Staying hydrated: the molecular journey of gaseous sulfur dioxide to a water surface

Abstract

A water surface is a dynamic and constantly evolving terrain producing a vast array of unique molecular properties and interactions with chemical species in the environment. The complex dynamics of water surfaces permit life on earth to continue, but also complicate the development of a complete microscopic picture of the specific behaviors that take place within interfacial aqueous environments. This computational study examines a piece of the water puzzle by elucidating the bonding, dynamic interactions, and hydrate structures of sulfur dioxide gas adsorbing to a water cluster. Results described herein address the specific ways in which sulfur dioxide gas molecules bind to a water cluster, and paint a more complete picture of the adsorption pathway than was previously developed from experimental and computational studies. Ab initio molecular dynamics have been employed to study sulfur dioxide and water interactions at two environmentally relevant temperatures on a water cluster. The results of this study on a common environmental and industrially important gas provide molecular insight to aid our understanding of interactions on aqueous surfaces, and gaseous adsorption processes.

Interaction of SO2 with the Surface of a Water Nanodroplet

“…■ RESULTS AND DISCUSSION Benchmark Test. The hydration behavior of SO 2 at the air−water interface was previously investigated by Richmond and co-workers, 30 using the BOMD simulation (based on the B3LYP hybrid functional) with the water layer containing 24 water molecules. Here, the same system is employed to reproduce previous simulation results.…”

“…To gain more insight into the SO Oppenheimer molecular dynamical simulations to investigate the hydration structure of SO 2 . 30,33 Both studies reported variability of the SO 2 hydrate structures. However, to our knowledge, few studies concerning the effects of water droplet sizes on SO 2 solvation have been reported, which could have important atmospheric implications because different sizes of droplets exist during the aerosol nucleation and growth process in the atmosphere.…”

“…On the water surface, the hydrogen bond formed between the O atom of SO 2 with the H atom of water appears to be the dominant interaction, whereas the “sandwich” structure is less likely to form. To gain more insight into the SO 2 /H 2 O complex on the water surface, two groups have employed Born–Oppenheimer molecular dynamical simulations to investigate the hydration structure of SO 2 . , Both studies reported variability of the SO 2 hydrate structures. However, to our knowledge, few studies concerning the effects of water droplet sizes on SO 2 solvation have been reported, which could have important atmospheric implications because different sizes of droplets exist during the aerosol nucleation and growth process in the atmosphere.…”

“…27−29 However, there is an ongoing debate about the existence and composition of SO 2 surface complexes, ranging from (SO 2 )(H 2 O) 0 to (SO 2 )(H 2 O) 3 . 27−29 Spectroscopy experiments designed to address issues of SO 2 complexes on the surface of water droplets have provided valuable information but still cannot fully characterize micro-scopic events and behavior, 30 such as orientation of SO 2 , hydration geometry, and dynamic behavior on surface of water droplets. The latter information would assist understanding details of various reactions of SO 2 in the atmosphere.…”

Quantification of SO2 Oxidation on Interfacial Surfaces of Acidic Micro-Droplets: Implication for Ambient Sulfate Formation

“…An efficient interfacial surface reaction may be the combined result of a lower activation energy under acidic conditions at the air-water interface, preferred molecule orientation resulting from the water structure right at the air-water interface, and a variation in reactivity with pH on the aquated aerosol surfaces. [7][8][9][38][39][40]…”