San Bernardino County ranked first and Riverside County second for the worst counties in the U.S. for ozone pollution. For the report, the American Lung Association looked at hourly ozone data from Environmental Protection Agency (EPA) for the years of 2018, 2019, and 2020.
Of the ten worst U.S. counties for ozone pollution, 7 were in California, including Los Angeles County, which ranked third, and Kern County, which ranked fourth. For counties with the cleanest year-round pollution, Gallatin County in Montana ranked first, and Kauai County in Hawaii ranked second.
