Evaluation of the IAGOS-Core GHG package H<sub>2</sub>O measurements during the DENCHAR airborne inter-comparison campaign in 2011
<p>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 meas...
| Main Authors: | , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-09-01
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| Series: | Atmospheric Measurement Techniques |
| Online Access: | https://www.atmos-meas-tech.net/11/5279/2018/amt-11-5279-2018.pdf |
| Summary: | <p>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, CO<sub>2</sub>, CH<sub>4</sub>, 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).</p><p>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 CO<sub>2</sub> was
evaluated.</p><p>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
H<sub>2</sub>O < 10 ppm, 20 % or 10 ppm (whichever is smaller)
for 10 ppm < H<sub>2</sub>O < 100 ppm, and 5 % or
30 ppm (whichever is smaller) for H<sub>2</sub>O > 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.</p> |
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| ISSN: | 1867-1381 1867-8548 |