Abstract
The effects of nonlinear (Brunauer-Emmett-Teller, BET) sorption on the rates of diffusion of volatile organic compounds (VOCs) within and from uniformly contaminated air-dry soils were evaluated by numerical solution of the one-dimensional gas-phase diffusion equation. A dimensionless sorption parameter, which accounts for the importance of BET sorption on the diffusive transport was identified. Numerical simulations demonstrated that the dimensionless gas-phase and total-soil concentration profiles, and the dimensionless emission rates of VOC from the soil surface, varied in response to changes in the initial concentration 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 linearization step in the derivation of the continuity equation of diffusion and BET sorption was used to obtain an analytical solution for the soil surface flux of VOC to the atmosphere, by substituting a linear sorption isotherm for the BET isotherm. The errors associated with this step were evaluated and the deviations were found to be < 20% for all cases tested in comparison to the full numerical solutions.
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