Ethylenediamine-Enhanced Iodic Acid Nucleation: Mechanistic Insights into Marine New Particle Formation

New particle formation (NPF) driven by iodic acid (IA) in marine regions has attracted considerable attention, but the limited understanding of IA-driven nucleation mechanisms hinders assessments of marine secondary aerosol formation and climate change. This study demonstrates that ethylenediamine (EDA), a strong basic diamine derived from marine and anthropogenic emissions (e.g., marine chemical activities, ship emissions, and coastal industrial processes), significantly enhances IA-driven nucleation via proton-transfer reactions to form stable clusters. At 278.15 K, parts per trillion (ppt)-level EDA increased aerosol formation rates by up to 10³-fold across IA concentrations from 10⁶ to 10⁸ cm^-3, with an enhancement factor ranging from 1.0 to 4.6 × 10³ even at 0.01 ppt EDA compared to pure IA nucleation. A comparison to field-measured nucleation rates suggests that IA-EDA nucleation may contribute to NPF in marine environments, where EDA concentrations were extrapolated from other sites rather than directly measured at polar or coastal locations. Alternatively, bases with similar properties could also be responsible, and the synergistic effects of multiple precursors require further investigation. These findings address a key gap in understanding marine aerosol formation and highlight the importance of incorporating IA-EDA nucleation into global climate models.