Molecular-level study on the role of methanesulfonic acid in iodine oxoacids nucleation

• Main Authors: Li, Jing, Wu, Nan, Ning, An, Zhang, Xiuhui
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2023
• Subjects: article; Verlagsveröffentlichung; Marambio; Ny-Ålesund; Ny Ålesund
• Online Access: https://doi.org/10.5194/egusphere-2023-2084; https://noa.gwlb.de/receive/cop_mods_00069252; https://noa.gwlb.de/servlets/MCRFileNodeServlet/cop_derivate_00067642/egusphere-2023-2084.pdf; https://egusphere.copernicus.org/preprints/2023/egusphere-2023-2084/egusphere-2023-2084.pdf

Iodic acid (HIO3) and iodous acid (HIO2) have been identified to nucleate effectively by the Cosmics Leaving OUtdoor Droplets (CLOUD) experiment at CERN (He et al., 2021, Science), yet it may be hard to explain all HIO3-induced nucleation. Given the complexity of marine atmosphere, other precursors may be involved. Methanesulfonic acid (MSA), as a widespread precursor over oceans, has been proven to play a vital role in facilitating nucleation. However, its kinetic impacts on synergistic nucleation of iodine oxoacids remain unclear. Hence, we investigated the MSA-involved HIO3-HIO2 nucleation process at the molecular level using density functional theory (DFT) and Atmospheric Clusters Dynamic Code (ACDC). The results show that MSA can form stable molecular clusters with HIO3 and HIO2 jointly via hydrogen and halogen bonds, as well as electrostatic attraction after proton transfer to HIO2. Thermodynamically, the MSA-involved clustering can occur nearly without free-energy barrier, following HIO2-MSA binary and HIO3-HIO2-MSA ternary pathway. Furthermore, adding MSA significantly enhance the rate of HIO3-HIO2-based cluster formation, even up to 104-fold at cold marine regions with rich MSA and scarce iodine, such as polar Ny-Ålesund and Marambio. Thus, the proposed more efficient HIO3-HIO2-MSA nucleation mechanism may provide theoretical evidence for explaining the frequent and intensive burst of marine iodine particles.