Xvi

Thianthrene

Examples of common names and structures of several S-PACs and nitro-S-PACs identified in combustion-generated emissions (including tobacco smoke condensate) and ambient air are given in Table 10.5.

4. Gas - Particle Partitioning, Sampling Techniques, and Ambient Levels of Selected PAHs and PACs

Whether or not a given PAH exists virtually entirely in the gas phase or in the particle phase, or is partitioned between them, is a critical factor in determining its physical and chemical fates in ambient air and in subsequent intra- and intermedia transport through our air/water/soil environments. This is true not only for physical processes such as wet and dry deposition but also for their chemical reactivity, lifetimes, and fates in VOC-NOx systems characteristic of polluted airsheds. For example, the homogeneous gas-phase reactions of pyrene and fluoranthene differ dramatically from the rates, mechanisms, and products of their particle-associated heterogeneous reactions (Sections E and F).

Similarly, the toxicological effects may depend on whether the compound is inhaled as a gas, inhaled as a particle, or adsorbed/absorbed on the surfaces of coexisting particles. The distribution between these forms varies with the particular compound as well as with a number of parameters such as temperature. For example, in hot weather in ambient air in Claremont and Riverside, California, up to 25% of the PAC 2-nitro-6//-dibenzo[6,i/]pyran-6-one (structure XI; vide supra)

was in the gas phase, rather than being adsorbed/absorbed on surfaces (Arey et al., 1994). This nitro-phenanthrene lactone, formed in a gas-phase atmospheric reaction of phenanthrene, is widely distributed in urban ambient air and is a powerful bacterial mutagen (Helmig et al., 1992a, 1992b; Arey et al., 1992), as well as being mutagenic in the MCL-5 human cell assay (Sasaki et al., 1997b).

Gas-particle partitioning of semivolatile organics, including PAHs, is discussed in more detail in Chapter 9.D. The reader is also referred to books by Mackay et al. (1992), Schwarzenbach et al. (1993), and Baum (1998) and articles by Pupp et al. (1974), Junge (f977), Cautreels and Van Cauwenberghe (1978), Yamasaki et al. (1982), Pankow (1987, 1991, f994a, f994b, 1998), Pankow et al. (1993, 1994), Bidleman and Foreman (1987), Bidleman (1988), Ligocki and Pankow (1989), Foreman and Bidleman (1990), Pankow and Bidleman (1992), Storey et al. (1995), Wilson et al. (1995), Liang and Pankow (1996), Jang et al. (1997b), Finizio et al. (1997a, 1997b), Liang et al. (1997), Chen and Preston (1997), Goss (1997), Goss and Schwarzenbach Q998), Harner and Bidleman (1998), Jang and Kamens (f998), Mackay and Callcott (f 998), and Feilberg et al. (f 999a).

We now consider sampling techniques and typical ambient concentrations of PAHs and PACs.

TABLE 10.6 Vapor Pressures, Subcooled Liquid Vapor Pressures ( pL ), Solubilities in Water (S, Cs), Logarithm of Octanol/ Water Partition Coefficient (logKow), Calculated Henry's Law Constant (H), and Calculated Logarithm of the Octanol-Air Partition Coefficient (logKOA) at 25°C for Selected PAHs of Atmospheric Interest"'6

Calculated

Vapor pressure Solubility d

PAH6 Pa Torr Pa Torr (mg/L) (mmol/m3) K(m mol"') K,

PAH6 Pa Torr Pa Torr (mg/L) (mmol/m3) K(m mol"') K,

Naphthalene

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