Emissions of volatile organic compounds (VOCs), especially aromatics, from motor vehicle exhausts significantly contribute to the observed air pollution by photo-oxidants widely observed in europe. Both VOCs and their resulting photo-oxidants, including ground ozone, endanger human health. Many photochemical products of aromatic oxidation have been shown to be mutagenic. This paper summarises the effects of VOCs in exhaust emissions from motor vehicles. Petrol exhaust emissions are one of the most important sources of aromatic hydrocarbon emissions. The atmospheric chemistry of aromatics is discussed, and some of the many observed photo-oxidant products are listed. The impact of nitrogen oxides (NOx) on the product distribution is not yet well established, but the presence of low levels of nox will not significantly alter the yields of the identified products. Ozone formation potential is especially difficult to define precisely, as it depends on VOC component ratios, NOx concentration, temperature, and especially reaction time. Health risks from photochemical products from emitted hydrocarbons have only recently been studied; many of them are known to be mutagenic, and some also cause cancer. Early morning traffic is important for ozone formation. Much more knowledge of VOC emissions is needed.
Abstract