Critical Evaluation of the Diffusion Hypothesis in the Theory of Porous Media Volatile Organic Compound (VOC) Sources and Sinks

Recently, reports by both the U.S. Environmental Protection Agency (EPA) and a study committee of the Commission of the European Communities have alluded to diffusion mechanisms that may play a role in Volatile Organic Compound (VOC) interactions with indoor sinks. This paper proposes three alternative, diffusion-limited mathematical models to account for this interaction, using the linear isotherm model as a reference point. Their taxonomy is keyed to the nature of the vapor-sink interface. While the linear isotherm model gave an adequate description of data when a pillow-sink was challenged with ethylbenzene, a new single-parameter diffusion model gave a much improved description of data when the same pillow-sink was challenged with perchloroethylene. A hybrid, sorption/desorption, diffusion-limited model was the only plausible model when a carpet-sink was challenged with ethylbenzene. Some new computational aids, particularly intervalweighted least squares, are introduced in the context of model validation.