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| Titel |
Accurate measurements of carbon monoxide in humid air using the cavity ring-down spectroscopy (CRDS) technique |
| VerfasserIn |
H. Chen, A. Karion, C. W. Rella, J. Winderlich, C. Gerbig, A. Filges, T. Newberger, C. Sweeney, P. P. Tans |
| 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. 4 ; Nr. 6, no. 4 (2013-04-17), S.1031-1040 |
| Datensatznummer |
250017876
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| Publikation (Nr.) |
 copernicus.org/amt-6-1031-2013.pdf |
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| Zusammenfassung |
| Accurate measurements of carbon monoxide (CO) in humid air have been made
using the cavity ring-down spectroscopy (CRDS) technique. The measurements
of CO mole fractions are determined from the strength of its spectral
absorption in the near-infrared region (~1.57 μm) after
removing interferences from adjacent carbon dioxide (CO2) and water
vapor (H2O) absorption lines. Water correction functions that account
for the dilution and pressure-broadening effects as well as absorption line
interferences from adjacent CO2 and H2O lines have been derived
for CO2 mole fractions between 360–390 ppm and for reported H2O
mole fractions between 0–4%. The line interference corrections are
independent of CO mole fractions. The dependence of the line interference
correction on CO2 abundance is estimated to be approximately −0.3 ppb/100 ppm
CO2 for dry mole fractions of CO. Comparisons of water
correction functions from different analyzers of the same type show
significant differences, making it necessary to perform instrument-specific
water tests for each individual analyzer. The CRDS analyzer was flown on an
aircraft in Alaska from April to November in 2011, and the accuracy of the
CO measurements by the CRDS analyzer has been validated against discrete
NOAA/ESRL flask sample measurements made on board the same aircraft, with a
mean difference between integrated in situ and flask measurements of
−0.6 ppb and a standard deviation of 2.8 ppb. Preliminary testing of CRDS
instrumentation that employs improved spectroscopic model functions for
CO2, H2O, and CO to fit the raw spectral data (available since the
beginning of 2012) indicates a smaller water vapor dependence than the
models discussed here, but more work is necessary to fully validate the
performance. The CRDS technique provides an accurate and low-maintenance
method of monitoring the atmospheric dry mole fractions of CO in humid air
streams. |
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