Glossary:Nitrogen dioxide

Nitrogen dioxide is a chemical compound with the formula NO2. It is one of several nitrogen oxides. NO2 is an intermediate in the industrial synthesis of nitric acid, millions of tons of which are produced each year for use primarily in the production of fertilizers. At higher temperatures it is a reddish-brown gas. It can be fatal if inhaled in large quantities.[8] Nitrogen dioxide is a paramagnetic, bent molecule with C2v point group symmetry. It is included in the NOx family of atmospheric pollutants.

The reddish-brown color is a consequence of preferential absorption of light in the blue region of the spectrum (400 – 500 nm), although the absorption extends throughout the visible (at shorter wavelengths) and into the infrared (at longer wavelengths). Absorption of light at wavelengths shorter than about 400 nm results in photolysis (to form NO + O, atomic oxygen); in the atmosphere the addition of the oxygen atom so formed to O2 results in ozone.

The most prominent sources of NO2 are internal combustion engines, as combustion temperatures are high enough to thermally combine some of the nitrogen and oxygen in the air to form NO2. Outdoors, NO2 can be a result of traffic from motor vehicles. Indoors, exposure arises from cigarette smoke, and butane and kerosene heaters and stoves. Workers in industries where NO2 is used are also exposed and are at risk for occupational lung diseases, and NIOSH has set exposure limits and safety standards. Workers in high voltage areas especially those with spark or plasma creation are at risk. Agricultural workers can be exposed to NO2 arising from grain decomposing in silos; chronic exposure can lead to lung damage in a condition called "silo-filler's disease".