Hydroperoxyl radical (HO 2 • ) oxidizes dibromide radical anion ( • Br 2 − ) to bromine (Br 2 ) in aqueous solution: Implications for the formation of Br 2 in the marine boundary layer

The release of photoactive halogen species such as Br 2 from sea‐salt particles, snowpack, and sea‐ice can have significant effects on chemistry in the marine boundary layer (MBL). Although the reaction of hydroperoxyl radical (HO 2 • ) with dibromide radical anion ( • Br 2 − ) might be a key step in the formation and release of Br 2 , there is currently no consensus on whether this reaction produces bromide (Br − ) or molecular bromine (Br 2 ). To address this question, we measured the formation of gaseous and aqueous oxidized bromide (primarily Br 2 ) in illuminated bromide solutions as a function of pH. Results from these two sets of experimental data are best explained by kinetic models where HO 2 • oxidizes • Br 2 − to Br 2 . Using this reaction in a simple aerosol model reveals that the hydroxyl radical‐induced oxidation of particulate bromide, followed by reaction of • Br 2 − with HO 2 • , could be an important source of Br 2 in the MBL.