Influence of relative humidity on SO2 oxidation by O3 and NO2 on the surface of TiO2 particles: Potential for formation of secondary sulfate aerosol

Xiang He; Yun-Hong Zhang

doi:10.1016/j.saa.2019.04.046

Influence of relative humidity on SO₂ oxidation by O₃ and NO₂ on the surface of TiO₂ particles: Potential for formation of secondary sulfate aerosol

Spectrochim Acta A Mol Biomol Spectrosc. 2019 Aug 5:219:121-128. doi: 10.1016/j.saa.2019.04.046. Epub 2019 Apr 18.

Authors

Xiang He¹, Yun-Hong Zhang²

Affiliations

¹ College of Resource and Environment Sciences, Xinjiang University, Urumqi 830046, PR China; Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, PR China.
² Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, PR China. Electronic address: yhz@bit.edu.cn.

PMID: 31030039
DOI: 10.1016/j.saa.2019.04.046

Abstract

The heterogeneous reactions of SO₂/O₃ and SO₂/NO₂ with TiO₂ particles were studied as a function of relative humidities (RHs). An in situ microscopic Fourier transform infrared (micro-FTIR) spectrometer was used to monitor the reaction kinetics. Rapid conversion of SO₂ to sulfate occurs on the surface of TiO₂ particles in the presence of O₃ or NO₂, which is sensitive to RHs. For unreacted (fresh) particles, the uptake coefficients for SO₂ in initial stage are both obviously enhanced over four times with the increasing RH from ~4% to ~85%. Moreover, the uptake coefficient in the system of SO₂/O₃ is about 40% higher than that of SO₂/NO₂ on TiO₂ particles at the similar RH conditions. For TiO₂ after exposure to SO₂/O₃ or SO₂/NO₂ (sulfated) particles, the uptake coefficients for SO₂ in moisture absorption stage are all higher than that on fresh particles in initial stage at the similar RH, indicating rapid mixture gases adsorption with particle hygroscopic growth. The high production of the secondary sulfate for heterogeneous reaction of mixture gases on TiO₂ surface from arid region to humid region provides new insights for better understanding the severe haze under the humid condition.

Keywords: Micro-FTIR; Reaction kinetic; Relative humidity; Secondary sulfate aerosol.