Numbers in the chart below show the Air Quality Index for today, based on an average over time. Because fires can cause high hourly levels of particulate matter (PM), which is harmful to breathe, it is important to check hourly readings on the Station Data page in addition to the chart below. 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. “NA” appears in the chart below for the PM10 reading at the Santa Barbara station. This station is operated by the California Air Resources Board, which will be restoring PM10 monitoring there in the next few months.