Iodous acid - a more efficient nucleation precursor than iodic acid

Iodous acid (HIO₂), a vital iodine oxyacid, potentially plays an important role in the formation of new particles in marine areas (He et al., Science, 2021, 371, 589-595). However, the nucleation mechanism of HIO₂ is still poorly understood. Herein, the self-nucleation of HIO₂ under different atmospheric conditions is investigated by a combination of quantum chemical calculations and the Atmospheric Cluster Dynamics Code (ACDC) simulations. The results indicate that HIO₂ can form relatively stable molecular clusters through hydrogen bonds and halogen bonds, and the self-nucleation of HIO₂ proceeds by sequential addition of HIO₂ or HIO₂-based small clusters. Besides, in order to better illustrate the role of HIO₂ in new particle formation (NPF) in marine areas, we compare its nucleation properties with those of iodic acid (HIO₃), a significant iodine-containing nucleation precursor in marine regions. We find that the cluster formation rate of the self-nucleation of HIO₂ is higher than that of the self-nucleation of HIO₃ although [HIO₂] is lower than [HIO₃], which indicates that the HIO₂ molecule is a more efficient nucleation precursor than the HIO₃ molecule. Therefore, the self-nucleation of HIO₂ could become one of the most important sources for NPF in marine areas, which could provide potential theoretical evidence for explaining the intensive NPF events observed in these areas.