Environ. Sci. Technol. 2008, 42, 1416–1422
Polychlorinated Biphenyls (PCBs) in Air and Seawater of the Atlantic Ocean: Sources, Trends and Processes R O S A L I N D A G I O I A , * ,† L U C A N I Z Z E T T O , ‡ RAINER LOHMANN,§ JORDI DACHS,| CHRISTIAN TEMME,⊥ AND KEVIN C. JONES† Centre for Chemicals Management and Department of Environmental Science, Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, U.K., Department of Chemical and Environmental Science, University of Insubria, Via Valleggio, 11, Como, Italy, Graduate School of Oceanography, University of Rhode Island, Narragansett, U.S., Department of Environmental Chemistry, IIQAB-CSIC, Jordi Girona 18-24, Barcelona 08034, Catalunya, Spain, and Department for Environmental Chemistry, Institute for Coastal Research, Forschungszentrum Geesthacht GmbH, GKSS, Max-Planck-Str. 1 D-21052 Geesthacht, Germany
Received June 14, 2007. Revised manuscript received October 17, 2007. Accepted November 1, 2007.
Air and seawater samples were collected on board the RV Polarstern during a cruise from Bremerhaven, Germany to Cape Town, South Africa from October–November 2005. Broad latitudinal trends were observed with the lowest Σ27PCB air concentration (∼10 pg m-3) in the South Atlantic and the highest (∼1000 pg m-3) off the west coast of Africa. ΣICESPCBs ranged from 3.7 to 220 pg m-3 in air samples and from 0.071 to 1.7 pg L-1 in the dissolved phase seawater samples. Comparison with other data from cruises in the Atlantic Ocean since 1990 indicate little change in air concentrations over the remote open ocean. The relationship of gas-phase partial pressure with temperature was examined using the Clausius-Clapeyron equation; significant temperature dependencies were found for all PCBs over the South Atlantic, indicative of close air–water coupling. There was no temperature dependence for atmospheric PCBs over the North Atlantic, where concentrations were controlled by advection of contaminated air masses. Due to large uncertainties in the Henry’s Law Constant (HLC), fugacity fractions and air–water exchange fluxes were estimated using different HLCs reported in the literature. These suggest that conditions are close to air–water equilibrium for most of the ocean, but net deposition is dominating over volatilization in parts of the transect. Generally, the tri- and tetrachlorinated homologues dominated the total flux (>70%). Total PCB fluxes (28, 52, 118, 138, and 153) ranged from -7 to 0.02 ng m-2 day –1.
* Corresponding author phone: +441524593974; fax: +441524593985; e-mail:
[email protected]. † Lancaster University. ‡ University of Insubria. § University of Rhode Island. | Department of Environmental Chemistry, IIQAB-CSIC. ⊥ Forschungszentrum Geesthacht GmbH. 1416
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 5, 2008
Introduction Polychlorinated biphenyls (PCBs) were widely used in western industrialized countries until the 1970s when restrictions and bans on their production came into force. Urban/industrial areas are major sources of atmospheric PCBs to surrounding regions (1–3). The atmosphere can serve as a pathway for the delivery of these pollutants to water and terrestrial surfaces. As a result of their semivolatility and persistence, PCBs have been found in the Arctic and in other remote areas of the globe, where they were not used (4–6). Many studies have shown that PCBs are declining in the atmosphere of source regions (7–11). However, 30 years after they were banned, PCBs remain ubiquitous in the environment and uncertainties remain over whether environmental reservoirs act as sources or sinks to the atmosphere (8, 10, 11). Diffusive primary sources are believed to still be ultimately controlling ambient levels in the environment (8, 10, 11). Deep oceans are believed to be a final sink of these pollutants, removing them from the environmental recycling pool (12, 13). Knowledge of the equilibrium status and/or net direction of the flux between air and water are essential to understand the global cycle of POPs. These processes have been extensively studied previously for PCBs in the Great Lakes region of North America, Chesapeake Bay, and other coastal areas of the mid-Atlantic region, and European seas (14–16). These studies identified the importance of air–water exchange in understanding the environmental fate of POPs at local, regional and global scales. Despite the importance of partitioning between air and water for these pollutants, few simultaneous air and seawater measurements over open oceans such as the Atlantic are reported in the literature. This may be because of the difficulties in collecting reliable air and water samples on board ships and the large volumes of seawater needed to detect POPs. The present study follows on a previous investigation conducted in 2001 (17) along a North–south transect in the Atlantic Ocean, which aimed to only delineate atmospheric spatial trends for a range of POPs. This paper will present PCB data in air and seawater collected on the RV Polarstern in October–November 2005 during transit from Germany to South Africa. Simultaneous air and water measurements of PCBs were performed across the same cruise track for the first time, while adopting measures to check for the occurrence of “ship-made” interferences (18, 19). The main aims of the study were to evaluate concentrations and distribution of PCBs in air and surface seawater, and assess their air–water exchange over the Atlantic Ocean. Our aims are to (i) establish, if possible, time-trends for atmospheric PCBs over the open ocean; (ii) compare results from the north and South Atlantic; (iii) explore the relationship between gas-phase concentrations and temperature and (iv) discuss their state of equilibrium between the air and the seawater.
Materials and Methods Sample Collection. Air and seawater samples were collected on board the RV Polarstern during a cruise from Germany to South Africa. Air samples were taken on the observation deck, about 20 m above the sea level. Two high-volume air samplers placed windward and operating at 0.25–0.27 m3 min-1 were used to collect samples for PCBs analysis. Twelve hours integrated air samples were collected with an average volume of 150 m3. The 12 h samples collected from the two high-vols operating in parallel were then bulked in the laboratory, to improve the detection of the target compounds. Both particulate and gas-phase were captured on a glass 10.1021/es071432d CCC: $40.75
2008 American Chemical Society
Published on Web 01/19/2008
fiber filter (GFF) and polyurethane foam (PUF), respectively. High volume air samplers were operated in “good conditions” either when the ship was steaming or, if stationary, when the relative wind direction was between 0–90° and 270–0° and the wind speed greater than 4 m/s, to minimize interference from any potential ship contamination. After sampling, the PUFs and GFFs were transferred into solvent rinsed aluminum tins and stored in freezers at -20 °C until analysis. Air sampling on ships needs to be consistent and respectful of strict quality control measures, to avoid ship contamination and detect low levels of POPs in remote regions (18). Passive air samplers (PUF disks) were deployed in different locations in and on board of the RV Polarstern, to monitor the background air concentrations of the ship and to determine if the ship has the potential to be a source of contamination for the samples. PCB data resulting from the passive air samplers and active air sampling on board (in this and previous campaigns) suggest that the RV Polarstern is a clean ship for these compounds (19). Seawater samples were collected from a stainless steel pipe at 8 m depth, using the ship’s intake system located in the keel. The average flow rate was ∼1.2 L min-1. A typical sample volume water was 600–700 L. Both particle and dissolved seawater phases were collected using a GFF (GFF 52 with 0.7 µm of nominal pore size) and a 95 mL XAD-2 resin column respectively. Only data for the dissolved phase are reported here because of contamination problems with particle phase field blanks. Sample Processing. Air Samples for PCBs Analysis. All samples were handled and extracted in a dedicated clean laboratory at Lancaster University, which has filtered, charcoal-stripped air and positive pressure conditions. PUF plugs were pre-extracted with dichloromethane (DCM) for 16 h using a Soxhlet apparatus. GFFs were precombusted at 450 °C. Each air sample (gas + particle) was spiked with a recovery standard of 13C12-labeled PCB congeners (13C12 PCB 28, 52, 101, 138, 153, 180) and individually extracted in a Buchi extraction unit for 18 h with hexane. The extracts were concentrated using rota-evaporation and nitrogen-evaporation. A multilayer 20 mm id acid silica column containing a small layer of sodium sulfate, 1 g activated silica (Merck Silica 60), 2 g of basic silica (Merck Silica 60), 1 g of activated silica (Merck Silica 60), 4 g of acid silica (Merck Silica 60), 1 g activated silica and a small layer of sodium sulfate (all baked at 450 °C overnight) was used to purify samples. The extracts were eluted through gel permeation columns containing 6 g of Biobeads SX 3 and concentrated to 100 uL. Each sample was solvent exchanged to 25 uL of dodecane containing PCB 30 [13C12] PCB 141 and [13C12] PCB 208 as internal standards. Seawater Samples. XAD-2 columns were pre-extracted with acetone, hexane, and DCM and exchanged to preextracted Milli-Ro water and analyzed separately. XAD-2 columns were eluted with 50 mL of methanol and then with 50 mL of DCM. Separation between the aqueous and organic phases was achieved by liquid/liquid extraction. Extracts were concentrated to ∼500 µL and fractionated in a glass column (10 mm ID) packed with 3 g of silica activated overnight at 450 °C and eluted in 32.5 mL of hexane, which contained the PCBs. Fraction 1 was processed by using the same methodology described for the air samples. The samples were analyzed by gas-chromatography– mass-spectrometry (GC-MS) with an EI+ source operating in selected ion mode (SIM). Details of the instruments, temperature program and monitored ions are given elsewhere (20, 21). The following compounds were monitored in air and seawater samples: tri-PCBs 18, 22, 28, and 31; tetraPCBs 44, 49, 52, 53, 70, and 74; penta-PCBs 87, 90/101, 95, 99, 105, 110, 118, and 123; hexa-PCBs 138, 141, 149, 151, 153/132; hepta- PCBs 180, 183, and 187.
Quality Assurance/Quality Control. All analytical procedures were monitored using strict quality assurance and control measures. Laboratory blanks, travel blanks (PUFs and GFFs that just traveled) and field blanks constituted 10, 10, and 30%, respectively, of the total number of samples analyzed. No analytes were detected in the laboratory blanks, showing there was no contamination during sample processing in the laboratory. Travel blanks and field blanks showed similar compound concentrations, indicating minimal contamination during storage, sampling and transport. Samples were blank corrected using the mean of the field blanks and the method detection limits (MDL) were derived from the field blanks and quantified as 3 times the standard deviation of the mean blank concentrations. MDLs ranged from 1 pg uL-1 to 9 pg uL-1. Five replicate air samples were collected on board the RV Polarstern during transit in October/November 2005 from Germany to Cape Town. PCB results from the replicates show that the uncertainty on the air sampling ranges from 10–20%. Breakthrough tests for air and water sampling were performed. These tests were done by deploying two GFF filters and two PUFs plugs for air, and two XAD columns and two GF/Fs one on the top of the other for water. The breakthrough tests were performed under different temperature conditions between 20 and 30 °C. Breakthrough tests showed that concentrations on the back up XAD column and PUFs of the lighter compounds were around 10–20% of the first column for both cruises suggesting that breakthrough was not a major concern for our samples. Recoveries were routinely monitored using the 13C -PCBs as surrogate standards for PCBs and they ranged 12 from 85–107% for air and dissolved phase samples. Results for PCBs in the water–particle phase are not reported, because of contamination problems with field blanks. Extraction and cleanup method efficiencies were monitored by spiking cleaned GFFs and PUFs plugs with validation standards for PCBs and extracting and analyzing those PUFs and GFFs in the same way as samples. Recoveries for matrix spikes range from 90 to 110% for all compounds. Meteorological Data and Back Trajectories. Meteorological data were from PODAS (Polarstern Data System) on board the vessel, an online management system that collects nautical and scientific parameters from a multitude of measuring devices installed on the vessel. Air and water temperature, wind speed and wind direction were obtained from the system every 5 min. NOAA’s HYSPLIT model and the NCEP/NCAR Global Reanalysis data set were used to calculate back trajectories (BTs) and atmospheric mixing height. BTs were traced for 7 days with 1 h steps at 00:00 coordinated universal time (UTC) at 500 m above sea level. Figure 1 shows the mean sampling locations and the prevalent wind directions.
Results and Discussion Air and Seawater Concentrations: Introductory Remarks. A total of 42 air samples were collected along the cruise transect. Supporting Information (SI) Tables 1 and 3 summarize the results for PCB air concentrations. The sum of the twenty-seven measured PCBs (Σ27PCBs) ranged from 10 to 1000 pg m-3 with 35–75% accounted for Cl3Bs and Cl4Bs in the North Atlantic and 50–85% in the South Atlantic. The ΣICESPCBs (PCB 28, 52, 90/101, 118, 138, 153, and 180) ranged from 3.7 to 220 pg m-3 and constituted ∼33% of the Σ27PCBs detected. Figure 1 shows the spatial distribution of the ΣICESPCBs along the transect. Highest PCB concentrations were observed in the Northern Hemisphere off the west coast of Africa from 22 °N to 7 °N (40–220 pg m-3, sites 14–21), whereas the lowest concentrations were measured in the South Atlantic Ocean. ΣICESPCBs were fAIR) is indicated by a negative quotient. An estimate of the errors around the fAIR/fW value, based on the random sampling and analytical error of air and water (perhaps ( 10%) and the uncertainty associated with the HLC values (perhaps ( 20%). (i.e., a propagated error in FFw is of ca. 40% is shown on SI Figure 5). Calculations suggested air–water equilibrium conditions dominate at most of the sites in South Atlantic, whereas net deposition dominates in the North (off the west coast of Africa and Europe), using the three different HLC values. However, if the Bamford et al. (42) HLC values are used, a decrease in the fugacity ratios by a factor of 2 is observed. This is more enhanced for the heavier PCBs which are characterized by higher HLC values compared to other studies (42). Air–Water Exchange Fluxes. Gas exchange rates were calculated using a modified version of the Withman twofilm resistance model as described elsewhere (13). The equation for the derivation of the air–water exchange is given in the Supporting Information. The net flux was calculated
for each location where simultaneous measurements of air and seawater were performed. The mass transfer coefficient (vaw) was calculated for every 5 min wind speed during sampling and the average was taken as the final value for the calculation of the flux. The absorptive fluxes were typically more than 90% of the volatilization fluxes. A negative flux means that absorption is dominating, while a positive flux indicates that volatilization is dominating. Generally, the tri and tetrachlorinated homologues dominated the flux profiles, accounting for more than 70% of the total flux. Σ5PCB flux (28, 52, 118, 138, and 153) ranged from -7 to 0.02 ng m-2 day-1 by using Li et al. (41) HLC values, from -6 to 0.7 ng m-2 day-1 by using HLC values from Bamford et al. (42) and from -6.6 to 0.6 ng m-2 day-1 by using the ten Hulscher et al. (43) values. There are very few studies that reported air–water exchange fluxes over the ocean. Iwata et al. (22) reported a Σ36PCBs adsorptive net flux of ca. -60 ng m-2 day –1 in the North Atlantic and ca. -20 ng m-2 day –1 in the Southern Indian Ocean, 2–3 times higher than those of this study.
Acknowledgments We thank the crew on the RV Polarstern as well as the scientists for their excellent support and cooperation. We would like to thank Armando Caba and Dr Annika Jahnke for their assistance during sampling on the ship and Dr Soenke Lakaschus for support and helpful discussions. We thank Dr. Gareth O. Thomas and Dr. Robert G. M. Lee for their invaluable help and support during the challenging analytical work. We gratefully acknowledge financial support from the Department of the Environment, Food and Rural Affairs (DEFRA) on POPs at Lancaster University.
(11)
(12)
(13)
(14)
(15)
(16)
(17)
(18)
(19)
Supporting Information Available
(20)
Additional information including three tables and five figures. This material is available free of charge via the Internet at http://pubs.acs.org.
(21)
Literature Cited (1) Offenberg, J. H.; Baker, J. E. Polychlorinated biphenyls in Chicago precipitation: enhanced wet deposition to near shore Lake MI. Environ. Sci. Technol. 1997, 31, 1534–1538. (2) Offenberg, J. H.; Baker, J. E. Influence of Baltimore’s urban atmosphere on organic contaminants over the northern Chesapeake Bay. J. Air Waste Manage. Assoc. 1999, 49, 959–965. (3) Simcik, M. F.; Zhang, H.; Franz, T. P.; Eisenreich, S. J. Urban contamination of the Chicago/coastal Lake MI atmosphere by PCBs and PAHs during AEOLOS. Environ. Sci. Technol. 1997, 31, 2141–2147. (4) Kucklick, J. R.; and Baker, J. E. Organochlorines in Lake Superior’s food web. Environ. Sci. Technol. 1998, 32, 1192–1198. (5) Halsall, C. A.; Bailey, R.; Stern, G. A.; Barrie, L. A.; Fellin, P.; Muir, D. C. G.; Rosenberg, B.; Rovinsky, F. Y. A.; Knonoy, E.; Ya and Pastuhov, B. Multi-year observations of organohalogen pesticides in the Arctic atmosphere. Environ. Pollut. 1998, 102, 51–62. (6) Muir, D. C. G.; Ford, C. A.; Rosenberg, B.; Norstrom, R. J.; Simon, M.; Béland, P. Persistent organochlorines in beluga whales (Delphinapterus leucas) from the St Lawrence River estuary-I. concentrations and patterns of specific PCBs, chlorinated pesticides and polychlorinated dibenzo-p-dioxins and dibenzofurans. Environ. Pollut. 1996, 93, 219–234. (7) Hillery, B. R.; Basu, I.; Sweet, C. W. and Hites, R. A. Temporal and spatial trends in a long-term study of gas-phase PCB concentrations near the Great Lakes. Environ. Sci. T echnol. 31, 1811–1816. (8) Gioia, R.; Steinnes, E.; Thomas, O. G.; Meijer, N. S.; Jones, K. C. Persistent organic pollutants in European background air: derivation of temporal and latitudinal trends. J. Environ. Monit. 2006, 8, 700–710. (9) Sweetman, A., J.; Jones, K. C. Declining PCB concentrations in the U. K. atmosphere: evidence and possible causes. Environ. Sci. Technol. 2000, 34, 863–869. (10) Meijer, S. N.; Ockenden, W. A.; Steinnes, E.; Corrigan, B. P.; Jones, K. C. Spatial and temporal trends of POPs in Norwegian
(22)
(23)
(24)
(25) (26) (27)
(28)
(29)
(30)
(31)
and UK background air: Implications for global cycling. Environ. Sci. Technol. 2003, 37, 454–461. Jaward, F. M.; Meijer, S. N.; Steinnes, E.; Thomas, G. O.; Jones, K. C. Further studies on the latitudinal and temporal trends of persistent organic pollutants in Norwegian and U.K. background air. Environ. Sci. Technol. 2004, 38, 2523–2530. Jurado, E.; Lohmann, R.; Meijer, S; Jones, K. C.; Dachs, J. Latitudinal and seasonal capacity of surface oceans as a reservoir of polychlorinated biphenyls. Environ. Pollut. 2004, 128, 149– 162. Dachs, J.; Lohmann, R.; Ockenden, W.; Mejanelle, L.; Eisenreich, S. J.; Jones, K. C. Oceanic biogeochemical controls on global dynamics of persistent organic pollutants. Environ. Sci. Technol. 2002, 36, 4229–4237. Nelson, E. D.; McConnell, L.; Baker, J. E. Diffusive exchange of gaseous polycyclic aromatic hydrocarbons and polychlorinated biphenyls across the air-water interface of the Chesapeake Bay. Environ. Sci. Technol. 1998, 32, 912–919. Hornbuckle, K. C.; Sweet, C. W.; Pearson, R. F.; Swackhamer, D. L. Assessing annual water-air fluxes of polychlorinated biphenyls in Lake MI. Environ. Sci. Technol. 1995, 29, 869–877. Dachs, J.; Bayona, J. M.; Albaiges, J. Spatial distribution, vertical profiles and budget of organochlorine compounds in Western Mediterranean seawater. Mar. Chem. 1997, 57 (3–4), 313–324. Jaward, M. F.; Barber, J. L.; Booij, K.; Dachs, J.; Lohmann, R.; Jones, K. C. Evidence for dynamic air-water coupling and cycling of persistent organic pollutants over open Atlantic Ocean. Environ. Sci. Technol. 2004, 38, 2617–2625. Lohmann, R.; Jaward, F. M.; Durham, L.; Barber, J.; Ockenden, W.; Jones, K. C.; Bruhn, R.; Lakaschus, S.; Dachs, J.; Booij, K. Potential contamination of shipboard air samples by diffusive emissions of PCBs and other organic pollutants: implications and solutions. Environ. Sci. Technol. 2004, 38, 3965–3970. Gioia, R.; Lohmann, R.; Nizzetto, L.; Dachs, J.; Temme, C.; Jones, K. C. Sampling POPs in the oceanic remote locations: dealing with ship-based contamination. In Chemical Pollution and Environmental Changes; Universal Academy Press, Inc.; Tokyo, 2007. Thomas, G. O.; Sweetman, A. J.; Parker, C. A.; Kreibich, H.; Jones, K. C. Development and validation of methods for the trace determination of PCBs in biological matrices. Chemosphere 1998, 36, 2447–2459. Gouin, T.; Thomas, G. O.; Cousins, I.; Barber, J.; Mackay, D.; Jones, K. C. Air-surface exchange of polybrominated diphenyl ethers and polychlorinated biphenyls. Environ. Sci. Technol. 2002, 38, 1426–1434. Iwata, H.; Tanabe, S.; Sakal, N.; Tatsukawa, R. Distribution of persistent organochlorines in the oceanic air and surface seawater and the role of ocean on their global transport and fate. Environ. Sci. Technol. 1993, 27, 1090–1098. Breivik, K.; Sweetman, A.; Pacyna, J. M.; Jones, K. C. Towards a global historical emission inventory for selected PCB congeners - a mass balance approach: 1. Global production and consumption. Sci. Total Environ. 2002, 290, 181–198. Breivik, K.; Sweetman, A.; Pacyna, J. M.; Jones, K. C. Towards a global historical emission inventory for selected PCB congeners - a mass balance approach: 2. Emissions. Sci. Total Environ. 2002, 290, 199–224. Schreitmuller, J.; Ballschmiter, K. Levels of polychlorinated biphenyls in the lower troposphere of the North- and SouthAtlantic ocean. Fresenius. J. Anal. Chem. 1994, 348, 226–239. International POPs Elimination Project Final Performance Report; September 2006. Harner, T.; Pozo Gallardo, K.; Gouin, T.; Macdonald, A-M.; Hung, H.; Cainey, J.; Peters, A. Global pilot study for persistent organic pollutants (POPs) using PUF disk passive air samplers. Environ. Pollut. 2006, 144, 445–452. Mandalakis, M.; Berresheim, H.; Stephanou, E. G. Direct evidence for destruction of polychlorobiphenyls by OH radicals in the subtropical troposphere. Environ. Sci. Technol. 2003, 37, 542– 547. Nigeria As E-Waste Dump, Daily champion (Lagos),editorial, 07 December 2006; http://allafrica.com/stories/200612080334. html. Crutzen, P. J.; Andreae, M. O. Biomass Burning in the Tropics: Impact on Atmospheric Chemistry and Biogeochemical Cycles. Science 1990, 250 (4988,), 1669–1678. Eckhardt, S.; Breivik, K.; Mano, S.; Stohl, A. Record high peaks in PCB concentrations in the Arctic atmosphere due to longrange transport of biomass burning emissions. ACPD 2007, 7, 6229–6254.
VOL. 42, NO. 5, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1421
(32) Schiefuss, E.; Ratmeyer, V.; Stuut, J-B. W.; Jansen, F. J. H.; Damste, S. S. J. Carbon isotope analyses of n-alkanes in dust from the lower atmosphere over the central eastern Atlantic. Geochim. Cosmochim. Acta 2002, vol 67, 1757–1767. (33) Lancaster group, 2002, unpublished data. (34) Panshin, S. Y.; Hites, R. A. Atmospheric concentrations of polychlorinated biphenyls at Bermuda. Environ. Sci. Technol. 1994, 28, 2001–2007. (35) Axelman, J.; Broman, D. Budget calculations for polychlorinated biphenyls (PCBs) in the Northern Hemisphere -a single-box approach. Tellus 2001, 53B, 235–259. (36) Bidleman, T. F.; Patton, G. W.; Hinckley, D. A.; Walla, M. D.; Cotham, W. E.; Hargrave, B. T. Chlorinated pesticides and polychlorinated biphenyls in the atmosphere of the Canadian Artic. In Long-Range Transport of Pesticides.; Kurtz, D., Ed.; Lewis Publisher: Chelsea, MI, 1999. (37) Yeo, H.-G.; Choi, M.; Chun, M.-Y.; Sunwoo, Y. Concentration distribution of polychlorinated biphenyls and organochlorine pesticides and their relationship with temperature in rural air of Korea. Atmos. Environ. 2003, 37, 3831–3839. (38) Watson, A. J.; Upstill-Goddard, R. C. Air-sea exchange in rough and stormy seas, measured by a dual tracer technique. Nature 1991, 349, 145. (39) Wanninkhof, R.; McGillis, W. R. A cubic relationship between air-sea CO2 exchange and wind speed. Geophys. Res. Lett. 1999, 26, 1889–1892.
1422
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 42, NO. 5, 2008
(40) Nightingale, P. D.; Liss, P. S.; Schlosser, P. Measurements of air-sea gas transfer during an open ocean algal bloom. Geophys. Res. Lett. 2000, 27, 2117–2120. (41) Li, N.; Wania, F.; Lei, Y. D.; Daly, G. L. A. Comprehensive and critical compilation, evaluation, and selection of physicalchemical property data for selected polychlorinated biphenyls. J. Phys. Chem. Ref. Data 2003, 32, 1545–1590. (42) Bamford, H. A.; Poster, D. L.; Huie, R.; Baker, J. E. Using extrathermodynamic relationships to model the temperature dependence of Henry’s Law Constants of 209 PCB congeners. Environ. Sci. Technol. 2002, 36, 4395–4402. (43) Ten Hulsher, T. E. M.; Van den Heuvel, H.; Van Noort, P. C. M.; Govers, H. A. J. Henry’s Law constants for eleven polychlorinated biphenyls at 20 °C. J. Chem. Eng. Data 2006, 51, 347–351. (44) Hoff, R. M.; Muir, D. C. G.; Grift, N. P. Annual cycle of polychlorinated biphenyls and organohalogen pesticides in air in southern Ontario. 2. Atmospheric transport and sources. Environ. Sci. Technol. 1992, 26, 276–283. (45) Wania, F.; Haugen, J.-E.; Lei, Y. D.; Mackay, D. Temperature dependence of atmospheric concentration of semi-volatile organic compounds. Environ. Sci. Technol. 1998, 32 (8), 1013– 1021. (46) Withman, W. G. The two film theory of gas-absorption. Chem. Metall. Eng. 1923, 29, 146–148.
ES071432D
