Analysis of Mercury Wet-Deposition Data Collected With a Newly Designed Sampler, Boston, Massachusetts Metropolitan Area, 2002-04

Abstract : Atmospheric mercury wet-deposition rates were determined by the use of a newly designed wet-deposition sampler at four sites around the Boston, Mass. metropolitan area. The new sampler design was evaluated to determine reliability and capture efficiency. Capture efficiency was lowest during cold and (or) windy winter storms when accumulated ice and (or) snow either overflowed or blew out of the funnel. High capture efficiency (median values of 0.95 and 1.01) occurred with the top-loading type of N-Con sampler, likely reflecting the enhanced collection efficiency of the optical infrared precipitation sensor during light precipitation, and the improved temperature distribution in the top-loading model. Wet-deposition samples collected from January 2002 to August 2004 were analyzed for total mercury (HgT), and a subset of samples from September 2003 to August 2004 were analyzed for methyl mercury (MeHg). MeHg concentrations at all four sites were below the detection level of 0.04 nanograms per liter (ng/L). Precipitation-weighted HgT concentrations during the study were 7.81 to 8.31 ng/L at the more urban sites, and 6.87 ng/L at the regional-reference site. Annual HgT deposition was 8.11 to 9.98 micrograms per square meter per year ( g/m2/yr) at urban sites, and 6.56 g/m2/yr at the regional- reference site. Precipitation-weighted HgT concentrations were 2 times higher in the summer than the winter, and the HgT deposition rate was 3 times higher in the spring and (or) summer than in the winter in the Boston metropolitan area.