Nitrogen_dioxide

Nitrogen dioxide
Identifiers
CAS number	[10102-44-0]
Properties
Molecular formula	NO2
Molar mass	46.0055
Appearance	brown gas
Density	1443 kg/m³, liquid 3.4 kg/m³, gas at 294.25 K
Melting point	-11.2°C (261.95 K)
Boiling point	21.1°C (293.25 K)
Hazards
EU classification	Highly toxic (T+)
NFPA 704	0 3 0
R-phrases	R26, R34
S-phrases	(S1/2), S9, S26, S28,S36/37/39, S45
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.

Nitrogen dioxide (NO₂) gas converts to the colorless gas dinitrogen tetroxide (N₂O₄) at low temperatures, and converts back to NO₂ at higher temperatures. Both bottles in this photograph contain equal amounts of gas at different temperatures.

Contents 1 Safety and pollution considerations 2 See also 3 References 4 External links

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 effectsHealth Aspects of Air Pollution with Particulate Matter,Ozone and Nitrogen Dioxide. Retrieved on 2008-02-25..

Nitrogen dioxide is formed in most combustion processes using air as the oxidant. At elevated temperatures nitrogen combines with oxygen to form nitrogen dioxide:

2O₂ + N₂ → 2 NO₂

The most important sources of NO₂ are internal combustion engines Son, Busoon; Wonho Yang, Patrick Breysse, Taewoong Chung and Youngshin Lee (March 2004). "Estimation of occupational and nonoccupational nitrogen dioxide exposure for Korean taxi drivers using a microenvironmental model". Environmental Research 94 (3): 291-296. Retrieved on 2008-02-25. , thermal power stations and, to a lesser extent, pulp mills.Air emissions. Botnia. Retrieved on 2008-02-25.

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. Sids Linked to Nitrogen Dioxide Pollution. Retrieved on 2008-02-25.

NO₂ pollution levels in Europe, from January 2003 to June 2004.

See also

• Nitryl
• 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.
• NO_x = all of the above in unspecified proportions but tending toward NO₂.

More esoteric nitrogen oxides include N₂O₅ and the blue species N₂O₃.

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⁻

• Birkeland-Eyde process

References

External links

• 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

This article is licensed under the GNU Free Documentation License. It uses material from Wikipedia