JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-AS Atmospheric Sciences, Meteorology & Atmospheric Environment

[A-AS07] Atmospheric Chemistry

convener:Naoko Saitoh(Center for Environmental Remote Sensing), Tomoki Nakayama(Graduate School of Fisheries and Environmental Sciences, Nagasaki University), Sakae Toyoda(Department of Chemical Science and Engineering, Tokyo Institute of Technology), Risa Uchida(Japan Automobile Research Institute)

[AAS07-21] Enhanced Sulfate Production During Nitrate Photolysis in the Presence of Halide Ions in Atmospheric Particles

*Masao Gen1, Chak Chan2, Ruifeng Zhang2, DanDan Huang3, Yongjie Li4 (1.Faculty of Frontier Engineering, Institute of Science and Engineering, Kanazawa University, 2.School of Energy and Environment, City University of Hong Kong, 3.Shanghai Academy of Environmental Sciences, 4.Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau)

Keywords:Enhanced nitrate photolysis, Halide ions, Sulfate production, Heterogeneous photochemistry

Heterogeneous oxidation of SO2 is an effective production pathway of sulfate in the atmosphere. We recently reported a novel pathway for the heterogeneous oxidation of SO2 by in-particle oxidants (OH, NO2 and NO2-/HONO) produced from particulate nitrate photolysis (Environ. Sci. Technol. 2019, 53, 8757−8766). Particulate nitrate is often found to coexist with chloride and other halide ions, especially in aged sea-salt aerosols and combustion aerosols. Reactive uptake experiments of SO2 with UV-irradiated nitrate particles showed that sulfate production rates were enhanced by a factor of 1.4, 1.3 and 2.0 in the presence of Cl-, Br- and I-, respectively, compared to those in the absence of halide ions. The larger sulfate production was attributed to enhanced nitrate photolysis promoted by the increased incomplete solvation of nitrate at the air-particle interface due to the presence of surface-active halide ions. Modeling results based on the experimental data show that the nitrate photolysis rate constants increase by a factor of 2.0, 1.7, and 2.1 in the presence of Cl-, Br- and I-, respectively. The present study demonstrates that the presence of halide ions enhances sulfate production produced during particulate nitrate photolysis and provides insights into the enhanced formation of in-particle oxidants that may increase atmospheric oxidative capacity.