Sulfate production by reactive bromine: Implications for the global sulfur and reactive bromine budgets

Sulfur and reactive bromine (Br-y) play important roles in tropospheric chemistry and the global radiation budget. The oxidation of dissolved SO2 (S(IV)) by HOBr increases sulfate aerosol abundance and may also impact the Br-y budget, but is generally not included in global climate and chemistry models. In this study, we implement HOBr + S(IV) reactions into the GEOS-Chem global chemical transport model and evaluate the global impacts on both sulfur and Br-y budgets. Modeled HOBr mixing ratios on the order of 0.1-1.0 parts per trillion (ppt) lead to HOBr + S(IV) contributing to 8% of global sulfate production and up to 45% over some tropical ocean regions with high HOBr mixing ratios (0.6-0.9 ppt). Inclusion of HOBr + S(IV) in the model leads to a global Br-y decrease of 50%, initiated by the decrease in bromide recycling in cloud droplets. Observations of HOBr are necessary to better understand the role of HOBr + S(IV) in tropospheric sulfur and Br-y cycles.