Dry deposition of gaseous oxidized mercury in Western Maryland

Abstract

The purpose of this study was to directly measure the dry deposition of gaseous oxidized mercury (GOM) in western Maryland. Annual estimates were made using passive ion-exchange surrogate surfaces and a resistance model. Surrogate surfaces were deployed for seventeen weekly sampling periods between September 2009 and October 2010. Dry deposition rates from surrogate surfaces ranged from 80 to 1512pgm−2h−1. GOM dry deposition rates were strongly correlated (r2=0.75) with the weekly average atmospheric GOM concentrations, which ranged from 2.3 to 34.1pgm−3. Dry deposition of GOM could be predicted from the ambient air concentrations of GOM using this equation: GOM dry deposition (pgm−2h−1)=43.2×GOM concentration−80.3. Dry deposition velocities computed using GOM concentrations and surrogate surface GOM dry deposition rates, ranged from 0.2 to 1.7cms−1. Modeled dry deposition rates were highly correlated (r2=0.80) with surrogate surface dry deposition rates. Using the overall weekly average surrogate surface dry deposition rate (369±340pgm−2h−1), we estimated an annual GOM dry deposition rate of 3.2μgm−2year−1. Using the resistance model, we estimated an annual GOM dry deposition rate of 3.5μgm−2year−1. Our annual GOM dry deposition rates were similar to the dry deposition (3.3μgm−2h−1) of gaseous elemental mercury (GEM) at our site. In addition, annual GOM dry deposition was approximately 1/2 of the average annual wet deposition of total mercury (7.7±1.9μgm−2year−1) at our site. Total annual mercury deposition from dry deposition of GOM and GEM and wet deposition was approximately 14.4μgm−2year−1, which was similar to the average annual litterfall deposition (15±2.1μgm−2year−1) of mercury, which was also measured at our site.