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| Titel |
Tunable diode laser in-situ CH4 measurements aboard the CARIBIC passenger aircraft: instrument performance assessment |
| VerfasserIn |
C. Dyroff, A. Zahn, S. Sanati, E. Christner, A. Rauthe-Schöch, T. J. Schuck |
| 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 ; 7, no. 3 ; Nr. 7, no. 3 (2014-03-13), S.743-755 |
| Datensatznummer |
250115645
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| Publikation (Nr.) |
 copernicus.org/amt-7-743-2014.pdf |
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| Zusammenfassung |
| A laser spectrometer for automated monthly measurements of methane (CH4)
mixing ratios aboard the CARIBIC passenger aircraft is presented. The
instrument is based on a commercial Fast Greenhouse Gas Analyser (FGGA, Los
Gatos Res.), which was adapted to meet the requirements imposed by unattended
airborne operation. It was characterised in the laboratory with respect to
instrument stability, precision, cross sensitivity to H2O, and accuracy.
For airborne operation, a calibration strategy is described that utilises
CH4 measurements obtained from flask samples taken during the same
flights. The precision of airborne measurements is 2 ppb for 10 s averages.
The accuracy at aircraft cruising altitude is 3.85 ppb. During aircraft
ascent and descent, where no flask samples were obtained, instrumental drifts
can be less accurately determined and the uncertainty is estimated to be
12.4 ppb. A linear humidity bias correction was applied to the CH4
measurements, which was most important in the lower troposphere. On average,
the correction bias was around 6.5 ppb at an altitude of 2 km, and
negligible at cruising flight level. Observations from 103 long-distance
flights are presented that span a large part of the northern hemispheric
upper troposphere and lowermost stratosphere (UT/LMS), with occasional
crossing of the tropics on flights to southern Africa. These accurate data
mark the largest UT/LMS in-situ CH4 dataset worldwide. An example of a
tracer-tracer correlation study with ozone is given, highlighting the
possibility for accurate cross-tropopause transport analyses. |
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