Significantly surfactant-enhanced photochemical conversion of SO2 to sulfates on photosensitive substances.

The photochemical conversion of SO2 to sulfates on 4-(benzoyl) benzoic acid (4-BBA) was investigated deeply in the presence of anionic and cationic surfactants. The types of surfactants determined their effect behaviors, and cationic surfactants can significantly enhance the SO2 oxidation on 4-BBA under irradiation, as shown by larger SO2 uptake coefficients and sulfate production. Hydrophilic moieties in cationic surfactants have a greater enhancement effect on the photochemical conversion of SO2 to sulfates than the corresponding hydrophobic moieties. Cationic surfactants obviously increased the accumulation of H2O on the surface, which was proved to be the main factor influencing the SO2 uptake and the sulfate formation on 4-BBA. SO2 lifetime and sulfate formation rate in the mixture system of photosensitive substances with surfactants were evaluated to be 2.25 days and 0.09 µg/(m3·h), respectively.