In addition to the 25 worst cities for each pollutant in the Report Cards section, the 25 most polluted counties for ozone and particle pollution are ranked in the tables below.
Thirty counties, listed alphabetically by state below, received failing grades for all three measures of pollution:
Arizona | Maricopa, Pinal |
California | Alameda, Butte, Contra Costa, Fresno, Imperial, Kern, Kings, Los Angeles, Madera, Merced, Orange, Placer, Riverside, Sacramento, San Bernardino, San Diego, Santa Clara, Shasta, Stanislaus, Sutter, Tehama, Tulare |
Colorado | Denver |
Michigan | Wayne |
Nevada | Clark, Washoe |
New Mexico | Bernalillo |
Utah | Salt Lake |
Page last updated: June 7, 2024