Nitrogen dioxide

Nitrogen dioxide is a chemical compound with the formula NO2, a reddish brown gas made of one nitrogen atom bonded to two oxygen atoms, and it behaves as a paramagnetic free radical with a bent molecular shape. It is produced naturally by bacterial activity in soil, by volcanoes, and by lightning, and industrially it is a key intermediate in the large scale manufacture of nitric acid. It also enters the environment from combustion, especially from vehicle engines and gas stoves, and it is toxic, capable of being fatal if inhaled in large quantities; research links elevated indoor concentrations to respiratory illness, making it one of the more closely watched urban air pollutants.