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| Titel |
Continuous-flow IRMS technique for determining the ¹⁷O excess of CO₂ using complete oxygen isotope exchange with cerium oxide |
| VerfasserIn |
D. J. Mrozek, C. Veen, M. Kliphuis, J. Kaiser, A. A. Wiegel, T. Röckmann |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 8, no. 2 ; Nr. 8, no. 2 (2015-02-18), S.811-822 |
| Datensatznummer |
250116137
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| Publikation (Nr.) |
 copernicus.org/amt-8-811-2015.pdf |
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| Zusammenfassung |
| This paper presents an analytical system for analysis of all single
substituted isotopologues (12C16O17O,
12C16O18O, 13C16O16O) in nanomolar quantities
of CO2 extracted from stratospheric air samples. CO2 is
separated from bulk air by gas chromatography and CO2 isotope ratio
measurements (ion masses 45 / 44 and 46 / 44) are performed using isotope ratio
mass spectrometry (IRMS). The 17O excess (Δ17O) is
derived from isotope measurements on two different CO2 aliquots:
unmodified CO2 and CO2 after complete oxygen isotope exchange with
cerium oxide (CeO2) at 700 °C. Thus, a single measurement of
Δ17O requires two injections of 1 mL of air with a CO2
mole fraction of 390 μmol mol−1 at 293 K and 1 bar pressure
(corresponding to 16 nmol CO2 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
17O excess analysis is 1.7‰. 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‰ for Δ
17O in 2.5 h of analysis. 100 repeat analyses of one air sample
decrease the standard error to 0.20‰. The instrument
performance was demonstrated by measuring CO2 on stratospheric air
samples obtained during the EU project RECONCILE with the high-altitude
aircraft Geophysica. The precision for RECONCILE data is 0.03‰ (1σ) for δ13C, 0.07‰ (1σ) for δ18O and 0.55‰ (1σ) for δ17O for a sample of 10
measurements. This is sufficient to examine stratospheric enrichments, which
at altitude 33 km go up to 12‰ for δ17O
and up to 8‰ for δ18O with respect to
tropospheric CO2 : δ17O ~
21‰ Vienna Standard Mean Ocean Water (VSMOW), δ18O ~
41‰ VSMOW (Lämmerzahl et al., 2002). The samples
measured with our analytical technique agree with available data for
stratospheric CO2. |
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