Application of the Guggenheim-Anderson-De Boer Model to Estimate Soil Specific Surface Area from Water Vapor Sorption Isotherms.

Application of the Guggenheim-Anderson-de Boer Model to Estimate Soil Specific Surface Area from Water Vapor Sorption Isotherms

Emmanuel Arthur^1,2, Markus Tuller², Per Moldrup³, Maria Knadel¹, and Lis W. de Jonge¹

¹ Department of Agroecology, Aarhus University, Blichers Allé 20, PO Box 50, DK-8830, Tjele, Denmark

² Department of Soil, Water, and Environmental Science, The University of Arizona, 1177 E. 4th Street, Tucson, AZ 85721, USA

³ Department of Civil Engineering, Aalborg University, Sofiendalsvej 11, DK-9200 Aalborg SV, Denmark

 

Abstract

Soil specific surface area (SA) governs numerous biological, chemical, and hydrological processes in soils. Laboratory methods for determination of SA include N₂ absorption in combination with the BET equation, EGME adsorption, and water vapor sorption, each with their associated advantages and challenges. The Guggenheim-Anderson-de Boer (GAB) isotherm equation accurately describes measured soil water vapor sorption isotherms for a wide water activity range, and is suggested as a replacement for the commonly applied BET equation for SA estimation. Soil water vapor sorption isotherms (water activity range from 0.03 to 0.93) have been measured for a global dataset of 327 soil samples. The monolayer parameter obtained from parameterization of the GAB equation with measured water sorption isotherms was used to compute SA (SA_G). The SA_G obtained from the adsorption isotherms was substantially smaller than the SA from desorption. The SA_G values for desorption data were significantly larger than SA values obtained from water sorption with the BET equation but compared favorably to SA from EGME adsorption and SA derived from a physically-based water film adsorption model. The water activity corresponding to the GAB monolayer water content coverage differed among various soil mineral groups. Thus, the GAB equation provides a practical alternative to the BET equation for estimation of SA from water sorption.