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| Titel |
Intercomparison of fast response commercial gas analysers for nitrous oxide flux measurements under field conditions |
| VerfasserIn |
Ü. Rannik, S. Haapanala, N. J. Shurpali, I. Mammarella, S. Lind, N. Hyvönen, O. Peltola, M. Zahniser, P. J. Martikainen, T. Vesala |
| 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 ; 12, no. 2 ; Nr. 12, no. 2 (2015-01-22), S.415-432 |
| Datensatznummer |
250117781
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| Publikation (Nr.) |
 copernicus.org/bg-12-415-2015.pdf |
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| Zusammenfassung |
| Four gas analysers capable of measuring nitrous oxide (N2O)
concentration at a response time necessary for eddy covariance flux
measurements were operated from spring until winter 2011 over a field
cultivated with reed canary grass (RCG, Phalaris arundinacea, L.),
a perennial bioenergy crop in eastern Finland. The instruments were TGA100A
(Campbell Scientific Inc.), CW-TILDAS-CS (Aerodyne Research Inc.),
N2O / CO-23d (Los Gatos Research Inc.) and QC-TILDAS-76-CS (Aerodyne
Research Inc.). The period with high emissions, lasting for about 2 weeks
after fertilization in late May, was characterized by an up to 2 orders of
magnitude higher emission, whereas during the rest of the campaign the
N2O fluxes were small, from 0.01 to 1 nmol m−2 s−1. Two
instruments, CW-TILDAS-CS and N2O / CO-23d, determined the N2O
exchange with minor systematic difference throughout the campaign, when
operated simultaneously. TGA100A produced the cumulatively highest N2O
estimates (with 29% higher values during the period when all instruments
were operational). QC-TILDAS-76-CS obtained 36% lower fluxes than
CW-TILDAS-CS during the first period, including the emission episode, whereas
the correspondence with other instruments during the rest of the campaign was
good. The reasons for systematic differences were not identified, suggesting
further need for detailed evaluation of instrument performance under field
conditions with emphasis on stability, calibration and any other factors that
can systematically affect the accuracy of flux measurements. The instrument
CW-TILDAS-CS was characterized by the lowest noise level (with a standard
deviation of around 0.12 ppb at 10 Hz sampling rate) as compared to
N2O / CO-23d and QC-TILDAS-76-CS (around 0.50 ppb) and TGA100A
(around 2 ppb). We identified that for all instruments except CW-TILDAS-CS
the random error due to instrumental noise was an important source of
uncertainty at the 30 min averaging level and the total stochastic error was
frequently of the same magnitude as the fluxes when N2O exchange was
small at the measurement site. Both instruments based on continuous-wave quantum cascade laser, CW-TILDAS-CS and N2O / CO-23d, were able to
determine the same sample of low N2O fluxes with a high mutual coefficient
of determination at the 30 min averaging level and with minor systematic
difference over the observation period of several months. This enables us to
conclude that the new-generation instrumentation is capable of measuring
small N2O exchange with high precision and accuracy at sites with low
fluxes. |
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