Adsorption onto aerosol soot carbon dominates gas-particle partitioning ofpolycyclic aromatic hydrocarbons

Gas-particle partitioning has an important influence on the fate of atmosph eric polycyclic aromatic hydrocarbons (PAHs) and other semivolatile organic compounds (SOCs). In the present paper, gas- and aerosol-phase PAH concent rations and organic and elemental carbon concentrations in the aerosols mea sured in the Baltimore atmosphere and over the adjacent Chesapeake Bay in J uly 1997 were used to assess the mechanisms driving gas-particle partitioni ng of PAHs. The relative importance of adsorption onto the soot carbon and absorption into aerosol organic matter is evaluated by means of estimated s oot/air (K-SA) and octanol/air (K-OA) partition coefficients, respectively. The results show that absorption into organic carbon may account for less than 10% of the total PAHs in the particulate phase. Adsorption onto the so ot phase predicts accurately the total suspended particulate matter normali zed partition coefficients (K-P) for PAHs. For example, K-SA predicts K-P v alues for phenanthrene over the Chesapeake Bay within a factor of 3. K-P pr edictions at the Baltimore atmosphere are within a factor of 5 to 10 of mea sured K-P values. This is consistent with a lack of equilibrium between the gas and aerosol soot phase.