Dynamic behavior of semivolatile organic compounds in indoor air

Exposures to a wide range of air pollutants are often dominated by those occurring in buildings because of three factors: (1) most people spend a large function of their time indoors, (2) many pollutants have strong indoor sources, and (3) the dilution volume in buildings is generally several orders of magnitude smaller than that of an urban airshed. Semivolatile organic compounds (SVOCs) are emitted by numerous indoor sources, including tobacco combustion, cooking, carpets, paints, resins, and glues, so indoor gasphase concentrations of these compounds are likely to be elevated relative to ambient levels. The rates of uptake and release of reversibly sorbing SVOCs by indoor materials directly affect both peak concentrations and persistence of the pollutants indoors after source elimination. Thus, accurate predictions of SVOC dynamics in indoor air require an understanding of contaminant sorption on surface materials such as carpet and wallboard.; The dynamic behaviors of gas-phase nicotine and phenanthrene were investigated in a 20 m3 stainless steel chamber containing carpet and painted wallboard. For the nicotine experiments in an empty chamber, more than 80% of the emitted mass was accounted for at the end of the experiment by thermally desorbing and collecting nicotine sorbed on small, wall-mounted stainless steel panels. More than 99% of the measured nicotine was sorbed to either the tested sorbent(s) or to the chamber surfaces at equilibrium at 25°C. Similar results were observed for phenanthrene experiments in the empty chamber.; The gas-phase data are interpreted using reversible sorption models. Phenanthrene-stainless steel sorption is adequately described by linear partitioning. For carpet and wallboard, a two-box sorption model which also incorporated the nonlinear equilibrium partitioning is successfully employed. In this model, deposition from the gas-phase to the sorbent's air-surface interface occurs on a time scale comparable to that observed for sorption on stainless steel and wallboard. A second sorbed-phase sink (for instance, the rubber backing of a carpet or the porous gypsum of wallboard) with a larger sorption capacity but slower uptake and release kinetics is coupled to the gas phase through bulk-phase diffusion.; The developed porous sorbent sorption model is successfully applied to resolve a discrepancy between concentrations of nicotine measured in laboratory and field studies of environmental tobacco smoke (ETS) that has been debated in the literature.; The sorption kinetic parameters obtained experimentally in this study are also incorporated into a comprehensive modeling framework which includes gas-particle partitioning, deposition of particles on indoor surfaces, adsorption and desorption of SVOC on deposited particles, and homogeneous and heterogeneous chemical decay. The resulting set of coupled ordinary differential equations is solved numerically to simulate five scenarios which illustrate the impacts of varying model parameters on indoor SVOC concentrations and persistence. (Abstract shortened by UMI.)...