Atmospheric Deposition of Trace Metals in the San Francisco Bay Area

A pilot Study was conducted from August 1999 through August 2000 to estimate the loading of selected pollutants from the atmosphere to the San Francisco Estuary. Particulate in the ambient air and precipitation samples were collected at three locations. Dry deposition flux of copper, nickel, cadmium, and chromium was approximately 1100?73, 600?35, 22?15, and 1300?90 μg/m/year, respectively. The volume-weighted average concentrations of these trace metals in the precipitation were 1.2, 0.4, 0.1, and 0.2 μg/L, respectively. Direct atmospheric deposition, via both dry deposition and wet deposition, contributed approximately 1900, 930, 93, and 1600 kg/year of copper, nickel, cadmium, and chromium, respectively, to the Estuary. Indirect inputs via runoff from the local watersheds contributed approximately twice as much as the loading from direct atmospheric deposition. Direct atmospheric deposition contributes less than 10% of the total loading from stormwater runoff, and, therefore, represents a minor contributor to the total load.