Technical ArticlesMODELING DIFFUSION AND REACTION IN SOILS: IX. THE BUCKINGHAM-BURDINE-CAMPBELL EQUATION FOR GAS DIFFUSIVITY IN UNDISTURBED SOILMoldrup, P.1; Olesen, T.1; Yamaguchi, T.2; Schjønning, P.3; Rolston, D. E.4Author Information 1Environmental Engineering Laboratory, Dept. of Civil Engineering, Aalborg University, Sohngaardsholmsvej 57, DK-9000 Aalborg, Denmark. Dr. Moldrup is corresponding author. E-mail: [email protected] 2Dept. of Civil and Environmental Engineering, Faculty of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, 739 Japan. 3Danish Institute of Agricultural Sciences, Dept. of Crop Physiology and Soil Science, Research Centre Foulum, P.O. Box 50, DK-8830 Tjele, Denmark. 4Soils and Biogeochemistry, Dept. of Land, Air and Water Resources, University of California, Davis, CA 95616. Received Dec. 10, 1998; Accepted March 30, 1999. Soil Science: August 1999 - Volume 164 - Issue 8 - p 542-551 Buy Abstract Accurate description of gas diffusivity (ratio of gas diffusion coefficients in soil and free air, DS/D0) in undisturbed soils is a prerequisite for predicting in situ transport and fate of volatile organic chemicals and greenhouse gases. Reference point gas diffusivities (Rp) in completely dry soil were estimated for 20 undisturbed soils by assuming a power function relation between gas diffusivity and air-filled porosity (ε). Among the classical gas diffusivity models, the Buckingham (1904) expression, equal to the soil total porosity squared, best described Rp. Inasmuch as our previous works (Parts III, VII, VIII) implied a soil-type dependency of DS/D0(ε) in undisturbed soils, the Buckingham Rp expression was inserted in two soil- type-dependent DS/D0(ε) models. One DS/D0(ε) model is a function of pore-size distribution (the Campbell water retention parameter used in a modified Burdine capillary tube model), and the other is a calibrated, empirical function of soil texture (silt + sand fraction). Both the Buckingham-Burdine-Campbell (BBC) and the Buckingham/soil texture-based DS/D0(ε) models described well the observed soil type effects on gas diffusivity and gave improved predictions compared with soil type independent models when tested against an independent data set for six undisturbed surface soils (11-46% clay). This study emphasizes that simple but soil-type-dependent power function DS/D0(ε) models can adequately describe and predict gas diffusivity in undisturbed soil. We recommend the new BBC model as basis for modeling gas transport and reactions in undisturbed soil systems. © 1999 Lippincott Williams & Wilkins, Inc.