The majority of U.S. counties don’t have monitors — which means that many communities, especially rural ones, don’t have official monitored information on their air quality. Please note that the population figures in this statistic are only for those places that collect air pollution data, and do not reflect the entire population of these groups in the U.S.
The 2021, 2022 and 2023 AQS hourly ozone data were used to calculate the daily 8-hour maximum concentration for each ozone-monitoring site. The highest 8-hour daily maximum concentration in each county for 2021, 2022 and 2023, based on EPA-defined ozone season, was identified. The current National Ambient Air Quality Standard for ozone is 70 parts per billion (ppb) measured over eight hours.Â
Grades are assigned based on the weighted averages as follows: A=0.0, B=0.3-0.9, C=1.0-2.0, D=2.1-3.2, F=3.3+.
Citation formats
Population at risk of unhealthy ozone levels in the U.S. 2021-2023, by grade
An estimated *** million Americans lived in the *** counties in ** states with failing grades (F) for unhealthy levels of ozone air pollution in the years 2021, 2022, and 2023. This accounted for around ** percent of the entire U.S. population. Many vulnerable Americans are exposed to unhealthy levels of ozone, which increases the risk of harm to their health
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American Lung Association. (April 24, 2025). Number of Americans at risk of unhealthy concentrations of ozone in the United States between 2021 and 2023, by grade (in millions) [Graph]. In ÌÇÐÄÆƽâ°æ. Retrieved July 31, 2026, from /statistics/1358123/population-risk-of-unhealthy-ozone-levels-us/
American Lung Association. "Number of Americans at risk of unhealthy concentrations of ozone in the United States between 2021 and 2023, by grade (in millions)." Chart. April 24, 2025. ÌÇÐÄÆƽâ°æ. Accessed July 31, 2026. /statistics/1358123/population-risk-of-unhealthy-ozone-levels-us/
American Lung Association. (2025). Number of Americans at risk of unhealthy concentrations of ozone in the United States between 2021 and 2023, by grade (in millions). ÌÇÐÄÆƽâ°æ. ÌÇÐÄÆƽâ°æ Inc.. Accessed: July 31, 2026. /statistics/1358123/population-risk-of-unhealthy-ozone-levels-us/
American Lung Association. "Number of Americans at Risk of Unhealthy Concentrations of Ozone in The United States between 2021 and 2023, by Grade (in Millions)." ÌÇÐÄÆƽâ°æ, ÌÇÐÄÆƽâ°æ Inc., 24 Apr 2025, /statistics/1358123/population-risk-of-unhealthy-ozone-levels-us/
American Lung Association, Number of Americans at risk of unhealthy concentrations of ozone in the United States between 2021 and 2023, by grade (in millions) ÌÇÐÄÆƽâ°æ, /statistics/1358123/population-risk-of-unhealthy-ozone-levels-us/ (last visited July 31, 2026)
Number of Americans at risk of unhealthy concentrations of ozone in the United States between 2021 and 2023, by grade (in millions) [Graph], American Lung Association, April 24, 2025. [Online]. Available: /statistics/1358123/population-risk-of-unhealthy-ozone-levels-us/
