Polycyclic Aromatic Hydrocarbons: Sources, Importance and Fate in the Atmospheric Environment

Polycyclic Aromatic Hydrocarbons (PAHs) are persistent organic pollutants (POPs) structurally composed of 2-7 fused aromatic rings. They are released from all processes involving incomplete combustion of organic materials. In the ambient air, they are present as vapors or adsorbed onto airborne particulate matter. They undergo several physicochemical reactions and photochemical reactions with atmospheric ozone, NOX, SOX and OH radicals. They have been recognized as priority pollutants by the United States Environmental Protection Agency and the European Commission due to their toxic properties being mutagenic and carcinogenic. This article presents the state-of-the-art knowledge on atmospheric PAHs concerning their sources, mechanism of formation and properties including current understanding and models employed to investigate their gas-particle partitioning. This article also briefly reviews their chemical reactions, deposition processes, bioconcentration, routes of exposure to humans and biomonitoring with a particular focus on their toxicity and associated health effects. Finally, the limits and standards imposed by various agencies and countries are addressed.