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| Titel |
Long-term greenhouse gas measurements from aircraft |
| VerfasserIn |
A. Karion, C. Sweeney, S. Wolter, T. Newberger, H. Chen, A. Andrews, J. Kofler, D. Neff, 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. 3 ; Nr. 6, no. 3 (2013-03-01), S.511-526 |
| Datensatznummer |
250017828
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| Publikation (Nr.) |
 copernicus.org/amt-6-511-2013.pdf |
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| Zusammenfassung |
In March 2009 the NOAA/ESRL/GMD Carbon Cycle and Greenhouse Gases Group
collaborated with the US Coast Guard (USCG) to establish the Alaska Coast
Guard (ACG) sampling site, a unique addition to NOAA's atmospheric
monitoring network. This collaboration takes advantage of USCG bi-weekly
Arctic Domain Awareness (ADA) flights, conducted with Hercules C-130
aircraft from March to November each year. Flights typically last 8 h
and cover a large area, traveling from Kodiak up to Barrow, Alaska, with
altitude profiles near the coast and in the interior. NOAA instrumentation
on each flight includes a flask sampling system, a continuous cavity
ring-down spectroscopy (CRDS) carbon dioxide (CO2)/methane (CH4)/carbon monoxide (CO)/water vapor (H2O) analyzer, a continuous ozone
analyzer, and an ambient temperature and humidity sensor. Air samples
collected in flight are analyzed at NOAA/ESRL for the major greenhouse gases
and a variety of halocarbons and hydrocarbons that influence climate,
stratospheric ozone, and air quality.
We describe the overall system for making accurate greenhouse gas
measurements using a CRDS analyzer on an aircraft with minimal operator
interaction and present an assessment of analyzer performance over a
three-year period. Overall analytical uncertainty of CRDS measurements in
2011 is estimated to be 0.15 ppm, 1.4 ppb, and 5 ppb for CO2,
CH4, and CO, respectively, considering short-term precision, calibration
uncertainties, and water vapor correction uncertainty. The stability of the
CRDS analyzer over a seven-month deployment period is better than 0.15 ppm,
2 ppb, and 4 ppb for CO2, CH4, and CO, respectively, based on
differences of on-board reference tank measurements from a laboratory
calibration performed prior to deployment. This stability is not affected by
variation in pressure or temperature during flight. We conclude that the
uncertainty reported for our measurements would not be significantly
affected if the measurements were made without in-flight calibrations,
provided ground calibrations and testing were performed regularly.
Comparisons between in situ CRDS measurements and flask measurements are
consistent with expected measurement uncertainties for CH4 and CO, but
differences are larger than expected for CO2. Biases and standard
deviations of comparisons with flask samples suggest that atmospheric
variability, flask-to-flask variability, and possible flask sampling biases
may be driving the observed flask versus in situ CO2 differences rather
than the CRDS measurements. |
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