriorating conditions.( 3 ) Air pollution was one of the areas of concern identified in this study. It was estimated that about 3000 metric tons of air pollutants were emitted every day in Delhi, with a major contribution from vehicular pollution (67%), followed by coal-based thermal power plants (12%). There was a rising trend from 1989 to 1997 as monitored by the Central Pollution Control Board (CPCB). The concentrations of carbon monoxide from vehicular emissions in 1996 showed an increase of 92% over the values observed in 1989, consequent upon the increase in vehicular population. The particulate lead concentrations appeared to be in control; this was attributable to the de-leading of petrol and restrictions on lead-handling industrial units. Delhi has the highest cluster of small-scale industries in India that contribute to 12% of air pollutants along with other industrial units.

Vehicular pollution is an important contributor to air pollution in Delhi. According to the Department of Transport, Government of National Capital Territory of Delhi, vehicular population is estimated at more than 3.4 million, reaching here at a growth rate of 7% per annum. Although this segment contributes to two-thirds of the air pollution, there has been a palpable decline compared to the 1995-1996 levels.

The PM 10 standard is generally used to measure air quality. The PM 10 standard includes particles with a diameter of 10 μm or less (0.0004 inches or one-seventh the width of a human hair). These small particles are likely to be responsible for adverse health effects because of their ability to reach the lower regions of the respiratory tract. According to the Air Quality Guideline by the World Health Organization, the annual mean concentration recommended for PM 10 was 20 μg/m 3 , beyond which the risk for cardiopulmonary health effects are seen to increase.( 4 ) Major concerns for human health from exposure to PM 10 include effects on breathing and respiratory systems, damage to lung tissue, cancer and premature death. Elderly persons, children and people with chronic lung disease, influenza or asthma are especially sensitive to the effects of particulate matter. The urban air database released by the World Health Organization in September 2011 reported that Delhi has exceeded the maximum PM 10 limit by almost 10-times at 198 μg/m 3 , trailing in the third position after Ludhiana and Kanpur.( 5 ) Vehicular emissions and industrial activities were found to be associated with indoor as well as outdoor air pollution in Delhi [ Table 1 ].( 6 – 9 )

Air pollutants in Delhi

Effects of Air Pollution on Health

A large number of studies in Delhi have examined the effect of air pollution on respiratory functions and the associated morbidity. The most comprehensive study among them was the one conducted by the Central Pollution Control Board in 2008, which identified significant associations with all relevant adverse health outcomes.( 10 ) The findings were compared with a rural control population in West Bengal. It was found that Delhi had 1.7-times higher prevalence of respiratory symptoms (in the past 3 months) compared with rural controls ( P < 0.001); the odds ratio of upper respiratory symptoms in the past 3 months in Delhi was 1.59 (95% CI 1.32-1.91) and for lower respiratory symptoms (dry cough,wheeze, breathlessness, chest discomfort) was 1.67 (95% CI 1.32-1.93). Prevalence of current asthma (in the last 12 months) and physician-diagnosed asthma among the participants of Delhi was significantly higher than in controls. Lung function was reduced in 40.3% individuals of Delhi compared with 20.1% in the control group. Delhi showed a statistically significant ( P < 0.05) increased prevalence of restrictive (22.5% vs. 11.4% in control), obstructive (10.7% vs. 6.6%) as well as combined (both obstructive and restrictive) type of lung functions deficits (7.1% vs. 2.0%). Metaplasia and dysplasia of airway epithelial cells were more frequent in Delhi, and Delhi had the greater prevalence of several cytological changes in sputum. Besides these, non-respiratory effects were also seen to be more in Delhi than in rural controls. The prevalence of hypertension was 36% in Delhi against 9.5% in the controls, which was found to be positively correlated with respirable suspended particulate matter (PM 10 ) level in ambient air. Delhi had significantly higher levels of chronic headache, eye irritation and skin irritation.

Several other community-based studies have found that air pollution is associated with respiratory morbidity.( 11 – 13 ) Numerous studies have reported an association between indoor air pollution and respiratory morbidity.( 14 – 19 )Some of these studies have concentrated on children's respiratory morbidity.( 15 , 17 , 19 ) Other studies in children have found similar correlations between particulate matter in ambient air and attention-deficit hyperactivity disorder( 20 ) between vehicular air pollution and increased blood levels of lead (a potential risk factor for abnormal mental development in children)( 21 ) and between decreased serum concentration of vitamin D metabolites and lower mean haze score (a proxy measure for ultraviolet-B radiation reaching the ground).( 22 )

Studies that have examined the compounding effect of meteorological conditions on air pollution found that winter worsened the air quality of both indoor air and outdoor air. They also found a positive correlation between the winter weather and rise in the number of patients with chronic obstructive airway disease in hospitals.( 12 , 16 )

There was a relative paucity of studies that measured outdoor air pollutant levels first hand and then tried to objectively correlate them to adverse health effects. However, some studies measured air pollutant levels and found a correlation with health-related events.( 17 , 19 )

A time-series study on air pollution and mortality from Delhi found that all-natural-cause mortality increased with increased air pollution.( 23 ) In another study, gaseous pollutants, in spite of being at a level lower than the permissible level, showed more consistent association with respiratory admissions.( 24 ) In a hospital-based study, an increase in emergency room visits for asthma, chronic obstructive airway disease and acute coronary events was reported with an increase in air pollutant levels.( 25 ) These studies are summarized in Table 2 .

Effects of air pollution in Delhi on health

Control Measures Instituted by the Government of Delhi

The nodal ministry for protecting the environment is the Ministry of Environment and Forests at the Centre and the Department of Environment of the Government of National Capital Territory of Delhi. The Central Pollution Control Board set up in 1974 under the Water Act is the principal watchdog for carrying out the functions stated in the environmental acts, implementation of National Air Quality Monitoring Programme and other activities. The Delhi Pollution Control Board is the body responsible at the state level.

From time to time, the judiciary has taken strong note of the deteriorating environmental conditions in Delhi in response to public litigations. One of the earliest such instances was the judgement passed by the Supreme Court of India to deal with the acute problem of vehicular pollution in Delhi in response to a writ petition filed in 1985. Subsequently, it ordered the shutdown of hazardous, noxious industries and hot-mix plants and brick kilns operating in Delhi.

Vehicular Policy

Control measures so far instituted include introduction of unleaded petrol (1998), catalytic converter in passenger cars (1995), reduction of sulfur content in diesel (2000) and reduction of benzene content in fuels (2000). Others include construction of flyovers and subways for smooth traffic flow, introduction of Metro rail and CNG for commercial transport vehicles (buses, taxis, auto rickshaws), phasing out of very old commercial vehicles, introduction of mandatory “Pollution Under Control” certificate with 3-month validity and stringent enforcement of emission norms complying with Bharat Stage II/Euro-II or higher emission norms. Introduction of The Air Ambience Fund levied from diesel sales and setting up of stringent emission norms for industries and thermal power stations are the other measures. Environmental awareness campaigns are also carried out at regular intervals. The Delhi Pollution Control Board conducts monthly Ambient Air Quality Monitoring at 40 locations in Delhi, and takes corrective action wherever necessary.

Industrial Policy

The first Industrial Policy for Delhi was introduced in 1982. Subsequently, a second Industrial policy (2010–2021) was issued by the Department of Industries, Government of Delhi. It is a comprehensive document envisioning higher industrial development in Delhi, with one of its mandates being to develop clean and non-polluting industries and details of steps to be undertaken in this direction have been described.

There are many other organizations that work synergistically with the government efforts to reduce air pollution. These include the Centre for Science and Environment and The Energy and Resources Institute, and the Indian Association for Air Pollution Control. Representatives of the industries include Confederation of Indian Industry and Society of Indian Automobile Manufacturers. Government agencies like Factories Inspectorate are also involved in the control of pollution. Research and academic institutions include National Environmental Engineering Research Institute, Indian Institute of Technology, Council of Scientific and Industrial Research institutions, Indian Agricultural Research Institute and various other academic institutions in and around Delhi. Professional organizations like the Indian National Science Academy, the Indian Institute of Chemical Engineers and the Indian Institute of Engineers are also involved in pollution control.

Benefits Accrued as a Result of Control Measures

Since the first act on pollution was instituted, huge progress has been made in terms of human resource, infrastructure development and research capability. Some studies tried to gather evidence for the effectiveness of control measures by comparing pre- and post-intervention health status. The study conducted by the Central Pollution Control Board demonstrated that spending 8-10 h in clean indoor environment can reduce health effects of exposure to chronic air pollution.( 10 ) A recent study found significant improvement in the respiratory health following large-scale government initiatives to control air pollution.( 26 ) It was reported that use of lower-emission motor vehicles resulted in a significant gain in disability-adjusted life-years in Delhi.( 27 ) Another study found significant evidence for reduction in respiratory illness following introduction of control measures.( 24 )

Most of the studies were ecological correlation studies, which are severely limited in their ability to draw causal inferences. But, considering the context that demanded the research, these were probably the best available designs to produce preliminary and,sometimes, policy-influencing evidences, as any other methodology would be unethical or operationally impossible.

The Government of National Capital Territory of Delhi has taken several steps to reduce the level of air pollution in the city during the last 10 years. The benefits of air pollution control measures are showing in the readings. However, more still needs to be done to further reduce the levels of air pollution. The already existing measures need to be strengthened and magnified to a larger scale. The governmental efforts alone are not enough. Participation of the community is crucial in order to make a palpable effect in the reduction of pollution. The use of public transport needs to be promoted. The use of Metro rail can be encouraged by provision of an adequate number of feeder buses at Metro stations that ply with the desired frequency. More frequent checking of Pollution Under Control Certificates needs to be undertaken by the civic authorities to ensure that vehicles are emitting gases within permissible norms. People need to be educated to switch-off their vehicles when waiting at traffic intersections. Moreover, the “upstream” factors responsible for pollution also need to be addressed. The ever-increasing influx of migrants can be reduced by developing and creating job opportunities in the peripheral and suburban areas, and thus prevent further congestion of the already-choked capital city of Delhi.

Health, as we all know, is an all-pervasive subject, lying not only within the domains of the health department but with all those involved in human development. Many great scholars from Charaka to Hippocrates have stressed the importance of environment in the health of the individual. Therefore, all those who play a role in modifying the environment in any way, for whatever reason, need to contribute to safeguard people's health by controlling all those factors which affect it.

Source of Support: Nil

Conflict of Interest: None declared.