Trouble in the Air

Millions of Americans breathed polluted air in 2020

Millions of Americans breathed polluted air in 2020

Wollertz via


Every year, millions of Americans are exposed to levels of pollution that American public health groups and international agencies consider unhealthy. Fossil fuels are the largest source of air pollution that comes from human activities.

In 2020, 237.6 million Americans – more than 70% of the population – were exposed to more than a month of elevated levels of ozone and/or fine particulate pollution. The map below shows the days on which pollution levels were elevated in locations across the country. (To see the counts of days of elevated pollution in your area, download the full “Trouble in the Air” report.)

There is no “safe” level of air pollution

The pollution in America’s air causes hundreds of thousands of premature deaths every year and contributes to health problems ranging from asthma to dementia.

The World Health Organization (WHO) and studies in the Journal of the American Medical AssociationEnvironmental Health Perspectives, and the New England Journal of Medicine have all concluded that any level of air pollution causes measurable health impacts.

Moreover, current EPA standards for allowable levels of air pollution include levels beyond those the WHO and other bodies consider acceptable. The EPA standard for ozone is 70 parts per billion (ppb) over 8 hours, while the WHO’s guidelines recommend 51 ppb. Similarly, the EPA’s standard for allowable fine particulates (PM2.5) in the air is more than twice as high as the WHO’s 2021 guidelines for protecting public health.

Global warming and air pollution are linked

Burning fossil fuels produces more than just health-threatening ozone and particulates – it also produces greenhouse gases that are warming our climate. Global warming is likely to make air pollution worse in the years to come. 

  • Higher temperatures, which global warming will make more frequent, can increase ozone levels.

  • Global warming could decrease air circulation, trapping pollution near the ground where it is most unhealthy.

  • Global warming will continue to increase the frequency and severity of wildfires. Global warming has already caused wildfires in western states to burn more land, burn for longer and burn during more of the year than they did a few decades ago. Wildfire smoke is a major source of particulate pollution. 

  • Global warming will also increase the rate at which the earth and plants naturally emit pollutants. 

Air pollution was widespread in 2020

The map below shows the total number of days of elevated air pollution — when ozone pollution and/or PM2.5 pollution were above the level that the EPA considers “good” — for each urban area and rural county that reported air quality to the EPA in 2020. Hover over or click on a particular area to see the data.

We need to act now

To protect Americans against health-threatening air pollution, policymakers need to take swift action to reduce the burning of fossil fuels and tighten limits on pollution. Key actions include:

  • Electrifying heating and hot water systems, industrial processes and the transportation sector.

  • Improving access to and the quality of public transportation and infrastructure for walking, biking and other non-driving forms of transportation. 

  • Increasing the use of renewable energy and incentivizing improved energy efficiency.

  • Strengthening air quality standards to levels fully protective of public health and ensuring strong and consistent enforcement of those standards. 

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.

Health icons: Treter via Shutterstock