CHAPIS Emissions Maps

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What are the Sources and Types of Air Pollution?


Air pollution includes smog-forming pollutants (criteria pollutants), as well as toxic air pollutants. Cars and trucks (on-road mobile) are the largest sources of air pollution in California. Other sources of air pollution can also contribute to important emissions. Some of these other sources include off-road mobile vehicles or equipment, such as trains, planes, and lawn and garden equipment; various stationary sources, such as large industrial facilities and small commercial businesses; as well as a miscellaneous category of emission sources that includes consumer products like hairspray, paints, and solvent use (area-wide sources). (A sample graph for benzene in an example location is shown for these source categories.)

The ARB receives information on criteria pollutants every year as part of the emission inventory, and information on toxic pollutants every four years as part of the Air Toxics "Hot Spots" program. Extensive review and processing of the data, however, may result in a considerable lag time between the occurrence of the emissions, their reporting to the local air districts, and finally their inclusion in the statewide emission inventory database used for CHAPIS. One of the benefits of developing CHAPIS was to encourage review and inclusion of the best available information on toxic air pollutants, either available through the "Hot Spots" program or other local air district or ARB data. To learn more about where the information comes from, click More about the data.

What does it all mean?
Emissions from mobile sources (on-road and off-road sources) dominate the regional health impacts of air pollution in California, and contribute the most to the total amount of air pollution. An individual facility's contributions are usually much lower than the pollution from mobile sources, although living very close to a stationary source that emits air pollution may cause elevated exposures.

While air pollutant emissions information can serve as an indicator of local air pollution, it is the exposure to emissions that influences health effects. Exposure is the amount of pollution that someone actually breathes or otherwise ingests in different locations. Exposure varies with how far away the source is, how the emissions are released into the air and dispersed by the wind, and in what locations a person spends their time doing various activities. Exposure to air pollutants can also occur from indoor sources such as cooking, cleaning, and smoking; however, CHAPIS does not address the contribution of indoor sources. The importance of the exposure to health risk also depends on the combination of multiple air pollutants, the relative toxicity of the pollutants, and many other factors. The CHAPIS web tool does not map the exposure levels or the health risks associated with the pollutants and sources it tracks. For a list of the relative pollutant toxicity values approved by the State Office of Environmental Health Hazard Assessment for cancer, chronic, or acute health risk assessment studies, see the Consolidated Table of OEHHA/ARB Approved Health Risk Assessment Toxicity Values.

The Air Resources Board works together with the 35 local air districts to keep track of all the various sources of air pollution in California. This initial release of CHAPIS contains a subset of facilities that include larger and higher priority facilities. This is an ongoing process where we will periodically make improvements and additions to the data. For a status of what is included to date, click More about the data.

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Emission Inventory

This page last reviewed March 10, 2008