THE EFFECTS OF NONLINEAR SORPTION ON THE DIFFUSION OF VOLATILE ORGANIC-COMPOUNDS FROM AIR-DRY SOILS - A THEORETICAL-STUDY

The effects of nonlinear (Brunauer-Emmett-Teller, BET) sorption on the rates of diffusion of volatile organic compounds (VOCs) within and fr om uniformly contaminated air-dry soils were evaluated by numerical so lution of the one-dimensional gas-phase diffusion equation. A dimensio nless sorption parameter, which accounts for the importance of BET sor ption on the diffusive transport, was identified. Numerical simulation s demonstrated that the dimensionless gas-phase and total-soil concent ration profiles, and the dimensionless emission rates of VOC from the soil surface, varied in response to changes in the initial concentrati on of the VOC in the soil, in marked contrast with the case of linear sorption of the VOC. The sensitivity of the numerical results towards the BET sorption parameters in the model was evaluated. A linearizatio n step in the derivation of the continuity equation of diffusion and B ET sorption was used to obtain an analytical solution for the soil sur face flux of VOC to the atmosphere, by substituting a linear sorption isotherm for the BET isotherm. The errors associated with this step we re evaluated and the deviations were found to be < 20% for all cases t ested in comparison to the full numerical solutions.