Diffusive Exchange of Polycyclic Aromatic Hydrocarbons across the Air−Water Interface of the Patapsco River, an Urbanized Subestuary of the Chesapeake Bay

Air−water exchange fluxes of 13 polycyclic aromatic hydrocarbons (PAHs) were determined along a transect in the Patapsco River from the Inner Harbor of Baltimore, MD, to the mainstem of the northern Chesapeake Bay. Sampling took place at six sites during three sampling intensives (June 1996, February 1997, and July 1997) and at one site every ninth day between March 1997 and March 1998 to measure spatial, daily, and annual variability in the fluxes. The direction and magnitude of the daily fluxes of individual PAHs were strongly influenced by the wind speed and direction, by the air temperature, and by the highly variable PAH concentrations in the gas and dissolved phases. Individual fluxes ranged from 14 200 ng m-2 day-1 net volatilization of fluorene during high winds to 11 400 ng m-2 day-1 net absorption of phenanthrene when prevailing winds blowing from the northwest across the city of Baltimore elevated gaseous PAH concentrations over the water. The largest PAH volatilization fluxes occurred adjacent to the stormwater discharges, driven by elevated dissolved PAH concentrations in surface waters. Estimated annual volatilization fluxes ranged from 1.1 μg m-2 yr-1 for chrysene to 800 μg m-2 yr-1 for fluorene.