Critical Role of Iodous Acid in Neutral Iodine Oxoacid Nucleation

Rongjie Zhang; Hong-Bin Xie; Fangfang Ma; Jingwen Chen; Siddharth Iyer; Mario Simon; Martin Heinritzi; Jiali Shen; Yee Jun Tham; Theo Kurtén; Douglas R Worsnop; Jasper Kirkby; Joachim Curtius; Mikko Sipilä; Markku Kulmala; Xu-Cheng He

doi:10.1021/acs.est.2c04328

Critical Role of Iodous Acid in Neutral Iodine Oxoacid Nucleation

Environ Sci Technol. 2022 Oct 4;56(19):14166-14177. doi: 10.1021/acs.est.2c04328. Epub 2022 Sep 20.

Authors

Rongjie Zhang¹, Hong-Bin Xie¹, Fangfang Ma¹, Jingwen Chen¹, Siddharth Iyer², Mario Simon³, Martin Heinritzi³, Jiali Shen⁴, Yee Jun Tham⁵, Theo Kurtén⁶, Douglas R Worsnop^{4

7}, Jasper Kirkby^{3

8}, Joachim Curtius³, Mikko Sipilä⁴, Markku Kulmala^{4

9

10}, Xu-Cheng He^{4

11}

Affiliations

¹ Key Laboratory of Industrial Ecology and Environmental Engineering (Ministry of Education), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
² Aerosol Physics Laboratory, Faculty of Engineering and Natural Sciences, Tampere University, Tampere 33014, Finland.
³ Institute for Atmospheric and Environmental Sciences, Goethe University Frankfurt, Frankfurt am Main 60438, Germany.
⁴ Institute for Atmospheric and Earth System Research/Physics, Faculty of Science, University of Helsinki, Helsinki 00014, Finland.
⁵ School of Marine Sciences, Sun Yat-sen University, Zhuhai 519082, China.
⁶ Department of Chemistry, University of Helsinki, Helsinki 00014, Finland.
⁷ Aerodyne Research, Inc., Billerica, Massachusetts 01821, United States.
⁸ CERN, the European Organization for Nuclear Research, CH-1211 Geneva 23, Switzerland.
⁹ Joint International Research Laboratory of Atmospheric and Earth System Sciences, School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China.
¹⁰ Aerosol and Haze Laboratory, Beijing Advanced Innovation Center for Soft Matter Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China.
¹¹ Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States.

Abstract

Nucleation of neutral iodine particles has recently been found to involve both iodic acid (HIO₃) and iodous acid (HIO₂). However, the precise role of HIO₂ in iodine oxoacid nucleation remains unclear. Herein, we probe such a role by investigating the cluster formation mechanisms and kinetics of (HIO₃)_m(HIO₂)_n (m = 0-4, n = 0-4) clusters with quantum chemical calculations and atmospheric cluster dynamics modeling. When compared with HIO₃, we find that HIO₂ binds more strongly with HIO₃ and also more strongly with HIO₂. After accounting for ambient vapor concentrations, the fastest nucleation rate is predicted for mixed HIO₃-HIO₂ clusters rather than for pure HIO₃ or HIO₂ ones. Our calculations reveal that the strong binding results from HIO₂ exhibiting a base behavior (accepting a proton from HIO₃) and forming stronger halogen bonds. Moreover, the binding energies of (HIO₃)_m(HIO₂)_n clusters show a far more tolerant choice of growth paths when compared with the strict stoichiometry required for sulfuric acid-base nucleation. Our predicted cluster formation rates and dimer concentrations are acceptably consistent with those measured by the Cosmic Leaving Outdoor Droplets (CLOUD) experiment. This study suggests that HIO₂ could facilitate the nucleation of other acids beyond HIO₃ in regions where base vapors such as ammonia or amines are scarce.

Keywords: atmospheric cluster dynamics simulation; iodic acid; iodine oxoacid nucleation; iodous acid; particle formation; quantum chemical calculation.