The San Diego Region has made great strides towards clean air.
Ozone concentrations have decline significantly during the past 20 years, and the number of days each year that the air basin exceeds the State and federal standards has also decreased. In addition, the San Diego Air Basin has not recorded a Stage I ozone episode (commonly called a smog alert) since 1991 nor a Stage II episode since 1979. A Stage I occurs when ozone levels reach 20 pphm and a Stage II alert is called at 35 pphm. The last health advisory for smog occurred in July 1998. A health advisory is issued when ozone levels reach 15 pphm.
Except for during the wildfires of October 2003 and 2007, particulate matter levels have also improved – the annual average declining 25% since 1986, the earliest year with comparable particulate data. This is in part due to reductions in emissions of ozone precursors, which also contribute to the formation of fine particulates.
Also, local emissions of toxic air contaminants from industrial sources have decreased about 82% since 1989 (the year when toxic air contaminant data became available).
To find out more about air quality, visit the San Diego Air Pollution Control District, APCD.