California Air Resources Board

The planting of new forests on lands where the preceding vegetation or land did not contain forests.

An air pollution abatement device that removes undesirable organic gases through incineration.

The intentional use of fire for vegetation management in areas such as agricultural fields, orchards, rangelands and forests. The regulation is described in the Agricultural Burning Guidelines, Title 17, California Code of Regulations. For more information, see our smoke management program website.

So-called "pure" air is a mixture of gases containing about 78 percent nitrogen; 21 percent oxygen; less than 1 percent of carbon dioxide, argon and other gases; and, varying amounts of water vapor. See also ambient air.

A land area with generally similar meteorological and geographic conditions throughout. To the extent possible, air basin boundaries are defined along political boundary lines and include both the source and receptor areas. California is currently divided into 15 air basins.

A political body responsible for managing air quality on a regional or county basis. California is currently divided into 35 air districts. (See also air pollution control district and air quality management district). For more information, see our local air district directory.

Sampling for and measuring of pollutants present in the atmosphere.

Amounts of foreign and/or natural substances occurring in the atmosphere that may result in adverse effects to humans, animals, vegetation and/or materials. (See also air pollution.)

Degradation of air quality resulting from unwanted chemicals or other materials occurring in the air. (See also air pollutants.)

A county agency with authority to regulate stationary, indirect and area sources of air pollution (e.g., power plants, highway construction and housing developments) within a given county and governed by a district air pollution control board composed of the elected county supervisors. (See also air quality management district or Air pollution control district).

A numerical index used for reporting severity of air pollution levels to the public. It replaces the formerly used Pollutant Standards Index (PSI). Like the PSI, the AQI incorporates five criteria pollutants -- ozone, particulate matter, carbon monoxide, sulfur dioxide and nitrogen dioxide -- into a single index. The new index also incorporates the 8-hour ozone standard and the 24-hour PM2.5 standard into the index calculation. AQI levels range from 0 (Good air quality) to 500 (Hazardous air quality). The higher the index, the higher the level of pollutants and the greater the likelihood of health effects. The AQI incorporates an additional index category -- unhealthy for sensitive groups -- that ranges from 101 to 150. In addition, the AQI comes with more detailed cautions. For more information, see our air quality index page.

A group of counties or portions of counties, or an individual county specified in law with authority to regulate stationary, indirect and area sources of air pollution within the region and governed by a regional air pollution control board comprised mostly of elected officials from within the region. (See also air pollution control district). For more information, please see our local air district directory.

A plan prepared by an APCD/AQMD, for a county or region designated as a non-attainment area, for the purpose of bringing the area into compliance with the requirements of the national and/or California ambient air quality standards. AQMPs are incorporated into the State Implementation Plan (SIP).

An individual employed by the local, state, or federal government to manage air quality.

A mathematical relationship between emissions and air quality which simulates on a computer the transport, dispersion and transformation of compounds emitted into the air. For more information, please see our software webpage.

The prescribed level of a pollutant in the outside air that should not be exceeded during a specific time period to protect public health. Established by both federal and state governments. (See also ambient air quality standards.) For more information please see our ambient air quality standards.

Advisory groups that provide forums for communication, cooperation and coordination in the development and implementation of air quality control measures. They may be comprised of representatives from the ARB, citizen groups, environmental groups, industry, local air districts and the U.S. EPA.

(See California Air Resources Board.)

A generic term referring to a harmful chemical or group of chemicals in the air. Substances that are especially harmful to health, such as those considered under U.S. EPA's hazardous air pollutant programor California's AB 1807 and/or AB 2588 air toxics programs, are considered to be air toxics. Technically, any compound that is in the air and has the potential to produce adverse health effects is an air toxic. For more information, visit our toxics website.

A control measure adopted by the ARB (Health and Safety Code Section 39666 et seq.), that reduces emissions of toxic air contaminants. For more information, see our ATCM webpage.