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| Titel |
Measurement of low-ppm mixing ratios of water vapor in the upper troposphere and lower stratosphere using chemical ionization mass spectrometry |
| VerfasserIn |
T. D. Thornberry, A. W. Rollins, R. S. Gao, L. A. Watts, S. J. Ciciora, R. J. McLaughlin, C. Voigt, B. Hall, D. W. Fahey |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 6, no. 6 ; Nr. 6, no. 6 (2013-06-04), S.1461-1475 |
| Datensatznummer |
250017905
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| Publikation (Nr.) |
 copernicus.org/amt-6-1461-2013.pdf |
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| Zusammenfassung |
| A chemical ionization mass spectrometer (CIMS) instrument has been developed
for the fast, precise, and accurate measurement of water vapor (H2O) at
low mixing ratios in the upper troposphere and lower stratosphere (UT/LS). A
low-pressure flow of sample air passes through an ionization volume
containing an α-particle radiation source, resulting in a cascade of
ion-molecule reactions that produce hydronium ions (H3O+) from
ambient H2O. The production of H3O+ ions from ambient
H2O depends on pressure and flow through the ion source, which were
tightly controlled in order to maintain the measurement sensitivity
independent of changes in the airborne sampling environment. The instrument
was calibrated every 45 min in flight by introducing a series of
H2O mixing ratios between 0.5 and 153 parts per million (ppm,
10−6 mol mol−1) generated by Pt-catalyzed oxidation of H2 standards while
overflowing the inlet with dry synthetic air. The CIMS H2O instrument
was deployed in an unpressurized payload area aboard the NASA WB-57F high-altitude
research aircraft during the Mid-latitude Airborne Cirrus
Properties Experiment (MACPEX) mission in March and April 2011. The
instrument performed successfully during seven flights, measuring H2O
mixing ratios below 5 ppm in the lower stratosphere at altitudes up to
17.7 km, and as low as 3.5 ppm near the tropopause. Data were acquired at 10 Hz
and reported as 1 s averages. In-flight calibrations demonstrated a typical
sensitivity of 2000 Hz ppm−1 at 3 ppm with a signal to noise ratio
(2 σ, 1 s) greater than 32. The total measurement uncertainty was 9
to 11%, derived from the uncertainty in the in situ calibrations. |
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