also known as PNAs (polynuclear aromatics): A group of petroleum-derived hydrocarbon compounds, present in petroleum and related materials, and used in the manufacture of materials such as dyes, insecticides, and solvents. The higher molecular weight PAHs (e.g., fluoranthene, benzo(a)pyrene) are products of combustion. The lower molecular weight PAHs (e.g., naphthalene, fluorene) generally derive from unburned petroleum sources. In general, the lower molecular weight PAHs are more soluble, more volatile, and more acutely toxic than the higher molecular weight PAHs, whereas the higher molecular weight PAHs have a stronger tendency to bioaccumulate and many are known or suspected carcinogens.

A class of chemical pollutants formed through the breakdown of other chemicals or substances. For example, the combustion of coal, wood, oil, and certain SOCs results in the formation of PAHs.

Polyaromatic hydrocarbons. PAH is the generic term for the group of hydrocarbon compounds containing two or more benzene rings. The most significant source of PAHs is via the simple combustion or pyrolysis of organic matter

Substances that occur through incomplete burning of organic substances such as wood, and are also manufactured and used in medicines or to make dyes, plastics and pesticides.