California has the largest concentration of petroleum refineries in the western United States, and the third largest number of refineries in the nation after Texas and Louisiana. These refineries are scattered throughout the state, from urban areas such as Los Angeles and the San Francisco Bay Area to rural communities in central California’s San Joaquin Valley. Refineries in the San Joaquin Valley are concentrated in and around Bakersfield within Kern County, the largest oil-producing and most polluted county in the state. This region suffers from the worst air quality in the United States, including harmful levels of lung-searing ozone that compromises lung development in children and causes other health complications. Oil and gas operations in the region exacerbate these unhealthy air conditions.