Ambient levels and dry deposition fluxes of mercury to Lakes Huron,Erie and St. Clair

Ambient concentrations and dry deposition fluxes of Hg in the gas and particle phase to Lakes St. Clair, Erie and Huron were estimated with a hybrid receptor-deposition model (HRD). The ambient gas and particulate phase Hg concentrations were predicted to vary by a factor of 12 to 18 during the transport of air masses traversing the lakes. The ensemble average deposition fluxes of fine particle Hg ranged from 7 pg/m²-h to 15.3 pg/m²-h over Lake St. Clair, 0.5 to 4.2 pg/m²-h over Lake Huron and 5.1 to 20.6 pg/m²-h over Lake Erie. The deposition flux of coarse particle Hg was in the range of 50 to 84 pg/m²-h over Lake St. Clair, 4.7 to 24.2 pg/m²-h over Lake Huron and 5.1 to 20.6 pg/m²-h over Lake Erie. Gaseous Hg volatilized at a rate of 0.21 to 0.52 ng/m²-h from Lake Huron and 0.13 to 0.36 from Lake Erie. Gas phase Hg was deposited at a rate of 5.9 ng/m²-h and/or volatilized at a rate of 0.5 ng/m²-h from Lake St. Clair depending upon the location of the sampling site used in the HRD model. The effect of meteorological conditions, particle size distributions and type and location of the sampling sites played an important role in the transfer of atmospheric Hg to and/or from the lakes.