A Study of the Mechanism of Gaseous Transfer Across an Air-Water Interface Using Carbon Dioxide

摘要

The rate constant for interphase molecular exchange was determined as a function of the relative velocity between gaseous and liquid phases. The experiment monitored the rate of dissolved 14CO2 depletion from a thermally regulated water container in a variable speed wind tunnel. The results provide substantial evidence for the existence of a laminar layer of non-turbulent flow on the surface of natural bodies of water. This pseudo membrane, which prevents turbulent mixing at the solution surface and restricts gaseous movement to molecular diffusion, was found to vary in thickness inversely with the air speed in the tunnel. The experimental routine used to verify the existence of this surface membrane simultaneously demonstrated that carbon dioxide interphase exchange is uniquely enhanced by a pH dependent molecular-ionic species interconversion within this layer. The enhancement of carbon dioxide transfer by hydration-dehydration reactions in the aqueous surface layer may permit this gas to be exchanged between the atmosphere and hydrosphere more rapidly than its non-reactive counterparts. It is suggested that carbon dioxide interphase transfer studies hereafter should consider the surface chemical reactions of this gas as well as the purely physical phenomenon of diffusion. (Author)