An emission inventory is an itemized list of pollutants in a given area for a specified time period. Present and future year inventories are important parts of air quality planning and modeling.

Air pollution comes from many sources such as large industrial facilities, as well as things we use in our daily lives such as cars and trucks, paints, and aerosol spray products. For convenience, sources of air pollution have been grouped into the categories listed below to reflect the source of emissions or the purpose of the estimate.

NOTE: To designate information as confidential, please forward the completed "Request For Confidential Classification Of Source Data" (PDF or MS Word) to the District. It will be determined whether the information can be classified as confidential under District Rule 1030.

Area Source Emissions Inventory

Area source emissions are from sources that are not regulated by the District, or are individually so small that they may not be included in our survey system. These small sources may not individually emit significant amounts of pollutants, but when aggregated can make an appreciable contribution to the emission inventory. Examples of these area sources are residential water heating and use of paints, varnishes, and consumer products. Emissions from these sources are grouped into categories and calculated based on surrogate variables.

Of the more than 500 area-wide source categories established by the California Air Resources Board (CARB), the District is responsible for estimating emissions from approximately 100. Emissions for the remaining categories are estimated by either CARB or the Department of Pesticide Regulation (DPR).

• District's Areawide Emissions Inventory Methodologies

Point Source Emissions Inventory

Facilities that have valid District permits are called point sources. Refineries, gas stations, dry cleaners and industrial plants are examples of point sources in our District. The District’s Technical Services Division collects and maintains a database with detailed information on each point source that submits data. Almost all facilities emitting greater than 2.5 tons/year of any air pollutant are included. The District’s database contains information for more than 4,000 facilities.

Data on the activity, seasonal variations, and hours of operation are collected from each facility each year through or survey process. Emissions are calculated using detailed data for each of the facilities by various processes. Each year the District provides point source emissions inventory data to CARB to be included in their CEIDARS database.

• District Point Source Emissions Inventory FAQs
  • Statement facilities FAQ
  • Survey facilities FAQ
• Request For Confidential Classification Of Source Data (PDF or MS Word)
• Link to CEIDARS

Mobile Source Emissions Inventory

Mobile sources consist of on-road motor vehicles and other mobile sources.

• Almanac Emission Projections

On-road motor vehicles consist of passenger cars, trucks, buses and motorcycles. Emissions from on-road motor vehicles are a major portion of the emission inventory, and are estimated by CARB using computer models.

• Motor Vehicle Emission Inventory Model (EMFAC)

Other mobile sources include boats and ships, trains, aircraft, garden, farm and construction equipment. The District estimates emissions for ships and aircraft in our area source inventory. The remaining sources are estimated by CARB as part of their off-road inventory.

• District's Areawide Emissions Inventory Methodologies
• OFFROAD Emissions Model

Natural Sources

In addition to man-made air pollution, there are significant quantities of pollutants from natural source. Natural Sources include biological and geological sources, wildfires, windblown dust, and biogenic emissions from plants and trees. Emissions from natural sources are estimated by CARB.

• Natural Sources Emissions Inventory