Car exhaust pipe. Close-up of the exhaust pipe of a motor vehicle. This is used to vent exhaust gases from the vehicle's engine following the combustion of its fuel. These gases are mainly carbon dioxide, carbon monoxide, and water vapour, as well as oxides of sulphur, nitrogen and other trace components, some of which are considered pollutants. Motor vehicles also produce particulate pollution, microscopic grains of unburnt fuel. Photographed in the UK.