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Trouble in the Air
Despite much progress in reducing levels of air pollution in the U.S., millions of Americans are exposed to unhealthy levels of pollution every year. Ozone and small particulate matter less than 2.5 microns in diameter (PM2.5), among other pollutants, are widespread in the U.S. and have serious health effects.
Currently, the U.S. Environmental Protection Agency (EPA) considers safe and acceptable levels of air pollution that many American public health groups and international agencies consider unhealthy. This report examines EPA air quality data from 2020 and shows how often Americans living in large urban areas, small urban areas and rural counties were exposed to air pollution that could damage their health.
Fossil fuel combustion is the primary human-caused source of air pollution – and the main driver of global warming, which threatens to make air quality even worse in the years to come.
Policymakers must move quickly to reduce air pollution, including by electrifying every sector of the economy and transitioning to clean, renewable sources of electricity.
Millions of Americans across the country experienced elevated levels of air pollution in 2020
More than one in six Americans – 58.4 million – living in 53 large and small urban areas and rural counties experienced over 100 days of air pollution at levels above what the EPA considers “good” during 2020.
179.2 million additional Americans – or more than half the country – living in 257 large and small urban areas and rural counties experienced between 31 and 100 days of elevated air pollution.
The 237.6 million people that experienced more than a month of elevated air pollution represents over 70% of the U.S. population.
Table ES-1. Ten most populous locations that experienced more than 100 days of elevated ozone and/or PM2.5 in 2020
Figure ES-1. Both urban and rural areas experienced frequent elevated air pollution levels in 2020
13.6 million Americans living in 11 large and small urban areas and rural counties experienced over 100 days of ozone pollution at levels above what the EPA considers “good” in 2020.
An additional 57.3 million Americans living in 90 large and small urban areas and rural counties experienced between 31 and 100 days of elevated ozone pollution.
Table ES-2. Ten most populous locations that experienced more than 100 days of elevated ozone in 2020
30.7 million Americans living in 26 large and small urban areas and rural counties experienced over 100 days of particulate pollution at levels above what the EPA considers “good.”
An additional 175.4 million Americans living in 194 large and small urban areas and rural counties experienced between 31 and 100 days of elevated particulate pollution.
Table ES-3. Ten most populous locations that experienced more than 100 days of elevated PM2.5 in 2020
Air pollution harms our health, even at low levels.
Exposure to ozone and particulate pollution has been linked to premature death; damage to the respiratory and cardiovascular systems; worsened mental health and neural functioning; problems with fertility, conception, pregnancy and birth; increased risk of many types of cancer; and harm to children. (See section “Air pollution threatens public health.”)
Air pollution, including ozone and particulate pollution, can weaken the immune system and help airborne pathogens spread. Air pollution has been linked to increased risk of infection from, and worse health outcomes due to, many infectious diseases, including influenza, pneumonia, the common cold, HIV-AIDS, Ebola and COVID-19. (See section “Air pollution threatens public health.”)
Levels of air pollution that meet current federal air quality standards can be harmful, especially with prolonged exposure. The World Health Organization, the American Thoracic Society, the American Lung Association and other groups recommend lower thresholds for what are considered acceptable pollution levels than those set by the U.S. Environmental Protection Agency. In fact, according to a 2021 literature review by an Australian government-funded air pollution research organization, “…current evidence suggests there is no ‘safe’ level of air pollution,” including both PM2.5 and ozone. (See section “Air pollution is harmful at levels the EPA considers safe.”)
Global warming and air pollution are intimately connected.
Extracting, transporting and burning fossil fuels produces not just the greenhouse gases that drive global warming, but also many of the air pollutants that damage our health.
Air pollutants that damage our health can also worsen global warming, and the increasing temperatures and changing weather patterns associated with global warming are likely to make air pollution, and its health effects, worse.
Higher temperatures have resulted in increased ozone levels in multiple years in the last decade.
Changes in weather patterns due to the changing climate are likely to increase concentrations of air pollution and to trap that air pollution near the ground, increasing exposure to unhealthy levels of pollution.
Global warming will likely continue to increase the frequency of wildfires and droughts in the U.S. and make wildfires more severe while extending the fire season. That means more smoke and dust polluting the air. Global warming will also increase the rate at which the earth and plants emit pollutants naturally, which could make air pollution even worse. (See section “Global warming will make air pollution worse.”)
To protect Americans against health-threatening air pollution, policy makers need to take swift action to curb emissions, including:
Electrifying buildings and equipment that currently burn fossil fuels directly. This includes switching fossil fuel-powered building systems and industry to electric alternatives and reducing emissions from transportation by accelerating the switch to electric cars and trucks.
Further transforming the way we move by improving access to and the quality of public transportation systems and infrastructure for walking, biking and other non-driving forms of transportation.
Increasing the use of renewable energy like wind, solar and geothermal and incentivizing improved energy efficiency.
Protecting and building upon the Clean Air Act by strengthening air quality standards to levels fully protective of public health and by ensuring strong and consistent enforcement.
Errata: The original version of this report contained an error regarding EPA's characterization of the impacts of a "Moderate" level of air pollution and an error regarding the number of air quality monitoring locations for a small subset of geographies in Appendix A. The errors have been corrected in this version and language concerning monitoring locations has been edited for clarity.
 U.S. Environmental Protection Agency, A Look Back: Ozone and PM in 2020, accessed 3 August 2021 at https://epa.maps.arcgis.com/apps/Cascade/index.html?appid=9f72fb0d74be4d398e794d1231f24ef0.
 Throughout this report, “large and small urban areas” refers to metropolitan areas (population above 50,000) and micropolitan areas (which have a population of 10,000 to 50,000 people). See: U.S. Census Bureau, Metropolitan and Micropolitan: About, archived at https://web.archive.org/web/20210824025452/https://www.census.gov/programs-surveys/metro-micro/about.html.
 See Methodology. 2020 U.S. population: U.S. Census Bureau, Table 2. Resident Population for the 50 States, the District of Columbia, and Puerto Rico: 2020 Census, archived at http://web.archive.org/web/20210722065941/https://www2.census.gov/programs-surveys/decennial/2020/data/apportionment/apportionment-2020-table02.pdf.
 Graeme Zosky et al., No level of air pollution should be considered ‘safe’: Implications for Australian policy, Centre for Air pollution, energy and health Research, March 2021, p. 5, archived at https://web.archive.org/web/20210722170150/https://eprints.utas.edu.au/36248/1/NoSafeLevelofAirPollution_FV.pdf.
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