AQI 78 · Ozone · Trend: Slowly improving
| Average AQI | 78 |
| Good Days / Year | 130 |
| Unhealthy Days / Year | 65 |
| Primary Pollutant | Ozone |
| PM2.5 Average | 13.5 µg/m³ |
| Trend | — Slowly improving |
| Monitoring Stations | 250 |
| Nonattainment Areas | 12 |
California has the worst overall air quality of any US state, driven by the San Joaquin Valley's devastating geography and LA Basin's trapped smog. Despite having the nation's strictest regulations, the state's massive population, vehicle fleet, and increasingly severe wildfire seasons create persistent challenges.
CARB (California Air Resources Board) sets the nation's strictest air quality standards. ZEV mandate, LCFS, cap-and-trade program, truck emission rules, and planned ban on new gas car sales by 2035. California can set its own vehicle emission standards under Clean Air Act Section 209.
San Joaquin Valley — PM2.5 and ozone (worst in nation). South Coast (LA Basin) — ozone. Imperial County — PM10. Sacramento Metro — ozone. 12 total nonattainment areas, the most of any state.