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| Titel |
Laser-based measurements of δ13 C and δ2 H methane isotope signatures: precisions competitive with mass spectrometry methods |
| VerfasserIn |
Tara Yacovitch, Joanne Shorter, David Nelson, Scott Herndon, Mike Agnese, Barry McManus, Mark Zahniser |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145208
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| Publikation (Nr.) |
 EGU/EGU2017-9125.pdf |
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| Zusammenfassung |
| In order to understand how and why methane (CH4 ) concentrations change over time, it is
necessary to understand their sources and sinks. Stable isotope measurements of
13 CH4 :12 CH4 and CH3 D:12 CH4 ratios constrain the inventory of these sinks
and sources. Current measurements often depend on Isotope Ratio Mass Spectrometry
(IRMS), which requires extensive sample preparation including cryogenic separation of
methane from air and subsequent conversion to either CO2 or H2 . Here, we detail
improvements to a direct-absorption laser spectrometer that enable fast and precise
measurements of methane isotope ratios (δ13 C and δ2 H ) of ambient air samples, without
such sample preparation.
The measurement system consists of a laser-based direct absorption spectrometer
configured with a sample manifold for measurement of discrete samples (as opposed to
flow-through measurements). Samples are trapped in the instrument using a rapid sample
switching technique that compares each flask sample against a monitor tank sample. This
approach reduces instrument drift and results in excellent precision.
Precisions of 0.054 o∕oo for δ13 C and 1.4 o∕oo for δ2 H have been achieved
(Allan-Werle deviations). These results are obtained in 20 minutes using 4 replicate
comparisons to a monitor tank. |
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