Unhealthy ozone exposure in the U.S. by grade

An estimated 101 million Americans lived in the 125 counties in 26 states with failing grades (F) for unhealthy levels of ozone air pollution in the years 2020, 2021, and 2022. Many vulnerable Americans are exposed to unhealthy levels of ozone, which increases the risk of harm to their health

Number of Americans at risk of unhealthy concentrations of ozone in the United States between 2020 and 2022, by grade (in millions)

Characteristic	Population in millions
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Release date

April 2024

More information

Region

United States

Survey time period

2020 to 2022

Special properties

Data from 855 counties

Supplementary notes

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 20209, 2021 and 2022 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 2019, 2020 and 2021, 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.

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+.

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