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| Titel |
A statistical approach to quantify uncertainty in carbon monoxide measurements at the Izaña global GAW station: 2008-2011 |
| VerfasserIn |
A. J. Gómez-Peláez, R. Ramos, V. Gomez-Trueba, P. C. Novelli, R. Campo-Hernandez |
| 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 (2013-03-20), S.787-799 |
| Datensatznummer |
250017848
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| Publikation (Nr.) |
 copernicus.org/amt-6-787-2013.pdf |
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| Zusammenfassung |
Atmospheric CO in situ measurements are carried out at the
Izaña (Tenerife) global GAW (Global Atmosphere Watch Programme
of the World Meteorological Organization – WMO) mountain station using a
Reduction Gas Analyser (RGA). In situ measurements at Izaña are
representative of the subtropical Northeast Atlantic free
troposphere, especially during nighttime. We present the
measurement system configuration, the response function, the
calibration scheme, the data processing, the Izaña 2008–2011
CO nocturnal time series, and the mean diurnal cycle by months.
We have developed a rigorous uncertainty analysis for carbon monoxide
measurements carried out at the Izaña station, which could be
applied to other GAW stations. We determine the combined standard measurement
uncertainty taking into consideration four contributing components: uncertainty of
the WMO standard gases interpolated over the range of measurement, the
uncertainty that takes into account the agreement between the standard
gases and the response function used, the uncertainty due to the
repeatability of the injections, and the propagated uncertainty
related to the temporal consistency of the response function parameters (which also
takes into account the covariance between the parameters). The mean
value of the combined standard uncertainty decreased significantly
after March 2009, from 2.37 nmol mol−1 to
1.66 nmol mol−1, due to improvements in the measurement
system. A fifth type of uncertainty we call representation uncertainty
is considered when some of the data necessary to compute the
temporal mean are absent. Any computed mean has also a propagated uncertainty
arising from the uncertainties of the data used to compute the
mean. The law of propagation depends on the type of uncertainty
component (random or systematic).
In situ hourly means are compared with simultaneous and collocated
NOAA flask samples. The uncertainty of the differences is computed
and used to determine whether the differences are significant.
For 2009–2011, only 24.5% of
the differences are significant, and 68% of the differences are
between −2.39 and 2.5 nmol mol−1. Total and annual mean
differences are computed using conventional expressions but also
expressions with weights based on the minimum variance method. The
annual mean differences for 2009–2011 are well within the
±2 nmol mol−1 compatibility goal of GAW. |
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