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| Titel |
Lag time determination in DEC measurements with PTR-MS |
| VerfasserIn |
Risto Taipale, Taina M. Ruuskanen, Janne Rinne |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035596
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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 conundrum, 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 resting 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 based on 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. |
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