| Abstract
| - Dissolved and gas-phase concentrations of nine polycyclicaromatic hydrocarbons and 46 polychlorinated biphenylcongeners were measured at eight sites on the ChesapeakeBay at four different times of the year to estimate netdiffusive air−water gas exchange rates. GaseousPAHsare absorbed into the bay's surface waters during thespring, and lighter compounds revolatilize in the latesummerand early fall due to seasonal changes in surface watertemperature and atmospheric PAH levels. On an annualbasis, the atmosphere is a net source of volatile PAHsto the Chesapeake Bay, and gas absorption may be thelargest external source of fluorene and phenanthrene,providing up to three times the combined loadings fromwet and dry aerosol deposition and from tributaries.LargestPAH absorptive fluxes occurred in the northern Chesapeakewhen prevailing winds carried PAH-enriched air from theBaltimore-Washington urban area over the bay. Incontrast to PAHs, PCBs volatilize from the Chesapeake Baythroughout the year, with the largest fluxes occurringin September and the smallest fluxes in June.However,higher chlorinated (−) homologuesare absorbed bybay waters during most of the year. Highest PCBvolatilizationrates were observed in the northern Chesapeake Bayand near the James River in the southern bay, indicatingvolatilization offsets PCB loading from the bay'stributaries.Volatilization is the dominant removal process for PCBsfromthe Chesapeake Bay, removing an estimated 400 kg/year. This value is larger than current external PCBloadings,suggesting that release of PCBs from historicallycontaminated sediments supports volatilization from thebay.
|
