California air quality today
Across the 12 California metros BreatheCheck measures, air is worst right now in Riverside at AQI 73 (Moderate) and cleanest in Sacramento at AQI 38. That is a 35-point spread inside one state — a state-level number would hide it, which is why this page does not publish one.
Which California city has the worst air quality right now?
| # | Metro | AQI | UV now | Dominant | |
|---|---|---|---|---|---|
| 1 | Riverside | 73Moderate | 5.7 | PM2.5 | |
| 2 | Fresno | 70Moderate | 4.8 | PM10 | |
| 3 | San Diego | 61Moderate | 5.6 | PM2.5 | |
| 4 | Los Angeles | 60Moderate | 5.4 | PM2.5 | |
| 5 | San Jose | 51Moderate | 5 | PM2.5 | |
| 6 | Stockton | 51Moderate | 4.5 | PM10 | |
| 7 | Bakersfield | 50Good | 5.3 | O3 | |
| 8 | Long Beach | 50Good | 5.5 | PM2.5 | |
| 9 | Oakland | 48Good | 4.7 | PM2.5 | |
| 10 | Irvine | 46Good | 5.5 | — | |
| 11 | Anaheim | 46Good | 5.5 | O3 | |
| 12 | Sacramento | 38Good | 4.6 | O3 |
What is the UV index in California today?
The strongest UV in California today is 9.4 (Very High) in Riverside, arriving around 1pm local time. The mildest of the 12 metros we model here peaks at 6.7 in Stockton.
Two basins, two seasons, thirty-five air districts
California does not run a single air agency. The California Air Resources Board sets statewide standards and the rules for vehicles and fuels, while 35 local air districts handle regional planning, monitoring and stationary-source permitting. Which rules apply to a backyard fire, a truck fleet or a new warehouse depends on which district line you are inside, and those lines follow counties and air basins rather than metro areas.
Two basins carry most of the load, with different pollutants in opposite seasons. The South Coast Air Basin, penned against the mountains behind Los Angeles, has a chronic ozone problem: strong sunlight, an enormous vehicle and freight fleet, and terrain that limits how far the afternoon sea breeze can push anything before it stalls against high ground. The San Joaquin Valley, walled by the Sierra Nevada on one side and the Coast Ranges on the other, does its worst work in the cold months, when surface-based inversions form on late-fall and winter nights and hold fine particulate near the ground. Both basins are designated nonattainment for the 2012 annual PM2.5 standard, and each has its own district writing the plans — the South Coast AQMD and the San Joaquin Valley Air Pollution Control District.
Wildfire smoke overrides both patterns for days at a time and reaches districts with no chronic problem of their own. It is the one mechanism here that ignores basin walls, ozone season and district boundaries alike, which is why a coastal county with clean annual numbers can post the state’s worst reading on a particular afternoon.
Where do these California readings come from?
11 of the 12 metros here report from a named regulatory monitor. 1 is running on modelled values instead, and it is labelled that way in the table. The dominant pollutant across California today is PM2.5 in some metros, O3 in some metros, PM10 in others.
We track 12 metropolitan areas in California, not the whole state, and 12 of them have a page of its own. There is no state-wide average here on purpose: averaging 12 metros into one figure would invent a value for all the ground between them. How we measure, and what we refuse to estimate →
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