Polycyclic Aromatic Hydrocarbons (PAHs) are large class of compounds comprising two or
more fused aromatic rings. PAHs are naturally occurring in fossil fuels and their derived products and can be formed during incomplete combustion of carbon based fuels. As such they are a by-product of many industrial processes. PAHs vary greatly in size, nature and hazard to human health, some are not classified as toxic, where as others are known carcinogens. The IARC specified 16 as being of particular interest, others have subsequently added this list. In all, over 100 PAHs have been described.