Water vapor adsorption on Mars

Near-surface air moisture observations from Phoenix and Curiosity display diurnal adsorption, which appears insensitive to mineralogy of regolith. To study this, adsorptive column model simulations are made for midsummer at Phoenix, validated against recalibrated TECP water vapor pressures p. Two standard-form (= obeying the van't Hoff equilibrium law) adsorption isotherms with quite different specific surface areas As do produce nearly identical good matches observed p, whereas a widely used non-standard isotherm fails. When standard, it also produces results. Adsorbed amounts differ in three but their fluxes concentrations nevertheless identical. Properties regolith except enthalpy shown disappear model's term, explaining insensitivity As. The plot ln p vs. 1/Tg during desorption suggests about 22 kJ/mol. Enthalpies close excellent match each other observations. Hence low-pressure martian essentially nonspecific is associated low enthalpy, as typical physisorption general.