Environ. Sci. Technol. 2010, 44, 8114–8120
Diurnal Fluctuations in Polybrominated Diphenyl Ether Concentrations During and After a Severe Dust Storm Episode in Kuwait City, Kuwait B O N D I G E V A O , * ,† F O D A Y M . J A W A R D , | MATTHEW MACLEOD,‡ AND KEVIN C. JONES§ Kuwait Institute for Scientific Research, P.O. Box 24885, 13109 Safat, Kuwait, Institute for Chemical and Bioengineering, ETH Zurich, CH-8093, Zurich, Switzerland, Lancaster Environment Center, Lancaster University, Lancaster LA1 4YQ, U.K., and Environmental and Occupational Health, College of Public Health, University of South Florida, 13201 Bruce B. Downs Blvd. MDC56, Tampa, Florida 33612-3805, United States
Received April 13, 2010. Revised manuscript received September 16, 2010. Accepted September 29, 2010.
Concentrations of polybrominated diphenyl ethers (PBDEs) were quantified in four-hour integrated air samples obtained serially over a five day period in May 2007 in Kuwait City during and after a severe dust storm. The ∑PBDE concentrations ranged from 51 to 1307 pg m-3 for the first two days of sampling and 20 to 148 pg m-3 for the rest of the sampling period. The first two days of sampling occurred during a severe dust storm episode when the total suspended particulates (TSP) in air exceeded 1000 µg/m3 with concentrations peaking during the day and decreasing at night. During this dust episode, the peak nighttime PBDE concentration was 30 times higher than the minimum daytime concentration. Although ∑PBDE concentrations peaked at night during the first two sampling days, the fluctuations in the BDE 47:99 ratio tracked changes in ambient temperature remarkably well, following a clear diurnal pattern. The fraction of congeners in the gas phase varied inversely with solar flux and was lower on days with a high number of hours of sunshine, suggesting that photolytic degradation of gas-phase PBDEs was occurring.
Introduction Persistent organic pollutants (POPs) have the propensity to enter the gas phase at ambient temperatures and undergo long-range atmospheric transport (1, 2). These chemicals have received intense international attention because of their ubiquity, persistence, high bioaccumulation potential, and harmful biological effects (3). These concerns eventually led to the development of the Stockholm Convention on POPs, a global treaty aimed at reducing and eventually banning an initial list of the 12 POPs including nine pesticides, poly* Corresponding author phone: (+965) 4989178; fax: (+965) 4845350; e-mail:
[email protected]. † Kuwait Institute for Scientific Research. | University of South Florida. ‡ ETH Zurich. § Lancaster University. 8114
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chlorinated biphenyls (PCBs) and polychlorinated dibenzop-dioxins and furans (PCDD/Fs), a byproduct of various combustion processes. PBDEs are similar in molecular structure to PCBs and PCDD/Fs and have been shown to have similar environmental properties. They have been widely used to flame retard a variety of consumer products, including electrical components, household appliances, furniture, textiles, etc. (4, 5). They are also highly hydrophobic, bioaccumulative (6), and have the propensity to enter the gas phase at ambient conditions and undergo long-range atmospheric transport (7, 8). They have been found to have a ubiquitous environmental distribution and have been measured at remote sites, like the Arctic, where they had never been used (9). These properties led to the inclusion of the penta- and octa-technical mixtures in Annex A (elimination) of the convention (SC-4/14 and SC-4/18) at the meeting of the conference of parties (COP) in May 2009 (10). Research on POPs has, in recent years, included efforts to understand their ambient sources (11), atmospheric transport (12, 8) and fate (13-15). Because these chemicals are trans-boundary pollutants and undergo long-range transport (14, 2) from source to remote regions, environmental data are needed from all regions of the globe to better understand the key processes that influence their global distribution. At present there is a paucity of reliable environmental data on the levels of most POP chemicals in the Middle East, most of Africa, and Asia, from which to assess the effectiveness of international efforts to minimize the release of these chemicals to the environment. Also lacking in the Middle East is an understanding of the role of dust storms on the levels, transport and fate of POPs. Dust storm episodes are important weather phenomena in arid countries around the world (16-18) and are brought about by highenergy winds eroding the top soil in regions with minimal vegetation cover. The rates of dust fallout in Kuwait have been reported to be one of the highest in the world (19) with concentrations reaching 1400 µg m-3 during severe dust storms. Dust storms have been reported to result in elevated concentrations of toxic metals (20, 21), viruses (22), fungal spores (23), and POPs (17, 18). Chi et al (17) observed a doubling in PCB and PCDD/F concentrations in Taipei City, and an almost three times increase in the levels at a coastal site in northern Taiwan during a dust storm episode in March, 2006. The goals of this study were to investigate short-term changes in the concentrations of PBDEs during and after a dust storm episode in Kuwait, and to study the factors influencing their concentrations during episodic spikes in particulate matter in air. This study is one of a few studies to investigate the role of dust storms in the distribution of chemicals and the first, that we are aware of, to investigate the diurnal fluctuations of PBDE concentrations during dust storms.
Materials and Methods All solvents used in this work were of analytical grade and purchased through VWR Scientific (USA). Silica (Baker, 100-200 mesh), alumina and sodium sulfate (Baker) were purchased through VWR Scientific (USA). The PUF plugs were certified as flame retardant free and purchased from Tisch Environmental (OH). The PUF plugs were cleaned for 48 h using dichloromethane in a giant Soxhlet, with the solvent replaced after 24 h. The pre-extracted PUF plugs were dried in a clean desiccator under vacuum and stored in solvent rinsed amber glass jars lined with solvent rinsed aluminum foil to avoid contamination during storage. During 10.1021/es101148j
2010 American Chemical Society
Published on Web 10/13/2010
the sampling campaign filters were baked on the previous day in a muffle furnace at 450 °C and wrapped in solvent rinsed aluminum foil. Sampling. The current study was carried out during a dust storm episode that lasted for five days. Sampling commenced on the third day of the storm and continued for three days after the episode. Sampling commenced at noon on the 19th of May and continued until noon on the 24th of May on the premises of the Kuwait Institute for Scientific Research located on the northwestern shore of the Arabian Gulf (29.30 N, 47.90 E). The sampler was stationed approximately 50 m from the nearest building. Over this period 30 samples were serially obtained over four-hour intervals using a modified high volume air sampler (Tisch Environmental, Inc.). The sampler was located about 1.5 m above ground. Approximately 170 m3 of air was pumped through a Whatman GFF (8′′ × 10′′) to trap particulate matter and the vapor phase compounds trapped on two PUF plugs (85 mm in diameter and 70 mm in length) located downstream of the GFF. Exact air volumes for each sample were determined with the use of a calibrated Magnehelic gauge (Tisch Environmental, Inc.) to measure pressure at the start and end of each sampling period. The average of the two readings was used to calculate the air sampled over that measurement period. Upon retrieval, the PUF and filter samples were stored in separate cleaned amber glass jars and kept at -15 °C until extraction to minimize losses by photolysis and/or volatilization. The GFF was weighed using a microbalance before and after deployment to determine the TSP concentration over that sampling period, which is nominally defined as the difference between the two measurements. Field blanks were collected daily and consisted of a PUF plug and filter assembled in the sampler, immediately removed and processed in an identical manner to actual samples. Extraction and Analyses. Details of the sample extraction and cleanup procedures are given elsewhere (24) and in the Supporting Information. In short, PUF plugs and filter samples were extracted in a Soxhlet apparatus using dichloromethane. Prior to extraction the samples were spiked with BDE congeners 35 and 181 to monitor analytical recovery. The extracts were reduced in volume on a Turbovap, solvent exchanged to hexane and interfering compounds removed by column chromatography (i.d. nine mm) using 2 g of silica gel (Merck, 60-230 mesh) and 1 g alumina (BDH, neutral alumina). The extracts were transferred to100 µL glass inserts, and spiked with Mirex (10 µL of 10 ng/µL) internal standard, used for volume correction and to adjust for variations in instrument response. The sample extracts were analyzed on a Shimadzu GC 2010 (Shimadzu, Tokyo, Japan) gas chromatograph using splitless injection on a 30 m DB5-ms column (0.25 mm i.d., 0.25 µm film thickness) and helium as carrier gas. This gas chromatograph was coupled to a Shimadzu 2010 mass selective detector operated in electron capture negative chemical ionization (ECNCI) using selected ion monitoring (SIM), with methane as reagent gas. The ions m/z 79 and 81 were monitored for PBDEs, and 402/404 for Mirex. Details of the temperature program and operating conditions of the mass spectrometer are given elsewhere (24) and in the Supporting Information. BDE 209 was analyzed separately on a 15 m DB 5 ms column. The ions m/z 484.7, 486.7, and 488.7 were used for identification and quantitation was by external standard method against a set of calibration standards. Quality control procedures are described in the Supporting Information and summarized here. Laboratory and field blanks comprised of pre-extracted PUF plugs and baked filters that were treated as a sample. The analytes present in the appropriate blank were subtracted from those in the sample extracts. The detection limits varied from 0.1-1.6 pg m-3 for
FIGURE 1. Concentrations of ∑PBDEs and ambient temperature measured between 19th May and 24th May 2007. PBDEs obtained from the results of the analysis of field blanks. Average recoveries (%) for surrogates spiked in samples for all samples were between 70 ((12 SD) for BDE 35 and 84 ((8 SD) for BDE 181. The accuracy and precision of the analytical method was further assessed by replicate analyses (n ) 6) of a certified indoor dust reference material (SRM 2585). The results (Supporting Information Figure SI-3) compared very well with the certified values of all the congeners. Meteorological Factors during Study Period. Meteorological data over the sampling period was obtained from the on-site weather station operated by the Institute and the NOAA Reanalysis data set. The meteorological conditions, including temperature, solar flux, wind speed, and boundary layer conditions, which may be relevant to understanding the diurnal fluctuations in concentrations of different pollutants over the five intensive sampling days are presented in the Supporting Information (Figure SI-1). The key meteorological factors over the sampling period were as follows: Daytime wind speeds about ∼8 m/s dropping to ∼2 m/s at night; relatively higher atmospheric pressure for first two sampling days relative to rest of sampling days; high mixing height during the day of ∼3500 m and lower mixing heights at night of ∼250 m. To examine the influence of air mass origin on the concentrations obtained in the study, back trajectory analyses (see Supporting Information Figure SI-2) were determined using the online HYSPLIT trajectory model (25). Taken together, the sampling campaign can be sorted out into two time groups based on the meteorology during sampling. The first two days of sampling were carried out towards the end of a dust storm that was influencing the region that lasted five days. The air mass over this period was from an easterly direction (from the direction of Iran) across the Arabian Gulf. The rest of the samples were collected when the dust storm had abated and air trajectories were originating from a northwesterly direction (from Iraq).
Results and Discussion A total of eight PBDE congeners routinely detected were monitored in samples and quantified. These were as follows: BDEs 28, 47, 99, 100, 153,154, 183, and 209. The samples were subsequently analyzed for BDEs 206, 207, and 208. The concentrations of ∑PBDEs (gas + particle), plotted as a function of time of day, is given in Figure 1 together with fluctuations in temperature over the entire study period. The ∑PBDEs concentrations (gas + particle phase) measured ranged from 51 to 1307 pg m-3 for the first two days of sampling and 20-148 pg m-3 for the rest of the sampling period (Figure 1). Congener-specific concentration data is VOL. 44, NO. 21, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Average (Range) Concentrations of PBDEs (A) During, and (B) After The Dust Storm A. During Dust Storm congener
average-day
average-night
28 47 100 99 153 154 183 209 ∑8PBDEs
8.5 (2.3-18) 110 (51-226) 18.2 (8-37.4) 86.1 (37-180) 6.2 (2.5-12.9) 6.3 (2.6-12.9) 0.5 (0.07-0.9) 2.8 (0.1-4.6) 238 (107-493)
6.0 (5.3-6.9) 294.5 (282-307) 66.8 (66.2-67.4) 280.8 (251-304) 18.4 (13.5-23.2) 16.2 (6.8-25.6) 0.6 (0.5-0.7) 1.8 (0.4-3.2) 688 (669-707)
B. After Dust Storm congener
average-day
average-night
28 47 100 99 153 154 183 209 ∑8PBDEs
2.7 (1.0-3.8) 26.5 (14-34.3) 3.2 (2.5-3.8) 11.9 (10.2-13.8) 0.7 (0.68-0.82) 0.57 (0.56-0.57) 0.14 (0.05-0.19) 1.3 (0.11-2.48) 47 (29-59)
2.4 (1.8-3.4) 26.9 (15-35.8) 4.0 (2.1-5.5) 16.1 (7.5-22.7) 1.0 (0.5-1.5) 1.0 (0.5-1.5) 0.2 (0.1-0.2) 2.1 (1.2-3.0) 54 (30-72)
summarized in Tables 1a and b for gas and particle phase concentrations during and after the dust storm, respectively. The full data set containing congener concentrations in each sample is given in the Supporting Information (Tables SI13). As can be expected, there is a strong periodicity to the daily temperature, with maxima around 2 p.m. and minima at around 2 a.m. The first two days of sampling occurred during a severe dust storm episode when the TSP in air exceeded 1000 µg/m3 with concentrations peaking during the day and decreasing at night. The data obtained in this study is higher than those estimated from a previous study using passive samplers between February and April 2004 (mean, 9.2 pg m-3; range, 2.5-32 pg m-3) (24) and between December and March of 2005 (mean, 17 pg m-3) (26). The differences in the concentrations obtained in this study to the previous studies may be related to the differences in sampling techniques and time of year. Passive samplers provide time integrated, semiquantitative concentration information as opposed to data obtained from calibrated high volume air samplers. The passive sampling data cited above were obtained at a time of year when average temperatures were lower (range, 10-25 °C) than in the current study (range, 30-45 °C). Moreover passive samplers do not account for short-term spikes in atmospheric concentration of pollutants, the type reported in this study. The concentrations in this study are comparable to those reported in early spring in Ontario, Canada (88-1250 pg m-3) (27) where, like in this study, concentrations spiked in the atmosphere over a short period of time. The concentrations measured after the dust storm (20-146 pg m-3) are similar to those reported in other urban locations like Davis, California (54-120 pg m-3) (28); Chicago (40-70 pg m-3) (29); Chendian (316 pg m-3) (29), and Guangzhou,(41.5-256.8) (30) in China. Clearly these differences suggest that the factors controlling PBDE levels measured during these two periods are different. Air mass back trajectory analyses showed that the air sampled during the dust storm, when levels spiked in the environment at night, was predominantly from the east, from the direction of Iran and passing across the Arabian Gulf. Following the dust storm (21st to 23rd May) the air mass was predominantly northeasterly from the direction of Iraq 8116
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(Supporting Information Figure SI-2). The source of the PBDEs measured during the dust storm event is entirely unknown at this point. It is likely that a source may exist east of Kuwait, probably in Iran, where the air masses originated when elevated concentrations were measured in nighttime samples. It may also be possible that the source of the dust that was depositing across the region and the contaminants might have similar origins. This may explain why the levels of PBDEs decreased to background levels in subsequent samples collected after the dust storm event. Episodic spikes in the atmospheric concentration of POPs, some associated with known events, have been reported in the literature. For example, an increase in the atmospheric concentration of PBDEs and PCBs was observed in the early spring of 2000 in Ontario, Canada (27). This “spring pulse” is hypothesized to be associated with the sudden release with snowmelt of pollutants accumulated in snow during winter months. In another study in the UK elevated concentrations of PBDEs and PAHs were measured during the national “bonfire night” festivities when many large fires are lit across the entire UK (31). The PAH concentration increased from ca. 20-30 ng m-3 to a maximum of ∼180 ng m-3; whereas the PBDE concentrations increased by a factor of 25 reaching concentrations of 95 pg m-3. The PBDE congener mixture in samples collected during the event, unlike our study, had a congener signature different from UK background air (31). There are other studies where spikes in the atmospheric concentrations of pollutants remain unexplained. Yao et al (32) (cited in (33)), for example, measured elevated concentrations of lindane of approximately 3000 pg m-3 in air samples collected from downtown Toronto and 600 pg m-3 further north on the 27th June, 2005 following a lindane ban in Canada. These short-term spikes in atmospheric concentrations of POPs have the potential to skew monitoring data. The maximum ∑PBDE concentration (1293 pg m-3) during the dust storm in this study was four times higher than the maximum concentration (340 pg m-3) after the dust storm. However, although nighttime concentrations during the dust storm were at least ten times higher than nighttime concentrations after the dust storm, daytime concentrations during and after the dust storm were similar (see Supporting Information Table SI 3). In an effort to determine whether the sources of PBDEs were different over the first two sampling days when concentrations were extremely high at night as compared to the rest of the study period, the congener mixtures were assessed. The congener mixtures of daytime and nighttime samples collected during and after the dust storm episode ranked in order of abundance, as BDE-47 > -99 > -100 > 28 > -154 > -153 > 183. The major congeners in all samples regardless of time of day were BDE 47, 99, and 100 which together contributed approximately 88-95% of the ∑PBDEs. In addition, the congener pattern is remarkably similar to the technical penta-PBDE formulations (34, 35) suggesting that the main source of PBDEs in the air during this period had a penta signature. Subtle differences in the percent contributions by different congeners relative to their proportions in the penta-technical mixture were (Figure 2) consistent with the differences in volatility (or reactivity) between the congeners. For example, the ratio of 47:99 in penta technical mixtures is ∼0.7 in DE 71 (34) and ∼1.1 in Bromkal 70-5 DE (35). However in this study the 47:99 ratio ranges between ∼3.5 and 9.5. The fluctuations in the ratio tracked changes in ambient temperature remarkably well, following a clear diurnal pattern (Figure 3). It has been suggested that high 47:99 ratio is indicative of photolytic debromination (36). The 47:99 ratio in this study is higher than those reported for Hazelrigg (1.9), Chilton (0.74), Mace Head (0.75) (37) Birmingham in the UK, (2.9-3.6) (38), Eagle Harbour (average, 1.4), Strungeon Point (average, 1.4),
FIGURE 2. Congener distribution expressed as a percent of ∑PBDEs during dusty and clear periods compared to the congener profile in Bromkal 70-5 DE, a technical penta-PBDE formulation.
FIGURE 3. Variations in the 47:99 ratio with temperature. Sleeping Bear dunes (average, 1.6) and Chicago (average, 2) in the United States (39), and from rural (1.36) (40), urban (1.2), semiurban (2-4) sites in Canada (27). Another notable difference between this study and some North American (41, 12, 42) and Asian (30, 43) studies is that BDE 209 was present in a limited number of samples as opposed to it being the dominant congener. The fact that the levels of BDE 209 are low in this study may probably be due to the fact that the deca product may not have been used in the Arabian Gulf. Another possible explanation for the “absence” of BDE 209 in these samples may be related to the rapid removal of 209 from the atmosphere by photolysis (36, 44, 45). This is a likely possibility given that nona BDE congeners
(BDEs 206, 207, and 208) were present in samples even in the absence of BDE 209. PCBs were also analyzed in this study and data are given in Supporting Information. The mean and range of various PCB congener concentrations in air samples collected are given in Supporting Information Table SI-4. The ∑PCB concentrations ranged from 20 to 564 pg/m3 and were dominated by a range of low molecular weight PCB congeners associated with vapor phase. Diurnal Variability in Concentrations. The diurnal fluctuations in concentrations of POPs are a function of several factors (some of which vary diurnally) acting individually or together and the eventual pattern that emerges is dependent on which of these factors (or combination of factors) is/are dominant. The most common processes that are known to control the atmospheric concentrations of semivolatile compounds include temperature mediated air-surface exchange (46-48), abiotic removal (e.g., photolysis, OH radical removal) from the atmosphere (49-51, 44, 15, 45), fluctuations in the atmospheric boundary height (52, 53), advection of contaminated air from source regions (17), and local meteorology (e.g., wind speed, temperature, humidity). The observed diurnal fluctuations in concentrations of pollutants at a given location therefore provide important clues about their behavior in that particular environment. It is thought for example that temperature mediated air-surface exchange is more important in determining the diurnal fluctuations of PCBs in urban areas with reservoirs from past usage (46-48) whereas abiotic removal processes and atmospheric transport may be more significant at remote background areas where emissions are negligible (54, 44). PCB gas concentrations analyzed in this study fluctuated with temperature over the sampling period indicating that they are driven by air-surface exchange (Supporting Information Figure SI 4). This suggests that there was no external source of PCBs transported into Kuwait during this period unlike what was observed for PBDEs. Strong PBDE nighttime signals were observed during the first two days of sampling with concentrations decreasing to background levels during the day. Over this period peak nighttime ∑PBDE concentrations (for samples collected between midnight and 4 a.m.) were approximately thirty times higher than daytime concentrations. The diurnal fluctuations following the dust storm was not as pronounced after the dust storm. Clearly there had to be a strong source of PBDEs either locally or from a nearby source to explain the difference in concentrations between the period of the dust storm and the period after the dust storm. This daytime depletion of about 80 ( 5% of ∑PBDEs may be due to fluctuations in the atmospheric boundary layer (ABL) height and abiotic removal processes (photolytic and/or OH removal) both of which lead to daytime reduction in pollutant concentrations. The ABL height over the entire study period (Supporting Information Figure SI-1b) was ∼250 m at night and increased to ∼3000 ( 50 m during the day. This fluctuation in ABL will have the effect of trapping pollutants in a smaller volume of air leading to increased ground level concentrations. During the day, the increased ABL coupled with increased turbulence brought about by the increased wind speed (Supporting Information Figure SI-1c) led to the dissipation of pollutants trapped in the lowered ABL. However if this was the overarching mechanism that controlled the ground level concentrations peak nighttime concentrations (samples collected between midnight and 4 a.m., N) should be higher than peak daytime (samples collected between noon and 4 p.m., D) concentrations throughout the study period. One should therefore expect the nighttime:daytime ratio (RN:D) ratio to be >1 throughout the study period. During the dust storm, however, the RN:D was 1. This inconsistency in this ratio VOL. 44, NO. 21, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 4. Gas-particle partitioning between 19 May and 24 May 2007. precludes changes in the ABL as the dominant mechanism for the depletion of PBDEs during the dusty period. A number of studies have shown that PBDEs are prone to gas phase photolytic (55, 51, 15) and hydroxyl radical removal (49, 51), with hydroxyl radical removal proceeding faster for lower molecular weight compounds containing 1-2 bromines (51) and photolysis being faster for higher molecular weight congeners containing 2-6 bromines (44). To investigate whether abiotic (photolytic) removal processes are playing the dominant role in daytime removal of PBDEs over the study period, the distribution of PBDEs between the gas and particulate phases, operationally defined by the fraction on the PUF and filter respectively, were plotted together with the solar flux (Figure 4a and b respectively). Also plotted in the figure is the approximate daily sunshine hours over the study period. Atmospheric aerosols drastically reduce the amount of sunlight infiltration. During the dust storm, there was no measurable sunshine compared with 6 and 10 h of sunshine after the dust storm. The plots show that the proportion of various congeners in the gas phase (amount on PUF as a percentage of the total) showed a clear diurnal periodicity with gas phase concentrations decreasing as the solar flux increases during the day, reaching a minimum at peak solar flux between noon and 4 p.m. This observation 8118
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indicates that photolytic degradation, not temperature, may be the dominant influence on the observed distribution of PBDEs between gas and particle phases. When temperature modulates gas-particle partitioning, a decrease in temperature increases the proportion of compounds on the particle phase and vice versa. In this study, however, the proportions of PBDE congeners in the gas phase increased with decreasing temperature since photolysis, a predominantly gas phase process, is insignificant at night when temperatures are relatively low. Further evidence to support the theory that photolysis is modulating gas-particle partitioning during this study period is the differences in the percentages of various congeners in the gas phase during and after the dust storm. The proportion of BDE 47, for example, in the gas phase in the samples collected between noon and 4 pm was on average 66% during the dust storm. After the dust storm, however, the proportion of BDE 47 in samples collected between noon and 4 p.m. when the solar flux was highest ranged from 26 and 50% suggesting that photolysis proceeded faster on clear days when there was more sunshine and the solar flux is high. In summary, nighttime PBDE concentrations measured during the dust storm were thirty times higher than daytime, with concentrations after the dust storm decreasing to levels
similar to levels in other urban locations. Although the congener distribution suggests a penta-technical source, the exact reason for the nighttime spike in concentration during the dust storm is unknown although it may be due to advection from another region. Air mass back trajectories suggest that the source may be from a southeasterly direction of Kuwait. The diurnal variability in the gas-particle distribution over the entire measurement period suggests that photolysis has an important influence on the atmospheric concentrations. Furthermore, the data showed that the meteorological conditions that may have influenced the PBDE concentrations had no similar effect on PCB concentrations.
Acknowledgments We are grateful to the management of Kuwait Institute for Scientific Research for funding this research. We also wish to thank Majed Bahloul, Jamal Zafar, and Khalid Matrouk for analytical support and to Dr Saif Uddin for assistance with data preparation.
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Supporting Information Available Details on the fluctuations of meteorological factors (Figure SI-1); back trajectories calculated using the online HYSPLIT trajectory model (Figure SI-2); figure showing data for the analysis of a certified reference material (Figure SI-3) and fluctuations in PCB concentrations during the study period (Figure SI-4). Also given are congener specific concentrations for PBDEs and PCBs all samples (Tables SI 1-4), and details of sample extraction and cleanup, QA/QC and analysis. This material is available free of charge via the Internet at http:// pubs.acs.org.
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