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Titel |
Non-reactive and reactive trace gas fluxes: Simultaneous measurements with ground based and vertically integrating methods |
VerfasserIn |
J.-C. Mayer, U. Rummel, M. O. Andreae, T. Foken, F. X. Meixner |
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 |
250024443
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Zusammenfassung |
The footprint area, i.e. the source region of a flux measured at a certain location, increases
with increasing height above ground of the flux measurements. For non-reactive trace gases
and horizontally homogeneous terrain (particularly with respect to deposition and emission
processes), an increase in height should not alter the actual measured flux (constant flux layer
assumption). For reactive trace gases, with chemical life times of about 30Â s – 300Â s,
chemical production and loss processes within the measuring layer lead to vertical flux
divergence. The magnitude of the flux divergence can be determined directly by comparing
fluxes of reactive trace gases being affected by chemistry with fluxes of the same species
being not altered by chemistry.
In August 2006, the field experiment LIBRETTO (LIndenBerg REacTive Trace gas
prOfiles) was carried out in cooperation with the German Meteorological Service
(DWD) at the field site of the Richard Aßmann Observatory in Lindenberg. At a
99Â m mast, profiles of air temperature, relative humidity, wind speed and direction
were measured. The mast is equipped with an elevator, where sensors for trace
gases (CO2, H2O, O3), air temperature and relative humidity have been installed.
During the experiment, the elevator system was run continuously, providing scanned
profiles of trace gas concentrations from 2Â m to 99Â m a.g.l. of the atmospheric
boundary layer (ABL) approx. every 10 minutes. Between 0.15Â m and 2.0Â m,
concentration differences of the trace gases CO2, H2O, O3, NO and NO2 were
measured.
Applying the modified Bowen ration (MBR) method to the measured concentration
differences and directly measured sensible heat flux (eddy covariance data from DWD) yields
surface fluxes of the trace gases. Integral fluxes of CO2, O3 and sensible heat were computed
simultaneously by applying the nocturnal boundary layer budget method to the scanned
elevator profiles.
A direct comparison showed little deviations between the two methods for the
passive CO2 and sensible heat. This demonstrates the validity of the assumption of
horizontal homogeneity. However, the fluxes of the reactive O3 deviated significantly,
with apparently higher deposition fluxes derived from the boundary layer budget
method.
We will present simultaneously measured fluxes of CO2, O3 and sensible heat.
Furthermore, we will discuss the reasons for the observed deviations between the two
methods. Particularly the attempt will be made to explain these deviations with the measured
quantities. |
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