Titanium dioxide (TiO2) is extensively used with the process of urbanization and potentially influences atmospheric chemistry, which is yet unclear. In this work, we demonstrated strong production of Cl2from illuminated KCl-coated TiO2membranes and suggested an important daytime source of chlorine radicals. We found that water and oxygen were required for the reactions to proceed, and Cl2production increased linearly with the amount of coated KCl, humidity of the carrier gas, and light intensity. These results suggested that water promotes the reactivity of coated KCl via interaction with the crystal lattice to release free chloride ions (Cl-). The free Cl-transfer charges to O2via photoactivated TiO2to form Cl2and probably the O2- radical. In addition to Cl2, ClO and HOCl were also observed via the complex reactions between Cl/Cl2and HOx. An intensive campaign was conducted in Shanghai, during which evident daytime peaks of Cl2were observed. Estimated Cl2production from TiO2photocatalysis can be up to 0.2 ppb/h when the TiO2-containing surface reaches 20% of the urban surface, and highly correlated to the observed Cl2. Our results suggest a non-negligible role of TiO2in atmospheric photochemistry via altering the radical budget.
ASJC Scopus subject areas
- Environmental Chemistry
- Water Science and Technology
- Waste Management and Disposal
- Health, Toxicology and Mutagenesis