The South Coast AQMD is the air pollution control agency for all of Orange County, California, and the urban portions of Los Angeles, Riverside and San Bernardino counties. This area of 10,743 square miles is the second most populated urban area in the United States and one of the smoggiest. AQMD continuously monitors air quality at 34 locations throughout the four-county area. This also allows AQMD to notify the public whenever air quality is unhealthful.

AQMD is responsible for controlling emissions primarily from stationary sources of air pollution: large power plants and refineries, the corner gas station, as well as consumer product applications. AQMD develops and adopts an Air Quality Management Plan, which serves as the blueprint to bring this area into compliance with federal and state clean air standards. Permits are issued to many businesses and industries to ensure compliance with air quality rules. AQMD staff conducts periodic inspections to ensure compliance with these requirements.

Source: http://www.aqmd.gov/