A study was conducted to measure atmospheric concentrations of PAHs and PCBs and estimate their fluxes between air and water in the northern San Francisco Estuary. Ambient air samples were collected once every 12 days at a single sampling site in Concord, CA, from June to November 2000, using a modified high-volume air-sampling device equipped with glass fiber filters and polyurethane foam. Concentrations of total PAHs and PCBs ranged from 5.7 to 56 and 0.17 to 0.32 ng/m{sup}3, respectively. PAHs and PCBs in the ambient air were predominantly in the vapor phase (83-99). Gaseous fluxes of PAHs in the estuary showed high seasonal variation, ranging from 110 ng·m{sup}(-2)·day{sup}(-1) efflux in August to 1050 ng·m{sup}(-2)·day{sup}(-1) influx in November. Gaseous PCBs showed consistent net volatilization (2.2-24 ng·m{sup}(-2)·day{sup}(-1)) for this period. Particle settling contributed estimated net deposition fluxes of 45-960 ng·m{sup}(-2)·day{sup}(-1) for PAHs and 0.39-2.1 ng·m{sup}(-2)·day{sup}(-1) for PCBs. Combining these fluxes, PAHs were either deposited to or lost from the estuary via the atmosphere, depending on the month. In contrast, there consistently was net emission of PCBs from the estuary to the atmosphere.
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