INCREASED ATMOSPHERIC MERCURY DEPOSITION NEAR MAJOR URBAN AREAS

Modeling of atmospheric deposition of Hg is generally in agreement with monitored wet deposition at the regional scale in North America, but, unlike monitoring, indicates large increases in deposition near major urban areas. Here we present lake-sediment core reconstructions of Hg deposition for remote and near-urban reference lakes confirming these large increases in atmospheric Hg deposition as one approaches major urban areas. Sediment cores from remote lakes from Alaska to Oregon to Maine indicate modern anthropogenic Hg deposition rates of about 5-15 mg/m² yr, similar to monitored wet deposition rates. Anthropogenic Hg deposition rates to reference lakes near New Haven, Conn., and Boston, Mass., in contrast, are about 60 and 80 mg/m² yr, respectively. Deposition to lakes near Chicago, Ill., and Atlanta, Ga., at 40-60 mg/m² yr, also is elevated compared to regional background. Modeling and comparison of core deposition rates to monitored wet deposition suggests greater dry deposition of Hg might be responsible for much of the near-urban fallout signal. Emissions of Hg(II) and particulate Hg and the formation of Hg(II) from oxidation of Hg(0) in the urban atmosphere could be important factors in the increased deposition.