Enhancement of Atmospheric Nucleation Precursors on Iodic Acid- Induced Nucleation: Predictive Model and Mechanism

Iodic acid (IA) has recently been recognized as a key driver for new particle formation (NPF) in marine atmospheres. However, the knowledge of which atmospheric vapors can enhance IA-induced NPF remains limited. The unique halogen bond (XB)-forming capacity of IA makes it difficult to evaluate the enhancing potential (EP) of target compounds on IA induced NPF based on widely studied sulfuric acid systems. Herein, we employed a three-step procedure to evaluate the EP of potential atmospheric nucleation precursors on IA-induced NPF. First, we evaluated the EP of 63 precursors by simulating the formation free energies (Delta G) of the IA-containing dimer clusters. Among all dimer clusters, 44 contained XBs, demonstrating that XBs are frequently formed. Based on the calculated Delta G values, a quantitative structure-activity relationship model was developed for evaluating the EP of other precursors. Second, amines and O/S-atom-containing acids were found to have high EP, with diethylamine (DEA) yielding the highest potential to enhance IA-induced nucleation by combining both the calculated Delta G and atmospheric concentration of considered 63 precursors. Finally, by studying larger (IA)(1-3)(DEA)(1-3) clusters, we found that the IA-DEA system with merely 0.1 ppt (2.5x10(6) cm(-3)) DEA yields comparable nucleation rates to that of the IA-iodous acid system.

Automated summary

Iodic acid (IA) has been identified as a significant contributor to new particle formation (NPF) in marine atmospheres. However, there is limited knowledge about which atmospheric vapors can enhance IA-induced NPF. In this study, a three-step procedure was employed to evaluate the enhancing potential (EP) of potential atmospheric nucleation precursors on IA-induced NPF. A quantitative structure-activity relationship model was developed to evaluate the EP of different precursors, and amines and O/S-atom-containing acids were found to have high EP.