Forest Trail


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A measurement of visibility. One deciview represents the minimal perceptible change in visibility to the human eye.


Equipment that removes grease, dirt, or unwanted materials from any part or product. Degreasers typically use aqueous or nonaqueous solvents, as liquid baths or condensing vapors, to remove such material.

Deposit Control Additives

Substances added to motor vehicle fuel to reduce and prevent deposits in the fuel delivery system and engine intake valves.

Design Value

The pollutant concentration used by air quality managers for designating attainment status of an air district with respect to the state and federal ambient air quality standards. Generally, the designation value is the highest concentration that remains after excluding certain qualifying values. For a specific pollutant, the designation value for the state and federal standards may not be the same.

Diesel Engine

A type of internal combustion engine that uses low-volatility petroleum fuel and fuel injectors and initiates combustion using compression ignition (as opposed to spark ignition that is used with gasoline engines).

Discrete Early Action Items

AB 32 directed ARB to identify and adopt climate change regulations for discrete early actions that could be enforceable on or before January 1, 2010. ARB identified nine discrete early action measures including regulations affecting landfills, motor vehicle fuels, refrigerants in cars, tire pressure, port operations and other sources in 2007 that included ship electrification at ports and reduction of high GWP gases in consumer products.

Dispersion Model

The amount of a pollutant that is absorbed. A level of exposure which is a function of a pollutant's concentration, the length of time a subject is exposed and the amount of the pollutant that is absorbed. The concentration of the pollutant and the length of time that the subject is exposed to that pollutant determine dose.


The relationship between the dose of a pollutant and the response (or effect) it produces on a biological system.


Solid particulate matter that can become airborne.