Gaseous Exchange of Polycyclic Aromatic Hydrocarbons across the Air−Water Interface of Southern Chesapeake Bay

The gas exchange fluxes of polycyclic aromatic hydrocarbons (PAHs) across the air−water interface of southern Chesapeake Bay were calculated using a modified two-film exchange model. Sampling covered the period January 1994−June 1995 for five sites on the southern Chesapeake Bay ranging from rural to urban and highly industrialized. Simultaneous air and water samples were collected, and the atmospheric gas phase and surface water dissolved phase analyzed via GC/MS for 17 PAHs. The instantaneous gas flux was calculated for each compound using Henry's law constants, diffusivities, and hydrological and meteorological parameters. The direction and magnitude of gas transfer were found to be controlled by water temperature and gas-phase concentrations. Fluxes were determined to vary in direction and magnitude both spatially and temporally across the air−water interface of southern Chesapeake Bay. The range of gas exchange is of the same order as atmospheric wet and dry depositional fluxes to southern Chesapeake Bay. The results of this study support the hypothesis that gas exchange is a major transport process affecting concentrations and exposure levels of PAHs in southern Chesapeake Bay.