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TABLE 10-1 Physical and Chemical Data on Nitrogen Dioxidea


CAS registry number


Molecular formula


Molecular weight


Boiling point


Melting point


Flash point

Explosive limits

Specific gravity

1.448 at 20°C/4°C (liquid)

Vapor pressure

908 mmHg at 25°C


Soluble in concentrated sulfuric and nitric acids

Conversion factors

1 ppm = 1.88 mg/m3; 1 mg/m3 = 0.53 ppm

aData on vapor pressure were taken from HSDB (2003); all other data were taken from Budavari et al. (1989).

Abbreviations: mg/m3, milligrams per cubic meter; mmHg, millimeters of mercury; ppm, parts per million; —, not available or not applicable.

NO2 is a component of smog and a precursor of ozone (Costa and Amdur 1996). Motor-vehicle exhaust and emissions from other commercial and industrial combustion processes are the major anthropogenic sources of NO2 (HSDB 2003). Natural sources include forest fires and atmospheric lightning discharges (HSDB 2003). The Navy has indicated that the primary sources of NO2 on board submarines are the vent fog precipitator, the diesel generator, and cigarette smoking (Crawl 2003).


NO2 irritates mucous membranes, inciting cough and dyspnea. Higher concentrations of NO2 produce changes in lung function in healthy subjects and lesions in the pulmonary tract of animals. Increased airway resistance has been reported to occur when exposures to NO2 exceed 2.5 ppm (Beil and Ulmer 1976; von Nieding et al. 1979, 1980; von Nieding and Wagner 1979). However, other investigators have not observed any NO2-induced changes in airway resistance or spirometry at concentrations between 2 and

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