The Air Resources Board collects data on ambient air quality in California air basins as well as data on pollutant releases from stationary and mobile sources.

The highest concentrations of the criteria pollutants carbon monoxide (CO) and ozone have both decreased by approximately 20% since 1982. PM10 (particulate matter less than 10 microns in diameter) has been monitored since the mid-1980's, and shows an increase followed by a reduction. These improvements have occurred while population has increased by almost 30% and vehicle miles travelled have increased by almost 60%.

Over a 20-year period, the releases of air criteria pollutants have decreased approximately 22%, or greater than 8,000 tons/day. The implementation of various regulatory control measures has resulted in the prevention of the release of approximately 24,000 tons/day, or almost 9 million tons/year, of these pollutants.