California Air Resources Board

Atmospheric gases such as carbon dioxide, methane, chlorofluorocarbons, nitrous oxide, ozone and water vapor that slow the passage of re-radiated heat through the Earth's atmosphere. (See also ClimateChange.ca.gov gloss.)

Greenhouse Gases, Regulated Emissions and Energy Use in Transportation model used to determine emissions from various vehicle and fuel combinations.

A motor vehicle originally intended by its manufacturer for sale outside of the United States. Such a vehicle does not have the same registration rights a vehicle intended by its manufacturer for sale in the United States.

A plan for a given geographical region containing demographic projections (i.e., housing units, employment and population) through some specified point in time and which provides recommendations for local governments to better manage growth and reduce projected environmental impacts.

An air pollutant listed under section 112 (b) of the Federal Clean Air Act as particularly hazardous to health. Emission sources of hazardous air pollutants are identified by U.S. EPA and emission standards are set accordingly. For more information, visit our Title III website area.

A phenomenon that results in reduced visibility due to the scattering of light caused by aerosols. Haze is caused in large part by man-made air pollutants.

A document that identifies the risks and quantities of possible adverse health effects that may result from exposure to emissions of toxic air contaminants. A health risk assessment cannot predict specific health effects; it only describes the increased possibility of adverse health effects based on the best scientific information available.

A dosage of air pollution scientifically determined to protect against human health effects such as asthma, emphysema and cancer.

This regulation authorizes random roadside smoke opacity testing of heavy-duty diesel trucks and buses. The opacity of exhaust emitted from these engines must not exceed 40 percent (1991 and newer engine model years) or 55 percent (all pre-1991 engines). Gasoline and diesel trucks and buses are also inspected for tampering and for engine certification label compliance.

(See toxic hot spot.)

A vehicle that combines an internal combustion engine with a battery and electric motor. This combination offers the range and refueling capabilities of a conventional vehicle, while providing improved fuel economy and lower emissions.

Compounds containing various combinations of hydrogen and carbon atoms. They may be emitted into the air by natural sources (e.g., trees) and as a result of fossil and vegetative fuel combustion, fuel volatilization and solvent use. Hydrocarbons are a major contributor to smog. (See also Reactive Organic Gases).

A colorless, flammable, poisonous compound having a characteristic rotten-egg odor. It is used in industrial processes and may be emitted into the air.

The act of burning a material to ashes.

The additional ozone formed in the atmosphere with the incremental addition of a certain amount of a volatile organic compound.