Liquid-phase mass-transfer coefficients are determined for the absorption of sulfur dioxide by water drops larger than 1.1 mm in dia. A local model based on the large eddy interfacial model proposed by Fortescue and Pearson ( 1967) is obtained by the characteristic interfacial scaling. In particular, the agitation process of the liquid phase in the interfacial region is characterized by the interfacial liquid friction velocity. Experiments of sulfur dioxide absorption and desorption from large individually free-falling water drops are also carried out in a 5-m rain shaft under various environmental conditions. These experimental results agree well with those from the local model characterizing the interfacial process in water drops greater than 1.1 mm in dia.

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A numerical procedure based on the MacCormack method was used for the simulation of one‐dimensional isothermal transient movement of liquid phase water in an unsaturated soil including precipitation, evaporation, and moisture removal from soil by the roots of transpiring plants. The numerical model utilized finite‐difference explicit predictor‐corrector equations and it was applied to a few flow problems. Comparison between the numerical results and laboratory or field experimental values was very promising. Our predicted values also agreed reasonably well with previously published numerical solutions. The proposed procedure was found to be easily adapted for solving the nonlinear soil‐water flow equation. However, it required only a knowledge of soil hydraulic conductivity and its water potential or diffusivity as functions of moisture content.