ATMOSPHERIC FATES OF PARTICLE-ASSOCIATED PAHs HETEROGENEOUS REACTIONS

ATMOSPHERIC FATES OF PARTICLE-ASSOCIATED PAHs HETEROGENEOUS REACTIONS 

As we have seen, a great deal is known about emission sources and strengths, ambient levels, and mutagenic/carcinogenic properties of the particle-phase PAHs in airborne POM. However, because of the tremendous physical and chemical complexity of the aerosol surfaces on which photolysis, photooxidations, and gas-particle interactions take place in real polluted ambient air, much less is known about the structures, yields, and absolute rates and mechanisms of formation of PAH and PAC reaction products, especially for the more polar PACs. This is one area in which there exists a major gap in our knowledge of their atmospheric chemistry and toxicology. 

In 1954, Kotin and co-workers reported the carcinogenicity of atmospheric extracts of Los Angeles air. Subsequently, in 1956, they reported the carcinogenic activity of oxidation products of aliphatic hydrocarbons and, in 1958, of ozonized gasoline. Concurrently, Falk and co-workers (1956) published results 

Based in part upon this pioneering research, a National Academy of Sciences Committee suggested in their 1972 document Particulate Polycyclic Organic Matter that photolysis, photooxidations, and gas-particle interactions might lead to significant degradation of PAHs in ambient particles and formation of products more polar than the parent PAHs (NRC, 1972). 

We discuss in this section four key aspects of heterogeneous reactions (1) theoretical and experimental structure and reactivity relationships (2) held measurements of relative and absolute PAH decay rates in near-source ambient air and during downwind transport (3) laboratory studies of the photolysis/photo-oxidation and gas-particle interactions with 03 and NOz of key 4- and 6-ring PAHs adsorbed on model substrates or ambient aerosols and (4) environmental chamber studies of the reactions of such PAHs associated with several physically and chemically different kinds of combustion-generated aerosols (e.g., diesel soot, wood smoke, and coal fly ash). Where such data are available, we also briefly consider some toxicological ramifications of these reactions. 

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E. ATMOSPHERIC FATES OF PARTICLE-ASSOCIATED PAHs HETEROGENEOUS REACTIONS... 

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