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| Titel |
First continuous measurements of δ18O-CO2 in air with a Fourier transform infrared spectrometer |
| VerfasserIn |
S. N. Vardag, S. Hammer, M. Sabasch, D. W. T. Griffith, I. Levin |
| 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 (2015-02-04), S.579-592 |
| Datensatznummer |
250116122
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| Publikation (Nr.) |
 copernicus.org/amt-8-579-2015.pdf |
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| Zusammenfassung |
| The continuous in situ measurement of δ18O in atmospheric CO2
opens a new door to differentiating between CO2 source and sink
components with high temporal resolution. Continuous
13C–CO2 measurement systems have already been commercially available for some time,
but until now, only few instruments have been able to provide a continuous
measurement of the oxygen isotope ratio in CO2. Besides precise
13C/12C observations, the Fourier transform infrared (FTIR)
spectrometer is also able to measure the 18O / 16O ratio in
CO2, but the precision and accuracy of the measurements have not yet
been evaluated. Here we present a first analysis of δ18O-CO2 (and δ13C-CO2) measurements with the
FTIR analyser in Heidelberg. We used Allan deviation to determine the
repeatability of δ18O-CO2 measurements and found that it
decreases from 0.25‰ for 10 min averages to about
0.1‰ after 2 h and remains at that value up to
24 h. We evaluated the measurement precision over a 10-month period
(intermediate measurement precision) using daily working gas measurements
and found that our spectrometer measured δ18O-CO2 to
better than 0.3‰ at a temporal resolution of less than
10 min. The compatibility of our FTIR-spectrometric measurements to
isotope-ratio mass-spectrometric (IRMS) measurements was determined by
comparing FTIR measurements of cylinder gases and ambient air with IRMS
measurements of flask samples, filled with gases of the same cylinders or
collected from the same ambient air intake. Two-sample t tests revealed
that, at the 0.01 significance level, the FTIR and the IRMS measurements do
not differ significantly from each other and are thus compatible. We
describe two weekly episodes of ambient air measurements, one in winter and
one in summer, and discuss what potential insights and new challenges
combined highly resolved CO2, δ13C-CO2 and δ18O-CO2 records may provide in terms of better understanding
regional scale continental carbon exchange processes. |
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