On the use of the similar media concept for scaling soil air permeability

• It is the first use of the similar media concept for scaling air permeability (ka).
• Four ka models are select to test tis method using two ka datasets.
• The results show satisfactory performance of this method.
• This method is particularly suitable for modeling subsurface gas transport.

Soil air permeability (ka) is an important factor that controls subsurface gas transport and exchange of gas across the soil–atmosphere interface. It is thus crucial to evaluate the spatial distribution of ka for both application and modeling purposes. However, relevant studies are still very limited, partly due to the fact that the dependence of ka on soil moisture levels cannot be directly included in the methods such as geostatistical techniques for analyzing the spatial distribution of ka. To tackle this problem, the scaling scheme based on the similar media concept, which has been widely used in soil hydrology for characterizing spatial variability of soil hydraulic properties, was employed for scaling ka in this study. Four air permeability models, including Millington and Quirk (1960)—MQ, Hunt (2005)—HT, Brooks and Corey (1964)—BC, and Kawamoto et al. (2006)—KA, were selected to test this method using two independent datasets. For the first dataset that included ka measured for river sediments, all of the four models were able to delineate the spatial distribution of ka with a reference curve of ka and a set of scaling factors. Specifically, the MQ model gave the least satisfactory results due to the less flexibility of its form; whereas, there were no significant differences in the performances for the HT, BC, and KA models. For the second dataset that contained ka measured for agricultural soils, the overall performance of the four models for scaling ka deteriorated, largely due to the alterations in the microscopic structures of soil samples caused by repacking and compression of soil samples. Nonetheless, as the first attempt, this study shows the viability of using the similar media concept for scaling ka. The merit of this method resides in the fact that the spatial variations of moisture conditions and soil properties can be simultaneously included for analyzing the spatial distribution of ka. With a reference curve of ka and the distribution of scaling factors, this method would be particularly suitable for modeling subsurface gas transport.