There are three major types of vehicle engines that release exhaust gases: gasoline, diesel, and turbine. The composition of exhaust gases is based primarily on the fuel and the temperature at which it is burned (by the vehicle) Fuels use additive chemicals for many different reasons: to aid in flow, prevent freezing, and clean internal parts. These additives are present in low concentrations but they may be important exhaust components. Diesel and turbine engines use similar fuels and produce similar exhaust gases; except that diesel engines generally release more unburned carbon as particulate matter. Gasoline is a more refined fuel, but chemicals are still added. The major components of vehicle exhaust gases include carbon (as very small particles), unburned hydrocarbons, carbon dioxide, carbon monoxide, nitrogen oxides, sulfur oxides, water vapor, and thousands more “low-level” chemicals. The peculiar odor of diesel exhaust is due to aldehydes, acrolein, and sulfur compounds. Gasoline engines generally produce more carbon monoxide than diesel or turbine engines; diesel and turbine engines produce higher. levels of nitrogen oxides. The use of emission control measures from fuel regulation, to air injection and catalytic conversion of the exhaust gases, greatly affects the types and amounts chemicals found in the exhaust gases.