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TABLE 9-1 Physical and Chemical Data on Nitric Oxidea


Nitrogen monoxide

CAS registry number


Molecular formula


Molecular weight


Boiling point


Melting point


Flash point

Explosive limits

Specific gravity

1.04 with respect to air

Vapor pressure

45,600 mmHg at –94.8°C


4.6 mL/100 mL of water at 20°C

Conversion factors

1 ppm = 1.23 mg/m3; 1 mg/m3 = 0.81 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; mL, milliliter; mmHg, millimeters of mercury; ppm, parts per million; —, not available or not applicable.

to NO2, which is more toxic, the two chemicals should be monitored simultaneously (ACGIH 2001).

NO primarily is used as an intermediate in the production of nitric acid (Budavari et al. 1989). In recent years, NO has been recognized for its role as a regulator of cardiovascular, immune, and nervous system functions (Kiss 2000; Weinberger et al. 2001). It has been investigated and used as a treatment for various pulmonary diseases (Troncy et al. 1997).

NO is a component of smog. Sources of NO include exhaust from internal-combustion engines, smoke from fires, and tobacco smoke (ACGIH 2001). The Navy has indicated that the primary sources of nitrogen oxides on submarines are the diesel generator, the vent fog precipitator, and cigarette smoking (Crawl 2003).


NO relaxes vascular smooth muscle making it an effective treatment for persistent pulmonary hypertension in newborns (Channick and Yung 1999; INO Therapeutics 2001). High NO exposures produce methemoglobinemia, a reversible event. Seger (1992) describes the clinical signs and symptoms at increasing concentrations of methemoglobin. Clinical cyanosis and “chocolate brown” blood occur in humans at about 15-20% methemo-

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