Health Assessment Document for Diesel Emissions - NSCEP | US ...

1 conditions (Pitts et al., 1985c ). However, this may not always be the case in air sheds that have
2 high N0 2 and nighttime N 2 0 5 concentrations.
3 The formation of nitro-PAHs during sampling may be an important problem for diesel
·4 particulate matter collection because ofthe presence ofN0 2 and HN0 3 . However, Schuetzle
5 (1983) concluded that the artifact formation of 1-NP during dilution tube sampling accounts for
6 less than 10% to 20% of the total1-NP present in diesel particles if the sampling time is less than
7 23 min (one FTP cycle) and if the sampling temperature is not higher than 4 3 o C.
8 The formation of nitroarenes during ambient high-volume sampling conditions has been
9 reported to be minimal, at least for the most abundant nitropyrene and nitrofluoranthene isomers
1 0 (Arey et al., 1988).
11
12 2.4.2.2.3. Ozonolysis ofparticulate polycyclic aromatic hydrocarbons. Numerous laboratory
13 studies have shown that P AHs deposited on combustion-generated fine particles and on model
14 substrates undergo reaction with 0 3 (e.g., Katz et al., 1979; Pitts et al., 1980, 1986; Van Vaeck
15 and Van Cauwenberghe, 1984; Finlayson-Pitts and Pitts, 1986). The dark reaction of several
16 P AHs deposited on model substrates toward 0 3 has been shown to be relatively fast under
17 simulated atmospheric conditions (Katz et al., 1979; Pitts et al., 1980, 1986). Half-lives ofthe.
18 order of one to several hours were reported for the more reactive PAHs, such as B[a]P,
19 anthracene, and benz[ a ]anthracene (Katz et al., 1979).
20 The reaction of P AH deposited on diesel particles with 1.5 ppm 0 3 under high-volume
21 sampling conditions has been shown to be relatively fast, and half-lives of the· order of 0.5 to 1 h .
22 have been reported for most PAHs studied (Van Vaeck and Van Cauwenberghe, 1984). The
23 most reactive PAHs include B[a]P, perylene, benz[a]anthracene, cyclopenta[cd]pyrene, and
24 benzo[ghi]perylene. The benzofluoranthene isomers are the least reactive of the PAHs studied,
25 and benzo[e]pyrene (B[e]P) is less reactive than its isomer B[a]P. The implications of this study
26 for the high-volume sampling of ambient POM are important: reaction ofPAHs with 0 3 could
27 possibly occur under high-volume sampling conditions during severe photochemical smog
28 episodes, when the ambient level of0 3 is high. However, the magnitude of this artifact is
29 difficult to assess from available data.
30 Exposures of P AH adsorbed on filters and ambient particulate matter to ambient levels of
31 . 0 3 in an environmental chamber under "passive" conditions, more nearly resembli.n,g
32 atmospheric transport (as opposed to filtration-type experiments analogous to high-volume
33 sampling of particles), also have been carried out (Pitts et al., 1986). These experiments showed
34 that significant degradation of more reactive P AHs adsorbed on ambient particulate matter, such
· 35 as B[a]P, pyrene, and benz[a]anthracene, may occur in Orpolluted atmospheres.
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2/1/98 2-43 DRAFT--DO NOT CITE OR QUOTE