Importance of Gaseous Elemental Mercury Fluxes in Western Maryland

The purpose of this study was to increase our understanding of the gaseous elemental mercury (GEM, Hg◦) fluxes between the atmosphere and soils. Moreover, we wanted to quantify the annual GEM flux, identify the controls, and compare the GEM flux to annual rates of gaseous oxidized mercury (GOM) dry deposition and wet deposition of total mercury. We measured GEM fluxes using the modified Bowen ratio (MBR) technique from 6 July 2009 to 6 July 2010 in western Maryland. The annual hourly mean (±std. dev.) GEM flux was −0.63 ± 31.0 ng·m−2·h−1. Hourly mean GEM fluxes were not strongly correlated with atmospheric trace gases, aerosols, or meteorology. However, hourly mean GEM emissions (15.3 ± 27.9 ng·m−2·h−1) and deposition (−14.6 ± 26.6 ng·m−2·h−1) were correlated with ultraviolet-B radiation (UV-B), wind speed (WS), ozone (O3), and relative humidity (RH). The annual net GEM flux was−3.33 μg·m−2·year−1 and was similar to the annual dry deposition rate of GOM (2.5 to 3.2 μg·m−2·year−1), and 40% less than the annual mean wet deposition (8 μg·m−2·year−1) of total mercury. Thus, dry deposition of GEM accounted for approximately 25% of the total annual mercury deposition (~14 ug·m−2·year−1) measured at our study site.