267 524 53-70-3

" Adapted Irom Mackay et al. (1992); data on indeno[l,2,3-crf]pyrene Irom Harvey (1997). Structures and their numbering are based on IUPAC recommendations as described by Loening et al. (1990). 6 U.S. EPA (1998) designation. Exceptions are noted by asterisks.

on combustion sources, see Björseth (1983), Baek et al. (1991a), Venkataraman and Friedlander (1994c), Schauer et al. (1996), Harrison et al. (1996), Howsam and Jones (1998), and Simoneit (1998); for diesel and gasoline engines, see IARC(f989), Benner et al. (1989), Westerholm et al. (1991), Bagley et al. (1992), Johnson et al. (1994), Lowenthal et al. (1994), Hammerle et al. (1994), WHO (1996), Miguel et al. Q998), and Schauer et al. (1999); for coal fly ash, see Gohda et al. (1993); and for municipal incinerators, see Lee et al. (1993). PAHs are also common constituents of air indoors, arising from coal and wood combustion (Mumford et al., 1990), wood combustion (Alfheim and Ramdahl, 1984), and environmental tobacco smoke, ETS (Gundel et al., 1995b; and the California EPA, 1997).

The physical and chemical processes by which PAHs and PACs are formed in combustion are very complex and beyond the scope of this book; the reader is referred to articles in the literature such as those by Badger (1962), Haynes (1991), and Vander Wal and co-workers (1997). Only a relatively few PAHs (ca. fOO) are stable enough to survive the combustion-pyrolysis process and enter our air environment as primary pollutants in complex combustion-generated mixtures in amounts sufficient to be of concern. The toxicity of such combustion-generated mixtures is reflected in the fact that POM is one of the 189 hazardous air pollutants (HAPs) cited in the 1990 U.S. Clean Air Act Amendments (Kelly et al., 1994; Kao, 1994). Their complexity is evident from the fact that the term POM includes not only PAHs, the most abundant and intensively studied chemical class in POM emissions and ambient air, but also a wide range of N-, O-, and S-atom polycyclic aromatic compounds, including ni-troarenes and azaarenes; PAH lactones, ketones, and quinones; and thioarenes. Structures and nomenclatures for selected PAHs and PACs relevant to atmospheric chemistry are discussed in Section A.2.

Some of these N-, O-, and S-atom-functionalized polycyclic aromatic compounds (PACs) are powerful bacterial mutagens and animal, and possible human, carcinogens, e.g., the exocyclic nitro-substituted PAH 1-nitropyrene, VI, which is a primary pollutant in diesel exhaust (IARC, 1989). The endocyclic heterocyclic PAC dibenz[a,/z]acridine, VII, is also classified as a "possible human carcinogen" (IARC, 1987; see Sections B and C).

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