# Counties in California by median Air Quality Index (US EPA), 2024

All 52 values come from U.S. Environmental Protection Agency for 2024, so the places are comparable. 6 counties have no value for that period and are not ranked.

- Indicator id: `aqi_median`
- Unit: index
- Definition: Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries. The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide). Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: median daily AQI (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Publisher page: https://invokely.ai/en/publishers/environmental-protection-agency
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/median-air-quality-index/california-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Riverside County | 87 |
| 1 | San Bernardino County | 87 |
| 3 | Los Angeles County | 80 |
| 4 | Kern County | 72 |
| 5 | San Diego County | 71 |
| 5 | Tulare County | 71 |
| 7 | Fresno County | 67 |
| 8 | Imperial County | 63 |
| 9 | Inyo County | 61 |
| 10 | Kings County | 60 |
| 11 | Colusa County | 54 |
| 11 | Orange County | 54 |
| 13 | Stanislaus County | 53 |
| 14 | Madera County | 52 |
| 14 | Merced County | 52 |
| 16 | Sacramento County | 51 |
| 16 | San Joaquin County | 51 |
| 18 | Placer County | 50 |
| 18 | Ventura County | 50 |
| 20 | Alameda County | 49 |
| 20 | San Luis Obispo County | 49 |
| 20 | Santa Barbara County | 49 |
| 20 | Sutter County | 49 |
| 24 | Contra Costa County | 48 |
| 24 | Plumas County | 48 |
| 26 | Santa Clara County | 47 |
| 27 | Butte County | 46 |
| 28 | Mariposa County | 45 |
| 28 | Yolo County | 45 |
| 30 | El Dorado County | 44 |
| 30 | Shasta County | 44 |
| 32 | Mendocino County | 43 |
| 32 | San Benito County | 43 |
| 32 | Tehama County | 43 |
| 35 | Calaveras County | 42 |
| 36 | Amador County | 40 |
| 36 | Siskiyou County | 40 |
| 36 | Tuolumne County | 40 |
| 39 | Glenn County | 39 |
| 39 | Monterey County | 39 |
| 39 | Santa Cruz County | 39 |
| 39 | Solano County | 39 |
| 43 | Humboldt County | 38 |
| 44 | Nevada County | 36 |
| 45 | San Francisco County | 33 |
| 46 | Del Norte County | 32 |
| 46 | Lake County | 32 |
| 48 | Trinity County | 31 |
| 49 | Marin County | 28 |
| 50 | San Mateo County | 27 |
| 51 | Mono County | 19 |
| 51 | Sonoma County | 19 |