Evaluation of the KCl Denuder Method for Gaseous Oxidized Mercury using HgBr₂ at an In-Service AMNet Site

Abstract

During the summer of 2013, we examined the performance of KCl-coated denuders for measuring gaseous oxidized mercury (GOM) by calibrating with a known source of GOM (i.e., HgBr₂) at the North Birmingham SouthEastern Aerosol Research and Characterization (SEARCH) site. We found that KCl-coated denuders have near 95% collection efficiency for HgBr₂ in zero air (i.e., air scrubbed of mercury and ozone). However, in ambient air, the efficiency of KCl-coated denuders in capturing HgBr₂ dropped to 20-54%. We also found that absolute humidity and ozone each demonstrate a significant inverse correlation with HgBr₂ recovery in ambient air. Subsequent laboratory tests with HgBr₂ and the KCl-coated denuder show that ozone and absolute humidity cause the release of gaseous elemental Hg from the denuder and thus appear to explain the low recovery in ambient air. Based on these findings, we infer that the KCl denuder method underestimates atmospheric GOM concentrations. A calibration system is needed to accurately measure GOM. The system described in this paper for HgBr₂ could be implemented with existing mercury speciation instrumentation and this would improve our knowledge of the response to one potentially important GOM compound.