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" Adapted from Fraser et al. (1998); study carried out September 8-9, 1993. Samples aggregated and averaged over 48 h at each sampling site.

h Peak ozone-290 ppb at Claremont. ' Class II reactivity scale (Nielsen, 1984; see Table 10.30).

The rapid depletion of these reactive PAHs during transport of this polluted air parcel is dramatic. Thus, as seen in Table 10.31, their concentrations (averaged over all times) drop from 1.04 and 0.29 ng m~3 for cyclopenta[cd]pyrene and BaP, respectively, at central Los Angeles to 0.03 ng m 3 for both PAHs at Claremont.

The physical effect of dilution of the aerosols due to increased mixing depths during transport of the air parcel inland is factored out by taking the ratios of the concentrations at Claremont to those at central Los Angeles. As seen in Table fO.32, the ratios are 0.2f and 0.20 for the low-reactivity PAHs benzo[/c]fluoranthene and indeno[f,2,3-c<i]pyrene (Class V, Table 10.30), reflecting dilution, whereas the ratios are 0.10 and 0.03 for reactive BaP and eye 1 ope n ta[«/ ]pyre ne (Class II), respectively, indicative of reactions in addition to dilution.

Conversely, as seen in Fig. 10.27 and Table 10.31, the concentrations of the gas-phase atmospheric reaction product 3-nitrobiphenyl increase during transport across the basin, going from 9.5 ng m~3 in central Los Angeles to 21.8 ng m~3 in Claremont. Concentrations of 1- and 2-nitronaphthalene (recall the latter is a human cell mutagen in the MCL-5 cell line; Sasaki et al., 1997b), which are also formed in gas-phase reactions (see Section F), increase significantly during transit. Finally, some O-PAHs, e.g., 1,8-naphthalic anhydride and cyclopenta[c<f]phenanthrone, were also

TABLE 10.32 Ratios of Two-Dayc Average Ambient Concentrations of Two "Reactive" (Class II)1' and Two "Low-Reactivity" (Class V)b PAHs in Fine Aerosols at Claremont and Central Los Angeles (Claremont/Central Los Angeles)"''1
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