Polycyclic aromatic hydrocarbons (PAHs) are omnipresent ambient air pollutants. These pollutants are generated from the incomplete combustion of organic (carbonaceous) material. Their occurrence in the ambient air has been substantial during the past centuries due to emissions from industrial processes and energy production, motor vehicular traffic, incineration of refuse, and residential heating. There is considerable concern about the relationship between PAH exposure in the ambient air and the potential to contribute to human cancer incidence.