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

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H ON0 2
·/HN0 3
N0 2
H
14 Table 2-13 summarizes the nitroarene product data for OH radical-initiated and N 2 0 5 gas-
15 phase reactions with several PAHs studied to date in environmental chambers (Arey et al., 1989; ·
16 · Zielinska et aL, 1990). Section 2.5.3 will discuss the fact that, generally, the same nitro-PAH
17 isomers that are formed from OH radical and N 20 5 reactions are observed in ambient air samples.
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19 2.4.2.2. Particulate-Phase Reactions
20 Organic compounds present in diesel exhaust are partitioned into the particulate phase
21 under atmospheric conditions. The following chemical processes are likely to contribute to the
22 degradation of these compounds in the troposphere (Atkinson, 1988):
23 • Photolysis,
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· 25 • Reaction with 0 3 ,
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27 • Reaction with N 20 5 during nighttime hours,
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29 • Reaction with N0 2 during nighttime and daytime hours,
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31 • Reaction with H 20 2 , and
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33 • Reaction with HN0 3 , HN0 2 , and H 2S0 4 •
34 However, the atmospheric lifetimes of particle-bound organic compounds are not well
35 known, partly because (1) these chemical processes depend on the nature ofthe substrate (e.g.,
36 Behymer and Hites, 1985, 1988) and (2) many of the laboratory studies have been done using
37 atmospherically unrealistic adsorbents, such as glass-fiber and Teflon-coated glass-fiber filters,
2/1198 2-40 DRAFT--DO NOT CITE OR QUOTE