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| Titel |
Gap-filling strategies for annual VOC flux data sets |
| VerfasserIn |
I. Bamberger, L. Hörtnagl, M. Walser, A. Hansel, G. Wohlfahrt |
| 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. 8 ; Nr. 11, no. 8 (2014-04-30), S.2429-2442 |
| Datensatznummer |
250117385
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| Publikation (Nr.) |
 copernicus.org/bg-11-2429-2014.pdf |
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| Zusammenfassung |
Up to now the limited
knowledge about the exchange of volatile organic compounds (VOCs) between the
biosphere and the atmosphere is one of the factors which hinders more
accurate climate predictions. Complete long-term flux data sets of several
VOCs to quantify the annual exchange and validate recent VOC models are
basically not available. In combination with long-term VOC flux measurements
the application of gap-filling routines is inevitable in order to replace
missing data and make an important step towards a better understanding of the
VOC ecosystem–atmosphere exchange on longer timescales.
We performed VOC flux measurements above a mountain meadow in Austria during
two complete growing seasons (from snowmelt in spring to snow reestablishment
in late autumn) and used this data set to test the performance of four
different gap-filling routines, mean diurnal variation (MDV), mean gliding
window (MGW), look-up tables (LUT) and linear interpolation (LIP), in terms
of their ability to replace missing flux data in order to obtain reliable VOC
sums. According to our findings the MDV routine was outstanding with regard
to the minimization of the gap-filling error for both years and all
quantified VOCs. The other gap-filling routines, which performed gap-filling
on 24 h average values, introduced considerably larger uncertainties. The
error which was introduced by the application of the different filling
routines increased linearly with the number of data gaps. Although average
VOC fluxes measured during the winter period (complete snow coverage) were
close to zero, these were highly variable and the filling of the winter
period resulted in considerably higher uncertainties compared to the
application of gap-filling during the measurement period.
The annual patterns of the overall cumulative fluxes for the quantified VOCs
showed a completely different behaviour in 2009, which was an exceptional
year due to the occurrence of a severe hailstorm, compared to 2011. Methanol
was the compound which, at 381.5 mg C m−2 and 449.9 mg
C m−2, contributed most to the cumulative VOC carbon emissions in
2009 and 2011, respectively. In contrast to methanol emissions, however,
considerable amounts of monoterpenes (−327.3 mg C m−2) were
deposited onto the mountain meadow during 2009 caused by a hailstorm. Other
quantified VOCs had considerably lower influences on the annual patterns. |
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