Fig. 6. Scatterplot comparison of predicted and measured gas diffusivities (D_P/D₀) in 18 undisturbed Andisols and four undisturbed Gray-lowland soils. Test of the (a) Penman (1940) model, Eq. [2]; (b) Millington and Quirk (MQ; 1960) model, Eq. [3]; (c) Millington and Quirk (1961) model, Eq. [4]; (d) Buckingham-Burdine-Campbell (BBC) model, Eq. [5]; (e) macroporosity-dependent (₁₀₀) model, Eq. [7], with D_P,100 predicted from Eq. [6]; and (f) macroporosity-dependent model, Eq. [7], using the measured D_P,100 value. Andi = Andisols; Gray = Gray-lowland soils; RMSE = root mean square error.