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Development of Surrogate Surfaces for Measurement of Mercury Dry Deposition

Seth Lyman
University of Nevada,
Department of Natural Resources and Environmental Science,
Reno, NV USA

Dry deposition of atmospheric mercury is thought to be an important pathway for input of mercury to aquatic and terrestrial environments. However, methods to measure mercury dry deposition flux are not well established. For the past three years, we have focused on development and characterization of a surrogate surface method for estimation of dry deposition of reactive gaseous mercury (RGM). The resulting method consists of a surface that is deployed facing down while mounted in an aerodynamic holder. The samplers are easy to deploy and inexpensive when compared with automated instrumentation. Minimum deployment time depends on RGM concentrations and may be as low at 12 hours. A polysulfone cation-exchange membrane is used as the surrogate surface. Accumulation of mercury on the surface is 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 surrogate surfaces is about three times greater than modeled RGM deposition to a desert ecosystem. The deposition velocity of RGM to the surrogate surface is 1.5 0.4 cm s-1 (mean standard deviation), similar to modeled deposition velocity in the absence of surface resistance (1.2 0.3 cm s-1). Performance of the surfaces has been evaluated extensively in a number of locations, including Nevada, Florida, Georgia, and Michigan. Additionally, performance of the surfaces has been examined under controlled conditions in a laboratory chamber. Environmental parameters that have been manipulated in the chamber to test surface response include temperature, humidity, ozone concentration, RGM concentration, and gaseous elemental mercury concentration.