Sorption of organic gases in residential bedrooms and bathrooms

Submitted to Indoor Air 2005 LBNL-56787 SORPTION OF ORGANIC GASES IN RESIDENTIAL BEDROOMS AND BATHROOMS BC Singer ∗1,2 , AT Hodgson 2 , T Hotchi 2 , KY Ming 1 , RG Sextro 2 , EE Wood 2 , NJ Brown 1 Atmospheric Sciences and 2 Indoor Environment Departments, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, USA ABSTRACT Experiments were conducted to characterize organic gas sorption in residential bedrooms (n=4), bathrooms (n=2), and a furnished test chamber. Rooms were studied “as-is” with material surfaces and furnishings unaltered. Surface materials were characterized and areas quantified. Experiments included rapid volatilization of a volatile organic compound (VOC) mixture with the room closed and sealed for a 5-h Adsorb phase, followed by 30-min Flush and 2-h closed-room Desorb phases. The mixture included n-alkanes, aromatics, glycol ethers, 2-ethyl-1-hexanol, dichlorobenzene, and organophosphorus compounds. Measured gas-phase concentrations were fit to three variations of a mathematical model that considers sorption occurring at one surface sink and one potential embedded sink. The 2-parameter sink model tracked measurements for most compounds, but improved fits were obtained for some VOCs with a 3-parameter sink-diffusion or a 4-parameter two-sink model. Sorptive partitioning and initial adsorption rates increased with decreasing vapour pressure within each chemical class. INDEX TERMS Adsorption, Field study, Modeling, Residence, Volatile organic compounds INTRODUCTION Gaseous air pollutants can reversibly sorb to material surfaces, affecting both the magnitude and timing of indoor concentrations. Sorption of VOCs to relevant indoor materials (e.g., carpet, gypsum wallboard, vinyl flooring) has been studied primarily through experiments in small (<1 m 3 ) chambers (Tichenor et al. 1991; Jorgensen et al. 1999; Won et al. 2001a-b; Zhang et al. 2002). Materials generally were aged by exposure to clean air and studied individually. Sorption models were fit to measured data to infer rate parameters for specific compound-material interactions. These interactions can be combined mathematically to simulate sorption in an entire room or house, but this has been reported in only a few studies (e.g., Tichenor et al. 1991; Won et al. 2001b; Singer et al. 2004). Our group has demonstrated an alternative approach in which sorption is studied in a room-sized 50 m 3 environmental chamber that is constructed, finished and furnished with typical materials (Singer et al. 2002; Singer et al. 2004). Furnishings have been aged over years of exposure to particulate and gaseous air pollutants, with intervening exposure to ambient air. Results indicate that sorption to the entire room can be modelled using one or two-sink models having 2 or 4 fitting parameters. Dynamics of low to moderately sorbing compounds such as toluene are captured with the one-sink model, whereas the behavior of highly sorbing compounds (e.g. nicotine and methylnaphthalene) is more closely reproduced with the two-sink model (Singer et al. 2004). Rooms in occupied residences contain many varied materials whose exposed surfaces may present sorption sites that differ from materials used in small chamber experiments. The objectives of this study were (1) to quantify sorption rate parameters for a suite of VOCs in Corresponding author e-mail: BCSinger@lbl.gov