Development of Surrogate Surfaces for Assessing Dry Deposition of Atmospheric Hg

Seth Lyman, Mae Gustin
University of Nevada, Reno, Department of Natural Resources and Environmental Science
Reno, Nevada 89557

Eric Prestbo
Tekran Instrument Corporation, 330 Nantucket Blvd., Toronto, ON M1P2P4

Phil Kilner
Frontier Geosciences, 414 Pontius Avenue North, Seattle, Washington 98109

Dry deposition is thought to be an important pathway for input of mercury to aquatic and terrestrial environments, but methods to measure mercury dry deposition flux are not well established. Polysulfone cation-exchange membranes are being developed as surrogate surfaces to estimate dry deposition of reactive gaseous mercury (RGM). In a preliminary study, accumulation of mercury on membranes was well correlated with air RGM concentrations (r = 0.93, p <0.001) and with modeled RGM deposition (r = 0.97, p <0.001), though deposition to membranes was about five times greater than modeled RGM deposition. Field experiments are being done in Reno, Nevada, USA to characterize uptake rates of ambient RGM under differing environmental conditions. Laboratory experiments are being done to characterize gaseous elemental mercury and RGM uptake by the membranes as a function of atmospheric concentrations as well as different temperature, humidity, light and atmospheric chemistry exposures. These will help us establish uptake rates as a function of exposure concentrations that can then be compared to field data and modeled deposition values. We have also begun deployment of the membranes at other field sites where air speciation and a variety of other environmental parameters are being measured in the United States. These data will allow us to assess membrane behavior in different environmental conditions. Additionally, optimal handling and deployment procedures are being developed, and the cation-exchange membranes are being compared against other surfaces for efficiency of RGM uptake.