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.
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