ABSTRACT

NO2 is a criteria pollutant with a National Ambient Air Quality Standard of 100 μg/m3, or 0.053 ppm, annual average. It is also a precursor to nitric acid, HNO3, in the atmosphere and is a major contributor to acid rain, although less important than SO2, which is discussed in Chapter 18. Nitric acid contributes only one proton per molecule, while sulfuric acid has two protons per molecule, and mass emissions of sulfur compounds are larger than oxides of nitrogen. Finally, NOx and volatile organic compounds react photochemically in a complex series of reactions to produce smog, which includes ozone, NO2, peroxyacetyl nitrate, peroxybenzoyl nitrate, and other trace oxidizing agents.