Results from an experimental and modeling investigation of the influence of thermodynamic properties of macromolecular NOMs on observed equilibrium and nonequilibrium sorption/desorption behaviors of vapor phase sorbates is presented. Identification of glass transition (Tg) behavior in Leonardite humic acid and Organosolv lignin enabled development of protocols to investigate equilibrium and nonequilibrium sorption behavior in glassy and rubbery NOM materials. Specific differences in vapor phase equilibrium behavior in highly purified NOM materials above and below their Tg were identified. In the glassy state (below Tg), sorption of trichloroethylene (TCE) could be described by micropore models, characteristic of glassy macromolecules. Above Tg, sorptive behavior was well-described by Flory-Huggins theory, indicating that the mobility and structural configuration of rubbery NOM materials is analogous to the characteristic sorption behavior observed in more mobile, rubbery macromolecules. Nonequilibrium sorption behavior yielded similar differences in diffusion mechanisms based on the apparent macromolecular mobility of the NOM materials.