A Double-Diffusion Model to Quantify the Sorption Effects of Indoor Surfaces on the Exposure to Chemicals Encapsulated in Products

摘要

Chemicals encapsulated in products can constitute a major emission source in the indoor environment. Recently, increasing attention has been paid to the sorption effects of indoor surfaces as a sink for chemicals released to indoor air, especially for semi-volatile organic compounds (SVOCs). Previous studies have used simple assumptions to model the sorption effects which may not reflect reality. This study thus aims to use a more sophisticated model to better elucidate the role of sorption effects on the release of chemicals and near-field human exposures. A double-diffusion model was developed which describes the diffusive emissions of chemicals from materials, the subsequent loss by ventilation, and the loss by diffusive sorption by indoor surfaces. A typical North American house was modeled. Chemicals were assumed to originate from a 3mm-thick vinyl flooring, and the indoor surfaces considered were gypsum walls and ceilings. The model system was solved numerically using Method of Lines discretization. The model was tested for three chemicals, a typical VOC (ethylbenzene), a typical SVOC (DEHP) and one intermediate (tetradecane). Results show that sorption on walls and ceilings can significantly lower the peak air concentration of chemicals emitted from flooring, from a factor of 2 for ethylbenzene to a factor of 6 for DEHP. The predicted air concentration converges with that predicted by a model not accounting for sorption after several days for ethylbenzene and tetradecane, but the factor of 6 reduction for DEHP remains even after 15 years. Sorption also significantly increases the mass of DEHP released from flooring. Overall, this study shows that for VOCs the sorption effect is negligible, while for SVOCs the indoor surfaces can be viewed as infinite sinks in the time scale of consumer use. Simplified models will be presented on intermediate chemicals, for which the indoor surfaces are nonnegligible finite sinks and may serve as secondary sources.