Vapor pressure:

720 mm Hg at 20°C

Vapor density:

1.58 (air = 1)

Flash point:

Not applicable

Explosive limit:

Not applicable


Soluble in concentrated nitric and sulfuric acids; decomposes in water; and nitric acid.


Reddish brown gas

Conversion factor:

1 ppm = 1.88 mg/m3 at 20°C


1 mg/m3 = 0.53 ppm at 20°C


In the ambient atmosphere, the major sources of NO2 are the combustion of fossil fuels and motor-vehicle emissions. Indoor sources include such appliances as gas stoves, water heaters, and kerosene space heaters. In the workplace, exposures to NO2 have been reported in such occupations as electroplating, acetylene welding, agriculture, space exploration, detonation of explosives, certain military activities, and burning of nitrogen-containing propellants (Mohsenin 1994). In such situations, exposure concentrations can be very high. For example, in armored vehicles during live-fire tests, peak concentrations of NO2 have been measured at over 2,000 parts per million (ppm). That decreases to about 500 ppm after 1 min and decreases to about 20 ppm within 5 min (Mayorga 1994).

Of concern to the Air Force is the presence of NOx/HNO3 emissions from rockets that use liquid propellants composed of nitrogen-based compounds. For normal launches, the nitrogen-associated emissions at ground level are negligible. However, in the case of a catastrophic abort, large quantities of nitrogen tetroxide can be released. That gas is rapidly converted to NO2 and HNO3, possibly resulting in production of quantities of NOx/HNO3 as high as 200,000 lb (see Appendix A).


When inhaled, NO2 reacts with the moisture in the respiratory tract, resulting in the formation of nitric acid (HNO3). The nitric acid dissoci-

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