Effect of bromine chemistry on the atmospheric mercury cycle

Bromine chemistry is believed to play a major role in the atmospheric oxidation of elemental mercury (Hg0) to divalent mercury (HgII). However, its effect on the speciation of atmospheric mercury (Hg) has been mostly ignored in models of the fate and transport of mercury. We investigate the effect of bromine chemistry on Hg speciation for various reaction kinetics and environmental conditions with a box model. Bromine chemistry was also added to the chemical mechanism of a global chemical transport model, and simulations of the global mercury cycle were conducted with different sets of bromine reaction kinetics. The global model simulations conducted with bromine chemistry lead to Hg0 concentrations that are consistent with observations only if the pressure dependence of the kinetics of the oxidation of Hg0 by Br is taken into account. Bromine chemistry is found to reduce the overall lifetime of Hg by about 10%.