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| Titel |
An unconventional approach to estimate the exchange of reactive trace gases at the soil - trunk space interface of a steep mountain forest site |
| VerfasserIn |
F. X. Meixner, M. Scheibe, K. Hens, G. T. Feig, M. O. Andreae |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027758
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| Zusammenfassung |
| On steep (45Ë ) mountain sites, flux measurements of trace gases (particularly
those of reactive trace gases) by conventional techniques (e.g., eddy covariance,
aerodynamic gradient, modified Bowen ratio; dynamic chambers) are difficult, if not
impossible. However, even at a steep mountainous forest site, vertical concentration
gradients can be measured quite easily in the first meter above the forest floor. But
there, vertical flux divergences have to be expected due to fast (photo-)chemical
reactions between reactive trace gases during the (slow) turbulent transport in this
layer. Particularly the determination of the bulk (turbulent) transfer velocity vtr
(necessary to infer corresponding fluxes from concentration gradients) may require
unconventional approaches under these conditions. One requires the combination
of measurements of vertical concentration differences and soil surface fluxes of
non-reactive trace gases, such as 222Rn and/or CO2 (surface fluxes by static chambers).
Once the bulk transfer velocity within the first meter of the trunk space has been
determined, it could be applied to vertical concentration differences of reactive
trace gases (NO, NO2, O3) in order to infer corresponding surface fluxes (which
have to be corrected for the fast (photo-)chemical reactions of the NO-NO2-O3
triad).
We will present results obtained during a field experiment in a steep Bavarian
mountainous spruce forest, Hohenpeissenberg (47,801Ë N, 11,009Ë E, 943 m a.s.l.)
performed in September-October 2005. Mean bulk transfer velocities in the first meter of the
trunk space was determined by the above mentioned approach and ranged between 0.005 and
0.03 m s-1 (equivalent to a bulk turbulent exchange coefficient of 0.45 – 5 x 10-2
m2Â s-1).
Corresponding fluxes of NO, NO2, and O3 were corrected for their flux divergencies due
to fast chemical interconversions by a new flux gradient numerical algorithm. We will present
diel variations of bulk transfer velocites, concentrations, vertical concentration differences,
and derived surface fluxes of NO, NO2, and O3 for a two week period in September 2005.
The overwhelming effect of near surface thermodynamic stability on surface fluxes will be
discussed. |
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