HNO3 is widely used by a number of industries. In the chemical industry, it is used for the manufacture of metallic nitrates, sulfuric acid, aqua regia, arsenic acid and derivatives, nitrous acid and nitrites, oxalic acid, phthalic acid, and so forth. HNO3 is used for the manufacture of trinitrophenol, trinitrotoluene, nitroglycerin, and various dyes and pharmaceuticals. Much of the NO and NO2 emitted to the atmosphere from air-pollution sources is converted to HNO3. EPA (1993) compiled measurements of average concentrations of HNO3 in the continental United States; those ranged from 0.5 to 3 µg/m3 for 13 rural sites and from 1.1 to 2.7 µg/m3 for 5 urban sites. A 9-day average concentration of HNO3 for Claremont, CA was 11 µg/m3 (4.4 ppb) (Wolff et al. 1991). Daily averages can be as high as 60 µg/m3 (26 ppb) and hourly averages as high as 200 µg/m3 (80 ppb) (EPA 1982; Lioy and Lippmann 1986; Lippmann 1989a,b). HNO3 is produced at very low concentrations in rocket emissions from the combustion of hydrazine and N2O4 under normal launch conditions but at significant concentrations when a launch is aborted after ignition for rockets using liquid propellants.
The disposition of HNO3 is not easily determined. It reacts immediately with respiratory mucous membranes after inhalation and does not appear to be absorbed after oral administration (Gosselin et al. 1984). Instead, it causes erosion of the gastrointestinal (GI) mucosal membranes, which produces severe GI distress. Following inhalation exposure, some HNO3 might decompose to other nitrogen oxides, which might be absorbed by the bloodstream (EPA 1993) (see Appendix E).
The toxicity of HNO3 is predominately associated with the extremely corrosive nature of this strong acid. In addition, it is an excellent oxidizing agent and reacts immediately with any tissue to cause such effects as skin burns, eye irritation, coughing, dyspnea, and pulmonary edema. Delayed toxicity, possibly as a result of the decomposition of HNO3 to