LPG (or Liquified Petroleum Gas), when used as a vehicle fuel, is a mixture of propane (95%), butane and other light hydrocarbons derived from refining crude oil, which gives better performance than the EU mix of 60% propane and 40% butane. At ambient temperature LPG is a gas but it can either be cooled or subjected to pressure to accommodate its storage and transportation.

Emissions
LPG has the potential to reduce harmful exhaust emissions from traffic. It is also a low carbon content fuel that can reduce the emission of carbon dioxide (main greenhouse gas).

Carbon Monoxide
CO is a colourless, odourless and tasteless gas, which reduces the ability of blood to carry oxygen around the body. It can cause headaches, respiratory problems and, at high concentrations, even death. Atmospheric concentrations increased during the 20th century, although there are indications that recent reductions are due to the widespread use of catalytic converters in vehicles.

Hydrocarbons
Hydrocarbons are a precursor to ground-level ozone, a serious air pollutant in cities across the world. A key component of smog, ground-level ozone is formed by reactions involving hydrocarbons and nitrogen oxides in the presence of sunlight. Hydrocarbon emissions result from incomplete combustion of fuel and from fuel evaporation. Modern cars are designed to minimise these through improvements to hardware and to combustion control.

Oxides of Nitrogen
During combustion, nitrogen oxides form in high temperature, fuel-lean conditions, which are common in modern vehicle engines. In order to reduce NOx emissions, new exhaust treatments are being developed.

Carbon Dioxide
Using LPG can potentially reduce harmful exhaust emissions from traffic. It is a low carbon-content fuel and so can be used to reduce the emission of carbon dioxide (CO2). This non-toxic gas is thought to have a large effect on global warming and on the greenhouse gas effect.

Particulate Matter
Particulate Matter is a collective name for the solid (or liquid) particles found in exhaust gases. Some particles are large or dark enough to be seen as soot or smoke, whilst fine particulate matter is generally not visible to the naked eye. This is evident from the different size (and visibility) of particulate matter emitted from diesel and petrol-engined vehicles.