Photobromination of phenol takes place upon UV/Vis irradiation of FeIII and bromide under acidic conditions, and most likely involves the brominating agent Br2(-*). Bromination is also observed in the presence of nitrate and bromide under UV irradiation, most likely involving Br2(-*) formed upon oxidation of bromide by *OH. Moreover, quantitative bromination of phenol is observed in the dark in the presence of hydrogen peroxide and bromide. This process is strongly favored under acidic conditions, but a residual, pH-independent bromination pathway is also present. The rates and yields of bromination (up to 100%) are considerably higher than those reported for chlorination under comparable conditions, suggesting that the higher activity of bromine species could compensate for the lower concentration of bromide ions in aerosol compared to chlorides. The reported processes are potent tial sources of reactive bromine species (Br2(-*), HBrO) and aromatic bromo derivatives in atmospheric aerosols, in particular after the acidification process linked with aerosol aging.