Polybrominated Diphenyl Ethers in Air across China: Levels

Jul 3, 2013 - Dalian Maritime University, Dalian, P. R. China. ‡. IJRC-PTS, State Key Laboratory of Urban Water Resource and Environment, Harbin Ins...
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Polybrominated Diphenyl Ethers in Air across China: Levels, Compositions, and Gas-Particle Partitioning Meng Yang,† Hong Qi,‡,§ Hong-Liang Jia,† Nan-Qi Ren,‡,§ Yong-Sheng Ding,∥ Wan-Li Ma,‡,§ Li-Yan Liu,‡,§ Hayley Hung,⊥ Ed Sverko,# and Yi-Fan Li*,‡,§,†,∇ †

International Joint Research Center for Persistent Toxic Substances (IJRC-PTS), College of Environmental Science and Engineering, Dalian Maritime University, Dalian, P. R. China ‡ IJRC-PTS, State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, P. R. China § School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090, P. R. China ∥ IJRC-PTS, Shanghai Maritime University, Shanghai 201306, P. R. China ⊥ Air Quality Processes Research Section, Environment Canada, Toronto, Ontario, Canada # NLET, Science and Technology Branch, Environment Canada, Burlington, Ontario, Canada ∇ IJRC-PTS-NA, Toronto, Ontario M2N 6X9, Canada S Supporting Information *

ABSTRACT: Air samples were concurrently collected using high volume air samplers for 24 h every week from September 2008 to August 2009 at 15 sites (11 urban, 1 suburban, and 3 background/rural) across China. Twelve polybrominated diphenyl ether (PBDE) congeners (BDE-17, -28, -47, -66, -85, -99, -100, -138, -153, -154, -183, and -209) were measured. Total PBDE concentrations (∑12PBDEs) in air (gas + particle phases) were in the range of 11.0−838 pg m−3 with a mean of 232 ± 72 (mean ± SE) pg m−3. The site with the highest concentration was Guangzhou (838 ± 126 pg m−3), followed by Beijing (781 ± 107 pg m−3). Significant positive correlations were found between PBDEs levels and urban population (R = 0.69, P < 0.05) and gross industrial output values (R = 0.87, P < 0.001) as well. BDE-209 was the dominating congener with the contribution of 64 ± 23% to ∑12PBDEs, followed by BDE-47(8 ± 8%) and -99(6 ± 5%) at all urban and suburban sites. At background/rural sites, however, BDE-47 was the dominating congener, followed by BDE-99, together accounting for 52 ± 21% of ∑12PBDEs, while BDE-209 was only 11 ± 2%. It was found that PBDEs at the 15 sites showed a primary distribution and fractionation pattern. This study produced more than 700 pairs of air samples in gaseous and particulate phases with a wide temperature range of ∼60 °C, providing a good opportunity to investigate gas−particle partitioning for individual PBDE congeners. The results of gas−particle partitioning analysis for PBDEs using both subcooled-liquid−vapor pressure (PL)-based and octanol−air partition coefficient (KOA)-based models indicated that PBDEs in air at all sampling sites had not reached equilibrium because the slope values (mO) in the KOAbased equation and the opposite slope values (mP) in the PL-based equation at all 15 sampling sites were less than 1. It also found that both mO and −mP were significantly and positively correlated with the annual average temperatures of sampling sites and also significantly and negatively correlated with the mole masses of PBDE congeners, indicating a general trend that the higher the temperature at the sampling site and the lower the mole mass of the PBDE congeners are, the closer to the equilibrium the congeners approach and vice versa. To our knowledge, this is the first study to report the correlations of the slope values for both the KOA-based and PL-based equations with temperatures at sampling sites and mole masses for individual PBDE congeners.

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were widely used in our daily lives. For example, ComPentaBDE was used in flexible polyurethane foam, which is used as cushioning in upholstered furniture; ComOctaBDE in acrylonitrile butadiene

INTRODUCTION Brominated flame retardants (BFRs), which have been widely used for more than 30 years, have effectively protected the safety of human lives and properties. Polybrominated diphenyl ethers (PBDEs), an important BFR, has three major commercial products: commercial pentabromodiphenyl ether (ComPentaBDE), commercial octabromodiphenyl ether (ComOctaBDE), and commercial decabromodiphenyl ether (ComDecaBDE).1 PBDEs © 2013 American Chemical Society

Received: Revised: Accepted: Published: 8978

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(glass fiber filters) and two layers of polyurethane foam (PUF) plugs were set to collect air samples in particulate and gaseous phases, respectively. After sampling, the sampled GFFs and PUF plugs were sent to IJRC-PTS laboratories for further treatment and analysis. All sampled GFFs and PUFs had been stored at −20 °C until extraction. Quality Assurance/Quality Control. Twelve PBDE congeners (Tri-BDE: BDE-17, -28; Tetra-BDE: BDE-47, -66; Penta-BDE: BDE-85, -99, -100; Hexa-BDE: BDE-138, -153, -154; Hepta-BDE: BDE-183; and Deca-BDE: BDE-209) were screened for both gaseous and particulate samples. One field blank and one laboratory blank were added for every 10 samples. No target compounds were found in these blanks. In this study, the air samples were spiked with PCB-155 as a surrogate and quantified with BDE-71 as an internal standard. Recoveries of PCB155 were 88 ± 10% (mean ± one standard deviation). The final reported concentrations were not surrogate recovery corrected. A spike test was performed to examine if PBDEs can be extracted effectively with the applied method. Average recoveries of spiked 12 PBDEs standards in clean PUF and GFF were 71% ± 5% and 78% ± 6%, respectively. Instrument detection limits (IDL) for PBDEs ranged from 0.02 to 0.83 ng mL−1 (Table S2, SI). Gas−Particle Partitioning. Partitioning of atmospheric semivolatile organic compounds (SVOCs) between gas and particle phases is usually presented by a dimensionless gas− particle partition coefficient KP′ given by

styrene; and ComDecaBDE in the high-impact polystyrene component of electronic equipments.2 The global production of PBDEs was ∼40 000 t in 19923 and increased to ∼70 000 t in early 2000s.4 ComDecaBDE was the dominating product, and it contributed more than 80% to the total PBDE production.5 In China, the manufacturers, located mainly in the provinces of Shandong, Hebei, and Jiangsu,6 also produced ComDecaBDE in a large amount, with a production of 15 000 t in 2006.7 PBDEs’ high production volume, widespread use, and environmental persistence, have led to their ubiquitous presence in the environment. PBDEs, maybe of developmental neurotoxicants, are causing neurochemical and hormonal deficiencies.8−10 As a result, ComPentaBDE and ComOctaBDE were regulated in Europe and the Unites States in 2002 and 2003, respectively,11 and added as new members of persistent organic pollutants (POPs) in the Stockholm Convention at the fourth Conference of the Parties (COP-4) held in May 2009.12 ComDecaBDE is still produced and used in many countries, including China, while the Europe Union (EU) restricted its use in 2008 and the United States also voluntarily planed to restrict its production, import, and sale in the country at the end of 2013 because of its potential harm to the environment and humans via debromination to form lower toxic brominated PBDE congeners.13 In China, many studies have been conducted to determine PBDEs in various environmental media and in human tissues.3 Most of the studies, however, only focused on point sources such as e-waste recycling sites,14−16 whereas little information is available about PBDE’s fate and pollution in atmosphere in a large scale,17 which is an important environmental compartment for transport and transformation of POPs. Urban regions have been an important source for PBDEs pollution in surrounding areas.18 Therefore, it is necessary to characterize the compositions and environmental behavior of PBDEs in ambient atmosphere in urban areas and beyond. The International Joint Research Center for Persistent Toxic Substances (IJRC-PTS) has carried out the Chinese POPs Soil and Air Monitoring Program phase I (SAMP-I) and phase II (SAMP-II) (See Section S1 in Supporting Information (SI)). While SAMP-I investigated POPs in both air and soil mainly in Chinese rural areas, SAMP-II focused on Chinese urban regions, under which some results have already been published for some individual cities.19−25 In this study, the results of PBDEs for the first year sampling under SAMP-II were presented. The main objectives of this work are to investigate the levels, composition of PBDEs in atmosphere across China and to analyze the gas−particle partitioning of PBDEs in this country based on a huge amount of gaseous and particulate PBDE pair data sets with a large range of ambient temperature of ∼60 °C.

KP′ = C P/CG

(1)

where CG and CP are concentrations of gas and particle phases (in pg m−3 of air), respectively. Partitioning of SVOCs between gas and particle phases is also defined by the gas−particle partition coefficient, KP (m3 μg−1) given by26 KP = (C P/TSP)/CG

(2)

where TSP is the concentration of total suspended particle in air (μg m−3). There are two models to calculate KP; one is a linear relationship between log KP and log PL (subcooled liquid vapor pressure), which is expressed as27 log KP = mP log PL + bP

(3)

where slope mP and intercept bP are fitting constants, and PL is a function of ambient temperature. The second model to calculate KP is a linear relationship between log KP and log KOA (octanol− air partition coefficient) when the absorption into organic matter is the dominant process and, similar to eq 3, is given by28 log KP = mO log K OA + bO

(4)

where slope mO and intercept bO are fitting constants. In eqs 3 and 4, the absolute values of mP and mO are equal to 1 when chemicals in gaseous and particulate phases reach equilibrium. The smaller the absolute values are, the farther away the states deviate from equilibrium. Influences by Temperature. It has been well-known that temperature dependence of air concentrations of SVOC, including PBDEs, can be described by the Clausius−Clapeyron (CC) equation, which can be expressed as

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MATERIALS AND METHODS The detail of this section can be found in SI, and only a brief description is presented here. Sample Collection. Air samples in both gaseous and particulate phases were synchronously collected using highvolume air samplers for 24 h every week from September 2008 to August 2009 at 15 sampling sites, including 11 urban sites (Beijing, Harbin, Dalian, Xi’an, Nanchang, Kunming, Chengdu, Lhasa, Guangzhou, Lanzhou, Shihezi); 1 suburban site (Shanghai (Lingang), 75 km away from the downtown of Shanghai); and 3 background/rural sites (Waliguan, Wudalianchi, and Xuancheng) (see Figure S2 and Table S1, SI). A layer of GFFs

ln P = m /T + b

(5)

where P is the partial pressure (atm), T is the temperature (K), and m and b are fitting parameters. The results of the CC plot can be used to determine the sources of PBDEs with a gas phase, 8979

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Figure 1. Annual average air concentrations of ∑12PBDEs from September 2008 to August 2009 at 15 sampling sites of China.

Figure 2. Correlation between ∑12PBDE concentrations at the 11 urban sites and populations (the left panel) and also gross industrial output values (the right panel) (data were from Chinese City Year Book 2009) (See Table S1, SI).

average concentrations of ∑12PBDE at the 11 urban sites with urban populations and also with gross industrial output values for these sites were analyzed. The results are depicted in Figure 2, indicating a significant correlation (R = 0.69, P < 0.05) for the former and even a more significant and stronger correlation (R = 0.87, P < 0.001) for the latter. This is not unexpected as PBDEs are a class of industrial chemicals and exist in many everyday consumer stuffs, such as furniture, textiles, and electronics.11 All these indicated the anthropogenic nature of PBDEs and showed a typical primary distribution pattern.31 There were some reports on PBDEs in Chinese urban air, mainly focusing on Guangzhou17,32,33 and Shanghai13 (See Table S4, SI). These published data are comparable to the results obtained in this study. For example, it was reported that air concentrations of PBDEs in Guangzhou were 353−7873 pg m−3 in 2004,17 240−9440 pg m−3 in 2007,32 and 5.40−4990 pg m−3 in 2006.33 Air concentrations of PBDEs only in particle phase were measured in Shanghai, and 744 pg m−3 was found in an industrial zone, higher than those in other three districts (108−367 pg m−3), and also higher than our results for Lingang, Shanghai (67.0 ± 98.0 pg m−3). This is not surprising since our sampling site was in a suburban district of the city close to sea. PBDEs in air

if they came from local sources, or if they are due to long-range atmospheric transport (LRAT).29,30

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RESULTS PBDE Concentrations. Annual mean, minimum, and maximum for gas and particle phase PBDEs at the 15 sampling sites from September 2008 to August 2009 are presented in Table S3, SI, whereas total air concentrations (particle plus gas phases) of 12 PBDE congeners (∑12PBDEs) at 15 sampling sites are summarized in Figure 1. The concentrations of ∑12PBDEs at all sites were in the range of 11.0−838 pg m−3 with a mean of 232 ± 72.0 (mean ± SE) pg m−3. Concentrations of ∑12PBDEs in Chinese air were in the order of urban (306 ± 20.0 pg m−3) > suburban (67.0 ± 14.0 pg m−3) > background/rural (14.0 ± 1.00 pg m−3). The highest concentration appeared in Guangzhou (838 ± 126 pg m−3), followed by Beijing (781 ± 107 pg m−3), and the lowest annual mean concentration was found in Waliguan (11.0 ± 0.49 pg m−3), a Global Atmospheric Watch (GAW) Station in northwestern China. Higher concentrations were generally observed in more developed cities, and lower concentrations in background/rural areas. Correlations of annual 8980

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BDE-47 and -99 were the dominated congeners and together contributed 75% to the overall ∑8PBDE in Chinese background/ rural air. It is interesting to compare the Chinese PBDE congener compositions produced in this study (Figure S5, SI) with those reported for the United States (Figure S6, SI). In both urban and background/rural sites, the ratio for BDE-209 to the total PBDE in Chinese ambient air was greater than that in air of the United States, while the ratios for BDE-47 and -99 in Chinese air were smaller than those in the U.S. air, which is possibly due to the larger usage of ComPentaBDE in the United States41 and ComDecaBDE in China.7 It is also noticeable that the tri-PBDE, such as BDE-17 and BDE-28, were quite abundant in Chinese air in the gas phase (together accounting for 25.6% at background/rural sites and 44.8% at urban sites), which is not consistent with the profile of the ComPentaBDE produced in the United States, in which both BDE-17 and -28 were below detection limits (see Figure S7, SI). This was also reported by Qiu et al,12 in which BDE-28 constituted 39.8% of total PBDEs in gas phase in air of Taihu Lake region, China (see Table S5, SI). This profile may be due to the PBDEs produced/used in China. Air samples were collected around a PBDEs production facility in China, and the compositional profile of PBDEs in air is depicted in Figure S8, SI. A high portion of BDE-28 (>12%) in gas phase was found, which was consistent with the monitoring data reported by Qiu et al.12 and ours, and also possibly indicated the existence of the ‘specific ComPentaBDE formulation’ suggested by Qiu et al.12 However, it is not clear that this high portion of BDE-28 was produced due to production of ComPentaBDE or a byproduct from the production of ComDecaBDE. As previously introduced, a large amount of ComDecaBDE was produced every year recently in the provinces of Shandong, Hebei, and Jiangsu6 at an annual production of ∼15 000 t.7 There was another source that needs to be pointed out: the PBDE emission from E-waste sites. As shown in Figure S9, SI, the di- and tri-BDEs consisted 17.9% of the total PBDEs, which could be one of emission sources to contribute to the less brominated PBDEs in Chinese air, at least to its surrounding areas.43 Primary Fractionation. PBDE homologue profiles at urban, suburban, and background/rural sites are depicted in Figure 3. The left panel shows that the concentrations of each PBDE homologue group decrease from source region (urban sites) to remote regions (background/rural), which is a typical primary distribution pattern.31 The right panel indicates that, while the portion for highly brominated PBDE homologue (10-Br)

at rural and background sites in China have also been reported. For example, annual average concentrations of PBDEs in air were 220 pg m−3 in Taihu Lake region in 2004,12 and ranged from 2 to 15 pg m−3 with a mean of 8 pg m−3 at Waliguan site in 2005,34 which is similar to our results (11.0 ± 0.49 pg m−3). In comparison, ambient concentrations of ΣPBDEs were 13− 35 pg m−3 in Vienna,35 106 pg m−3 in Ispra, Italy,36 6.2−150 pg m−3 at an industrial site in Izmir, Turkey,37 and 4.5−110 pg m−3 at an urban site in Kyoto, Japan.38 Average concentrations of ΣPBDEs were 100 ± 35 pg m−3 in 2002−200339 and 65 ± 4 pg m−3 in 2005− 200640 in Chicago and 87 ± 8 pg m−3 in 2005−2006 in Cleveland.40 Compared with these reported data, the total PBDE pollution levels in China were higher than those in the United States, which was the major PBDE production country in the world before the 21 century and accounted for approximately 98% of the global production of penta-formulation based on 1999 data.41 PBDE Profiles. Compositions of annual PBDEs in air with both gas and particle phases at 15 sampling sites are listed in Table S5 and shown in Figure S4, SI. Compositions of PBDEs at urban and suburban sites were similar, in which BDE-209 was the dominated congener with an annual average contribution to ∑12PBDEs of 64 ± 23%, ranging from 50 ± 21% (Kunming) to 86 ± 16% (Beijing). This result is expected since BDE-209 is the main component of ComDecaBDE that is still largely used in China. Following BDE-209, BDE-47 and -99 respectively contributed 8 ± 8% and 6 ± 5% to the total PBDEs. In the background/rural air, however, the dominant PBDE congener was BDE-47 with an annual average contribution to ∑12PBDEs as 28 ± 11%, followed by BDE-99 (25 ± 10%). The contribution by BDE-209 was 11 ± 20%, much lower than those at the urban/ suburban sites. Data in Table S5 (SI) also indicated that BDE209 presented exclusively in particulate phase, whereas the other congeners had both gaseous and particulate phases with a general trend that the portions in gas phase increased from the highly brominated congeners to less brominated congeners. These differences can be explained as BDE-209 is easy to bound to particles and hence less subject to migrate with air mass movement to the background/rural sites in comparison to other less brominated PBDEs. This observation is consistent with that of an early study,42 in which air samples were collected between September 21 and November 16, 2004, using PUF-based passive air samplers (PASs) at 77 sampling sites across several Asian countries, including 32 Chinese sites (19 urban and 13 background/rural). Eight PBDE congeners (BDE-17, -28, -32, -47, -49, -75, -99, and -100) in air (mainly with gaseous phase) were detected. The results indicated that

Figure 3. Concentrations (the left panel) and compositional profiles (the right panel) of PBDE homologues at the three different sites. 8981

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Figure 4. Values of −mP and mO, along with (A) annual ambient temperature (T (°C)) and (B) mole mass for each PBDE congener at 15 sampling sites.

PBDEs in air for the four seasons actually depends on the variation of PBDEs in particle phase. Seasonal variation also appeared for PBDEs in background/rural atmosphere. As is the case in urban centers, the highest level of PBDEs in gas phase and the lowest level in particle phase also happened in summer; the highest level of PBDEs in particle phase and the lowest level in gas phase, however, did not occur in winter. The reason for these differences could be complicated since the PBDEs at the background/rural sites came from the source regions due to long-range and/or short-range atmospheric transport, and their compositions were influenced by many factors other than temperature alone, such as strength and directions of wind at the sites. Gas−Particle Partitioning of PBDEs. The fate, transport, and removal of PBDEs from the atmosphere by dry and wet deposition processes depend strongly on their gas−particle partitioning.44 The proportions in gas and particle phases of each PBDE congener in four seasons at 15 sampling sites are demonstrated in Figure S11 (SI,) which shows that BDE-209 was only found in the particle phase, while the other PBDE congeners existed in both gaseous and particulate phases. For the same city, the fractions of PBDEs in gas phase increased from the winter to summer, and this trend was more obvious for the less brominated congeners than the highly brominated ones. In winter, the proportions of PBDEs in particulate phase were higher in Chinese northern cities (such as Lanzhou and Xi’an), than those in the south cities (such as Kunming and Guangzhou). In addition, more PBDEs existed in gas phase in the atmosphere of background/rural sites, especially in Waliguan, than in urban/suburban sites. Figure S12 (SI) presents the values of KP′ for each PBDE homologue at two different types of sampling sites (urban/ suburban and background/rural) in four seasons. The seasonality of KP′ for these homologues is obvious: higher in the winter and lower in the summer, indicating the value of KP′ is associated with ambient temperature. Figures S13 and S14 (SI) show the log−log plots of KP vs PL and KOA, respectively, for PBDEs at 15 sampling sites for a whole year. The values of KP were used only when the congeners were detected in both gaseous and particulate phases. As presented in Figures S13 and S14 (SI), significant linear correlations were observed between log KP and log PL (r2 = 0.09−0.69, P < 0.0001, for Lhasa P < 0.05) and also between log KP and log KOA (r2 = 0.07−0.67, P < 0.0001, for Lhasa P < 0.01). At equilibrium, the value of mP in eq 3 should equal to −1 and the value of mO in eq 4 should equal to 1.45,46 However, the values of mP ranged from −0.67 to −0.09, all greater than −1, and the values of mO ranged from 0.18 to 0.64, all less than 1, both with a big margin. These results indicated that PBDEs in air at all 15 sites did not reach equilibrium between gas and particle phases.

decreased from urban sites to background/rural sites, the reverse was observed for lighter homologues (3−6Br). In addition, the average percentage of BDE-209 in the two rural sites, 17 ± 29% in Xuancheng and 10 ± 18% in Wudalianchi, were higher than that at the background site Waliguan (8 ± 11%). Together, the two panels in Figure 3 present a primary fractionation.31 Influence of Ambient Temperature. The CC eq 5 was applied to the gaseous PBDEs at all the 15 sites, and the results are presented in Table S6 of the SI. The results for the two sites, the urban site Beijing and the background site Waliguan, show apparent differences in temperature dependence of the PBDE concentrations and are the best examples to explain the sources of PBDEs in gas phase. The positive correlation between gaseous PBDE concentrations and temperatures (p = 0.01 ± 0.02), together with steeper slopes of the CC plots (−4336 ± 2305) at the Beijing site, indicate a strong local source; while much weaker correlation between gaseous PBDE concentrations and temperatures or lacking in temperature dependence (p = 0.11 ± 0.14), together with much flatter slopes of the CC plots (−1274 ± 449) at the Waliguan site, suggest a source due to a long-range atmospheric transport. For the other sites, the influence of ambient temperature to the PBDE levels might be not so obvious. For example, the PBDEs in air at the two rural sites, Wudaliachi and Xuancheng, showed a pattern like that for the urban site: a positive correlation between gaseous PBDE concentrations and temperatures was found at these two sites, especially for the less brominated PBDEs (see Table S6, SI). This is probably due to close distance from source regions, and thus the PBDEs in air at the rural sites kept the same pattern of temperature dependence as the source region. It was also reported that a strong temperature dependence of air PBDE concentrations was identified at a rural site, which was 40 km away from an e-waste site.43 Seasonality. Since the variation of PBDE concentrations in the urban centers responded strongly to the changes of ambient temperature, the PBDE concentration in these regions will show seasonality. Figure S10 (SI) depicts the variation of PBDE levels in four seasons at urban and background/rural areas, which shows that PBDEs in particle phase were highest in winter, followed by fall and spring, and the lowest in summer, while PBDEs in gas phase were highest in summer, followed by fall and spring, and the lowest in winter. This is possible because in summer, PBDE congeners can volatile more easily due to high temperature, resulting in the highest concentration of PBDEs in gas phase and the lowest concentration in particle phase. The opposite results happened in winter, when the highest concentration of PBDEs in particle phase and the lowest concentration of PBDEs in gas phase occurred due to the low temperature. The major PBDEs in urban centers were in particulate phase, and the variation of total 8982

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Figures S15 and S16 show the log-log plots of KP vs. PL and KOA, respectively, for 11 PBDE congeners, presenting significant linear correlations between log KP and log PL and also between log KP and log KOA for all congeners but not for BDE-138, -153 and -183. The values of −mP from eq 3 and mO from eq 4 as a function of annual mean ambient temperature at the 15 sampling sites and also as a function of mole mass for each PBDE congener are presented in Figure 4. It was found that these values are significantly and positively correlated with the annual average temperature of each site with r2 = 0.50 (P < 0.05) for −mP and r2 = 0.48 (P < 0.05) for mO; and significantly negatively correlated with the mole mass of each PBDE congener with r2 = 0.73 (P < 0.05) for −mP and r2 = 0.71 (P < 0.05) for mO. The general trend is that the higher is the temperature at the sampling site, the higher the values of −mP and mO are, which explained approximately 50% of the variation; and the higher the moll mass is, the lower the values of −mP and mO are, which explained approximately 70% of the variations. In other words, the distribution pattern of PBDEs in gas and particle phases depends on the physiochemical properties (mole mass for example) and the environment parameters (ambient temperature for example). These results also indicated that the two approaches (KOA-based and PL-based) are essentially equivalent. Implication and Discussion. A large number of data sets for PBDEs not only revealed a spatial pattern and a temporal trend for levels and compositions of PBDEs in air across China but also provided an opportunity to study gas−particle partitioning more comprehensively over a wide range of temperatures and for individual congeners. In addition, eqs 3 and 4 can be used to calculate gas−particle partition coefficients, KP, but the slope m (mP and mO) and intercept b (bP and bO) depend on the ambient conditions and are site- and temperature-specific. In other words, the monitoring data of PBDE concentrations in gas and particle phases are still needed to determine the values of m and b in these two equations, which is, unfortunately, not very useful to environmental modelers, since their task is to predict the environmental behavior, including their concentrations in air with both gaseous and particulate phases based on physiochemical properties of chemicals, their emissions, climate, and meteorological conditions. Further research is needed to find an equation or equations to accurately estimate air concentrations in both gaseous and particulate phases, which is the next objective of our research.

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Government of Canada Program for International Polar Year (IPY) and International Joint Research Center for Persistent Toxic Substances (IJRC-PTS), China.

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ASSOCIATED CONTENT

S Supporting Information *

Detailed chemicals and reagents, procedures on sample extraction and cleanup, and many other tables and figures to show the relationships between subcooled liquid vapor pressure based and octanol−air partition coefficient based equations. This material is available free of charge via the Internet at http://pubs.acs.org.

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*Phone: (411)-23625373; fax: (411)-23928821; e-mail: IJRC_ [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China (20977022 and 41101493). The air monitoring at the three background/rural sites was financially supported by the 8983

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