An Investigation of Sources and Processes Impacting Mercury Dry Deposition

Atmospheric deposition of mercury (Hg) is a major process that contributes mercury loadings to ecosystems resulting in the bioaccumulation of mercury in fish and other wildlife. Methods for measuring Hg that is wet deposited have been well studied, but there are few established methods for directly measuring dry deposition of atmospheric Hg. We developed a new method of direct Hg dry deposition measurement using an artificial turf surrogate surface (ATSS) sampler. It was found that there was a collocated precision of 9%, low blanks (0.8 ng), high extraction efficiency (97%- 103%) and a quantitative matrix spike recovery of 100%. Utilizing this method, ATSS samplers were deployed on a large-scale for the first time during measurement campaigns conducted as part of a Hg Total Maximum Daily Load (TMDL) project in Florida to investigate spatial patterns and temporal variability of wet and dry deposition of Hg as well as major ionic species and a suite of trace elements. As part of this project, wet and dry deposition of Hg and trace elements were measured concurrently at 15 monitoring sites in Florida in 2009 and 11 monitoring sites in 2010. The dry deposition of Hg measured during these month-long measurement campaigns ranged from 0.6 µg/m2 to 2.1 µg/m2. Wet deposition of Hg measured during the intensive periods ranged from 1.5 µg/m2 to 6.9 µg/m2. A north to south increasing spatial gradient was observed for wet deposition of Hg. Deposition from the trace elements and ionic species was integrated with the Hg deposition to investigate source impacts. Correlation coefficients and enrichment factors both suggested that at certain sites much Hg deposition was primarily impacted by specific sources but also indicated that more work is needed to continue grow the understanding of Hg dry deposition. This ATSS sampling method has allowed widespread and in-depth study of the dry deposition of Hg for this project in the state of Florida, enabling unique direct field measurement comparisons of wet versus dry Hg deposition contributions at a variety of site types (coastal, urban, rural) in Florida. Results demonstrate that the ratio of wet to dry deposition of mercury is highly variable spatially and temporally in Florida. Additionally, the ATSS method is widely applicable across site types as well as for various trace elements and ionic species. The method is especially advantageous in regions with frequent precipitation and for longer-term sampling.PhDEnvironmental Health SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/147579/1/hallnai_1.pd