A comprehensive Eulerian modeling framework for airborne mercury species: Development and testing of the Tropospheric Chemistry module (TCM)

A comprehensive mercury model system using the Eulerian reference frame of the Acid Deposition and Oxidant Model (ADOM) is being developed to study the regional transport of atmospheric mercury species. A stand-alone version of the ADOM cloud mixing, scavenging, chemistry and wet deposition model components referred to as the Tropospheric Chemistry Module (TCM) is used to investigate the sensitivity of various chemical and meteorological parameters, assumed to be important for mercury deposition phenomena. The TCM chemistry scheme was developed by systematic simplification of the detailed Chemistry of Atmospheric Mercury (CAM) process model, which is based on the current knowledge of physico-chemical forms and transformation reactions of atmospheric mercury species. The first part of the paper describes the general approach to the TCM formulation. The second part presents sensitivity studies of the TCM behavior under different environmental conditions and a comparison of TCM results with observed concentrations of total mercury concentrations in precipitation (Hg(tot)). The results indicate that the TCM has capabilities to examine the relative importance and sensitivity of numerous mercury processes in the troposphere and to reproduce observed Hg(tot) concentrations reasonably well justifying its ultimate use in the full ADOM model.