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| Titel |
Measuring fast variations of δ18O and δ2H in atmospheric water vapour using laser spectroscopy: an instrument inter-comparison and characterisation study |
| VerfasserIn |
F. Aemisegger, P. Sturm, P. Graf, H. Sodemann, S. Pfahl, A. Knohl, H. Wernli |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068775
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| Zusammenfassung |
| Fast variations of stable water isotopes in water vapour have become measurable lately using
novel laser spectroscopic techniques. This allows us to perform process-based investigations
of the atmospheric water cycle at the time scales of significant weather events. An important
prerequisite for such studies implying automatic field measurements lasting for several weeks
or even months is a detailed knowledge about sources of uncertainty and instrument
properties. We present a comprehensive characterisation and comparison study of two
commercial laser spectroscopic systems based on cavity ring-down spectroscopy (Picarro)
and off-axis integrated cavity output spectroscopy (Los Gatos Resarch). The old versions
(L1115-i, WVIA) and the new versions (L2130-i, WVIA-EP) of both systems were tested.
The uncertainty components of the measurements were assessed in laboratory experiments,
focussing on effects of (i) water vapour mixing ratio, (ii) measurement stability, (iii)
uncertainties due to calibration and (iv) response times of the isotope measurements due
to adsorption-desorption processes on the tubing and measurement cavity walls.
Knowledge from our laboratory experiments was used to setup a one-week field
campaign for comparing measurements of the ambient isotope signals from the
L1115-i and WVIA systems. The optimal calibration strategy determined for both
instruments was applied as well as the correction functions for water vapour mixing
ratio effects. Using this field measurement data we address the question of how
well the deuterium excess (d=δ2H-8δ18O) of atmospheric water vapour can be
determined with laser spectroscopy. The deuterium excess is an interesting parameter for
process-based atmospheric water cycle studies, which depends on humidity and
temperature conditions at source location of water vapour. Up to now only very
few high-time-resolution measurements of deuterium excess exist. Our concurrent
measurements of atmospheric isotopes in water vapour using the two analysers allow us to
evaluate the precision and accuracy of atmospheric deuterium-excess measurements. |
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