Evaluation of the IAGOS-Core GHG package H<sub>2</sub>O measurements during the DENCHAR airborne inter-comparison campaign in 2011
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Published:2018-09-19
Issue:9
Volume:11
Page:5279-5297
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ISSN:1867-8548
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Container-title:Atmospheric Measurement Techniques
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language:en
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Short-container-title:Atmos. Meas. Tech.
Author:
Filges Annette, Gerbig ChristophORCID, Rella Chris W., Hoffnagle John, Smit Herman, Krämer MartinaORCID, Spelten Nicole, Rolf ChristianORCID, Bozóki ZoltánORCID, Buchholz Bernhard, Ebert VolkerORCID
Abstract
Abstract. As part of the DENCHAR (Development and Evaluation of Novel Compact
Hygrometer for Airborne Research) inter-comparison campaign in northern
Germany in 2011, a commercial cavity ring-down spectroscopy (CRDS) based gas
analyzer (G2401-m, Picarro Inc., US) was installed on a Learjet to measure
atmospheric water vapor, CO2, CH4, and CO. The CRDS
components were identical to those chosen for integration aboard commercial
airliners within the IAGOS (In-service Aircraft for a Global Observing
System) project. Since the quantitative capabilities of the CRDS water vapor
measurements were never evaluated and reviewed in detail in a publication
before, the campaign allowed for an initial assessment of the long-term IAGOS
water vapor measurements by CRDS against reference instruments with a long
performance record (Fast In-situ Stratospheric Hygrometer (FISH) and CR-2
frost point hygrometer (Buck Research Instruments L.L.C., US), both operated
by Research Centre Jülich). For the initial water calibration of the instrument it was compared against a
dew point mirror (Dewmet TDH, Michell Instruments Ltd., UK) in the range from
70 000 to 25 000 ppm water vapor mole fraction. During the
inter-comparison campaign the analyzer was compared on the ground over the
range from 2 to 600 ppm against the dew point hygrometer used for
calibration of the FISH reference instrument. A new, independent calibration
method based on the dilution effect of water vapor on CO2 was
evaluated. Comparison of the in-flight data against the reference instruments showed
that the analyzer is reliable and has a good long-term stability. The flight
data suggest a conservative precision estimate for measurements made at
0.4 Hz (2.5 s measurement interval) of 4 ppm for
H2O < 10 ppm, 20 % or 10 ppm (whichever is smaller)
for 10 ppm < H2O < 100 ppm, and 5 % or
30 ppm (whichever is smaller) for H2O > 100 ppm.
Accuracy of the CRDS instrument was estimated, based on laboratory
calibrations, as 1 % for the water vapor range from 25 000 ppm down to
7000 ppm, increasing to 5 % at 50 ppm water vapor. Accuracy at water
vapor mole fractions below 50 ppm was difficult to assess, as the reference
systems suffered from lack of data availability.
Publisher
Copernicus GmbH
Subject
Atmospheric Science
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