Massachusetts Vehicle Check - Mass08 Management Module ...

Non-Commercial
Understanding Major Pollutants
After combustion, fossil fuels release pollutants including hydrocarbons (HC,) carbon
monoxide (CO,) nitrogen oxides (NOX,) sulfur dioxide (SO2,) and particulate matter into the
atmosphere. Ozone is a major pollutant that is not released by the combustion of fossil fuels,
but instead is a product of a photochemical reaction of HC and NOx. Following is a brief
overview of the different pollutants.
Hydrocarbons
Hydrocarbons (HC) are the unburned fuel of any class of
organic compounds composed only of carbon and hydrogen. The
carbon atoms form the framework and the hydrogen atoms attach to
them. Hydrocarbons, the principal constituents of petroleum and
natural gas, serve as fuels, lubricants, and raw materials for production
of plastics, fibers, rubbers, solvents, explosives, and industrial chemicals. Excessive
hydrocarbons (HC) are emitted by vehicles through two (2) sources: (1) incomplete
combustion; and (2) fuel evaporation. Tailpipe hydrocarbon emissions can be caused by
ignition system misfiring, improper ignition timing, rich fuel mixtures, engine mechanical
deficiencies, uneven fuel injector delivery or anything else that would adversely influence the
combustion process.
With advances in OBD II systems, computers, fuel control, ignition, and emission
systems, tailpipe hydrocarbons emissions have been drastically reduced. Hydrocarbons
emitted by fuel evaporation are a major source of pollution that can be caused by a
compromised on-board fuel storage tank, fuel line or fuel related component. The
evaporation of hydrocarbons emitted to the atmosphere is still a major concern. The OBD II
systems installed on today's vehicles check many engine management components, including
those of the Evaporative Emissions System (EVAP).
Massachusetts Vehicle Check
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