A study of gas/particle partitioning of SVOCs in the tropical atmosphere of Southeast Asia

Gas- and particle-phase polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) were collected at a tropical site in Southeast Asia over 12-h periods during November and December 2006 to determine their gas/particle distributions by analyzing integrated quartz filter and polyurethane foam samples. Gas/particle partitioning coefficients, K_p, were calculated, and their relationship with the subcooled liquid vapor pressure p_L^o for both PAHs and PCBs was investigated. The regressions of log K_p vs. log p_L^o for most of samples gave high correlations for both PAHs and PCBs and the slopes were statistically shallower than -1, but they were relatively steeper than those obtained in temperate zones of the Northern Hemisphere. By comparison, the particle-bound fraction of low molecular weight (LMW) PAHs was underestimated by both Junge-Pankow adsorption and K_OA (octanol-air partition coefficient) absorption models, while the predicted values agree relatively better with those observed ones for high molecular weight (HMW) PAHs. In addition, the adsorption onto the soot phase (elemental carbon) predicted accurately the gas/particle partitioning of PAHs, especially for LMW compounds. On the other hand, the K_OA absorption model using the measured organic matter fraction (f_OM) value fitted the PCB data much better than the adsorption model did, indicating the sorption of nonpolar compounds to aerosols might be dominated by absorption into organic matters in this area.