Nitrogen Fixation

Atmospheric dinitrogen can be fixed by inorganic reactions occurring in combustion, lightning strikes, and other circumstances involving high temperatures. Overall, naturally occurring non-biological fixation has been estimated to be equivalent to 10-20% of biological fixation of dinitrogen.

Nitrogen fixation is also associated with certain activities of humans. The internal combustion engines of automobiles burn fuels under conditions of very high temperature and pressure which favors the oxidation of nitrogen gas to nitric oxide, an important air pollutant and source of fixed nitrogen. The combustion of coal and other organic fuels also results in the formation of nitric oxide through both the fixation of nitrogen gas and the oxidation of the organic nitrogen of the fuel. Also, as noted previously, nitrogen gas is fixed industrially in enormous amounts to provide agricultural fertilizers. The industrial reaction is known as the Haber process, and it involves the use of hydrogen gas generated from the methane of natural gas to fix ammonium from dinitrogen.