ABSTRACT
This chapter considers four of the major gaseous air pollutants, that is, sulfur oxides (SOx), nitrogen oxides (NOx), ozone (O3), and carbon monoxide (CO). Sulfur oxide emission results from the combustion of sulfur-containing fossil fuels such as coal and oil. In the United States, sulfur dioxide emission from stationary sources and industry accounts for about 95" of all SO2 emission. Sulfur dioxide is rapidly absorbed in the nasopharynx of humans. There are six forms of nitrogen oxides that are present, that is, nitrous oxide (N2O), nitric oxide (NO), nitrogen dioxide (NO2), nitrogen trioxide (N2O3), nitrogen tetroxide (N2O4), and nitrogen pentoxide. Of these, NO2 is the major toxicant because of its relatively high toxicity and its ubiquity in ambient air. Studies on the pathological and physiological effects of NO2 on animals are done at concentrations much higher than those found in ambient air. The toxic action of NO2 is mainly on the deep lung and peripheral airway.
