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FIGURE 10.32 GC-MS selected ion monitoring (SIM) scan of the molecular ions (m/z 247) of nitrofluoranthene (NF) and nitropy-rene (NP) isomers in extracts of ambient particles collected in Torrance, California, January 1986 (adapted from Arey et al., 1988b, and Atkinson and Arey, 1997).

OH adduct radical (e.g., see Atkinson, 1994, and Chapter 6.G). However, in the presence of sufficient N02, 2-nitrofluoranthene and 2-nitropyrene are formed and subsequently condense out on particle surfaces (see Pitts, f987, Atkinson and Arey, 1994, Arey, 1998a, and references therein).

For this mechanism to be effective, several requirements must be met:

• Under ambient conditions, a substantial portion of the fluoranthene and pyrene must be in the gas phase, which is indeed the case (see Figs. 10.2 and 10.3).

• Attack by OH radicals on the gas-phase fluoranthene and pyrene must be fast. As seen in Table 10.35, again this is true. In Table 10.36, the calculated atmospheric lifetimes of selected gas-phase PAHs due to reaction with OH are shown, e.g., lifetimes of ~2.9 h for fluoranthene and pyrene.

• Products (and their mutagenicities) of the gas-phase reactions of these and other 2- to 4-ring PAHs (fluorene, naphthalene, etc.) carried out under simulated atmospheric conditions should be consistent with the nitroarenes and nitro-PACs that have been identified in ambient air. This criterion has been well established over the years in environmental chamber studies conducted in several laboratories (e.g., see reviews by Atkinson and Arey, 1994; and Arey, 1998a; articles by Kamens et al., 1994; Fan et al., 1995; Feilberg et al., 1999a; and references therein).

FIGURE 10.33 Mechanism of oxidation of fluoranthene by OH in air (adapted from Arey, 1998a).

FIGURE 10.33 Mechanism of oxidation of fluoranthene by OH in air (adapted from Arey, 1998a).

For example, Fig. 10.34 shows the mutagram (TA98, — S9) of an extract of ambient particles collected in Claremont, California, August 1987 (Harger et al., f 992) together with mutagrams of extracts of environmental chamber reaction products for the simulated OH radical initiated reactions of phenanthrene, fluoranthene, and pyrene, respectively (Arey et al., 1992; Sasaki et al., 1995; Atkinson and Arey, f994; Arey, 1998a). It can be seen that, in combination, the mutagrams of the pho-tooxidation reaction products of phenanthrene, pyrene, and fluoranthene are very similar to the mutagen profile of the ambient air sample.

2-Nitrofluoranthene, found in fraction 4, dominated the fluoranthene reaction products, consistent with extracts of ambient POM. The more polar fraction 6 of the OH radical initiated phenanthrene reaction products contained the two nitrophenanthrene lactones previously identified in ambient air (Helmig et al., 1992a, 1992b), the potent direct mutagen 2-nitro-6 H-dibenzo[6,c?]pyran-6-one (XI) and its less mutagenic 4-N02 isomer (see Table 10.20). Recall that this 2-nitro-PAC XI has been estimated to account for up to 20% of the direct mutagenicity of an ambient aerosol extract (Helmig et al., 1992b). Two nitropyrene lactone isomers were tentatively identified in fraction 6 of the pyrene reaction products. El-Bayoumy and Hecht (1986) reported earlier that two nitropyrene lactones were strong mutagens in the standard Ames plate incorporation assay (Maron and Ames, 1983).

Figure 10.35 is the GC-MS m /z 247 profile of the nitrofluoranthenes and nitropyrenes in an extract of an ambient particle sample collected at night (Arey et al., 1988b). The high ratio of 2-nitrofluoranthene to 2-nit-ropyrene observed in this nighttime sample is indicative of nighttime gas-phase NO-, radical reactions (for a review, see Kwok et al., f994b). An N03 radical initiated mechanism for atmospheric formation of 2-nitrofluoranthene is shown in Fig. 10.36 (Atkinson and Arey, 1997; Arey, f998a, and references therein). Analogous to the OH reaction, N03 is proposed to add to the ring to form a fluoranthene-N03 adduct, followed by ortho addition of N02 and subsequent loss of HN03. This reaction is noteworthy because of its selectivity; i.e., only 2-nitrofluoranthene is formed, and in high yield (24%) compared to the OH-initiated daytime reaction (3%).

Another example is the atmospheric formation levels, fates, and mutagenicities of 1- and 2-nitronaphtha-lenes (f-NN and 2-NN) and certain methylnitronaph-thalene isomers (MNN). Naphthalene is the most abundant of the PAHs and its role, and that of the abundant MNNs, in the atmospheric chemistry of PAHs are being increasingly recognized as being important; e.g., see Pitts et al., 1985c; Atkinson et al., f987b,

TABLE 10.35 Room Temperature Rate Constants, k, for the Gas-Phase Reactions of Selected PAHs and Nitro-PAHs with the

Hydroxyl Radical, the Nitrate Radical, and Ozone (from Arey 1998a)

k (cm3 molecule ' s 1) for reaction with

TABLE 10.35 Room Temperature Rate Constants, k, for the Gas-Phase Reactions of Selected PAHs and Nitro-PAHs with the

Hydroxyl Radical, the Nitrate Radical, and Ozone (from Arey 1998a)

k (cm3 molecule ' s 1) for reaction with

PAH or nitro-PAH

OH"

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