11 Oct 2023
 | 11 Oct 2023

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

Jing Li, Nan Wu, An Ning, and Xiuhui Zhang

Abstract. 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.

Jing Li et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2084', Anonymous Referee #2, 18 Oct 2023
  • RC2: 'Comment on egusphere-2023-2084', Anonymous Referee #1, 23 Oct 2023
  • RC3: 'Comment on egusphere-2023-2084', Anonymous Referee #4, 24 Oct 2023
  • RC4: 'Comment on egusphere-2023-2084', Anonymous Referee #3, 30 Oct 2023

Jing Li et al.


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Short summary
Iodic acid (HIO3) nucleates with iodous acid (HIO2) efficiently in marine areas, however, whether methanesulfonic acid (MSA) can synergistically participate in the HIO3-HIO2-based nucleation is unclear. Our study provides molecular-level evidence that MSA can efficiently promote the formation of HIO3-HIO2-based clusters using a theoretical approach. The proposed MSA-enhanced iodine nucleation mechanism may help to deeply understand marine NPF events with burst of iodine particles.