Air quality in California
EPA monitors report from 53 of California’s 58 counties. That is the honest limit of this page: the other 5 are not measured, not clean. In 2025 the most affected monitored county was San Bernardino County, with 110 days above the moderate category.
53
Counties with monitors
5
Counties without
631
Days above moderate, 2025
Summed across monitored counties
9.3%
Adults with asthma
Population-weighted county estimate
County by county
Monitored California counties
GoodModerateUnhealthy for sensitive groupsUnhealthyVery unhealthyHazardous
EPA Air Quality System annual summaries by county, 2025. The 90th percentile AQI describes a day worse than nine out of ten, which is a steadier measure than the annual maximum a single wildfire can set.
Not measured
5 counties without a monitor
No EPA monitor reported from these counties, so there is no air quality record to publish. Their radon zone is known, and radon is measured in the building rather than the air outside it.
Other states
Air quality elsewhere
- Alabama
- Alaska
- Arizona
- Arkansas
- Colorado
- Connecticut
- Delaware
- Florida
- Georgia
- Hawaii
- Idaho
- Illinois
- Indiana
- Iowa
- Kansas
- Kentucky
- Louisiana
- Maine
- Maryland
- Massachusetts
- Michigan
- Minnesota
- Mississippi
- Missouri
- Montana
- Nebraska
- Nevada
- New Hampshire
- New Jersey
- New Mexico
- New York
- North Carolina
- North Dakota
- Ohio
- Oklahoma
- Oregon
- Pennsylvania
- Rhode Island
- South Carolina
- South Dakota
- Tennessee
- Texas
- Utah
- Vermont
- Virginia
- Washington
- West Virginia
- Wisconsin
- Wyoming