"Air pollution is made up of gases and tiny particles in the atmosphere. These can come from human activities (anthropogenic) and natural sources, such as dust or volcano emissions. They also include <a href=\"https://stats.oecd.org/glossary/detail.asp?ID=2405\" rel=\"noopener noreferrer\" target=\"_blank\">secondary pollutants</a>, formed in the atmosphere when recently emitted pollutants react with previously emitted or transported pollutants to produce new pollutants. The air we breathe is a product of emissions that have undergone chemical and physical processes in the atmosphere. The <a href=\"https://www.who.int/news-room/fact-sheets/detail/ambient-(outdoor)-air-quality-and-health\" rel=\"noopener noreferrer\" target=\"_blank\">World Health Organization</a> (WHO) air quality guidelines set thresholds for air pollutants that pose a risk to human health. These key pollutants include particulate matter with a diameter of 2.5 microns or less (PM2.5), ground-level ozone (O3), sulfur dioxide (SO2), and nitrogen dioxide (NO2). Furthermore, there are various air pollutant precursors that contribute to the formation of particulate matter and ozone in the atmosphere. These precursors are gases and compounds, such as volatile organic compounds (VOCs), ammonia (NH3), methane (CH4), black carbon (BC), and a family of oxygen containing nitrogen gases called nitrogen oxides (NOx). In addition to the examples listed above there are many pollutants that are toxic for humans and ecosystems, such as benzene, heavy metals, and polyaromatic hydrocarbons."

"Air quality is affecting many people around the world, especially those in and around <a href=\"https://enviroliteracy.org/air-climate-weather/air-quality/urban-air-quality/\" rel=\"noopener noreferrer\" target=\"_blank\">urban centers</a>. This is due to increased human activity, as well as increased extreme weather events like <a href=\"https://thecityfix.com/blog/heat-emissions-dangerous-urban-air-quality/\" rel=\"noopener noreferrer\" target=\"_blank\">heat waves</a>. Around <a href=\"https://www.who.int/health-topics/air-pollution#tab=tab_2\" rel=\"noopener noreferrer\" target=\"_blank\">91%</a> of the global population lives in areas where air quality levels exceed the WHO recommended limits. Exposure to air pollution is associated with <a href=\"https://www.sciencedirect.com/science/article/pii/S0140673695901736\" rel=\"noopener noreferrer\" target=\"_blank\">higher risk</a> for both respiratory and cardiovascular diseases, such as asthma and heart disease."

"The adverse effects of air pollution aren’t limited to human health. For example, acid rain, which is <a href=\"https://www.epa.gov/acidrain/what-acid-rain\" rel=\"noopener noreferrer\" target=\"_blank\">formed</a> when nitrogen dioxide and sulfur dioxide react with precipitation, causes the <a href=\"https://www.epa.gov/acidrain/effects-acid-rain\" rel=\"noopener noreferrer\" target=\"_blank\">acidification and/or eutrophication</a> of ecosystems and deterioration of the built environment. Vegetation is also <a href=\"https://www.nps.gov/subjects/air/nature-ozone.htm\" rel=\"noopener noreferrer\" target=\"_blank\">sensitive to ozone</a>, which could impact its health and capacity to fight against diseases. Many governments have ground-level monitors that report real-time air quality data, so people can protect their health and manage their environment."

"Air quality is a cross-boundary issue resulting from local, regional, and global sources. It is therefore essential to understand air pollution beyond ground-level monitoring to recognize its global impacts."

"Atmospheric circulation drives the distribution of air pollutants <a href=\"https://www.epa.gov/international-cooperation/transboundary-air-pollution\" rel=\"noopener noreferrer\" target=\"_blank\">beyond the immediate boundaries</a> of the source. In the process, chemical reactions and physical processes can reconfigure the mixture of air pollutants. The result is a “cocktail” of air pollutants that influences air quality across local, regional, and international boundaries."

"<h1>What Does Air Pollution Mean for Human Health and Environmental Systems?</h1>"

"The complexities of air pollution extend beyond its effects on human health, affecting global climate and environmental resources. Air pollution impacts <a href=\"https://www.wri.org/blog/2019/06/5-under-recognized-impacts-air-pollution\" rel=\"noopener noreferrer\" target=\"_blank\">global systems</a> like weather, water and biochemical cycles, and energy and food production. The impacts manifest in many ways, including unpredictable weather events, disrupted rainfall and biological patterns, and reduced energy and crop yields."

"Short-lived climate pollutants (SLCPs) are a class of pollutants with brief but powerful impacts on climate change. <a href=\"https://www.ipcc.ch/sr15/chapter/spm/\" rel=\"noopener noreferrer\" target=\"_blank\">The Intergovernmental Panel on Climate Change (IPCC) Special Report</a> states that reducing emissions from short-lived climate pollutants, like methane and black carbon, is key to avoiding a 1.5 degree Celsius warming by the end of the century. One of the key suggestions of the IPCC report is to cut SLCPs by 35% or more by 2050. From a human health perspective, the inhalation of black carbon is associated with <a href=\"http://www.euro.who.int/__data/assets/pdf_file/0004/162535/e96541.pdf\" rel=\"noopener noreferrer\" target=\"_blank\">respiratory problems and cardiovascular diseases</a>. In addition to contributing to the effects of climate change, methane is a <a href=\"https://www.ccacoalition.org/en/slcps/methane\" rel=\"noopener noreferrer\" target=\"_blank\">precursor to ground-level ozone</a> – which can negatively <a href=\"https://www.ccacoalition.org/ar/slcps/methane\" rel=\"noopener noreferrer\" target=\"_blank\">affect</a> human health and damage crops and vegetation. In fact, the impact of methane on climate change is <a href=\"https://www.ipcc.ch/site/assets/uploads/2018/02/SYR_AR5_FINAL_full.pdf\" rel=\"noopener noreferrer\" target=\"_blank\">28</a> times greater than the impact of carbon dioxide. Reducing short-lived climate pollutant emissions can have an immediate positive impact for both human, ecosystem, and climate health."

"<h1>How Do We Manage Air Pollution?</h1>"

"Air quality is challenging to manage because, as noted above, it is a cross-boundary issue that originates from many different sources. One of the most effective solutions to improve global air quality is to focus on reducing the original emissions from major sources. It will be essential to make such reductions in conjunction with efforts to contain or capture emissions at the source."

"Global energy needs increased by <a href=\"https://www.iea.org/reports/global-energy-co2-status-report-2019\" rel=\"noopener noreferrer\" target=\"_blank\">2.3%</a> in 2018, with more than 72% of the demand met by burning fossil fuels. Fossil fuel powered power plants that generate electricity and heat are the <a href=\"http://cait.wri.org/\" rel=\"noopener noreferrer\" target=\"_blank\">largest</a> emitters of greenhouse gas emissions. These practices <a href=\"https://www.eia.gov/energyexplained/electricity/electricity-and-the-environment.php\" rel=\"noopener noreferrer\" target=\"_blank\">produce</a> sulfur dioxide, nitrogen dioxide, black carbon, and volatile organic compounds as by-products. Moving away from fossil fuel energy in favor of clean, renewable sources (like wind and solar) can help to responsibly meet the world’s energy needs and better manage our air. In the meantime, it is important that air pollution control devices be installed on operating power plants to <a href=\"https://www.ifc.org/wps/wcm/connect/2ab161f5-13fc-4f67-902e-9d8491ee73ff/HandbookSulfurOxidesPollutionPreventionAndControl.pdf?MOD=AJPERES&amp;CVID=jkD0Czx\" rel=\"noopener noreferrer\" target=\"_blank\">reduce</a> the harm of current emissions."

"<a href=\"https://www.wri.org/blog/2014/12/more-rice-less-methane\" rel=\"noopener noreferrer\" target=\"_blank\">Rice cultivation</a>, <a href=\"https://www.wri.org/blog/2019/04/6-pressing-questions-about-beef-and-climate-change-answered\" rel=\"noopener noreferrer\" target=\"_blank\">animal agriculture</a>, and related agricultural <a href=\"https://www.wri.org/blog/2014/05/everything-you-need-know-about-agricultural-emissions\" rel=\"noopener noreferrer\" target=\"_blank\">land-use changes</a> contribute to an assortment of methane, black carbon, ammonia, and particulate matter emissions. <a href=\"https://www.ncbi.nlm.nih.gov/pubmed/11077155\" rel=\"noopener noreferrer\" target=\"_blank\">Flooded rice fields</a> and animal agriculture are a major source of methane emissions. Agricultural waste burning is responsible for about <a href=\"https://www.ccacoalition.org/en/activity/open-agricultural-burning\" rel=\"noopener noreferrer\" target=\"_blank\">30%</a> of all black carbon emissions and is the source of <a href=\"https://www.eea.europa.eu/ds_resolveuid/MWU9XE0TKP\" rel=\"noopener noreferrer\" target=\"_blank\">other pollutants</a>, including particulate matter, nitrogen oxides, carbon monoxide, and volatile organic compounds. This practice is particularly prevalent in developing countries but also still occurs in developed countries. An important step in reducing agricultural emissions is improved regulation of agricultural management, such as reducing the use of fertilizers, burning of biomass waste, and flooding of rice fields."

"Intensive animal agriculture practices contribute an estimated <a href=\"https://www.wri.org/blog/2014/05/everything-you-need-know-about-agricultural-emissions\" rel=\"noopener noreferrer\" target=\"_blank\">13%</a> to global greenhouse gas emissions. These practices are also responsible for about <a href=\"https://www.ccacoalition.org/en/slcps/methane\" rel=\"noopener noreferrer\" target=\"_blank\">33%</a> of global methane emissions annually, <a href=\"http://www.fao.org/3/a0701e/a0701e03.pdf\" rel=\"noopener noreferrer\" target=\"_blank\">80%</a> of which can be attributed to livestock flatulence, belching, and manure management. However, it is important to take into account the emissions caused by the land-use changes that enable animal agriculture. These emissions occur when forests are <a href=\"https://www.winrock.org/westool/greenhouse-gas-emissions-from-land-use-and-land-use-change/\" rel=\"noopener noreferrer\" target=\"_blank\">cleared</a> for crop and pasture lands. Shifting the global diet away from animal products and changing livestock practices can significantly reduce the agricultural sector’s share of air pollution."

"Industrial processes use a wide range of materials and chemicals that are known to produce environmentally negative by-products, like sulfur dioxide from <a href=\"https://www.americangeosciences.org/geoscience-currents/air-quality-impacts-oil-and-gas\" rel=\"noopener noreferrer\" target=\"_blank\">oil refineries</a>. Some of the most common pollutants produced by industrial practices are sulfur dioxide, nitrogen dioxide, particulate matter, and <a href=\"https://www.c2es.org/content/regulating-industrial-sector-carbon-emissions/\" rel=\"noopener noreferrer\" target=\"_blank\">volatile organic compounds</a>. Almost all industrial processes play some role in this problem. For example, even the biomass materials to <a href=\"http://ccacoalition.org/en/initiatives/bricks\" rel=\"noopener noreferrer\" target=\"_blank\">produce bricks</a> in parts of Asia, Africa, and Latin America contribute heavily to black carbon, particulate matter, and sulfur dioxide. Cleaning up emissions from all types of industrial processes will require integrating more efficient production techniques and air emissions treatment technologies.&nbsp;"

"Vehicles are a key emission source in all countries, making it a key emission source that should be targeted for reduction. Large vehicles, like commercial trucks and buses, account for nearly <a href=\"https://theicct.org/news/nature-impacts-diesel-nox-may2017\" rel=\"noopener noreferrer\" target=\"_blank\">76%</a> of global nitrogen oxide emissions annually. This percentage can be even higher in <a href=\"https://theicct.org/publications/nox-emissions-us-hdv-diesel-vehicles\" rel=\"noopener noreferrer\" target=\"_blank\">urban areas</a>. Encouragingly, emissions of particulate matter, volatile organic compounds, carbon monoxide, and nitrogen dioxide from road transportation have continued to decrease over the <a href=\"https://www.eea.europa.eu/data-and-maps/indicators/transport-emissions-of-air-pollutants-8/transport-emissions-of-air-pollutants-8\" rel=\"noopener noreferrer\" target=\"_blank\">past two decades</a>."

"<a href=\"https://business.un.org/en/entities/13\" rel=\"noopener noreferrer\" target=\"_blank\">Ninety percent</a> of global trade is made possible by ships that move freight around the world. Traditionally, these ships have been powered by crude oil, which contains high levels of nitrogen and sulfur. The combustion of these fuels produces high levels of sulfur dioxide emissions, among other gases, and are visible by satellite, <a href=\"https://www.bbc.com/news/science-environment-43926232\" rel=\"noopener noreferrer\" target=\"_blank\">outlining common shipping routes</a> such as the one through the Suez Canal. According to a <a href=\"http://www.imo.org/en/MediaCentre/HotTopics/Documents/Finland%20study%20on%20health%20benefits.pdf\" rel=\"noopener noreferrer\" target=\"_blank\">study</a> submitted to the International Maritime Organization, air pollution from ships could contribute to an additional 570,000 premature deaths between 2020 and 2050 if international regulations aren’t put into place.&nbsp;"

"There are also some natural sources of air pollutants, such as volcanic activity, fires, dust, and <a href=\"https://www.eea.europa.eu/themes/air/air-pollution-sources-1/air-pollution-sources\" rel=\"noopener noreferrer\" target=\"_blank\" style=\"color: rgb(51, 51, 51);\">p</a><a href=\"https://www.eea.europa.eu/themes/air/air-pollution-sources-1/air-pollution-sources\" rel=\"noopener noreferrer\" target=\"_blank\">lants</a>. In some cases, like volcanic activity, human activity does not influence natural sources of air pollution. However, in many instances, human activity can influence emissions from natural sources, like forest fires. From 1992 to 2012, human-started wildfires, whether intentional or accidental, accounted for <a href=\"https://www.pnas.org/content/early/2017/02/21/1617394114\" rel=\"noopener noreferrer\" target=\"_blank\">84%</a> of all wildfires in the United States. Local and national efforts to address the potential risks of wildfires could significantly reduce the frequency and intensity by which human influence affects these natural processes."

"More and more cities urgently need to clean their air. Lowering air pollution in&nbsp;densely&nbsp;populated cities plays an important role in reducing health problems. It is also a priority of the <a href=\"https://www.un.org/sustainabledevelopment/\" rel=\"noopener noreferrer\" target=\"_blank\">United Nations Sustainable Development Goals</a> (SDGs) to achieve sustainable development for future generations. The choices made by cities today contribute to SDG targets 3.4 and 3.9 for health and well-being, SDG target 7.2 for affordable and clean energy, SDG target 11.6 for sustainable cities and communities, and SDG target 13 for climate action. In some <a href=\"https://www.ccacoalition.org/en/news/mexicos-mega-city-advances-fight-cleaner-air\" rel=\"noopener noreferrer\" target=\"_blank\">cases</a>, cities are making real progress in reducing air pollution. However, air pollution is not contained by city, regional, or international boundaries.&nbsp;To effectively combat the world’s increasing rate of air pollution, air quality management strategies need to be integrated across political boundaries and airsheds."

Air Quality

Air pollution is one of the world’s largest environmental health risks. It is linked to 7 million premature deaths every year. The impacts of worsening air quality extend beyond human health, affecting climate change, weather patterns, and even energy and food production. The air we breathe comes from a mixture of local, regional, and global emission sources, making it a worldwide issue. To effectively address air pollution, it must be discussed on a global scale so new solutions can be integrated locally and internationally. 

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