Hydrocarbons are a major component of motor vehicle emissions. Hydrocarbon emissions react with other compounds in the atmosphere to produce photo-chemical smog.
Under the high temperatures and pressure of combustion, nitrogen from the air combines with oxygen to produce oxides of nitrogen. Oxides of nitrogen can be produced in any operating internal combustion engine.
In spark-ignition engines, particulates are caused by incomplete combustion of rich air-fuel mixtures. In compression-ignition engines, they are caused by a lack of turbulence and lack of oxygen.
Carbon monoxide is produced during combustion when there are not enough oxygen molecules around the hydrocarbon molecules. This can be caused by an incorrect air-fuel ratio. Carbon monoxide is an extremely poisonous gas.
