Photoactivation of Chlorine and Its Catalytic Role in the Formation of Sulfate Aerosols
Yiqun Cao, Jiarong Liu, Qingxin Ma, Chunyan Zhang, Peng Zhang, Tianzeng Chen, Yonghong Wang, Biwu Chu, Xiuhui Zhang, Joseph S. Francisco, Hong He
Abstract
We present a novel mechanism for the formation of photocatalytic oxidants in deliquescent NaCl particles, which can greatly promote the multiphase photo-oxidation of SO 2 to produce sulfate. The photoexcitation of the [Cl – –H 3 O + –O 2 ] complex leads to the generation of Cl and OH radicals, which is the key reason for enhancing aqueous-phase oxidation and accelerating SO 2 oxidation. The mass normalization rate of sulfate production from the multiphase photoreaction of SO 2 on NaCl droplets could be estimated to be 0.80 × 10 –4 μg·h –1 at 72% RH and 1.33 × 10 –4 μg·h –1 at 81% RH, which is equivalent to the known O 3 liquid-phase oxidation mechanism. Our findings highlight the significance of multiphase photo-oxidation of SO 2 on NaCl particles as a non-negligible source of sulfate in coastal areas. Furthermore, this study underscores the importance of Cl – photochemistry in the atmosphere.