A chemical kinetic mechanism for atmospheric inorganic mercury.

A chemical kinetic mechanism for the atmospheric chemistry of inorganic 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 Cl2 in a nocturnal marine layer and for reactions with oxidants such as H202 in the ambient atmosphere. However, large uncertainties exist in the gasphase reaction rates of Hg(0) with Cl2, 03, and H202, and the overall half-life of Hg(0) due to chemical reactions in the atmosphere cannot be assessed with certainty without further laboratory kinetic data. In the presence of an atmospheric liquid phase, oxidation and reduction reactions lead toward an equilibrium between Hg(0) and Hg(I1). This equilibrium is a strong function of pH, liquid water content, and concentrations of SO2 and HC1. Under most simulation conditions, Hg(0) concentrations exceed Hg(I1) concentrations by at least 1 order of magnitude, which is consistent with observations.