Nitrogen Oxides

Several air-polluting gases composed of nitrogen and oxygen which play an important role in the formation of photochemical smog. Nitrogen oxides are collectively referred to as NO_x, where x represents a changing proportion of oxygen to nitrogen.

Internal combustion engines are significant contributors to the worldwide nitrogen oxide emissions. For the purpose of emission regulations, NO_x is composed of colourless nitric oxide (NO), and the reddish-brown and very toxic and reactive nitrogen dioxide (NO₂).

Other nitrogen oxides, such as nitrous oxide N₂O, are not regulated emissions.

See also: Nitrogen, Nitrous Oxide, Oxygen.