ABSTRACT
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Nitrogen oxides (NOx) are very simple molecules that are naturally present in the atmosphere.
The natural sources of these oxides include nitrogen fixation by lightening, volcanic activity,
and microbial activity. For a long time, there was little concern about these nitrogen oxides.
However, the levels of NOx have now increased to an extent that they have become an
extremely important family of air polluting compounds. The increase in NOx emissions is
due to the significant rise in anthropogenic (human) activities. This chapter will discuss the
problems associated with these pollutants, their sources and currently available NOx abate-
ment technologies. In particular, selective catalytic reduction (SCR) of NOx using ammonia
will be discussed.
