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Liu C.,Nanjing Southeast University | Liu C.,Beijing Key Laboratory of Indoor Air Quality Evaluation and Control | Cao J.,Tsinghua University | Cao J.,Beijing Key Laboratory of Indoor Air Quality Evaluation and Control | And 2 more authors.
International Journal of Heat and Mass Transfer | Year: 2016

Dynamic mass transfer between semi-volatile organic compounds (SVOCs) and particles needs accurate and simple description for exposure assessment. The lumped parameter method (LPM) is such a simplified approach. The classical condition under which LPM applies in mass transfer is that the Little number (Lt = vtL/D/K, dimensionless ratio of internal resistance to external one) is less than 0.1 when dimensionless excessive concentration is constrained to be less than 5%. It should be noted that the condition above justifies application of LPM from time = 0 to ∞. However, in indoor environments, lifetime of airborne particles tends to be finite, e.g., on the order of one hour. The application condition of LPM for such finite duration has not been clarified. Using dimensionless analysis, we derived a correlation to relates the critical Little number (Ltc) with Fom (Fom = Dt/r2, a dimensionless parameter for duration time). It shows that the applied condition of LPM for finite duration is less strict. For example, if Fom < 10-4, Ltc is smaller than 5.2. To illustrate application of the simplified approach and corresponding accuracy of the results, an example is presented for analyzing the transient mass transfer processes between SVOCs and airborne particles in practical residential buildings. The approach is also useful to address various transient mass transfer problems within finite time. © 2016 Elsevier Ltd. All rights reserved.


Cao J.,Tsinghua University | Cao J.,Beijing Key Laboratory of Indoor Air Quality Evaluation and Control | Weschler C.J.,Tsinghua University | Weschler C.J.,Beijing Key Laboratory of Indoor Air Quality Evaluation and Control | And 5 more authors.
Environmental Science and Technology | Year: 2016

The concentration of a gas-phase semivolatile organic compound (SVOC) in equilibrium with its mass-fraction in the source material, y0, and the coefficient for partitioning of an SVOC between clothing and air, K, are key parameters for estimating emission and subsequent dermal exposure to SVOCs. Most of the available methods for their determination depend on achieving steady-state in ventilated chambers. This can be time-consuming and of variable accuracy. Additionally, no existing method simultaneously determines y0 and K in a single experiment. In this paper, we present a sealed-chamber method, using early-stage concentration measurements, to simultaneously determine y0 and K. The measurement error for the method is analyzed, and the optimization of experimental parameters is explored. Using this method, y0 for phthalates (DiBP, DnBP, and DEHP) emitted by two types of PVC flooring, coupled with K values for these phthalates partitioning between a cotton T-shirt and air, were measured at 25 and 32 °C (room and skin temperatures, respectively). The measured y0 values agree well with results obtained by alternate methods. The changes of y0 and K with temperature were used to approximate the changes in enthalpy, ΔH, associated with the relevant phase changes. We conclude with suggestions for further related research. © 2015 American Chemical Society.


Gong M.,Tsinghua University | Gong M.,Beijing Key Laboratory of Indoor Air Quality Evaluation and Control | Weschler C.J.,Tsinghua University | Weschler C.J.,Beijing Key Laboratory of Indoor Air Quality Evaluation and Control | And 3 more authors.
Environmental Science and Technology | Year: 2016

Clothing can either retard or accelerate dermal exposure to phthalates. To investigate the impact of clothing on dermal exposure to six phthalates (DMP/DEP/DiBP/DnBP/BBzP/DEHP) in real environments, two sets of experiments have been conducted: (1) Skin wipes were collected from 11 adults to examine the phthalate levels on both bare-skin (hand/forehead) and clothing-covered body locations (arm/back/calf); (2) Five adults were asked to wear just-washed jeans for 1 day (1st experiment), 5 days (2nd experiment), and 10 days (3rd experiment). Phthalate levels on their legs were measured on selected days during the wearing period, and phthalate levels in the jeans were measured at the end of each experiment and again after washing. Measured phthalate levels on body locations covered by clothing were lower than those on uncovered locations, but still substantial. Dermal uptake would be underestimated by a factor of 2 to 5 if absorption through body locations covered by clothing were neglected. Phthalate levels in the jeans and on the legs increased with the wearing time. However, the levels in the jeans and on the legs were not strongly correlated, indicating that other pathways, e.g, contact with bedding or bedclothes, likely contribute to the levels on the legs. The efficiency with which laundering washing removed phthalates from the jeans increased with decreasing Kow; median values ranged from very low (<5%) for DEHP to very high (∼75%) for DMP. © 2016 American Chemical Society.

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