Those sources for which a methodology is used to estimate emissions. This can include area-wide, mobile and natural sources, and also groups of stationary sources (such as dry cleaners and gas stations). The California Clean Air Act requires air districts to include area sources in the development and implementation of the AQMP. In the California emission inventory all sources which are not reported as individual point sources are included as area sources. The federal air toxics programme defines a source that emits less than 10 tonnes per year of a single hazardous air pollutant (HAP) or 25 tonnes per year of all HAPs as an area source. For more information, please visit our area-wide source methodologies website.