A CHEMICAL KINETIC MECHANISM FOR ATMOSPHERIC INORGANIC MERCURY

A chemical kinetic mechanism for the atmospheric chemistry of inorgani c mercury has been developed. Computer simulations conducted with this mechanism suggest that the half-life of elemental mercury could be of the order of hours for reaction with Cl-2 in a nocturnal marine layer and for reactions with oxidants such as H2O2 in the ambient atmospher e. However, large uncertainties exist in the gasphase reaction rates o f Hg(0) with Cl-2, O3, and H2O2, and the overall half-life of Hg(0) du e to chemical reactions in the atmosphere cannot be assessed with cert ainty without further laboratory kinetic data. In the presence of an a tmospheric liquid phase, oxidation and reduction reactions lead toward an equilibrium between Hg(0) and Hg(II). This equilibrium is a strong function of pH, liquid water content, and concentrations of SO2 and H Cl. Under most simulation conditions, Hg(0) concentrations exceed Hg(I I) concentrations by at least 1 order of magnitude, which is consisten t with observations.