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| Titel |
Lag time determination in DEC measurements with PTR-MS |
| VerfasserIn |
R. Taipale, T. M. Ruuskanen, J. Rinne |
| 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 ; 3, no. 4 ; Nr. 3, no. 4 (2010-07-07), S.853-862 |
| Datensatznummer |
250001205
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| Publikation (Nr.) |
 copernicus.org/amt-3-853-2010.pdf |
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| Zusammenfassung |
| The disjunct eddy covariance (DEC) method has emerged as a popular
technique for micrometeorological flux measurements of volatile organic
compounds (VOCs). It has usually been combined with proton transfer
reaction mass spectrometry (PTR-MS), an online technique for VOC
concentration measurements. However, the determination of the lag time
between wind and concentration measurements has remained an important
challenge. To address this issue, we studied the effect of different lag
time methods on DEC fluxes. The analysis was based on both actual DEC
measurements with PTR-MS and simulated DEC data derived from high frequency
H2O measurements with an infrared gas analyzer. Conventional eddy
covariance fluxes of H2O served as a reference in the DEC simulation.
The individual flux measurements with PTR-MS were rather sensitive to the
lag time methods, but typically this effect averaged out when the median
fluxes were considered. The DEC simulation revealed that the maximum
covariance method was prone to overestimation of the absolute values of
fluxes. The constant lag time methods, one based on a value calculated from
the sampling flow and the sampling line dimensions and the other on a
typical daytime value, had a tendency to underestimate. The visual
assessment method and our new averaging approach utilizing running averaged
covariance functions did not yield statistically significant errors and
thus fared better than the habitual choice, the maximum covariance method.
Given this feature and the potential for automatic flux calculation, we
recommend using the averaging approach in DEC measurements with PTR-MS. It
also seems well suited to conventional eddy covariance applications when
measuring fluxes near the detection limit. |
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