Investigation of Atmospheric Mercury Concentrations and Dry Deposition Rates Using Established and Novel Methods
AuthorLyman, Seth N.
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This work presents new methods for and measurements of concentrations and dry deposition of atmospheric mercury. Chapter 2 reports on measurements of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and mercury bound to particles (PBM), mercury soil flux, and mercury in precipitation at two locations in northern Nevada, U.S.A. Concentrations of GEM were influenced by both local substrate emission and transport from regional source areas. Concentrations of GOM and PBM were within ranges reported for other rural sites, and mercury wet deposition rates were similar to other sites in the arid West. In Chapter 3, multiple methods were used simultaneously at the same sites to estimate dry deposition of atmospheric mercury. The ratio of dry to wet deposition was between 10 and 90%, and varied with season and with the methods used for dry deposition approximations. Chapter 4 reports on two years of measurements of atmospheric mercury fractions in Reno, Nevada. Concentrations of GEM and PBM were influenced by emission from local sources and meteorological conditions. Concentrations of GOM were higher during periods with higher temperature and lower dew point, confirming the findings of others that warm, dry air from the free troposphere is a source of GOM to the surface. Chapter 5 details work focused on development of a surrogate surface for estimating GOM dry deposition. Deposition of mercury to surfaces was well correlated with GOM concentrations (r2 = 0.84, p < 0.01, n = 326) and was not significantly influenced by temperature, humidity, or ozone concentrations. The surrogate surface is not able to mimic natural surface variability, but it is useful to measure the maximum potential for and spatial and temporal trends of GOM dry deposition. Chapter 6 reports on the development of a passive sampler for characterizing GOM concentrations. Uptake of Hg by the passive sampler was correlated with measured air GOM concentration (r2 = 0.89, p < 0.01, n = 22), and did not appear to be significantly affected by changes in temperature, humidity, or ozone concentration, but sampler performance did appear to be slightly dependent on wind speed. The detection limit for a 14 day sample was ~5 pg m-3.