Most ozone-polluted cities in the United States

Cities and areas with the highest average days with unhealthy ozone pollution levels in the United States between 2019 and 2021

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Release date

April 2023


United States

Survey time period

2019 to 2021

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 2019, 2020 and 2021 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.

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