Nitric oxide (NO) and nitrogen dioxide (N02
) are the two most important nitrogen oxide
air pollutants. They are frequently lumped together underthe designation NOx
, although
analytical techniques can distinguish clearly between them. Ofthe two, N02
is the more
toxic and irritating compound.
Nitric oxide is a principal by-product of combustion processes, arising from the
high-temperature reaction between N2
and O2
in the combustion air and from the oxidation of organically bound nitrogen in certain fuels such as coal and oil. The oxidation
of N2
by the O2
in combustion air occurs primarily through the two reactions