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

• Published in: Atmospheric Chemistry and Physics
• Main Authors: Li, Jing, Wu, Nan, Chu, Biwu, Ning, An, Zhang, Xiuhui
• Format: Text
• Language: English
• Published: 2024
• Subjects: Ny Ålesund; Ny-Ålesund
• Online Access: https://doi.org/10.5194/acp-24-3989-2024; https://acp.copernicus.org/articles/24/3989/2024/

Iodic acid (HIO 3 ) and iodous acid (HIO 2 ) have been identified as nucleating effectively by the Cosmics Leaving Outdoor Droplets (CLOUD) experiment at CERN, yet it may be hard to explain all HIO 3 -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 the synergistic nucleation of iodine oxoacids remain unclear. Hence, we investigated the MSA-involved HIO 3 –HIO 2 nucleation process at the molecular level using density functional theory (DFT) and the Atmospheric Cluster Dynamics Code (ACDC). Our results show that MSA can form stable molecular clusters with HIO 3 and HIO 2 jointed via hydrogen bonds, halogen bonds, and electrostatic attraction after proton transfer to HIO 2 . Thermodynamically, the MSA-involved clustering can occur nearly without a free-energy barrier, following the HIO 2 –MSA binary and HIO 3 –HIO 2 –MSA ternary pathway. Furthermore, our results show that considering MSA will significantly enhance the calculated rate of HIO 3 –HIO 2 -based cluster formation, by up to 10 4 -fold in cold marine regions containing rich MSA and scarce iodine, such as the polar regions Ny-Ålesund and Marambio. Thus, the proposed more efficient HIO 3 –HIO 2 –MSA nucleation mechanism may provide theoretical evidence for explaining the frequent and intensive bursts of marine iodine particles.