Spontaneous Molecular Bromine Production in Sea-Salt Aerosols.

Bromine chemistry is responsible for the catalytic ozone destruction in the atmosphere. The heterogeneous reactions of sea-salt aerosols are the main abiotic sources of reactive bromine in the atmosphere. Here, we present a novel mechanism for the activation of bromide ions (Br - ) by O 2 and H 2 O in the absence of additional oxidants. The laboratory and theoretical calculation results demonstrated that under dark conditions, Br - , O 2 and H 3 O + could spontaneously generate Br and HO 2 radicals through a proton-electron transfer process at the air-water interface and in the liquid phase. Our results also showed that light and acidity could significantly promote the activation of Br - and the production of Br 2 . The estimated gaseous Br 2 production rate was up to 1.55×10 10  molecules cm -2  ⋅ s -1 under light and acidic conditions; these results showed a significant contribution to the atmospheric reactive bromine budget. The reactive oxygen species (ROS) generated during Br - activation could promote the multiphase oxidation of SO 2 to produce sulfuric acid, while the increase in acidity had a positive feedback effect on Br - activation. Our findings highlight the crucial role of the proton-electron transfer process in Br 2 production; here, H 3 O + facilitates the activation of Br - by O 2 , serves as a significant source of atmospheric reactive bromine and exerts a profound impact on the atmospheric oxidation capacity.