HIO 3 -HIO 2 -Driven Three-Component Nucleation: Screening Model and Cluster Formation Mechanism.

Iodine oxoacids (HIO 3 and HIO 2 )-driven nucleation has been suggested to efficiently contribute to new particle formation (NPF) in marine atmospheres. Abundant atmospheric nucleation precursors may further enhance HIO 3 -HIO 2 -driven nucleation through various multicomponent nucleation mechanisms. However, the specific enhancing potential (EP) of different precursors remains largely unknown. Herein, the EP-based screening model of precursors and enhancing mechanism of the precursor with the highest EP on HIO 3 -HIO 2 nucleation were investigated. The formation free energies (Δ G ), as critical parameters for evaluating EP, were calculated for the dimers of 63 selected precursors with HIO 2 . Based on the Δ G values, (1) a quantitative structure-activity relationship model was developed for evaluating Δ G of other precursors and (2) atmospheric concentrations of 63 (precursor) 1 (HIO 2 ) 1 dimer clusters were assessed to identify the precursors with the highest EP for HIO 3 -HIO 2 -driven nucleation by combining with earlier results for the nucleation with HIO 3 as the partner. Methanesulfonic acid (MSA) was found to be one of the precursors with the highest EP. Finally, we found that MSA can effectively enhance HIO 3 -HIO 2 nucleation at atmospheric conditions by studying larger MSA-HIO 3 -HIO 2 clusters. These results augment our current understanding of HIO 3 -HIO 2 and MSA-driven nucleation and may suggest a larger impact of HIO 2 in atmospheric aerosol nucleation.