PlainAirData · EPA AQS 2025

Most polluted, top counties

Annual good-day share among counties with ≥100 monitored days. Not a live AQI advisory.

1. 1 Maricopa, Arizona 8.8%
2. 2 Riverside, California 10.7%
3. 3 Los Angeles, California 10.7%
4. 4 Harris, Texas 11.0%
5. 5 San Bernardino, California 12.6%
6. 6 Pinal, Arizona 17.0%
7. 7 Kern, California 17.5%
8. 8 San Diego, California 17.5%
9. 9 El Paso, Texas 18.1%
10. 10 Tulare, California 24.1%

Source: PlainAirData worst-air ranking, derived from EPA AQS Annual AQI by County (2025). CC BY 4.0 with attribution.