Select date from calendar below. Numbers 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 Today’s Air Quality for current information, and Station Data for hourly levels at individual stations. Data should be considered preliminary until reviewed and approved.