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| Titel |
In-situ observations of the isotopic composition of methane at the Cabauw
tall tower site |
| VerfasserIn |
Thomas Röckmann, Simon Eyer, Carina van der Veen, Maria E. Popa, Béla Tuzson, Guillaume Monteil, Sander Houweling, Eliza Harris, Dominik Brunner, Hubertus Fischer, Giulia Zazzeri, David Lowry, Euan G. Nisbet, Willi A. Brand, Jaroslav M. Necki, Lukas Emmenegger, Joachim Mohn |
| 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 |
250154283
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| Publikation (Nr.) |
 EGU/EGU2017-19358.pdf |
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| Zusammenfassung |
| High precision analyses of the isotopic composition of methane in ambient air can potentially
be used to discriminate between different source categories. Due to the complexity of isotope
ratio measurements, such analyses have generally been performed in the laboratory on air
samples collected in the field. This poses a limitation on the temporal resolution at
which the isotopic composition can be monitored with reasonable logistical effort.
Here we present the performance of a dual isotope ratio mass spectrometric system
(IRMS) and a quantum cascade laser absorption spectroscopy (QCLAS) based
technique for in-situ analysis of the isotopic composition of methane under field
conditions. Both systems were deployed at the Cabauw experimental site for atmospheric
research (CESAR) in the Netherlands and performed in-situ, high-frequency (approx.
hourly) measurements for a period of more than 5 months. The IRMS and QCLAS
instruments were in excellent agreement with a slight systematic offset of +0.05 ± 0.03
‰ for δ13C-CH4 and -3.6 ± 0.4 ‰ for δD-CH4. This was corrected for, yielding a
combined dataset with more than 2500 measurements of both δ13C and δD. The high
precision and temporal resolution dataset does not only reveal the overwhelming
contribution of isotopically depleted agricultural CH4 emissions from ruminants at
the Cabauw site, but also allows the identification of specific events with elevated
contributions from more enriched sources such as natural gas and landfills. The final
dataset was compared to model calculations using the global model TM5 and the
mesoscale model FLEXPART-COSMO. The results of both models agree better with the
measurements when the TNO-MACC emission inventory is used in the models than
when the EDGAR inventory is used. This suggests that high-resolution isotope
measurements have the potential to further constrain the methane budget, when they are
performed at multiple sites that are representative for the entire European domain. |
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