Entry of gas molecules into liquids

Abstract

Heterogeneous gas–liquid interactions play a fundamental role in many atmospheric processes. Pivotal for the understanding of such processes is the rate of gas uptake by the relevant liquid. Accurate experimental techniques have been developed to study uptake of gases by liquids. Gas–liquid interactions have already been investigated for more than thirty gas-phase species encompassing two classes of molecules: (1) those that do not react in the liquid but are readily solvated by it and (2) those that have low solubility in the liquid but react in the liquid rapidly to form highly soluble species. Uptake studies of non-reactive gas molecules in water have been explained by a model which treats the water surface as a narrow region of a dense gas-like state within which trace gas–solvent collisions occur. Gas accommodation occurs via nucleation of solvent molecules. Uptake studies for reactive gas molecules indicate that, for some species, reaction rates are much more rapid at the liquid interface than in the bulk liquid. The results of non-reactive and reactive uptake experiments are brought together here. The uptake model is briefly described, and the implication of the model for the kinetic nature of liquid surfaces is examined. Reaction-driven uptake studies which provide clear evidence for reactions at the gas/liquid interface are presented. The nature of interfacial reactions and their connection to the uptake model are examined.