Mercury deposition in southern New Hampshire, 2006–2009
1Department of Earth Sciences, University of New Hampshire, Durham, New Hampshire, 03824, USA
2Department of Chemistry, State University of New York's College of Environmental Science and Forestry, Syracuse, New York, 13210, USA
3Department of Earth and Atmospheric Sciences, University of Houston, Houston, Texas, 77204, USA
Abstract. Mercury (Hg) is a global contaminant due to its toxicity and ubiquitous presence in the atmosphere. The primary source of Hg to terrestrial and aquatic ecosystems is atmospheric deposition. In an effort to understand the atmospheric cycling and depositional characteristics of Hg, event-based wet deposition samples were collected from July 2006 to September 2009 at Thompson Farm (TF), a near-coastal rural site in Durham, NH, part of the University of New Hampshire AIRMAP Observing Network. Total aqueous mercury exhibited seasonal trends in Hg wet deposition at TF. The lowest Hg wet deposition occurred in the winter with an average total seasonal deposition of 1.56 μg m−2 compared to the summer average of 4.71 μg m−2. Inter-annual differences are generally linked with precipitation volume, with the greatest deposition occurring in the wettest year. Comparisons of Hg wet deposition trends with meteorological data and ambient gas phase mixing ratios revealed weak correlations. The strongest correlation was observed between maximum hourly precipitation rate and Hg wet deposition, and the relationship was strongly driven by extreme events. Dry deposition of reactive gaseous Hg (RGM) was estimated based on continuous RGM measurements at TF from October 2006 to September 2009 using an order-of-magnitude approach. Comparisons between Hg wet deposition and RGM dry deposition suggest that the seasonal ratios of Hg wet deposition to RGM dry deposition vary by up to a factor of 80. Additional studies of seasonal differences in Hg deposition mechanisms (wet vs. dry) may provide a better understanding of the biogeochemical cycling of Hg.