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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.


Xiang J.,Tsinghua University | Xiang 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 7 more authors.
Environmental Science and Technology | Year: 2016

This study investigates the impacts of outdoor and indoor ozone concentrations, ESP operation and occupancy on particle number concentrations within a modern office in Changsha, China. The office's one-pass air handling system contains a mini-bag filter (MERV 12) followed by an electrostatic precipitator (ESP) and high efficiency particulate air (HEPA) filter. Over a five-week period the system was operated either without the ESP (Stage 1, first-third week) or with the ESP (Stage 2, fourth and fifth week). Ozone and particle number concentrations were measured on working days. During both stages, indoor ozone and particle number concentrations tracked the outdoor ozone concentration. When operating, the ESP produced approximately 29 mg h-1 of ozone, increasing supply air ozone by 15 ppb and steady-state indoor ozone by about 3 ppb. Occupancy tended to decrease indoor ozone and increase particle levels. During occupancy, indoor particle levels were low (∼2600 particle/cm3) when the supply air ozone level was less than 18 ppb. Above this threshold, the supply air ozone concentration and indoor particle number concentration were linearly related, and ESP operation increased the average indoor particle level by about 22000 particles/cm3. The implications for worker exposure to both ozone and particles are discussed. © 2016 American Chemical Society.


Cao J.,Tsinghua University | Cao J.,Beijing Key Laboratory of Indoor Air Quality Evaluation and Control | Xiong J.,Beijing Institute of Technology | Wang L.,Beijing University of Civil Engineering and Architecture | And 3 more authors.
Environmental Science and Technology | Year: 2016

Solid-phase microextraction (SPME) is regarded as a nonexhaustive sampling technique with a smaller extraction volume and a shorter extraction time than traditional sampling techniques and is hence widely used. The SPME sampling process is affected by the convection or diffusion effect along the coating surface, but this factor has seldom been studied. This paper derives an analytical model to characterize SPME sampling for semivolatile organic compounds (SVOCs) as well as for volatile organic compounds (VOCs) by considering the surface mass transfer process. Using this model, the chemical concentrations in a sample matrix can be conveniently calculated. In addition, the model can be used to determine the characteristic parameters (partition coefficient and diffusion coefficient) for typical SPME chemical samplings (SPME calibration). Experiments using SPME samplings of two typical SVOCs, dibutyl phthalate (DBP) in sealed chamber and di(2-ethylhexyl) phthalate (DEHP) in ventilated chamber, were performed to measure the two characteristic parameters. The experimental results demonstrated the effectiveness of the model and calibration method. Experimental data from the literature (VOCs sampled by SPME) were used to further validate the model. This study should prove useful for relatively rapid quantification of concentrations of different chemicals in various circumstances with SPME. © 2016 American Chemical Society.


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.


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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