{"DOI":"10.5194/amt-8-811-2015","abstract":"<p><strong>Abstract.</strong> This paper presents an analytical system for analysis of all single substituted isotopologues (<sup>12</sup>C<sup>16</sup>O<sup>17</sup>O, <sup>12</sup>C<sup>16</sup>O<sup>18</sup>O, <sup>13</sup>C<sup>16</sup>O<sup>16</sup>O) in nanomolar quantities of CO<sub>2</sub> extracted from stratospheric air samples. CO<sub>2</sub> is separated from bulk air by gas chromatography and CO<sub>2</sub> isotope ratio measurements (ion masses 45 / 44 and 46 / 44) are performed using isotope ratio mass spectrometry (IRMS). The <sup>17</sup>O excess (\u0394<sup>17</sup>O) is derived from isotope measurements on two different CO<sub>2</sub> aliquots: unmodified CO<sub>2</sub> and CO<sub>2</sub> after complete oxygen isotope exchange with cerium oxide (CeO<sub>2</sub>) at 700 \u00b0C. Thus, a single measurement of \u0394<sup>17</sup>O requires two injections of 1 mL of air with a CO<sub>2</sub> mole fraction of 390 \u03bcmol mol<sup>\u22121</sup> at 293 K and 1 bar pressure (corresponding to 16 nmol CO<sub>2</sub> each). The required sample size (including flushing) is 2.7 mL of air. A single analysis (one pair of injections) takes 15 minutes. The analytical system is fully automated for unattended measurements over several days. The standard deviation of the <sup>17</sup>O excess analysis is 1.7&permil;. Multiple measurements on an air sample reduce the measurement uncertainty, as expected for the statistical standard error. Thus, the uncertainty for a group of 10 measurements is 0.58&permil; for &Delta; <sup>17</sup>O in 2.5 h of analysis. 100 repeat analyses of one air sample decrease the standard error to 0.20&permil;. The instrument performance was demonstrated by measuring CO<sub>2</sub> on stratospheric air samples obtained during the EU project RECONCILE with the high-altitude aircraft Geophysica. The precision for RECONCILE data is 0.03&permil; (1&sigma;) for \u03b4<sup>13</sup>C, 0.07&permil; (1&sigma;) for \u03b4<sup>18</sup>O and 0.55&permil; (1&sigma;) for &delta;<sup>17</sup>O for a sample of 10 measurements. This is sufficient to examine stratospheric enrichments, which at altitude 33 km go up to 12&permil; for &delta;<sup>17</sup>O and up to 8&permil; for \u03b4<sup>18</sup>O with respect to tropospheric CO<sub>2</sub> : &delta;<sup>17</sup>O ~ 21&permil; Vienna Standard Mean Ocean Water (VSMOW), \u03b4<sup>18</sup>O ~ 41&permil; VSMOW (L\u00e4mmerzahl et al., 2002). The samples measured with our analytical technique agree with available data for stratospheric CO<sub>2</sub>.</p>\n ","author":[{"family":"Mrozek"},{"family":"Veen"},{"family":"Kliphuis"},{"family":"Kaiser"},{"family":"Wiegel"},{"family":"R\u00f6ckmann"}],"id":"unknown","issued":{"date-parts":[[2015,2,18]]},"language":"en","page-first":"811","publisher":"Copernicus GmbH","title":"Continuous-flow IRMS technique for determining the 17O excess of CO2 using complete oxygen isotope exchange with cerium oxide","type":"article-journal"}