
Nitrogen Oxides (NOx) are formed from agricultural sources,
waste management as well as from combustion.
In terms of energy nitrogen oxide emissions from vehicles are most
concerning.

Nitrogen oxides (1) Are one of the main ingredients involved in the
formation of ground-level ozone, which can trigger serious respiratory
problems. (2) react to form nitrate particles, acid aerosols, as well as NO2,
which also cause respiratory problems. (3) contribute to formation of acid
rain. (4) contribute to nutrient overload that deteriorates water quality.
(5) contribute to atmospheric particles, that cause visibility impairment
most noticeable in national parks. (6) react to form toxic chemicals. (7)
contribute to global warming.
Combustion Sources of NOx Emissions (U.S.-2003)
(Source: U.S. Environmental Protection Agency)
Header: Smog in New York City-1988
(Source:http://en.wikipedia.org/wiki/Image:SmogNY.jpg)