October 1987

Document Type


Degree Name



Dept. of Environmental Science and Engineering


Oregon Graduate Center


The transport of a gas across a gas/liquid interface is of fundamental importance in environmental and geophysical sciences. In many cases of interest, it is desired to predict the flux of a particular gas into or out of a body of water. Modeling of this process requires knowledge of how changes in fluid mechanical and chemical parameters will affect the gas exchange rate. In many instances, the rate may be determined to a large extent by the intensity of turbulence in the liquid phase in addition to the cleanliness of the liquid surface. Therefore, understanding how variations in turbulence intensity, length scale, and interfacial cleanliness can affect the gas/liquid transport process is central to modeling fluxes. The liquid phase rate controlled transport of CO2 across a gas/liquid interface into water was studied using a non-invasive laser-induced fluorescence technique. Turbulence in the liquid layer was generated by a vertically-oscillating grid. This allowed the transport process to be studied as a function of known levels of aqueous phase turbulence. The liquid phase mass transfer coefficient kL and surface [CO2] fluctuation timescales were measured under conditions of varying turbulence intensity and length scale for cleaned, uncleaned and organic monolayer-covered water surfaces. In addition, eddy approach distances were calculated from the surface [C02] fluctuation data. The cleaned-interface results show that surface renewal is an accurate physical description of the hydrodynamics associated with gas/liquid mass transport at film-free liquid interfaces. The monolayer-covered data show that surface renewal is not an appropriate hydrodynamical description of the transport process at film-covered interfaces. The results also show that surface penetration models are able to describe gas/liquid transport at both clean and film-covered liquid surfaces. The present cleaned-interface kL results were also compared to kL values measured in wind tunnels by use of an aerodynamic surface renewal model. This comparison suggests that in the case of a clean liquid surface, the hydrodynamical dependence of wind-driven gas exchange is the same as found for transport governed by mechanically generated turbulence.





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