Dancing on Water: The Choreography of Sulfur Dioxide Adsorption to Aqueous Surfaces

Abstract

One might expect the high surface tension of water to be a barrier to absorption of a gas into the liquid phase, but we know that gaseous adsorption onto and subsequent absorption into a water surface is a common phenomenon on this planet. What is not commonly known is how an atmospheric gas such as SO2 and molecules at the water surface can overcome the barrier created by strong water–water surface bonding interactions. What this interplay looks like, the distances from the water surface at which these attractive interactions begin, and how they influence the orientational nature of both SO2 and surface water molecules is the focus of this computational study. The results fill a void in the information about this system existing from previous experimental studies by providing information about the dimensional nature of the gas–surface interactions, and the details of how the two species twist and turn orientationally with increased surface interactions. Classical molecular dynamics have been employed in both equilibrium and steered molecular dynamics (SMD) simulations for SO2 at a neat-water surface and at a surface with high interfacial SO2 concentrations. The results provide new molecular insights for understanding the interaction of this prevalent gas on aerosols and other aqueous surfaces in the environment.

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

“…Although other recent works have studied binding of small molecules, 12,13 we believe this to be the first temperature study using quantum MD to study the binding of small SO 2 gas molecules on a water cluster. We improve on our previous work 7 by use of quantum instead of classical MD and investigate the effect of temperature which was not explored by Baer et al 8 We show how temperature affects the bonding behavior of the surface-adsorbed SO 2 to neighboring waters, and propose a sequential binding mechanism for SO 2 adsorbing to a water cluster. We also examine SO 2 binding behavior when bound to the surface waters.…”

“…The quantum MD technique described herein allows more accurate and realistic simulation than our previous classical MD. 7 It is also superior to static DFT studies because it does not assume geometry optimized configurations, and the extended interactions of a larger water cluster are incorporated. In our previous classical MD study we determined net orientational behavior of SO 2 binding to a water cluster, and the orientation of the waters as they respond to the presence of an adsorbing gas.…”

Theoretical study of the auto-catalyzed hydrolysis reaction of sulfur dioxide

“…As a result, substantial efforts have been dedicated to the understanding of the chemical processes of SO2 in the atmosphere [3][4][5][6][7][8][9]. A critical step in many atmospheric processes is the adsorption of SO2 on the gas-liquid surface [10][11][12][13]. However, the chemical mechanism for the subsequent reactions of SO2 after adsorption is still poorly understood.…”

Enhanced heterogenous hydration of SO 2 through immobilization of pyridinic-N on carbon materials

“…Substantial efforts have been dedicated to investigate the hydration of SO 2 in aqueous aerosols or gas phase both from experimental [ 10 ] and computational perspectives [ 11 , 12 ]. The adsorption and subsequent hydration process lead to the wet deposition of SO 2 , which has a significant impact on the formation of sulfate aerosols [ 13 ].…”