Chemical Implications of Rapid Reactive Absorption of I₂O₄ at the Air-Water Interface

Abstract

Marine aerosol formation involving iodine-bearing species significantly affects the global climate and radiation balance. Although recent studies outline the critical role of iodine oxide in nucleation, much less is known about its contribution to aerosol growth. This paper presents molecular-level evidence that the air− water interfacial reaction of I 2 O 4 mediated by potent atmospheric chemicals, such as sulfuric acid (H 2 SO 4 ) and amines [e.g., dimethylamine (DMA) and trimethylamine (TMA)], can occur rapidly on a picosecond time scale by Born−Oppenheimer molecular dynamics simulations. The interfacial water bridges the reactants while facilitating the DMA-mediated proton transfer and stabilizing the ionic products of H 2 SO 4 -involved reactions. The identified heterogeneous mechanisms exhibit the dual contribution to aerosol growth: (i) the ionic products (e.g., IO 3 − , DMAH + , TMAH + , and HSO 4 − ) formed by reactive adsorption possess less volatility than the reactants and (ii) these ions, such as alkylammonium salts (e.g., DMAH + ), are also highly hydrophilic, further facilitating hygroscopic growth. This investigation enhances not only our understanding of heterogeneous iodine chemistry but also the impact of iodine oxide on aerosol growth. Also, these findings can bridge the gap between the abundance of I 2 O 4 in the laboratory and its absence in field-collected aerosols and provide an explanation for the missing source of IO 3 − , HSO 4 − , and DMAH + in marine aerosols.

Size-Dependent Sigmoidal Reaction Kinetics for Pyruvic Acid Condensation at the Air–Water Interface in Aqueous Microdroplets

“…Aqueous microdroplets have been shown to largely enhance reaction rates and/or initiate reactions that do not occur to any great extent compared to bulk solutions. − The high surface-to-volume ratio and the unique environment at the air–water interface have been suggested as the origins of these enhanced rates. − Reactions in microdroplets of organic solvents have also been shown to be accelerated compared to bulk solutions. , …”

Computational Chemistry as Applied in Environmental Research: Opportunities and Challenges

“…This conclusion was supported by free-energy profile calculations, which showed that the free-energy barrier for intermediate formation was almost negligible. The air–water interfacial reaction mechanism that occurs on aerosols between iodine oxides, sulfuric acid, dimethylamine, and trimethylamine was revealed by BOMD simulations . The lowest free energy for iodine oxide occurred at the air–water interface compared with bulk water and air (Figure e).…”

“…The air−water interfacial reaction mechanism that occurs on aerosols between iodine oxides, sulfuric acid, dimethylamine, and trimethylamine was revealed by BOMD simulations. 301 The lowest free energy for iodine oxide occurred at the air−water interface compared with bulk water and air (Figure 9e). Iodine oxide hydrolysis occurs at ∼1.78 ps and around ∼2.64−6.00 ps in the presence of amines (e.g., DMA and TMA) and sulfuric acid, respectively.…”