Hygroscopicity of Hofmeister Salts and Glycine Aerosols-Salt Specific Interactions

Hamad Ashraf; Yaxin Guo; Na Wang; Shufeng Pang; Yun-Hong Zhang

doi:10.1021/acs.jpca.0c10710

Hygroscopicity of Hofmeister Salts and Glycine Aerosols-Salt Specific Interactions

J Phys Chem A. 2021 Feb 25;125(7):1589-1597. doi: 10.1021/acs.jpca.0c10710. Epub 2021 Feb 12.

Authors

Hamad Ashraf¹, Yaxin Guo¹, Na Wang¹, Shufeng Pang¹, Yun-Hong Zhang¹

Affiliation

¹ The Institute of Chemical Physics, School of Chemistry and Chemical Engineering, Beijing Institute of Technology, Beijing 100081, P R China.

PMID: 33576639
DOI: 10.1021/acs.jpca.0c10710

Abstract

The Hofmeister effect of inorganic ions to precipitate proteins has been used to understand the coagulation phenomenon in colloid and protein science. Herein, for the first time, this effect is studied on the hygroscopicity of aerosols using ATR-FTIR spectroscopy. The representative Hofmeister salts (MgSO₄, KCl, NH₄NO₃) and amino acid (glycine) with different amino acid/salt molar ratios (ASRs) are mixed and atomized into micrometer-sized particles. For mixed kosmotrope (MgSO₄)/glycine and chaotrope (NH₄NO₃)/glycine with an ASR of 1:1, both ERHs (efflorescence relative humidities) and DRHs (deliquescence relative humidities) are absent. However, for the mixtures of glycine and neutral salt (KCl), no DRH is observed while 66.2 and 61.4% ERH of glycine is detected for mixtures with ASRs of 1:1 and 1:3, respectively, which is similar to pure glycine. For the mixture of NH₄NO₃/glycine with an ASR of 1:3, ERH and DRH are found to be 15.4 and 32.2% RH, less than that of pure NH₄NO₃. Further, interactions between glycine-salt and/or water is also studied in the mixtures during hydration and dehydration. Water-mediated ion-glycine interaction is detected based on the two glycine bands merging into one band. Glycine-SO₄^2- interaction is present for glycine/sulfate in all ASRs, while glycine-NO₃^- interaction is only seen for 1:3 glycine/NH₄NO₃ mixtures during hydration. This work opens a window to understand the Hofmeister effect on the hygroscopicity of atmospheric aerosols.