Study of the resistances to transfer of gaseous pollutant between material and indoor air

The main parameters which control the emission of volatile organic compounds between wall materials and indoor air were examined. A physically based model considers that the global emission phenomenon results from three elementary physical phenomena: diffusion through the boundary layer separating the wall from environment, diffusion within the porous network of the materials, and sorption of the gas molecules on the active sites of the materials. The pollutant transfer between porous material and air is therefore subjected to two complementary resistances and we identify first the resistance which controls the transfer. Then, we predict the global emission time constant from the mass transfer coefficient of convection and the thickness of the material. Experimental results from a small scale chamber are compared to predicted values in the case of acetone emission from chipboard in humid air and for high initial acetone concentration. Good agreement is obtained at the beginning of emission but an acetone retention effect by chipboard is observed, showing that it will be necessary to take into account the interactions of water vapor with materials and the pollutants to achieve accurate modeling of the material VOC emission process.