Numbers below present the Air Quality Index and rating for: ozone, a principal component of smog; particulate matter smaller than 2.5 microns in diameter (PM2.5); and particulate matter smaller than 10 microns in diameter (PM10). See The Air Quality Index for more information on pollutants and the Index. See AQI Summary by Date for previous AQI readings. Note: numbers below are based on averages over time, and all data are preliminary and subject to verification. To view hourly readings by station see Station Data. To view exceedances of standards, see this page.
An Air Quality Watch is issued when there is potential for poor air quality in some part of the county; an Air Quality Warning is issued when there is already poor air quality in some part of the county. For more on air quality advisories, see this page.
In the event of a wildfire, see information on Smoke and Health.