The influence of ozone on atmospheric emissions of gaseous elemental mercury and reactive gaseous mercury from substrates

Experiments were performed to investigate the effect of ozone (03) on mercury (Hg) emission from a variety of Hg-bearing substrates. Substrates with Hg(II) as the dominant Hg phase exhibited a 1.7 to 51-fold increase in elemental Hg (Hg-o) flux and a 1.3 to 8.6-fold increase in reactive gaseous mercury (RGM) flux in the presence of O-3-enriched clean (50 ppb O-3; 8 substrates) and ambient air (up to similar to 70 ppb 03; 6 substrates), relative to clean air (oxidant and Hg free air). In contrast, Hg-o fluxes from two artificially Hg-o-amended substrates decreased by more than 75% during exposure to O-3-enriched clean air relative to clean air. Reactive gaseous mercury emissions from Hgo-amended substrates increased immediately after exposure to O-3 but then decreased rapidly. These experimental results demonstrate that O-3 is very important in controlling Hg emissions from substrates. The chemical mechanisms that produced these trends are not known but potentially involve heterogenous reactions between O-3, the substrate, and Hg. Our experiments suggest they are not homogenous gas-phase reactions. Comparison of the influence of O-3 versus light on increasing Hgo emissions from dry Hg(II)-bearing substrates demonstrated that they have a similar amount of influence although O-3 appeared to be slightly more dominant. Experiments using water-saturated substrates showed that the presence of high-substrate moisture content minimizes reactions between atmospheric O-3 and substrate-bound Hg. Using conservative calculations developed in this paper, we conclude that because O-3 concentrations have roughly doubled in the last 100 years, this could have increased Hgo emissions from terrestrial substrates by 65-72%. (c) 2005 Elsevier Ltd. All rights reserved.