Numbers in the chart below show the Air Quality Index for today, based on an average over time. The Index numbers represent a ranking for the pollutant, not the measurement of a pollutant. When air quality is expected to be worse — such as during wildfires, which produce elevated levels of particulate matter (PM) — it is important to check hourly readings, which do show the measurement of the pollutant. Hourly readings are available on the Station Data page. See information on Smoke and Health. The Index below presents ratings 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). Note: all data are preliminary and subject to verification. To view exceedances of standards, see Days Exceeding Ozone and Particulate Standards. Also see outlooks and smoke reports for California wildfires posted on California Smoke Information site.