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Response to Comment on “Measurements of Atmospheric Mercury Species at a Coastal Site in the Antarctic and over the South Atlantic Ocean during Polar Summer” Mercury researchers involved in measurements of atmospheric mercury in polar regions met last year for the first international “Arctic Atmospheric Mercury Research Workshop” August 26-28, 2002, in Toronto, Canada. One of the authors of the Comment on our paper (1) was also a participant at this workshop. The main results were presented in a final report in December 2002 by the Meteorological Service of Canada (MSC) and were sent to all contributors and presenters. A concise version of this report has been accepted by Atmos. Environ. for publication (2). A major goal of this workshop was to examine, compare, and discuss speciated atmospheric mercury measurements in cold climates and to address the question: “how much confidence do we have in chemically speciated atmospheric mercury measurement methods (gaseous elemental mercury, GEM; reactive gaseous mercury, RGM; and particulate mercury, PM) when used in cold climates”. There was general agreement that chemically speciated atmospheric mercury measurements are significantly more difficult to perform as compared with the determination of GEM. Furthermore, RGM and PM could conceivably consist of more than just one chemical species of mercury (each of which may have a substantially different vapor pressure). It was recognized that, at present, the procedures utilized for making speciated atmospheric mercury measurements represent operationally defined methods and are not yet official “standard reference methods” sanctioned by, for example, ASTM or ISO, which would require a full (stepby-step) method validation including determination of the measurement uncertainty associated with the results from each sampling/analytical step. All workshop participants unanimously agreed that there is a critical need for a rugged, reliable, and portable calibration unit for performing HgXY calibrations in the field. The authors commenting on our paper (1) mainly refer to the paper published by Landis et al. (3). That paper is a significant advancement in the harmonization and standardization for the determination of RGM in ambient air. However, the workshop in Toronto showed that an international debate is still ongoing about the necessity of a validation (including the measurement uncertainty) for this operationally defined method. According to the IUPAC Recommendations 2000 (4), we cannot even speak of a “speciation analysis” in the case of RGM in the atmosphere but rather are dealing with “fractionation”swhich is a process of classification of an analyte or a group of analytes from a certain sample according to physical (e.g., size, solubility) or chemical (e.g., bonding, reactivity) properties. We are still far away from a rigorous analytical method to measure individual inorganic gaseous mercury species such as mercuric chloride or other mercury halides. With the method of Landis et al. (3), we collect an operationally defined fraction of atmospheric mercury on a KCl-coated denuder and analyze the thermally desorbed Hg0 (resulting from decomposition of RGM retained by the KCl coating) by atomic fluorescence spectroscopy 10.1021/es030462n CCC: $25.00 Published on Web 06/12/2003
2003 American Chemical Society
coupled with a gold amalgamation preconcentration technique. We agree with the recommendations given by Landis and Stevens (1) regarding the measurements of atmospheric mercury and the SOP for the collection and analysis of inorganic reactive gaseous mercury and gaseous elemental mercury (3). We would even recommend the technique described by Landis et al. (3) as the status quo for measurements of RGM in the atmosphere. But, on the basis of the foregoing comments by Landis and Stevens (1), the reader might get the impression that a fully validated and standardized method for unambiguous speciation of airborne inorganic mercury already exists; however, this is not the case (2). Our RGM measurements in the Antarctic and over the South Atlantic Ocean during polar summer in 2000/ 2001 took place before the paper of Landis et al. (3) had been published. They were carried out under generally accepted procedures for the determination of RGM in ambient air, which have been refined in the meantime by Landis et al. (3). We believe that our measurements are neither of questionable reliability nor incorrect and that they support the conclusions in our recently published paper (5). We have never claimed to find “true” RGM or TPM levels with a pre-defined precision and an exact confidence interval. In our paper, we indicated the “range” of the obtained RGM and TPM concentrations, and at low environmental levels we used a robust statistic with a median instead of a mean because the data set was not normally distributed and concentrations determined at, or near, the MDL cannot be specified with high precision (5). According to the U.S. EPA (6) and the German DIN (7), there are also different procedures for the determination of the method detection limit. Generally speaking, the low RGM concentrations obtained onboard the R/V Polarstern over the South Atlantic Ocean show the relatively strong difference as compared to the high RGM concentrations found at Neumayer Station during Antarctic summer. The technical and analytical details of the comments submitted by Landis and Stevens (1), by going beyond the information contained in their paper (3), are very helpful for researchers conducting future work in this field. They found interesting new results about the application of the annular denuder methodology under different atmospheric conditions and made progress in calibrating the denuder with different Hg species (8). Furthermore, efforts to compare different automatic and manual methods to measure GEM, RGM, and PM during atmospheric mercury depletion events (AMDEs) were recently carried out in an international process study in Ny Alesund/Spitsbergen, Norway. We are looking forward to the results being published (8).
Literature Cited (1) Landis, M. S.; Stevens, R. K. Environ. Sci. Technol. 2003, 37, 3239-3240. (2) Schroeder, W. H.; Steffen, A.; Scott, K.; Bender, T.; Prestbo, E.; Ebinghaus, R.; Lu, J. Y.; Lindberg, S. E. Summary Report: First International Arctic Atmospheric Mercury Research Workshop. Atmos. Environ. (in press). (3) Landis, M. S.; Stevens, R. K.; Schaedlich, F.; Prestbo, E. M. Environ. Sci. Technol. 2002, 36, 3000-3009. VOL. 37, NO. 14, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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(4) Templetion, D. M.; Ariese, F.; Cornelius, R.; Danielsson, L.-G.; Muntau, H.; Van Leeuwen, H. P.; Lobinski, R. Pure Appl. Chem. 2000, 72 (8), 1453-1470. (5) Temme, C.; Einax, J. W.; Ebinghaus, R.; Schroeder, W. H. Environ. Sci. Technol. 2003, 37, 22-31. (6) Environmental Protection Agency (EPA). Definition and Procedure for the Determination of the Method Detection Limit. 40 CFR, Part 136, Appendix B, rev. 1.11, pp 554-555. (7) DIN 32645. Nachweis-, Erfassungs- und Bestimmungsgrenze; Beuth Verlag: Berlin, 1994. (8) Landis, M. S.; Stevens, R. K. Personal communication during a recent international process study in Ny Alesund/ Spitsbergen, Norway, about the reaction mechanism of atmospheric mercury during atmospheric mercury depletion events (AMDEs) in polar regions and their impact on the concentrations in the snowpack, April/ May 2003.
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Christian Temme* and Ralf Ebinghaus GKSS Research Centre Geesthacht Institute for Coastal Research/Physical and Chemical Analysis D-21502 Geesthacht, Germany
Ju1 rgen W. Einax Friedrich Schiller University of Jena Institute of Inorganic and Analytical Chemistry Department of Environmental Analysis D-07743 Jena, Germany
William H. Schroeder Meteorological Service of Canada Downsview, Ontario, M3H 5T4 Canada ES030462N
