Human Sources of Nitrogen Oxides:
At normal temperatures the oxygen and nitrogen gases do not
react together. In the presence of very high temperatures nitrogen
and oxygen do react together to form nitric oxide.
These conditions are found in the combustion of coal and oil
at electric power plants, and also during the combustion of
gasoline in automobiles. Both of these sources contribute
about equally to the formation of nitrogen oxides.
In areas of high automobile traffic, such as in large cities,
the amount of nitrogen oxides emitted into the atmosphere can
be quite significant. In the Los Angeles area, the main source
of acid rain is from automobiles.
In certain national parks such as Yosemite and Sequoia, automobile
traffic is banned to limit the amount of air pollution damage
to the trees and plants. This also has the effect of reducing
the visual smog in the air.