+ 0.02

" Adapted from Hannigan et al. (1996).

6 For discussion ol assay, see Busby et al. (1994a); EOC = equivalent organic carbon. ' See map of these sites in southern California, Fig. 10.23.

'' These are not the values in the article by Hannigan et al. (1996). They are larger by a factor of 1.7 to "reflect recalibration of airflow rates." The mutagenic potency data are not affected (Cass, personal communication; see Hannigan et al., 1998).

primary emissions (e.g., central Los Angeles) prior to transport downwind (see review by Arey (1998a) and references therein).

in an analogous set of studies at four cities across southern California (see Fig. f0.23), Hannigan and co-workers (1996) employed the Salmonella typhimurium TM677 forward mutation bacterial assay (Skopek et al., f 978b; Busby et al., 1994a) to determine the seasonal and spatial variation of the bacterial mutagenicities of fine ambient aerosols. The 1993 annual average bacterial mutagenic properties of the fine aerosols collected at the four urban and one upwind "background" site are summarized in Table 10.23. Consistent with the 1988a study of Atkinson and coworkers, the mutagen densities of ambient air at the four urban locations are more than an order of magnitude higher than at San Nicolas Island upwind. In this study, at most sites the monthly averages did not show a significant seasonal variation.

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