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

1 polarity, more than 65% of the mutagenic activity for HDD particulate extract is concentrated in
2 the most polar fraction. However, because of the serious analytical difficulties, only preliminary
3 data exist on the identification of compounds that are responsible for the mutagenic activity of
4 this fraction (so-called "polar mutagens"). Schuetzle and co-workers (1985) employed the
5 concept of"bioassay directed chemical analysis" (see Section 2.6) for the isolation and
6 identification of polar P AH derivatives from the extracts of HDD particulate matter (National
7 Institute of Standards and Technology [NIST] standard reference material SRM 1650). Several
8 hydroxynitro-PAHs, hydroxy-PAHs, and nitrated heterocyclic compounds were tentatively
9 identified in the polar fraction. It has to be noted, however, that NIST SRM.1650 was not
10 intended to be representative ofHDD engines but was a material made available to investigators
11 for the purpose of methods development.
12 In another study (Bayona et al., 1988), the polar HPLC fractions ofthe same NIST SRM
13 1650 were analyzed by fused silica capillary GC with low- and high-resolution mass MS, using ·
14 electron impact (EI) and negative ion chemical ionization (NICI) techniques. In addition, direct-
15 probe EI and NICI-MS analyses were performed. More than 80 polycyclic aromatic compounds
16 (PAC) belonging to several different chemical classes (anhydrides, carboxaldehydes, diazaarenes,
17 cyclic imides, hydroxynitro-PAH, nitroaza-PAC, nitrolactones, and quinones) were tentatively.
18 identified. Ten were positively identified by comparison ·of retention times with authentic
19 standards. Among them, phenazine and phthalic anhydride were positively identified for the first
20 time in diesel exhaust particles. In addition, cyclic imides and their alkylated derivatives were
21 tentatively identified.
22
23 2.3.3. Gaseous-/Particulate-Phase Emission Partitioning of Polycyclic Aromatic
24 Hydrocarbons
25 The distribution of the emissions between the gaseous and particulate phases is
26 determined by the vapor pressure of the individual species, by the amount and type of the
27 particulate matter present (adsorption surface available), and by the temperature (Ligocki and
28 Pankow, 1989). Table 2-11 gives the vapor pressures at 25 oc of some representative PAHs
29 ranging from naphthalene to benzo[ a ]pyrene.
30 The factor of"' 10 7 in the range of vapor pressures is reflected in the fact that, at
31 equilibrium at ambient temperature, naphthalene exists almost entirely in the gas phase, whereas
32 B [a ]P, other five-ring P AHs, and higher-ring P AHs are predominantly adsorbed on particles.
33 The intermediate three- and four-ring P AHs are distributed between the two phases.
34 However, the vapor pressures of these intermediate P AHs can be significantly reduced by
35 their adsorption on various types of surfaces. Because of this phenomenon, the amount and type
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