Forest Trail


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An intermediate gasoline distribution facility where delivery of gasoline to and from the facility is solely by pipeline.

Thermal Spraying

A process in which metallic or nonmetallic materials are heated to a molten or nearly molten state and are sprayed onto a surface to form a coating. The material may originate in the form of powder, rod, or wire before it is heated, prior to spraying and deposition. Materials can be heated by combustion of fuel gases (similar to welding) or by using electricity. Thermal spraying includes processes such as flame spraying, plasma spraying, high velocity oxyfuel (HVOF) spraying and twin wire electric arc spraying.


The outermost layer of the Earth's atmosphere extending from about 60 miles to several hundred miles above the planet's surface. The temperature of this layer varies from many hundreds to thousands of degrees Celsius.

Title III

A section of the 1990 amendments to the federal Clean Air Act that addresses the control of toxic air emissions. For more information, visit our Title III website.

Title V

A section of the 1990 amendments to the federal Clean Air Act that requires a federally enforceable operating permit for major sources of air pollution. For more information, visit our Title V website.

The configuration of a surface, especially the Earth's surface, including its relief and the position of its natural and man-made features.
Total Organic Gases (TOG)

Gaseous organic compounds, including reactive organic gases and the relatively unreactive organic gases such as methane.

Total Suspended Particulate (TSP)

Particles of solid or liquid matter -- such as soot, dust, aerosols, fumes and mist -- up to approximately 30 microns in size.

Toxic Air Contaminant (TAC)

An air pollutant, identified in regulation by the ARB, which may cause or contribute to an increase in deaths or in serious illness, or which may pose a present or potential hazard to human health. TACs are considered under a different regulatory process (California Health and Safety Code section 39650 et seq.) than pollutants subject to CAAQSs. Health effects to TACs may occur at extremely low levels and it is typically difficult to identify levels of exposure which do not produce adverse health effects. For more information, visit our toxics website.

Toxic Best Available Control Technology (T-BACT)

The most effective emission limitation or control technique which has been achieved in practice or found by the ARB Executive Officer or Air Pollution Control Officer of the local districts to be technologically feasible.

Toxic Hot Spot

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.

Transfer Efficiency

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.

Transport Refrigeration Unit (TRU)

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.

Transportation Control Measure (TCM)

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.