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| Titel |
Evaluating the performance of commonly used gas analysers for methane eddy covariance flux measurements: the InGOS inter-comparison field experiment |
| VerfasserIn |
O. Peltola, A. Hensen, C. Helfter, L. Belelli Marchesini, F. C. Bosveld, W. C. M. van den Bulk, J. A. Elbers, S. Haapanala, J. Holst, T. Laurila, A. Lindroth, E. Nemitz, T. Röckmann, A. T. Vermeulen, I. Mammarella |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 12 ; Nr. 11, no. 12 (2014-06-17), S.3163-3186 |
| Datensatznummer |
250117467
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| Publikation (Nr.) |
 copernicus.org/bg-11-3163-2014.pdf |
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| Zusammenfassung |
The performance of eight fast-response methane (CH4) gas analysers
suitable for eddy covariance flux measurements were tested at a grassland
site near the Cabauw tall tower (Netherlands) during June 2012. The
instruments were positioned close to each other in order to minimise the
effect of varying turbulent conditions. The moderate CH4 fluxes observed
at the location, of the order of 25 nmol m−2 s−1, provided a
suitable signal for testing the instruments' performance.
Generally, all analysers tested were able to quantify the concentration
fluctuations at the frequency range relevant for turbulent exchange and were
able to deliver high-quality data. The tested cavity ringdown spectrometer
(CRDS) instruments from Picarro, models G2311-f and G1301-f, were superior to
other CH4 analysers with respect to instrumental noise. As an open-path
instrument susceptible to the effects of rain, the LI-COR LI-7700 achieved
lower data coverage and also required larger density corrections; however,
the system is especially useful for remote sites that are restricted in power
availability. In this study the open-path LI-7700 results were compromised
due to a data acquisition problem in our data-logging setup. Some of the
older closed-path analysers tested do not measure H2O concentrations
alongside CH4 (i.e. FMA1 and DLT-100 by Los Gatos Research) and this
complicates data processing since the required corrections for dilution and
spectroscopic interactions have to be based on external information. To
overcome this issue, we used H2O mole fractions measured by other gas
analysers, adjusted them with different methods and then applied them to
correct the CH4 fluxes. Following this procedure we estimated a bias of
the order of 0.1 g (CH4) m−2 (8% of the measured mean flux)
in the processed and corrected CH4 fluxes on a monthly scale due to
missing H2O concentration measurements. Finally, cumulative CH4
fluxes over 14 days from three closed-path gas analysers, G2311-f (Picarro
Inc.), FGGA (Los Gatos Research) and FMA2 (Los Gatos Research), which were
measuring H2O concentrations in addition to CH4, agreed within
3% (355–367 mg (CH4) m−2) and were not clearly different
from each other, whereas the other instruments derived total fluxes which
showed small but distinct differences (±10%,
330–399 mg (CH4) m−2). |
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