ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-1685-2011 Continuous isotopic composition measurements of tropospheric CO<sub>2</sub> at Jungfraujoch (3580 m a.s.l.), Switzerland: real-time observation of regional pollution events Tuzson B. 1 Henne S. 1 Brunner D. 1 Steinbacher M. 1 Mohn J. 1 Buchmann B. 1 Emmenegger L. 1 Empa, Swiss Federal Laboratories for Materials Science and Technology, Laboratory for Air Pollution and Environmental Technology, Überlandstr. 129, 8600 Dübendorf, Switzerland 22 02 2011 11 4 1685 1696 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/1685/2011/acp-11-1685-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/1685/2011/acp-11-1685-2011.pdf

A quantum cascade laser based absorption spectrometer (QCLAS) is applied for the first time to perform in situ, continuous and high precision isotope ratio measurements of CO<sub>2</sub> in the free troposphere. Time series of the three main CO<sub>2</sub> isotopologue mixing ratios (<sup>12</sup>C<sup>16</sup>CO<sub>2</sub>, <sup>13</sup>C<sup>16</sup>CO<sub>2</sub> and <sup>12</sup>C<sup>18</sup>O<sup>16</sup>O) have simultaneously been measured at one second time resolution over two years (from August 2008 to present) at the High Altitude Research Station Jungfraujoch (3580 m a.s.l., Switzerland). This work focuses on periods in February 2009 only, when sudden and pronounced enhancements in the tropospheric CO<sub>2</sub> were observed. These short-term changes were closely correlated with variations in CO mixing ratios measured at the same site, indicating combustion related emissions as potential source. The analytical precision of 0.046&permil; (at 50 s integration time) for both &delta;<sup>13</sup>C and &delta;<sup>18</sup>O and the high temporal resolution allowed the application of the Keeling plot method for source signature identification. The spatial origin of these CO<sub>2</sub> emission sources was then determined by backward Lagrangian particle dispersion simulations.

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