Determination of building materials' transport properties for modeling VOC emissions

Material transport properties, such as diffusion coefficients and partition coefficients, are necessary for modeling VOC emissions from building materials and their potential impact on indoor air quality. A modified experimental procedure for VOC emission testing was developed in this study to determine these properties. It consists of a static period (i.e., zero air exchange) followed by a dynamic period. The concentrations measured at the end of the static period were used to represent the equilibrium concentration and, together with the data from the dynamic period, to determine the initial VOC content in the test specimen. An iterative numerical procedure with simulated annealing method was developed for analyzing the experimental data to determine the partition and diffusion coefficients. The numerical procedure uses the measured data to estimate the initial value of the partition coefficient, and it was able to give a unique estimation of the partiction and diffusion coefficients from regresssion analysis of the measured data. Uncertainties of the experimental and numerical procedures were analyzed. Six building materials (vinyl siding, spunbonded olefin [Tyvek TM], oriented strand board, fiber batt insulation, gypsum wallboard, and interior paint) that are typically used in a wood-framed residential wall assembly were tested using a small stainless steel environmental chamber (50 L volume). VOCs emitted from each material were identified using thermal desorption GC/MS analyses of air samples collected in sorbent tubes. A thermal desorption-GC/ FID system was used to analyze the air samples to determine the VOC concentrations in the chamber as functions of time, and the VOC emission rates over time were also calculated. The numerical procedure developed was used to determine the partition coefficient (K _ma) and diffusion coefficient (D_m) for selected VOCs The relationships between D_m and molecular weight and between K _ma and vapor pressure were compared with previous findings. This would allow for the estimation of material transport properties for other VOCs.