Polycyclic Aromatic Hydrocarbons (PAHs) are a group of chemicals that are
formed during the incomplete burning of coal, oil, gas, wood, garbage, or other
organic substances, such as tobacco and charbroiled meat. There are more than
100 different PAHs. PAHs generally occur as complex mixtures (for example, as
part of combustion products such as soot), not as single compounds. PAHs usually
occur naturally, but they can be manufactured as individual compounds for
research purposes; however, not as the mixtures found in combustion products. As
pure chemicals, PAHs generally exist as colorless, white, or pale yellow-green
solids. They can have a faint, pleasant odor. A few PAHs are used in medicines
and to make dyes, plastics, and pesticides. Others are contained in asphalt used
in road construction. They can also be found in substances such as crude oil,
coal, coal tar pitch, creosote, and roofing tar. They are found throughout the
environment in the air, water, and soil. They can occur in the air, either
attached to dust particles or as solids in soil or sediment.
