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|Density||1443 kg/m³, liquid|
3.4 kg/m³, gas at 294.25 K
|S-phrases||, , , ,,|
|Except where noted otherwise, data are given for|
materials in their standard state
(at 25 °C, 100 kPa)
Infobox disclaimer and references
Nitrogen dioxide is the chemical compound NO2. It is one of the several nitrogen oxides. This reddish-brown gas has a characteristic sharp, biting odor. NO2 is one of the most prominent air pollutants and a poison by inhalation.
Safety and pollution considerations
Nitrogen dioxide is toxic by inhalation. Symptoms of poisoning (lung edema) tend to appear several hours after one has inhaled a low but potentially fatal dose. Also, low concentrations (4 ppm) will anesthetize the nose, thus creating a potential for overexposure.
Long-term exposure to NO2 at concentrations above 40–100 µg/m³ causes adverse health effects . The most important source of NO2 is internal combustion engines, which emit nitrogen oxides near people. A major industrial source is pulp mills.
The map shown below, depicting results of satellite measurements over Europe, illustrates nitrogen dioxide as large scale pollutant, with rural background ground level concentrations in some areas around 30 µg/m³, not far below unhealthful levels. Nitrogen dioxide plays a role in atmospheric chemistry, including the formation of tropospheric ozone. A recent study by researchers at the University of California, San Diego, suggests a link between NO2 levels and Sudden Infant Death Syndrome .
- Nitrous oxide or N2O, "laughing gas", a linear molecule, isoelectronic with CO2 but with a nonsymmetric arrangement of atoms (NNO)
- Nitric oxide or NO, a problematic pollutant, related to CO but with one additional electron.
- NOx = all of the above in unspecified proportions but tending toward NO2.
Oxidized (cationic) and reduced (anionic) derivatives of many of these oxides exist: nitrite (NO2−), nitrate (NO3−), nitronium or NO2+, and nitrosonium or NO+. NO2 is intermediate between nitrite and nitronium:
- NO2+ + e− → NO2
- NO2 + e− → NO2−
- International Chemical Safety Card 0930
- National Pollutant Inventory - Oxides of nitrogen fact sheet
- NIOSH Pocket Guide to Chemical Hazards
- WHO-Europe reports: Health Aspects of Air Pollution (2003) (PDF) and "Answer to follow-up questions from CAFE (2004) (PDF)
- Nitrogen Dioxide Air Pollution
- Nitrogen dioxide pollution in the world (image)
- Computational Chemistry Wiki