Relating Soil Specific Surface Area, Water Film Thickness and Water Vapor Adsorption.

Estimation of soil specific surface area (SSA) and dry-end water vapor adsorption are important for porous media characterization and for prediction of water and vapor fluxes in arid environments. The objective of the presented study was to model water adsorption, film thickness and SSA based on t-curve theory originally developed for N₂ adsorption. Data from 21 source soils with clay contents ranging from 0.6 to 52.2%, was used to estimate specific surface area based on water retention, a t-curve type method, the linear prediction method and a simplified monolayer method. The water retention and the t-curve methods were found to be mathematically analogous and were among the most precise and accurate with regard to correlation coefficient (r = 0.97) and root mean square error (RMSE = 11.36 m²/g) when compared to the standard ethylene glycol monoethyl ether (EGME) method. The corrected t-curve method significantly overestimated SSA when compared to EGME data. The N₂-BET (BET) method was found to be the less reliable when compared to the mathematical methods and to the EGME method. For soil studies, the vapor adsorption in conjunction with the t-curve or water retention methods should be preferred for SSA estimation as they show much higher correlation with soil clay content and EGME measurements.