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| Titel |
Improved retrieval of global tropospheric formaldehyde columns from GOME-2/MetOp-A addressing noise reduction and instrumental degradation issues |
| VerfasserIn |
I. Smedt, M. Roozendael, T. Stavrakou, J.-F. Müller, C. Lerot, N. Theys, P. Valks, N. Hao, R. der A. |
| 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 ; 5, no. 11 ; Nr. 5, no. 11 (2012-11-28), S.2933-2949 |
| Datensatznummer |
250003184
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| Publikation (Nr.) |
 copernicus.org/amt-5-2933-2012.pdf |
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| Zusammenfassung |
| We present a new dataset of formaldehyde vertical columns retrieved from
observations of GOME-2 on board the EUMETSAT MetOp-A platform between 2007
and 2011. The new retrieval scheme, which has been optimised for GOME-2,
includes a two-step fitting procedure that strongly reduces the impact of
spectral interferences between H2CO and BrO, and a modified DOAS
approach that better handles ozone absorption effects at moderately low sun
elevations. Owing to these new features, the noise in the H2CO slant
columns is reduced by up to 40% in comparison to baseline retrieval
settings used operationally. Also, the previously reported underestimation
of the H2CO columns in tropical and mid-latitude regions has been
largely eliminated, improving the agreement with coincident SCIAMACHY
observations. To compensate for the drift of the GOME-2 slit function and to
mitigate the instrumental degradation effects on H2CO retrievals, an
asymmetric Gaussian line-shape is fitted during the irradiance calibration.
Additionally, external parameters used in the tropospheric air mass factor
computation (surface reflectances, cloud parameters and a priori profile
shapes of H2CO) have been updated using most recent databases. Similar
updates were also applied to the historical datasets of GOME and SCIAMACHY,
leading to the generation of a consistent multi-mission H2CO data
record covering the time period from 1997 until 2011. Comparing the
resulting time series of monthly averaged H2CO vertical columns in 12
large regions worldwide, the correlation coefficient between SCIAMACHY and
GOME-2 columns is generally higher than 0.8 in the overlap period, and
linear regression slopes differ by less than 10% from unity in most of
the regions. In comparison to SCIAMACHY, the largely improved spatial
sampling of GOME-2 allows for a better characterisation of formaldehyde
distribution at the regional scale and/or at shorter timescales, leading to
a better identification of the emission sources of non-methane volatile
organic compounds. |
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