Aromatics, historically so called because of their distinctive perfumed smell of the main aromatic molecules, are a group of hydrocarbons including, mainly, benzene, toluene and the xylenes. These are mainly formed during petrol reforming. Not all aromatic are hydrocarbons compounds and not all of them have a “perfumed smell”, for instance pyridine contains nitrogen and has a very strong, and extremely unpleasant odour.