The effects of ambient temperature (25°C to 40°C) and relative humidity (0% to 30%) on the adsorption of toluene, and 1,1,1 trichloroethane on silica alumina, silica alumina impregnated with KMnO4, and activated carbon granules and pellets were determined. VOC concentrations in the range 1–1000 ppm were studied. Measurements of the weight of the adsorbed VOCs as a function of time were made in a thermogravimetric analyzer (TGA). Linear isotherms were tested in all cases. Values of the Henry coefficient H were in the range 0.01–0.10 mm3 air/mm2 BET area; they decreased with both increasing temperature and relative humidity. The highest values of H were consistently observed with KMnO4-impregnated silica alumina. Empirical correlations relating H to the parameters employed in this study were derived. There was good agreement between the values of H calculated from equilibrium and kinetic data obtained in the TGA and corresponding values measured in a glass test chamber. Improved correlation of the data was obtained using the nonlinear Freundlich, Toth and Dubinin isotherms. The determined fitting parameters for toluene and 1,1,1-trichloroethane on activated carbon were in good agreement with data published in the literature.