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Abstract Knowledge of the diffusion coefficient is necessary for modeling gas movement through soil. Various equations have been proposed relating apparent gas diffusion to soil parameters. A laboratory study was conducted to measure gas diffusion through soil at low air‐filled porosity (0.05, 0.10, and 0.15) using an inert gas (Freon: CCl 2 F 2 ). The Penman model D S /D A = 0.66 a , where D A and D S are gas diffusion coefficients in air and soil, respectively, and a is the volumetric soil air content, greatly overestimated the measured D S at all porosities. The Millington‐Quirk model D S /D A = a 3.33 /φ 2 , where φ is the soil porosity, had the same curve shape but slightly underestimated the measured D S . Much better agreement between calculated and measured D S was obtained by reducing the exponent 3.33 in the Millington‐Quirk model to 3.10.
Sallam et al. (Sun,) studied this question.