Investigating the hygroscopicities of calcium and magnesium salt particles aged with SO2 using surface plasmon resonance microscopy

Bo Yang; Zhibo Xie; Jianguo Liu; Huaqiao Gui; Jiaoshi Zhang; Xiuli Wei; Jie Wang; Zetao Fan; Douguo Zhang

doi:10.1016/j.scitotenv.2023.161588

Investigating the hygroscopicities of calcium and magnesium salt particles aged with SO₂ using surface plasmon resonance microscopy

Sci Total Environ. 2023 Apr 1:867:161588. doi: 10.1016/j.scitotenv.2023.161588. Epub 2023 Jan 13.

Authors

Bo Yang¹, Zhibo Xie², Jianguo Liu³, Huaqiao Gui⁴, Jiaoshi Zhang⁵, Xiuli Wei⁵, Jie Wang⁵, Zetao Fan⁶, Douguo Zhang⁶

Affiliations

¹ Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China; University of Science and Technology of China, Hefei 230026, China.
² Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China. Electronic address: zbxie@aiofm.ac.cn.
³ Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China; University of Science and Technology of China, Hefei 230026, China; CAS Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China. Electronic address: jgliu@aiofm.ac.cn.
⁴ Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China; CAS Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
⁵ Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei 230031, China.
⁶ Advanced Laser Technology Laboratory of Anhui Province, Department of Optics and Optical Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China.

PMID: 36642280
DOI: 10.1016/j.scitotenv.2023.161588

Abstract

The hygroscopicities of calcium and magnesium salts strongly affect the environment and climate, but the aging products of these salts at high relative humidities (RHs) are still poorly understood. In this study, surface plasmon resonance microscopy (SPRM) was used to determine the hygroscopic growth factors (GFs) of Ca(NO₃)₂ and Mg(NO₃)₂ separately or mixed with galactose at different mass ratios at different RHs before and after aging. For all particles, the measured GFs showed no indication of deliquescence across the range of RHs tested, and overall hygroscopicity was clearly lower after than before aging. The Ca(NO₃)₂ and Mg(NO₃)₂ GFs at 90 % RH were 1.80 and 1.66, respectively, before aging and 1.33 and 1.42, respectively, after 4 h aging, meaning aging decreased the GFs by 26.11 % and 14.46 %, respectively. Aging decreased the hygroscopicity because insoluble or sparingly soluble substances (CaSO₃, CaSO₄, MgSO₃) formed and strongly changed the overall hygroscopicity. For bicomponent aerosols with different mass ratios, the GFs (calculated using the Zdanovskii-Stokes-Robinson method) of the other components except galactose at 90 % RH after 1 h aging were all lower, respectively, than the measured GFs of pure Ca(NO₃)₂ and Mg(NO₃)₂ after aging for 1 h, especially with the mass ratio of 1:2, their GFs have decreased by 14.63 % and 7.50 %, respectively. Subsequently, Ion chromatograms indicated that the peak area ratio of SO₄^2- to NO₃^- ratios were higher for the aged bicomponent particles than aged single-component particles, possibly because adding galactose improved the gas-liquid state stability during drying after the aging process and therefore promoted nitrate consumption and sulfate formation. The results indicated that organic components may play important roles in heterogeneous reactions between trace gases and multicomponent aerosols and should be considered in evaluating the impacts on submicron aerosol composition of high atmospheric SO₂ concentrations at high humidities.

Keywords: Aging; Calcium and magnesium salts; Hygroscopic growth; Surface plasmon resonance; Ultrafine particle.