Release of mercury halides from KCl denuders in the presence of ozone

KCl-coated denuders have become a standard method for measurement of gaseous oxidized mercury, but their performance has not been exhaustively evaluated, especially in field conditions. In this study, KCl-coated and uncoated quartz denuders loaded with HgCl2 and HgBr2 lost 29-55% of these compounds, apparently as elemental mercury, when exposed to ozone (range of 6-100 ppb tested). This effect was also observed for denuders loaded with gaseous oxidized mercury at a field site in Nevada (3-37% of oxidized mercury lost). In addition, collection efficiency decreased by 12-30% for denuders exposed to 50 ppb ozone during collection of HgCl2. While data presented were obtained from laboratory tests and as such do not exactly simulate field sampling conditions, these results indicate that the KCl denuder oxidized mercury collection method may not be as robust as previously thought. This work highlights needs for further testing of this method, clear identification of gaseous oxidized mercury compounds in the atmosphere, and development of field calibration methods for these compounds.