Air Pollution


Category Description

Air pollutants negatively affect ecosystem integrity and function. Both sulfur oxides (SOX) and nitrogen oxides (NOX) can cause acidification, which can degrade soil and water quality. NOX deposition can further cause eutrophication, the excessive enrichment of nutrients. The addition of reactive nitrogen to a system can further trigger a cascade of ecological effects that reduce plant biodiversity. As a result, these pollutants are very harmful to both natural vegetation and agricultural crops. Acidification and eutrophication driven by atmospheric pollutants can be difficult or impossible to reverse, persisting long after emissions reduction policies are implemented. It is therefore imperative, especially in industrializing nations, to reduce emissions of long-range air pollutants to protect the health of global ecosystems.

Indicators Included

The two indicators used for air pollution are NOX and SO2 emission intensity. The 2018 Environmental Performance Index (EPI) uses data from the Emissions Database for Global Atmospheric Research (EDGAR) v4.3.1 global anthropogenic emissions inventory of gaseous and particulate air pollutants.

Air Pollution Indicators
Sulfur oxide Mt/constant 2011 international $
Nitrogen oxide Mt/constant 2011 international $

Category Overview

Long-range air pollutants are a significant threat to ecosystem health. These pollutants can be transported across distances greater than 100 km through the atmosphere, extending the range of their harmful effects far from their original sources (United Nations, 1997). The pollutants of concern include sulfur, nitrogen, ground-level ozone, particulate matter, heavy metals, and persistent organic pollutants (Wit, Hettelingh, & Harmens, 2015, p. 9). Emissions of sulfur oxides (SOX) and nitrogen oxides (NOX) typically co-occur with other air pollutants and are therefore a useful metric for assessing overall air quality impacts on ecosystems. These compounds cause a variety of negative environmental impacts through the chemical and biological processes of acidification and eutrophication.

Both pollutants are emitted from anthropogenic sources. Sulfur oxides are principally released from coal combustion (Lovett et al., 2009, p. 101). The shipping sector represents a major source of sulfur emissions today (United Nations Environment Programme, 2012, p. 43). Any type of combustion can result in the emissions of nitrogen oxides (Lovett et al., 2009, p. 101), with 58% of total NOX emissions originating from fuel combustion (Fowler et al., 2015, p. 13861). Emissions of reactive nitrogen[1] have major environmental consequences, as atmospheric transport and deposition is now the principle mechanism for the distribution of reactive nitrogen (J. N. Galloway et al., 2008, p. 88). NOX emission and deposition levels are projected to double by 2050 as compared to 1995 levels (J. N. Galloway et al., 2008, p. 88). After traveling through the atmosphere, the pollutants then enter ecosystems through both wet and dry deposition. Wet deposition, commonly called acid rain, is the process in which pollutants reach the earth incorporated into rain, snow, or vapor. However, SOX and NOX can also be deposited directly on systems as particulates and as gases through dry deposition (Burns, Aherne, Gay, & Lehmann, 2016, p. 1). The introduction of these pollutants can then negatively affect the health and functioning of ecosystems.

Environmental: Scientists recognize atmospheric deposition of NOX to be a major threat to biodiversity loss worldwide due to the suite of complex impacts it generates (Clark et al., 2013, p. 519). Nitrogen is necessary for the production of proteins and other biological molecules. As a result, it is often a limiting nutrient for primary production in ecosystems. When reactive nitrogen is deposited onto an otherwise nitrogen-limited system, it can then cause a cascade of harmful effects, including eutrophication, direct toxicity to sensitive plants, increased ammonia and ammonium availability, soil and water acidification, and increased vulnerability of plants to secondary stressors (Bobbink et al., 2010; James N. Galloway et al., 2003 Clark et al., 2013, p. 522, Throop & Lerdau, 2004, p. 31). In addition, NOx is a precursor to ozone, which can also have harmful effects on plants (Royal Society (Great Britain) & Fowler, 2008). The effects of NOX deposition can vary widely across ecosystems depending on the degree of nitrogen loading and the typical inputs of reactive nitrogen into the system. Historic characteristics of the system, such as previous deposition and the sensitivity of plants living in the ecosystem, can also influence the magnitude of the effect of NOx inputs (Bobbink et al., 2010, pp. 31, 42, 44, 51). More research is needed to understand the effects of air pollution on animals species (Clark et al., 2013, p. 519). Ongoing impacts on global plant communities is a serious concern for biodiversity conservation.

The effects of sulfur deposition are less complicated than those of nitrogen, but SOX emissions still have severe consequences for ecosystems. Sulfur is not typically a limiting nutrient in many ecosystems, so it does not cause the same cascading effects (Lovett et al., 2009, p. 108). However, sulfur deposition can similarly lead to acidification of both aquatic and terrestrial systems (Lovett et al., 2009, p. 99). In forested systems, acidic rain flows through tree canopies and soils, leaching critical nutrients like calcium and magnesium. Acidic soils also risk mobilizing aluminum, as ions of the metal are released into an aqueous solution, which is toxic to plants (Lovett et al., 2009, p. 103)In wetlands, increased sulfate deposition can lead to the methylation of mercury by bacteria, which makes this toxic metal more bioavailable in surrounding ecosystems (Lovett et al., 2009, p. 106). In aquatic systems, increased acidity can affect species composition. Acidification can also clarify water. Increased sunlight can then warm the water column and affect physical characteristics of water bodies (Lovett et al., 2009, p. 117). The effects on animals, as with nitrogen deposition, are less well-known when compared to plants, but acidification can be toxic to fish (Burns et al., 2016, p. 1). Some studies have further shown that invertebrates are also sensitive to acidity, with ramifications for bird species that feed on them (Lovett et al., 2009, p. 109). Reducing global SOX emissions is critical to protect ecosystems from acidification.

Acidification and eutrophication can have long-term impacts that are difficult or impossible to reverse (Clark et al., 2013, p. 532; Driscoll et al., 2001). Even if current emissions were abated, the buildup of pollutants can reach levels that make regions unsuitable for native species. For example, the consequences of acidification, including the loss of base cation nutrients in soils, linger for decades or even centuries after leaching stops (Driscoll et al., 2001). Sulfate remains the dominant cause of soil acidification today, even in regions with reduced emissions levels. Legacy sulfur is still being released from soils, which are efficient at retaining these pollutants (Wit et al., 2015, p. 10). Even in the United States where significant air emissions reductions were achieved after the passage of the Clean Air Act and Amendments in 1990, surface waters have only shown limited recovery from acidification (Burns et al., 2016, p. 3). Similarly, reductions in nitrogen deposition have been found to be insufficient to reverse changes in species composition (Payne et al., 2017, p. 4). The latent and chronic nature of these impacts mean policy change is even more urgent to address global emissions.

These impacts are of particular concern for natural areas. SOX and NOX deposition is concentrated regionally around sources such as coal plants and downwind of industrial centers (Burns et al., 2016, p. 1). However, 7–17% of the global area of natural ecosystems exceed harmful levels of acidification, and similarly 7–18% of these systems exceed critical loads for eutrophication (Bouwman, Beusen, & Billen, 2009, p. 349). An estimated 16.3 million km2of natural vegetation is impacted by harmful levels of nitrogen deposition (Dentener et al., 2006, p. 1). It is predicted that atmospheric nitrogen deposition will increase in most regions by 2030 (Dentener et al., 2006). The fate of these pollutants varies, with 36–51% of SOX emissions deposited over oceans. 50–58% of SOX deposition on land is on non-agricultural vegetation (Vet et al., 2014, p. 10). Many of the world’s biodiversity hot spots are exposed to or will be exposed to harmful levels of nitrogen deposition. Hot spots in developing countries in the tropics and Asia, which will experience increased emissions and deposition, are at significant risk of degradation (Phoenix et al., 2006). Some of the ecoregions most vulnerable to reductions in plant diversity in response to nitrogen deposition are tropical areas in Latin America and Africa, Mediterranean ecoregions, and eastern and southern Asia (Bobbink et al., 2010, p. 30). Policy interventions to protect these natural systems must address the threat of air pollutants to normal ecosystem functioning.

Social: Air pollution has negative impacts on ecosystem health, with further consequences for global biodiversity, and thus for communities. Biodiversity loss threatens human populations reliant on a range of services including food production and human health needs. The social dimensions of biodiversity are further explored in Chapter 8 on Biodiversity & Habitat of this report. In addition to natural ecosystems, air pollution threatens global crop yields, with consequences for sustainable agriculture (Gurjar, Molina, & Ojha, 2010, p. 463). These negative impacts can threaten food security and nutrition, as further reported in Chapter 14 on Agriculture. Finally, air pollution threatens our cultural heritage. Many pollutants can cause the recession or corrosion of materials used in historic buildings, monuments, and artworks. For example, limestone is vulnerable to erosion due to acid rain, and other materials can become discolored from interaction with sulfate deposition. Corrosion of copper and bronze is also caused by air pollution (Di Turo et al., 2016, p. 586). Recent work has further identified that dry deposition may play a greater role in the degradation of outdoor marble and bronze sculptures than previously thought (Livingston, 2016). Particulate matter and certain gases resulting from air pollution can also negatively affect visibility, degrading natural vistas and cultural experiences (Malm, 1999). The loss of irreplaceable cultural heritage is a major concern motivating regulations to curb NOX and SOX emissions.

Economic: As developing nations pursue food and energy security, air pollution can be a significant economic concern. Industrialization can lead to increased air emissions, risking the degradation of ecosystems, agriculture, and public health. For example, acidification can have negative impacts on farms, reducing yields of many crop species, as much as it harms vegetation in natural systems (Gurjar et al., 2010, p. 463). Air pollution threatens many valuable ecosystem services including crop yields, capture fisheries, aquaculture, wild foods, timber, fiber crops like cotton, genetic resources, natural medicines, climate regulation, recreation and tourism, nutrient cycling, and primary production (Persson et al., 2010, p. 39). When considering public health consequences, the benefits of policies to limit air pollution can vastly outweigh their costs. In the experience of the United States, the Clean Air Act created over $2 trillion in benefits, while resulting in only $65 billion in costs. Specifically, improved crop and timber yields generated $5.5 billion in benefits in those sectors, while improved visibility in national parks and metropolitan areas generated $34 billion (United States Environmental Protection Agency, 2011). The reduction of air pollution impacts on ecosystems can provide significant economic benefits.

Global Impact

The environmental impacts of air pollution are significant concerns due to their latent and chronic effects. The slow recovery of ecosystems following SOX and NOX deposition threatens the biodiversity of developing countries, currently experiencing increased air emissions. These areas are of particular concern as the risks of acidification and eutrophication are expected to significantly increase in Asia, Africa, and South America, as they decline in North America and Western Europe (Bouwman, Vuuren, Derwent, & Posch, 2002, p. 349).

Figure 12-1

Figure 12-1. Regional trends in SO2intensity.
Source: Emissions Database for Global Atmospheric Research (EDGAR).


Nations have addressed the negative effects of SOX and NOX by defining critical loads, or levels of deposition that, when exceeded, can harm ecosystems. Policymakers have developed regulations to limit atmospheric deposition levels accordingly to protect their environments (Burns et al., 2016, p. 3). Additional research is necessary to establish accurate critical loads for ecosystems outside of Europe and North America (WallisDeVries & Bobbink, 2017, p. 387). To address these and other knowledge gaps in addressing the effects of air pollution, a variety of international research and monitoring networks have emerged.

Table 12-1. International research and monitoring networks.
Acid Deposition Monitoring Network in East Asia EANET
Canadian Air and Precipitation Monitoring Network CAPMoN
Co-Operative Programme for monitoring and Evaluation of the Long Range Transmission of Air Pollutants in Europe EMEP
Deposition of Biogeochemically Important Trace Species DEBITS
US Global Precipitation Chemistry Program GPCP
US National Atmospheric Deposition Program NADP
World Meteorological Organization Global Atmosphere Watch Scientific Advisory Group for Precipitation Chemistry WMO GAW SAG-PC
World Data Centre for Precipitation Chemistry WDCPC

There is no specific Sustainable Development Goal (SDG) for air pollution, although the problem is mentioned in two targets under SDG3 (Good Health and Well-Being) and SDG11 (Sustainable Cities and Communities). The impacts of air pollution on ecosystems are also related to the following Goals:

Goal 7: Affordable and Clean Energy

Goal 14: Life Below Water

Goal 15: Life on Land

No international agreement has been created to control global SOX emissions or regulate human inputs of reactive nitrogen into the atmosphere (Fowler et al., 2015, p. 13850). However, several regional and bilateral agreements have developed to control SOX and NOX emissions.

Multilateral Efforts

Aichi Biodiversity Targets: The Aichi Biodiversity Targets of the Convention on Biological Diversity present goals for the protection of global biodiversity. Target 8 is to reduce pollution, including from excess nutrients, to levels not detrimental to ecosystem functions and biodiversity by 2020 (Convention on Biological Diversity, 2018).

Association of Southeast Asian Nations (ASEAN) Agreement on Transboundary Haze Pollution: The ten governments of the Association of Southeast Asian Nations signed the ASEAN Haze Agreement to address transboundary haze pollution from land and forest fires. The Agreement created the ASEAN Coordinating Centre for Transboundary Haze Pollution Control to facilitate cooperation among member countries in addressing air pollution (Association of Southeast Asian Nations Secretariat, 2018).

Convention on Long-Range Transboundary Air Pollution (CLRTAP): The CLRTAP is composed of eight protocols which establish targets for pollutants including sulfur, nitrogen oxide, persistent organic pollutants, volatile organic compounds, ammonia, and toxic heavy metals. Within this agreement, the 1999 Gothenburg Protocol to Abate Acidification, Eutrophication and Ground-Level Ozone further created stricter targets for sulfur dioxide, nitrogen oxides, volatile organic compounds, and ammonia (United Nations Economic Commission for Europe, 2013). 32 nations are signatories to the CLRTAP, and 51 are parties to the agreement, including European Union countries, Canada, Russia, and the United States (United Nations, 1979).

European Union Directives for Air Quality: The European Union has passed legislation establishing health-based standards and objectives for air pollutants including sulfur dioxide and nitrogen dioxide (European Commission, 2017). Directive 2008/50/EC merged much existing legislation into an encompassing directive, which was amended by Directive 2015/1480/EC, establishing rules for reference methods, data validation, and sampling points (European Commission, 2017).

International Convention for the Prevention of Marine Pollution from Ships (MARPOL): MARPOL Annex VI establishes emissions limits for sulfur oxides and nitrous oxides in ship exhaust gas. The agreement further bans deliberate emissions of ozone depleting substances. Finally, Annex VI regulates incineration on ships, and in particular the emissions of volatile organic compounds from tanker ships (International Maritime Organization, 2017).

The Canada-U.S. Border Air Quality Strategy: The Strategy refers to ongoing efforts building upon the U.S.-Canada Air Quality Agreement. The two nations have jointly completed three projects, including creating pilot airsheds to study human health effects and a feasibility study of a cap and trade program (United States Environmental Protection Agency, 2017).

U.S.-Canada Air Quality Agreement: The United States and Canada created the U.S.-Canada Air Quality Agreement in 1991 to regulate transboundary air pollution between the two nations. The agreement explicitly builds upon a series of previously established air pollution agreements. The 2000 Ozone Annex was added to address transboundary smog emissions (United States Environmental Protection Agency, 2016).


To best address the effects of air pollution, policymakers would ideally have access to measurements of pollutant emissions and deposition, as well as a greater understanding of the complex factors shaping ecosystem impacts. Relevant measurements would include connections between sources of air pollution and ambient concentrations, studies of precipitation chemistry, deposition rates, and the effects of pollutants on biogeochemical and broader ecological systems globally. Research efforts have so far focused mainly on biogeochemical impacts and studies of responses in plant communities. Less is known about the impacts of air pollutants on biodiversity (Clark et al., 2013, p. 525). To address the lack of global precipitation chemistry measurements, some studies base estimates of precipitation composition and deposition rates on transport model predictions (Vet et al., 2014, p. 4). However, many research gaps remain.

Box 12-1. Missing sulfur dioxide sources

Studies of emissions using satellite monitoring, such as the Ozone Monitoring Instrument aboard NASA’s Aura satellite, provide significant insight into emissions of pollutants including NO2 and SO2 (Vet et al., 2014, p. 10). Local monitoring efforts to measure sulfur dioxide often prove to be inadequate. While some nations measure emissions directly on industrial sites, others, especially in the developing world, rely largely on estimates. However, monitoring efforts using NASA’s Aura satellite, which was launched in 2002, have helped scientists bridge some of the gaps in our current understanding of emissions levels (Chung, 2016). Scientists found that of the nearly 500 large sources in their satellite-based global emissions inventory, 40 had not been identified in conventional emissions reporting programs. The missing sources came principally from developing countries lacking emissions reporting requirements and sophisticated measurement infrastructure. Roughly one third of sources originated around the Persian Gulf. By including missing anthropogenic sources, as well as sulfur dioxide emissions from volcanoes, the corrected satellite measurements highlighted discrepancies with conventional emissions measures as large a factor of three (McLinden et al., 2016).

Map 12-1
Map 12-1. Percent of SO2 emissions missing from global inventories.
Source: McLinden et al., 2016.


Global standards for sampling and analytical methodologies should be established to allow for the evaluation of international data and benchmarking across nations. Inadequate information currently exists on how air pollution deposition occurs differently across its various forms, such as wet deposition from fog (Vet et al., 2014, pp. 5, 90–91). Furthermore, much uncertainty remains about how atmospheric chemistry works over the long-term (Pascaud et al., 2016, p. 28). NOx in particular poses a monitoring challenge. Not all nitrogenous species are measured in existing monitoring schemes (Clark et al., 2013, p. 533), which presents a significant knowledge gap. NOX enters systems in a variety of oxidized and reduced forms, causing cascading effects through biological and chemical transformations before returning to the atmosphere as N2 (Fowler et al., 2015, p. 13850). More complex monitoring could address these dynamics. Finally, because there is an overall lack of data on long-term atmospheric deposition, researchers find it challenging to identify overall trends (Burns et al., 2016, p. 2). Increased monitoring to account for these complexities is needed on a global scale to address air pollution challenges.

Ecological responses to NOX and SOX depositions should also be further characterized. More research is needed into how soils affect ecosystem recovery and which factors affect how biota respond to varying levels of deposition. Furthermore, gaps in knowledge regarding how SOX and NOX interact with other pollutants, climate change, and the carbon cycle limit the ability to identify appropriate solutions (Burns et al., 2016, p. 1). Additional research is needed to improve models used to determine critical loads (Bobbink et al., 2010, p. 47). Current knowledge about ecological responses is also geographically limited. South America, remote areas of North America, Asia, Africa, Oceania, the polar regions, and the ocean have all been insufficiently studied (Vet et al., 2014, p. 4). The magnitude of acidification in oceans caused by NOX and SOX are also largely uncertain because of gaps in knowledge about the flux of these pollutants into the ocean and subsequent biogeochemical responses (Doney et al., 2007, p. 14584). Ecological studies are needed to address these uncertainties.

Taking these measurement and knowledge gaps into consideration, the 2018 EPI uses two indicators to measure NOX and SO2 emission intensity. To construct these indicators, the EPI used data from the EDGAR v4.3.1 global anthropogenic emissions inventory of gaseous and particulate air pollutants. The advantage of the EDGAR data is the near completeness and consistency of estimated emissions of multiple pollutants. EDGAR includes continues time-series data for emissions across the globe (Janssens-Maenhout et al., 2017).

Indicator Background

The 2018 EPI evaluates national performance in the reduction of air pollution through emissions intensity trends, the rate of emissions per unit of GDP. The construction of the indicator reflects the importance of decoupling economic growth from emissions by standardizing each country’s pollution levels by its economic activity. For NOX and SO2, emissions are divided by GDP to allow for cross-country comparison on a common scale. Then, to account for annual variations in emissions intensity tied to regular economic cycles, a ten-year average of emissions intensity is also used for the indicator construction.

The construction of the indicator compares countries to their economic peers. Countries at similar levels of economic development are assumed to have roughly equivalent capacities for decoupling emissions from their growth. The 2018 EPI compares the trend in every country against its wealth in per capita GDP. As it is easier for richer nations to decouple their growth from emissions, their average emissions intensity predictably decreases. Each individual country’s performance can then be compared to this trend. Countries with emissions intensities below the trendline receive improved scores for performing better than expected, while countries above the trendline are penalized.

Finally, the construction of the indicator identifies top performing nations that have approached the lower limit of emissions intensity following successful decoupling. The Netherlands is an example of a country whose SO2 emissions trend is flat rather than declining. To account for nations that would be scored poorly based on their flat trend line, EPI places greater weight on the single-year indicator. As a result, the indicator reflects past policy successes of nations that have significantly reduced their emissions.

Figure 12-2
Figure 12-2. Comparing trends in SO2 intensity.
Source: Emissions Database for Global Atmospheric Research (EDGAR).


The final indicator therefore represents trends in emissions intensity of NOX and SO2 relative to economic peers. A more complete description of the construction and calculation of the Air Pollution indicators can be found in the Technical Appendix online.

Data Description

EDGAR is a collaborative research effort of the European Commission Joint Research Centre (JRC) and the Netherlands Environmental Assessment Agency (PBL). Emissions data are calculated using a technology-based emissions factor approach. Emissions for each pollutant of interest are calculated by sector for every country annually. Abatement by end-of-pipe measures are accounted for in the calculation. A geographical database includes the location of sources such as energy facilities, roads, shipping routes, areas of high population density, and agricultural land use. Emissions data related to the energy sector are based on energy balance statistics from the International Energy Agency. Agricultural data are collected from the Food and Agriculture Organisation. The full dataset is publicly available for download from the EDGAR website (European Commission Joint Research Centre and the Netherlands Environmental Assessment Agency, 2017).


The EDGAR data set has several limitations with regard to the pollutants of interest for this indicator. The data cannot account for sources beyond those gleaned from the combustion of fossil fuels. In addition, the data cannot be used to attribute emissions to actual damages resulting from their deposition. Finally, the most recent year included in the data set is 2010. Ideally, more recent data would be used to conduct EPI’s analysis. SO2 emissions are used in the creation of the indicator, rather than all SOx compounds, because SO2 data are most readily available and will be highly correlated with other SOx emissions.

Box 12-2. The Sentinal-5P Satellite

On October 13, 2017, the European Union and the European Space Agency’s (ESA) Copernicus program launched the most sophisticated air-pollution satellite ever created. The Sentinel-5P satellite will be used to measure the chemistry of earth’s atmosphere and analyze the global distribution of pollutants using its TROPOspheric Monitoring Instrument (Tropomi). The device will be able to capture extremely high-resolution data on NOX and SOX emissions, and address many existing uncertainties about pollution transport and chemical reactions in the atmosphere (Pultarova, 2017). The first images were returned from the satellite in December of 2017, highlighting elevated concentrations of NO2 over parts of Europe and high levels of emissions from power plants in India. The satellite’s data are processed at the DLR German Aerospace Center, where daily maps of the entire earth will be generated. Data from the Sentinel-5P will be invaluable in informing air pollution mitigation policies globally as more data become available (European Space Agency, 2017).


Global Trends

The results of the 2018 EPI demonstrate that progress is being made globally to address air pollution. Emissions of SO2 and NOx have both fallen from 2000 to 2010, with strong improvements in the scores for each indicator. However, progress may continue to be uneven as industrialized nations curb their emissions, while those of developing nations are expected to increase (Bouwman et al., 2002, p. 349). This trend is reflected in the 2018 EPI results. With some exceptions, the leaders were generally wealthier nations than the laggards. Globally, nations performed better on NOx than SO2 emissions, highlighting long-term acidification as a serious concern in terms of ecosystem health. Much more progress is needed on reducing air pollution to protect the world’s ecosystems, and in particular vulnerable biodiversity hot spots (Phoenix et al., 2006).

Table 12–2. Global trends in Air Pollution.
Note: Metrics are in units of Mt/constant 2011 international $. Current refers to data from 2010, and Baseline refers to historic data from 2000.
Indicator Metric Score
  Baseline Current Baseline Current
SO2 Emissions 1,360.5 1,019.5 32.42 40.48
NOx Emissions 1,341.9 1,047.0 43.70 54.99

Leaders & Laggards

Table 12-3. Leaders in Air Pollution.
Rank Country Score
1 Equatorial Guinea 99.97
2 Switzerland 98.70
3 Singapore 97.76
4 France 96.82
5 Netherlands 96.56
6 Azerbaijan 95.36
7 Germany 93.30
8 Afghanistan 91.44
9 Taiwan 89.75
10 Italy 88.55

One of the leaders in this category, Switzerland has significantly improved its air quality over the past 25 years (European Environment Agency, 2015). As a result, Switzerland rose from fourth to second place in the EPI rankings between the baseline and current years. Switzerland’s Ordinance on Air Pollution Control came into force in 1986, and is enforced in two stages. The first stage, called the Precautionary stage, implements best available technologies which are economically feasible for several classes of pollutants. Quality requirements for fuel and gasoline are also set through this law. In the second stage, air pollution is assessed according to ambient air quality standards, which must be achieved through emission control measures. The Ordinance is largely enforced at the local level by cantons. In addition to the Ordinance, the Swiss government also implements an overall air pollution control strategy specifically to limit sulfur dioxide, nitrogen oxides, and volatile organic compounds (VOCs) (Purghart, 1992).

Switzerland’s regulatory framework has evolved over time. Existing regulations include strict emission rules for heating systems, industrial facilities, and vehicles. In addition, Switzerland has implemented incentive-based measures including the mileage-related heavy vehicle tax (MRHVT) and a levy on VOCs (European Environment Agency, 2010). The Swiss Federal Council has taken the nation’s commitments under the UNECE’s CLRTAP very seriously. The National Focal Center (NFC) was established in the Federal Office for the Environment, charged with modelling and mapping critical loads and ecosystem sensitivity across Switzerland (Federal Office for the Environment, 2016, p. 11). The Swiss Federal Council has set a target to reduce ammonia emissions by 40% and nitrogen oxide emissions by 50% as compared to 2005 levels (Federal Office for the Environment, 2017). As of 2011, Switzerland was meeting emissions levels set forth by the EU National Emissions Ceilings (NEC) Directive and LRTAP Convention’s Gothenburg Protocol for NH3, non-methane VOCs (NMVOCs), NOx, and SO2 (European Environment Agency, 2017).

Table 12-4. Laggards in Air Pollution.
Rank Country Score
171 Honduras 17.68
172 Liberia 15.49
173 Djibouti 11.01
174 Bahamas 10.60
175 Zimbabwe 8.21
176 Chile 3.37
177 Seychelles 2.63
178 Brunei Darussalam 2.51
179 Oman 0.65
180 Uruguay 0.01

Because of the transboundary nature of long-range air pollutants, the poor performance of laggards is a global concern for ecosystem health. Both India and China are dependent on coal, which can contain up to three percent sulfur, for their energy production. Because of their coal consumption, both countries face significant challenges in addressing air pollution from sulfur dioxide emissions. Recent satellite studies have found that while Chinese emissions of sulfur dioxide have declined by 75% since 2007, India’s emissions have increased by 50%. As a result, India has overtaken China as the world’s largest emitter of anthropogenic sulfur dioxide (Li et al., 2017). International cooperation on pollution control is needed to curb transboundary emissions. For example, a 2015 study calculated that the rapid industrialization of China has offset more than 40% of the improvements in air quality seen in the western United States between 2005 and 2010 (Verstraeten et al., 2015). Both India and China must address their air pollution emissions to prevent acidification and other negative ecosystem impacts.

As expected from the NASA Aura Satellite results (McLinden et al., 2016), many Persian Gulf nations were lower in the rankings, including Oman (179), Iran (167), Kuwait (162), Saudi Arabia (159), and Iraq (133). These results suggest that increased attention should be paid to curbing air emissions from the oil refinery and natural gas infrastructure in this region. For example, the World Health Organization reported in 2016 that among the world’s top ten most polluted cities, Zabol in Iran was at the top of the list, with Riyadh and Al Jubail in Saudi Arabia placing fourth and fifth, respectively (Reuters, 2016). In 2010, when trade sanctions restricted Iranian imports of refined gasoline, Iran started producing greater amounts of gasoline, and in 2014, Oil Minister Bijan Zanganeh acknowledged that the main source of the smog was sub-standard gasoline (The Guardian, 2014). Our results show that Iran’s score decreased by 9.2 points to 20.7 in 2010, further emphasizing the effects of Iran’s increase in sub-standard gasoline production. Middle Eastern nations would benefit from the implementation of improved policies to control air pollution.

Stringent national air pollution regulations, as well as compliance with strong regional agreements, are key tools to improve environmental performance on air pollution. Industrializing nations will likely face policy and enforcement challenges to curb harmful emissions while growing their economies. Nations with ecosystems sensitive to acidification and eutrophication will be vulnerable to the effects of increased emissions. Continued reductions in SOx and NOx emissions will be essential to protect global ecosystems. While the 2018 EPI reveals positive trends in tackling long-range air pollutants, much work remains to promote environmental health and ecosystem vitality.


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[1] Reactive nitrogen refers to all forms of nitrogen except atmospheric N2 (Clark et al., 2013, p. 519). Of particular consideration in the EPI are biologically active forms, which are limiting nutrients in many ecosystems.