California Air Resources Board

A location where emissions from specific sources may expose individuals and population groups to elevated risks of adverse health effects -- including but not limited to cancer -- and contribute to the cumulative health risks of emissions from other sources in the area. For more information, visit our toxics hot spots website.

For coatings, a measure of the percent of the total amount of coating used which is transferred to a unit surface by a spray gun or other device.

Refrigeration systems powered by integral internal combustion engines designed to control the environment of temperature-sensitive products that are transported in trucks and refrigerated trailers. TRUs may be capable of both cooling and heating.

Any control measure to reduce vehicle trips, vehicle use, vehicle miles traveled, vehicle idling, or traffic congestion for the purpose of reducing motor vehicle emissions. TCMs can include encouraging the use of carpools and mass transit.

The layer of the Earth's atmosphere nearest to the surface of the Earth. The troposphere extends outward about five miles at the poles and about 10 miles at the equator.

A vehicle that meets the ARB's ultra-low emission standards of 0.125 grams per mile of NMOG + NOx. The average 2010 car sold in California is a ULEV. See our Drive Clean website.

Refers to tanks used to store gasoline underground. For more information, visIt the underground storage tank website.

The number of potential excess cancer cases from a lifetime exposure to one microgram per cubic meter (µ/m3) of a given substance. For example, a unit risk value of 5.5x10-6 would indicate an estimated 5.5 cancer cases per million people exposed to an average concentration of 1 µ/m3 of a specific carcinogen for 70 years.

The federal agency charged with setting policy and guidelines and carrying out legal mandates for the protection of national interests in environmental resources. For more information, visit the U.S. EPA website.

Emissions from processes that take place up to when the fuel enters a vehicle---typically during extraction, production, distribution and dispensing of the fuel.

A three-dimensional photochemical grid model designed to calculate the concentrations of both inert and chemically reactive pollutants in the atmosphere. It simulates the physical and chemical processes that affect pollution concentrations.

Any vehicle that has been transferred after being issued a title and has over 7,500 miles. (Reference statute: H&S code 43150-43156.)

The gaseous phase of liquids or solids at atmospheric temperature and pressure.

The vapor density is expressed in grams per liter (g/L) and is compared to the density of air (air=1).

The pressure, often expressed in millimeters of mercury (mm Hg) or pounds per square inch (PSI), that is characteristic at any given temperature of a vapor in equilibrium with its liquid or solid form.

Mechanical systems that collect and recover chemical vapors resulting from transfer of gasoline from operations such as tank-to-truck systems at refineries, tanker-to-pipeline systems at offshore oil operations and pump-to-vehicle systems at gasoline stations. For more information, visit our vapor recovery website.

Permission granted for a limited time (under stated conditions) for a person or company to operate outside the limits prescribed in a regulation.

The miles traveled by motor vehicles over a specified length of time (e.g., daily, monthly or yearly) or over a specified road or transportation corridor.

A way to reduce emissions of NOx, SOx, diesel PM and CO₂ from oceangoing vessels. Emissions are decreased when vessels slow their speeds, thereby reducing the energy requirements of the main engine. The Ports of Los Angeles (POLA), Long Beach (POLB), and San Diego (POSD) currently have a voluntary VSR program in place which requests that vessels slow to 12 knots from certain distances from port (20 nautical miles (nm) for POSD and 20 or 40 nm for POLA and POLB). Ports typically offer incentives for complying.

The degree to which a fluid resists flow under an applied force.

A measurement of the ability to see and identify objects at different distances. Visibility reduction from air pollution is often due to the presence of sulfur and nitrogen oxides, as well as particulate matter.

Any particles in the atmosphere that obstruct the range of visibility.

Any substance that evaporates readily.

Carbon-containing compounds that evaporate into the air (with a few exceptions). VOCs contribute to the formation of smog and/or may themselves be toxic. VOCs often have an odor and some examples include gasoline, alcohol and the solvents used in paints.

Water used as the solvent for coatings such paint.

The solubility of a substance in water provides information on the fate and transport in the environment. The higher the water solubility, the greater the tendency to remain dissolved and the less likely to volatilize from the water. Low water soluble substances will volatilize more readily in water and will partition to soil or bioconcentrate in aquatic organisms.

The extent to which the available information supports the hypothesis that a substance causes an effect in humans. For example, factors which determine the weight-of-evidence that a chemical poses a hazard to humans include the number of tissue sites affected by the agent; the number of animal species, strains, sexes, relationship, statistical significance in the occurrence of the adverse effect in treated subjects compared to untreated controls; and, the timing of the occurrence of adverse effect.

An air quality standard that prevents, reduces, or minimizes injury to agricultural crops and livestock, damage to and the deterioration of property and hazards to air and ground transportation.

Emissions associated with a fuel from extraction to the tank it sits in prior to entering a vehicle.

Emissions associated with a fuel from extraction to when it enters and is used by a vehicle.