ABSTRACT
Pollutants enter the atmosphere primarily from natural sources and human activity. This pollution is called primary pollution, in contrast to secondary pollution, which is caused by chemical changes in substances in the atmosphere. Sulfur dioxides, nitric oxides, and hydrocarbons are major primary gaseous pollutants, while ozone is a secondary pollutant, the result of atmospheric photochemistry between nitric oxide and hydrocarbons. A basic chemical process in the atmosphere is the oxidation of substances by atmospheric oxygen. Thus, sulfur dioxide is oxidized to sulfur trioxide, and nitric oxide to nitrogen dioxide. Similarly, many organic substances are oxidized, for example, aldehydes to organic acids and unsaturated hydrocarbons. Sulfur oxides, in particular SO2, have been studied with respect to atmospheric chemistry. Atmospheric reactions are strongly affected by the number of suspended solid particles and their properties. Other long-range problems caused by atmospheric chemical reactions occur in addition to those of sulfur and nitrogen compounds.
