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SCAQMD
South Coast Air Quality Management District.
Selective Catalytic Reduction (SCR)
Term frequently used as a synonym for catalytic reduction of NOx in diesel exhaust or flue gases by nitrogen containing compounds, such as ammonia or urea. Such SCR systems are commercially available for stationary applications and are being developed for mobile diesel engines. Since “selective catalytic reduction” is a generic term which also applies to other reactions, its use may lead to confusion in some situations.
Size Selective Sampling (SSS)
A method of measuring ambient DPM exposures through a mechanical separation (inertial impaction) of particles into two fractions: above and below (typically) 0.8 µm, followed by gravimetric analysis. Based on air quality research in underground mining, it is believed that the particle fraction below the 0.8 µm cut point can be attributed to diesel exhaust.
Soluble Organic Fraction (SOF)
The organic fraction of diesel particulates. SOF includes heavy hydrocarbons derived from the fuel and from the engine lubricating oil. The term “soluble” originates from the analytical method used to measure SOF which is based on extraction of particulate matter samples using organic solvents.
Super Ultra Low Emission Vehicle (SULEV)
A vehicle that meets the SULEV emission standards set by the California Air Resources Board. The SULEV standards are more stringent than the ULEV standards.
Supercharger
A compressor device to compress the combustion air or the air/fuel mixture before it enters the engine cylinder. Superchargers are typically driven by the engine itself, through a system of gears, a belt drive, or by an electrical motor.
Swirl Combustion
A combustion chamber configuration which uses curved mixing ridges in the intake ports and/or a re-entrant piston bowl (a bowl whose top edges curve inward). Some swirl combustion chambers have a larger rim around the outside of the piston and a more compact combustion chamber or bowl. The swirl is used to reduce particulate emissions.
Total Particulate Matter (TPM)
The total particulate matter emissions including all fractions of diesel particulates, i.e. the carbonaceous, organic (SOF), and sulfate particulates.
Transitional Low Emission Vehicle (TLEV)
A vehicle that is certified to meet the TLEV emission standards established by the California Air Resources Board (CARB). The TLEV standards are less stringent than the LEV standards.
Threshold Limit Value (TLV)
Time-weighted average concentration of an air pollutant at the workplace for a conventional 8-hour workday and a 40-hour workweek, to which nearly all workers may be repeatedly exposed without adverse health effects.
Total Carbon (TC)
The sum of the elemental carbon and organic carbon associated with diesel particulates. Typically amounts to 80-85% of the total DPM mass.
Turbine
A rotary machine which extracts mechanical shaft power from the working fluid (gas or liquid) using rotor vanes.
Turbo Lag
The time delay between injecting fuel to accelerate and delivering air to the intake manifold by the turbocharger. This phenomenon may cause black smoke emissions in some turbocharged diesel engines during acceleration.
Turbocharging
A process of compressing the engine intake air charge in order to allow more air and fuel into the cylinder and, thus, to increase the engine power output. The compressor, called the turbocharger, is driven by an exhaust gas propelled turbine.
Turbo Generator
Gas turbine combined with an electrical generator.
Ultra-Low Emission Vehicle (ULEV)
A vehicle that meets the ULEV emission standards set by the California Air Resources Board. The ULEV standards are more stringent than the LEV standards.
Unit Injector
An injector which is camshaft-driven and incorporates a plunger. The plunger works in conjunction with orifices in the injector body to determine the beginning and end of injection. The plungers has a helix and is rotated by a rack so the beginning and end of injection can occur closer together or farther apart, thus shortening or lengthening the injection period and changing metering. A special pump which supplies fuel through an orifice to the injector operates at a pressure which is precisely controlled depending on the changes in engine speed.
VMT
Vehicle miles traveled.
Volatile Organic Compounds (VOC)
Hydrocarbon-based emissions released through evaporation or combustion. The term VOC is usually used in regard to stationary emission sources.
Volatile Organic Fraction (VOF)
The organic fraction of diesel particulate matter as determined by vacuum evaporation. It may or may not be equivalent to the SOF fraction. Depending on the exact analytical procedure, the VOF may include the organic material (SOF) as well as some of the sulfate particulates which, being composed primarily of hydrated sulfuric acid, are also volatile.
White Smoke
The smoke emitted during a cold start from a diesel engine, composed mainly of unburnt fuel and particulate matter.
Zero Emission Vehicle (ZEV)
A vehicle that is certified to meet the most stringent emission standards established by the California Air Resources Board (CARB). These standards require zero regulated emissions of nonmethane organic gases (NMOGs), carbon monoxide (CO) and nitrogen oxides (NOx). A ZEV is most likely powered by electricity, fuel cells or hydrogen.

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