Photocatalytic Oxidation of SO by TiO: Aerosol Formation and the Key Role of Gaseous Reactive Oxygen Species.

Photocatalytic materials are proved to effectively eliminate gaseous pollutants and are widely used in the environment. However, as one of the rare experiments focusing on their influence on secondary aerosol formation generated in the gas phase (SA), our study demonstrated the high-yield SA formation in the photocatalysis process. In this study, the photodegradation of SO by TiO under various relative humidity (RH) conditions was deeply explored with multiple methods. Unexpectedly, HSO aerosols (SA) in yields of 10.10-32.64% were observed under the studied RH conditions for the first time. Gaseous OH and HO generated from the oxidation of HO and reduction of O by TiO were directly detected in the photocatalysis process, and they were identified as the determining factor for SA formation. The formation of SA was also influenced by RH, the heterogeneous reaction of SO, and the uptake of HSO. The role of the released gaseous OH and HO on atmospheric chemistry was proved to be unignorable by adopting the obtained parameters into the real environment. These findings provided direct experimental evidence of secondary pollution in the photocatalysis process and are of great significance to the field of atmospheric environment and photocatalytic materials.