An investigation of source-receptor relationships for atmospheric mercury in the Great Lakes region using receptor modeling techniques

The Great Lakes Atmospheric Mercury Assessment Project (GLAMAP) was begun in 1994 to obtain a region-wide assessment of the spatial and temporal trends in atmospheric mercury levels for the Great Lakes region. The GLAMAP database included two years of concurrent gas- and particle-phase mercury measurements, as well as particulate trace element concentrations, from 10 rural monitoring sites across the entire Great Lakes region.; Spatial differences in atmospheric mercury levels were observed between the GLAMAP sites. Average gas-phase mercury concentrations for the two-year study period differed by 25% across the Great Lakes region (1.63-2.03 ng/m{dollar}sp3{dollar}) and average particle-phase mercury levels differed by nearly a factor of three (8.7-24.5 pg/m{dollar}sp3{dollar}). Concentrations of both gas- and particle-phase mercury were higher on average at sites located in the eastern and southern parts of the Great Lakes region. Seasonal trends were also observed, with higher concentrations of gas-phase mercury during the spring and higher particle-phase concentrations during the winter.; Receptor modeling techniques were used to investigate the meteorological and source-related influences that contributed to these trends. Above average concentrations of gas- and particle-phase mercury were associated with specific synoptic-scale meteorological conditions. In addition, air mass transport from anthropogenic source areas within the Great Lakes region was associated with the highest levels of gas- and particle-phase mercury at the GLAMAP sites.; The impact of these anthropogenic source areas on atmospheric mercury concentrations within the region was quantified using a hybrid-receptor model that combined air mass trajectories with measured levels at the receptor sites. The model results confirmed that air mass transport from the major urban/industrial areas of the Great Lakes region, as well as the upper and lower Ohio River valley areas, contributed to above average concentrations of both gas- and particle-phase mercury within the region.; The types of sources that impacted atmospheric mercury levels in the Great Lakes region were also identified using principal component analysis applied to particulate trace element data. Emissions from mixed urban/industrial sources and coal combustion sources both had measurable impacts on atmospheric mercury levels at rural locations in the Great Lakes region.