HIO₃-HIO₂-Driven Three-Component Nucleation: Screening Model and Cluster Formation Mechanism

Area of Science:

• Atmospheric Chemistry
• Aerosol Science
• Chemical Kinetics

Background:

• Iodine oxoacids, specifically iodous acid (HIO2) and iodic acid (HIO3), are recognized contributors to new particle formation (NPF) in marine environments.
• The presence of abundant atmospheric nucleation precursors can potentially amplify HIO2-HIO3-driven nucleation via multicomponent mechanisms.
• However, the precise enhancing potential (EP) of various precursors on this nucleation process remains poorly understood.

Purpose of the Study:

• To develop and apply an EP-based screening model to identify atmospheric precursors that enhance HIO2-HIO3 nucleation.
• To investigate the nucleation-enhancing mechanism of the precursor exhibiting the highest EP.
• To assess the role of methanesulfonic acid (MSA) as a potential enhancer of HIO2-HIO3 nucleation.

Main Methods:

• Calculated formation free energies (ΔG) for dimers of 63 selected precursors with HIO2 to evaluate their EP.
• Developed a quantitative structure-activity relationship (QSAR) model to predict ΔG for other precursors.
• Assessed atmospheric concentrations of (precursor)1(HIO2)1 dimer clusters and combined with prior HIO3 nucleation data to identify high-EP precursors.

Main Results:

• Methanesulfonic acid (MSA) was identified as a precursor with a high enhancing potential (EP) for HIO2-HIO3 nucleation.
• The QSAR model provides a framework for predicting the ΔG of various precursors with HIO2.
• Analysis of larger MSA-HIO2-HIO3 clusters confirmed MSA's ability to enhance HIO2-HIO3 nucleation under atmospheric conditions.

Conclusions:

• This study enhances the understanding of HIO2-HIO3 and MSA-driven nucleation mechanisms in the marine atmosphere.
• The findings suggest that HIO2 plays a significant role in atmospheric aerosol nucleation, potentially more than previously recognized.
• The developed EP-based screening model offers a valuable tool for identifying and evaluating the impact of various precursors on NPF.