Emission Inventory Background Information

The page last reviewed April 25, 2011

About Emissions Data

The California Air Resources Board (ARB) has collected information on emissions from air pollution sources since 1969.  This information is periodically compiled by State and local air pollution control agencies to create an emission inventory --- an important building block in the development of the State's air pollution control program.

The staff at the ARB compiles data to create the criteria pollutant emission inventory which includes information on the emissions of reactive organic gases (ROG), oxides of nitrogen (NOx), oxides of sulfur (SOx), carbon monoxide (CO), and particulate matter (PM10).  Data are gathered on an ongoing basis and stored in the California Emission Inventory Development and Reporting System (CEIDARS). A summary of the criteria pollutant inventory is published annually. The California emission inventory contains information on the following air pollution sources:

  • Stationary sources - approximately 13,000 individual facilities, called point sources.  Point sources are fixed pollution sources such as electric power plants and refineries. There are also about 135 aggregated point source categories.  These categories estimate emissions for the non-point source stationary sources;
  • Area-wide sources - approximately 80 source categories.  An area-wide source category is made up of sources of pollution mainly linked to the activity of people.  Examples of these sources include consumer products and architectural coatings used in a region; and
  • Mobile sources - all on-road vehicles such as automobiles and trucks; off-road vehicles such as trains, ships, aircraft; and farm equipment.

The principal agencies contributing data to the stationary and area-wide source inventory are the ARB and the California air pollution control and air quality management districts.  The ARB, the California Department of Transportation (CALTRANS), and regional transportation agencies are the principal agencies involved in developing the mobile source inventory.

The information represented in the California emission inventory is a snap-shot of a variety of dynamic and variable processes. As such, the emission inventory can only represent an estimate of what is actually occurring. Due to the importance of the inventory in air quality planning and management, the ARB and local air pollution control agencies are working together to further refine estimation methods to improve the inventory.

Toxics Emission Inventory Data

The ARB also collects toxic emissions from thousands of facilities in California. The toxic pollutant inventory is updated every four years and is stored in CEIDARS.  For more information concerning the toxic program, see the Air Toxics "Hot Spots" Program.

Find Emissions Data

You can find emissions data on our Emissions Inventory page.

How to Request Data from the Emission Inventory Branch

The Air Resources Board, Emission Inventory Branch is the keeper of all California emissions data. Members of the public, regulatory agencies, industry groups, and environmental groups can search for criteria and toxics emissions information on particular facilities using the Facility Search Engine.  For more information, please contact the Emission Inventory Branch at (916) 322-5350.