Polycyclic aromatic hydrocarbons (PAHs) are a mixture of organic compounds released into the atmosphere as gases or particles during the incomplete combustion of organic material.
PAHs have a number of sources including:
- mobile-cars, trucks, ships and aircraft
- industrial-power generation, steelworks, coke ovens, aluminium production, cement kilns, oil refining and waste incineration
- domestic-primarily combustion for heating and cooking, especially solid fuel heaters using wood and coal
- fires-burning of vegetation in agricultural processes and bushfires.
The smallest member of the PAH group is naphthalene, a two-ring compound, which is a gas at normal temperatures. Three- to five-ring PAHs occur as either gases or particles in air. PAHs with five or more rings tend to be solids which attach themselves to the surface of other particulate matter in the atmosphere.
Although many different PAHs have been identified,there is limited published toxicological data on them. One of the best characterised and most toxic PAH is benzo(a)pyrene, which is generally used as the indicator PAH. The US EPA has identified 16 priority PAHs, based on concerns that they do or might cause cancer in animals and humans.
Page last updated: 26 February 2011