Adsorption of SO2 on mineral dust particles influenced by atmospheric moisture. (October 2018)

• Record Type: Journal Article
• Authors: Wang, Tao; Liu, Yangyang; Deng, Yue; Fu, Hongbo; Zhang, Liwu; Chen, Jianmin
• Is Part Of: Atmospheric environment. Volume 191(2018)
• Page Start: 153
• Page End: 161
• Publication Date: 2018-10
• Subjects: Sulfur dioxide (SO2) -- Hematite particle -- Heterogeneous -- Moisture -- Relative humidity; Air -- Pollution -- Periodicals; Air -- Pollution -- Meteorological aspects -- Periodicals; 551.51
• DOI: 10.1016/j.atmosenv.2018.08.008
• Languages: English
• ISSNs: 1352-2310

Abstract

Abstract: Moisture plays a crucial role in the heterogeneous formation of sulfur compounds on mineral dust particles. The heterogeneous uptake of SO2 under various humidity conditions, however, is not well explained. In this study, heterogeneous reaction of SO2 on hematite particles are investigated using an in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The interaction of SO2 with H2 O is divided into the initial moisture absorption stage and the subsequent heterogeneous oxidation stage, indicating physical adsorption and chemical conversion of SO2, respectively. Uptake coefficients were estimated by Brunauer-Emmett-Teller (BET) surface area and geometric surface area. For unreacted (fresh) particles, the coefficients peak at 33% RH and then decline with increasing RH in both stages, implying the competition between SO2 and large amount of adsorbed H2 O besides the promoting effect of water. For hematite after in-situ exposure to SO2 (sulfated particles), the coefficients increase as a function of RH in moisture absorption stage, indicating SO2 adsorption with particle hygroscopic growth. Nevertheless, the coefficients exhibit similar variation with that for fresh particles in heterogeneous oxidation stage, highlighting the competition effect after H2 O accumulation. Generally, H2 O plays both positive and negative roles in the adsorption of SO2 . Reaction on sulfated hematite is significantly influenced by previously formed sulfate compounds with low hygroscopicity. Moreover, sulfate products may influence particle acidity after H2 O introduction, and further result in diverse existence forms of S(IV) species. The extremely great uptake capacity of sulfated particles in moisture absorption stage may offer opportunities to explain the severe haze in high RH. Graphical abstract: Image 1 Highlights: The heterogeneous reaction of SO2 on typical mineral dust under various humidity conditions is poorly understood. Water plays both positive and negative roles during the heterogeneous formation of sulfur-containing aerosols. Sulfate species formed on dry particles influence the particle acidity and SO2 adsorption after water introduction. Rapid adsorption of SO2 accompanied by particle hygroscopic growth could be used to explain the haze events in high RH.