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" Adapted from Mackay et al. (1992). There are their "selected" (i.e., "best") values given in their Summary Table 2.2 (some were rounded off). See also Sonnefeld et al. (1983) for "conventional" vapor pressures.

''Abbreviations: B[a]A, benz[ö]anthracene; B[6]F, benzo[6]fluoranthene; B[£]F, benzo[£]fluoranthene; B[g/ii]P, benzo[g///]perylene; DB[a,A]A, dibenz[ö,/;]anthracene. ' Source: Finizio et al. (1997).

d This H is for Henry's law expressed as H = P/[PAH], where P is the gas-phase concentration in pascals and [PAH] is the liquid-phase concentration in moles per cubic meter. Traditionally in atmospheric chemistry, Henry's law is expressed as H = [X]/Px. ' Source: Table 1, Mackay and Callcott (1998).

a. PAHs

Sampling quantitatively each compound in the spectrum of relevant PAHs present in urban ambient air is challenging because their conventional vapor pressures cover a range of some f0l() Torr, e.g., ~8 X 10~2 for naphthalene vs 1.5 X 10"12 for coronene (see Table 10.6).

Furthermore, the concentrations of the gas phase 2-and 3-ring PAHs are generally far higher than those of the 5- and 6-ring particle-phase species. Thus, as seen in Fig. 10.2, average concentrations in urban southern California air at four sites (shown in Figure 10.23) were ~6000, 30, and 50 ng m"3 for gas phase naphthalene, fluorene, and phenanthrene, compared to ~0.14, 0.29, and 0.77 ng m"3 for BaP, indeno[f,2,3-c<i]pyrene and benzo[g/z/]perylene, respectively in the particle phase (Fraser et al., 1998). Although the temperatures were quite high during this period (27°C day and 22°C night), similar relative concentrations of gas-phase vs particle-phase PAHs have also been seen in other studies at lower temperatures. For example, Fig. 10.3 shows measured PAHs in Chicago, Illinois, during February/ March 1995 when the mean day/night temperatures were ~1°C (Harner and Bidleman, 1998). As seen in Fig. 10.3, ~96% of the fluorene and phenanthrene were in the gas phase (naphthalene was not sampled) and accounted for ~56% of the total mass of the measured PAHs.

Table 10.8 summarizes some measured concentrations of various PAHs in a variety of locations as well as the percentage of each found in the particle phase. Consistent with the data in Figs. 10.2 and 10.3, the percentage found in the particle phase increases with the size of the PAH. For example, phenanthrene con-

TABLE 10.7 Vapor Pressures (Pascals)" as a Function of Temperature between 283.15 and 323.15 K for Several Polycyclic Aromatic Hydrocarbonsb log P° = -A /T + B

TABLE 10.7 Vapor Pressures (Pascals)" as a Function of Temperature between 283.15 and 323.15 K for Several Polycyclic Aromatic Hydrocarbonsb log P° = -A /T + B

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