Molecular-level nucleation mechanism of iodic acid and methanesulfonic acid

Both iodic acid (HIO3, IA) and methanesulfonic acid (CH3S(O)(2)OH, MSA) have been identified by field studies as important precursors of new particle formation (NPF) in marine areas. However, the mechanism of NPF in which IA and MSA are jointly involved is still unclear. Hence, we investigated the IA-MSA nucleation system under different atmospheric conditions and uncovered the corresponding nucleating mechanism at the molecular level for the first time, using a quantum chemical approach and Atmospheric Cluster Dynamics Code (ACDC). The findings show that the pure-IA nucleation rate was much lower than the results of CLOUD (Cosmics Leaving Outdoor Droplets) experiments. MSA can promote IA cluster formation through stabilizing IA via both hydrogen and halogen bonds, especially under conditions with lower temperatures, sparse IA, and rich MSA. However, the nucleation rate of the IA-MSA mechanism is much lower than that of field observations, indicating that the effect of additional nucleation precursors needs to be considered (e.g., H2SO4, HIO2, NH3, and amines). The IA-MSA nucleation mechanism revealed in this study may help to gain insight into the joint effect of marine sulfur- and iodine-containing components on marine NPF.

Automated summary

Through a quantum chemical approach and Atmospheric Cluster Dynamics Code (ACDC), this study investigated the IA-MSA nucleation system and revealed the corresponding nucleating mechanism under different atmospheric conditions for the first time. The findings showed that MSA can promote IA cluster formation by stabilizing IA, especially under conditions with lower temperatures, sparse IA, and rich MSA. However, the nucleation rate of the IA-MSA mechanism was much lower than field observations, indicating the need to consider additional nucleation precursors.