Rapid iodine oxoacid nucleation enhanced by dimethylamine in broad marine regions

Abstract

Recent experiments have revealed a vital nucleation process of iodic acid (HIO3) and iodous acid (HIO2) under marine boundary layer conditions. However, HIO3-HIO2 nucleation may not effectively drive the observed rapid new particle formation (NPF) in certain coastal regions influenced by urban air masses. Dimethylamine (DMA) is a promising basic precursor to enhance nucleation considering its strong ability to stabilize acidic clusters and the wide distribution in marine atmosphere, while its role in HIO3-HIO2 nucleation remains unrevealed. Hence, a method combining quantum chemical calculations and Atmospheric Cluster Dynamics Code (ACDC) simulations was utilized to study the HIO3-HIO2-DMA nucleation process. We found that DMA can preferentially accept the proton from HIO3 as a basic precursor in the most stable configurations of HIO3- HIO2-DMA clusters. Kinetically, the participation of DMA in the cluster formation pathways of the iodine oxoacid system could be significant at the 10-1 to 1 pptv level of [DMA]. Furthermore, DMA can enhance the cluster formation rates of the HIO3-HIO2 system in marine and polar regions near DMA sources more than 103-fold. Compared to the classical nucleation mechanism, the HIO3-HIO2-DMA mechanism exhibits strong nucleation ability, worthy of consideration as a promising mechanism in marine and polar regions rich in amine sources. The newly proposed HIO3-HIO2-DMA ternary mechanism might provide an explanation for some missing fluxes of atmospheric iodine particles.