Partitioning Between the Gas and Aerosol Phases

PAH vapor pressures vary over seven orders of magnitude (Table 13.18). As a result, at 25 °C at equilibrium, naphthalene exists exclusively in the gas phase, while BaP, chrysene, and other PAHs with five and six rings exist predominantly in the aerosol phase. The dis- 

TABLE 13.18 Partitioning Estimation for Selected PAHs Based on Data Collected in Osaka, Japan, Assuming a Total Aerosol Mass of 100 jig m  

The partitioning coefficient Kp for PAHs is found to depend on temperature according to 

Baek et al. (1991) proposed as a rule of thumb that two- and three-ring PAHs (naphthalene, fluorene, phenanthrene, anthracene, etc.) are predominantly in the gas phase, four-ring PAHs (pyrene) exist in both phases, while five- and six-ring PAHs exist primarily in the aerosol phase. Calculations of the ratios of the aerosol- to gas-phase concentrations for a series of PAHs based on data collected in Osaka and assuming an aerosol mass concentration of 100 / gm are presented on Table 13.19. Such estimates should be used with caution as there is considerable variability in the coefficients of (13.45) even when obtained by the same researchers sampling in the same location. 

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