Introduction One of the major problems confronting modern civilization is the continuing degradation of air quality in major urban complexes. An Important symptom of air pollution is the Increased concentration of airborne particulates over cities@ resulting in increased health hazards@ decreased visibility@ and corrosive destruction of property. The formation of aerosols by man's activity is perhaps the most easily identified manifestation of air pollution. However@ the details of the mechanisms of formation of airborne particles and their evolution and removal from the atmosphere@ remain poorly understood despite considerable effort devoted to this subject. A number of years ago@ workers recognized that aerosol particles could appear in the atmosphere via two different routes. The first involves primary emissions from sources such automobile exhaust@ or smokestacks. The other Is secondary in nature@ where particles are produced by physicochemical processes in the atmosphere itself. The possibility of chemical aerosol formation was probably first demonstrated by Tyndall in the 19th century.The significance of such a mechanism for removal of reactive trace gases from the atmosphere has not been fully appreciated until recently. There is mounting evidence that the formation of aerosols by photochemical reactions in the atmosphere plays a significant local role in air pollution over many cities. In fact@ the formation of a haze of such suspended material is an integral part of photochemical smog. It was recognized in the classical work on smog reactionsthat aerosols would form in photochemical1y reactive atmospheres containing hydrocarbon vapors@ water vapor@ and nitrogen oxides. More recent studies In smog chambers have elucidated the relation between SO2 and photochemical aerosol formation. Other work@ such as that of Bricard et al. and Goetz and coworkers@ have indicated that significant gas-particle interactions take place in air containing pollutant gases Irradiated by sunlight.
API 4193-1973 history
1973API 4193-1973 MECHANISMS OF FORMATION & COMPOSITION OF PHOTOCHEMICAL AEROSOLS