Particulate emissions from road transport arise as direct emissions from vehicle exhausts, tyre and brake wear and resuspension of road dust. In urban areas, emissions from road transport are thought to be the major source of PM10. In general, diesel engine vehicles emit a greater mass of fine particulate matter, per vehicle, than petrol engines. Diesel emissions are mainly composed of soot particles, volatile hydrocarbons and some sulphate from the fuel sulphur. When hydrocarbons and sulphates are released by the car exhaust they condense on airborne particles, mainly on the freshly emitted carbon. The size distribution of these particles tends to be bimodal, with particles of.
