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| Titel |
Areal-averaged trace gas emission rates from long-range open-path measurements in stable boundary layer conditions |
| VerfasserIn |
K. Schäfer, R. H. Grant, S. Emeis, A. Raabe, C. Heide, H. P. Schmid |
| 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 ; 5, no. 7 ; Nr. 5, no. 7 (2012-07-10), S.1571-1583 |
| Datensatznummer |
250003000
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| Publikation (Nr.) |
 copernicus.org/amt-5-1571-2012.pdf |
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| Zusammenfassung |
| Measurements of land-surface emission rates of greenhouse and other gases at
large spatial scales (10 000 m2) are needed to assess the spatial
distribution of emissions. This can be readily done using
spatial-integrating micro-meteorological methods like flux-gradient methods
which were evaluated for determining land-surface emission rates of trace
gases under stable boundary layers. Non-intrusive path-integrating
measurements are utilized. Successful application of a flux-gradient method
requires confidence in the gradients of trace gas concentration and wind, and
in the applicability of boundary-layer turbulence theory; consequently
the procedures to qualify measurements that can be used to determine the
flux is critical. While there is relatively high confidence in flux
measurements made under unstable atmospheres with mean winds greater than
1 m s−1, there is greater uncertainty in flux measurements made under
free convective or stable conditions. The study of N2O emissions of
flat grassland and NH3 emissions from a cattle lagoon involves
quality-assured determinations of fluxes under low wind, stable or
night-time atmospheric conditions when the continuous "steady-state"
turbulence of the surface boundary layer breaks down and the layer has
intermittent turbulence. Results indicate that following the Monin-Obukhov similarity
theory (MOST) flux-gradient methods that assume a log-linear profile of the
wind speed and concentration gradient incorrectly determine vertical
profiles and thus flux in the stable boundary layer. An alternative approach
is considered on the basis of turbulent diffusivity, i.e. the measured
friction velocity as well as height gradients of horizontal wind speeds and
concentrations without MOST correction for stability. It is shown that this
is the most accurate of the flux-gradient methods under stable conditions. |
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