A comparative study of the gas-particle partitioning of PCDD/Fs, PCBs, and PAHs

Air samples were taken concurrently for four sampling events in the winter of 1998 at three contrasting sites: an urban center and two rural sites. The rural sites were characterized by the extensive usage of coal and wood for space heating. Samples were analyzed for PCDD/Fs, PCBs, and PAHs. Recently measured octanol-air partition coefficients (K-oa) for PCDD/Fs enabled a comparison of the K-oa-based versus the subcooled liquid vapor pressure (p(L))-based partition model for all three compound classes. Both K-oa and p(L) were found to be excellent descriptors of the gas-particle partitioning of PCDD/Fs, PCBs, and PAHs. However, regressions for log K-p-log p(L) gave higher regression coefficients than for log K-p-log K-oa. Both models showed roughly similar relative states of equilibrium for PCDD/Fs, PCBs, and PAHs. PCBs were closest to equilibrium at the urban site. It is argued that newly released particles at the rural sites caused nonequilibrium partitioning at those sites for PCBs. PAHs were released at all sites and were, in line with expectations, approaching equilibrium. The K-oa-based and the p(L)-based model gave contradictory results for PCDD/Fs: according to the p(L)-model, PCDD/Fs were in equilibrium for event 1 but not for the other events, whereas the K-oa-model showed the PCDD/Fs not being in equilibrium for event 1. A simple K-oa-model, combining advective transport and locally released PCDD/Fs and PAHs, can explain the observed nonequilibrium partitioning for the first sampling event.