Diagnostic Evalutation of Bromine Reactions on Mercury Chemistry

This model study about the influence of chemical reactants on the transport of mercury is part of an international mercury model inter-comparison (MMTF) coordinated by the EU-FP7 Research Project GMOS (Global Mercury Observation System). GMOS focuses on the improvement and validation of mercury models to assist establishing a global monitoring network and to support the implementation of the Minamata Convention. For the model inter-comparison, several global and regional Chemistry Transport Models (CTM) were used to simulate the influence of reactants on mercury oxidation. For this, gas and aqueous phase reactions of mercury with bromine were implemented into the models. As reactants, precalculated bromine concentrations were taken from the global bromine models P-TOMCAT and GEOS-CHEM. The modelled concentrations of oxidized mercury were compared to observations from GMOS measurement stations, and air craft campaigns. It was found that, even outside of polar regions, bromine plays an important role in the oxidation of mercury. Moreover, the chosen reactant influenced the vertical distribution of mercury in the atmosphere. While little difference was found for GOM concentrations at the surface level, the bromine reaction was able to explain the elevated concentration of GOM observed in the free troposphere.