Atmospheric exchange of PAHs, PCBs, and ammonia with the Chesapeake Bay

This study combines long term measurements of precipitation, gas and aerosols at urban and rural settings in the mid-Atlantic to provide a holistic analysis of the impact from direct transmission of semi-volatile compounds between the atmosphere and the Chesapeake Bay. Three groups of semi-volatile compounds were investigated, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and ammonia. Elevated levels of these contaminants contribute to impairing the Chesapeake Bay water quality.; The geometric mean concentrations (and geometric standard deviation) of the total gas phase PAHs (sum of 32 PAHs) were 41 (1.9), 29 (2), and 5.6 (2.2) ng m−3 at Baltimore, Solomons, and Stillpond, respectively. The geometric mean concentrations (and geometric standard deviation) of the Σ32 particle bound PAHs at Baltimore, Solomons, and Stillpond were 3.2 (1.9), 0.51 (2.1), and 0.74 (1.5) ng m−3, respectively. The geometric mean (and geometric standard deviation) at Baltimore and Stillpond for total PCB concentrations were 435 (2) and 95 (2) pg m−3 in the gas phase, respectively. Mean and arithmetic standard deviations of atmospheric total ammonia concentrations at Baltimore and Solomons were 2.7 ± 1.7 and 1.0 ± 0.8 μg N m−3, respectively.; Results of three source apportionment models suggested that sources of atmospheric PAHs in Baltimore were vehicles (17 to 22%), coal (26 to 32%), oil (18 to 22%), and wood/other sources (17 to 40%).; The net direct fluxes of these compounds to the Chesapeake Bay were calculated from these measurements. The primary mechanism for the transfer of most of these chemicals across the air-water interface was gas exchange. The degraded air and water quality of Baltimore with respect to these compounds resulted in significant fluxes both into and out of the water. For example, fluxes in Baltimore were ±1000 μg N m−2 d−1 for ammonia, 114 μg m−2 y−1 for the ΣPCB, and 780, μg m−2 y −1 for fluorene. The magnitude of the net air-water exchange in Baltimore Harbor was greater than in the Chesapeake mainstem. However, when the exchange is normalized to the water column contaminant inventory, it appears that the northern Chesapeake Bay is impacted to a greater degree by direct air-water fluxes.