Physically Based Mathematical Models of the Water Vapor Sorption by Soils

Models for the quantitative description of the water vapor sorption isotherms in soils were developed on the basis of fundamental equations of equilibrium thermodynamics and the molecular-kinetic theory of gases. The derivation of the corresponding equations, their analytical study, and real data for some isotherms of the water vapor sorption by soils of different genesis and degree of dispersion were described. The models adequately described typical S-shaped sorption isotherms in the entire range of the relative water pressure with high determination coefficients (0.98 <= R(2) <= 1) and statistically reliable parameters of the non-linear regression. Along with the variable relative water content (pressure) of the water vapor in the atmosphere and the content of water in the soil, the parameters of the solid phase (specific surface), soil solution (concentration, electrolyte charges), and temperature were used as the base parameters of the models, which theoretically enable the prediction of changes in the sorption isotherms under the effect of these factors.