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要旨:
In the course of the ICOS (Integrated Carbon
Observation System) Demonstration Experiment a feasibility
study on the usefulness of a travelling comparison instrument
(TCI) was conducted in order to evaluate continuous
atmospheric CO2 and CH4 measurements at two European
stations. The aim of the TCI is to independently measure
ambient air in parallel to the standard station instrumentation,
thus providing a comprehensive comparison that includes the
sample intake system, the instrument itself as well as its calibration
and data evaluation. Observed differences between
the TCI and a gas chromatographic system, which acted
as a reference for the TCI, were −0.02±0.08 μmol mol−1
for CO2 and −0.3±2.3 nmol mol−1 for CH4. Over a
period of two weeks each, the continuous CO2 and
CH4 measurements at two ICOS field stations, Cabauw
(CBW), the Netherlands and Houdelaincourt (Observatoire
P´erenne de l’Environnement, OPE), France, were
compared to co-located TCI measurements. At Cabauw
mean differences of 0.21±0.06 μmol mol−1 for CO2 and
0.41±0.50 nmol mol−1 for CH4 were found. For OPE
the mean differences were 0.13±0.07 μmol mol−1 for
CO2 and 0.44±0.36 nmol mol−1 for CH4. Offsets arising
from differences in the working standard calibrations or
leakages/contaminations in the drying systems are too
small to explain the observed differences. Hence the most
likely causes of these observed differences are leakages
or contaminations in the intake lines and/or their flushing
pumps. For the Cabauw instrument an additional error
contribution originates from insufficient flushing of standard
gases. Although the TCI is an extensive quality control
approach it cannot replace other quality control systems.
Thus, a comprehensive quality management strategy for atmospheric monitoring networks is proposed as well.
