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| Titel |
Diurnal, seasonal and long-term variations of global formaldehyde columns inferred from combined OMI and GOME-2 observations |
| VerfasserIn |
I. De Smedt, T. Stavrakou, F. Hendrick, T. Danckaert, T. Vlemmix, G. Pinardi, N. Theys, C. Lerot, C. Gielen, C. Vigouroux, C. Hermans, C. Fayt, P. Veefkind, J.-F. Müller, M. Van Roozendael |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 21 ; Nr. 15, no. 21 (2015-11-10), S.12519-12545 |
| Datensatznummer |
250120154
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| Publikation (Nr.) |
 copernicus.org/acp-15-12519-2015.pdf |
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| Zusammenfassung |
| We present the new version (v14) of the BIRA-IASB algorithm for the retrieval
of formaldehyde (H2CO) columns from spaceborne UV–visible sensors.
Applied to OMI measurements from Aura and to GOME-2 measurements from MetOp-A
and MetOp-B, this algorithm is used to produce global distributions of
H2CO representative of mid-morning and early afternoon conditions. Its
main features include (1) a new iterative DOAS scheme involving three fitting
intervals to better account for the O2–O2 absorption, (2) the use
of earthshine radiances averaged in the equatorial Pacific as reference
spectra, and (3) a destriping correction and background normalisation
resolved in the across-swath position. For the air mass factor calculation, a
priori vertical profiles calculated by the IMAGES chemistry transport model
at 09:30 and 13:30 LT are used. Although the
resulting GOME-2 and OMI H2CO vertical columns are found to be highly
correlated, some systematic differences are observed. Afternoon columns are
generally larger than morning ones, especially in mid-latitude regions. In
contrast, over tropical rainforests, morning H2CO columns significantly
exceed those observed in the afternoon. These differences are discussed in
terms of the H2CO column variation between mid-morning and early
afternoon, using ground-based MAX-DOAS measurements available from seven
stations in Europe, China and Africa. Validation results confirm the capacity
of the combined satellite measurements to resolve diurnal variations in
H2CO columns. Furthermore, vertical profiles derived from MAX-DOAS
measurements in the Beijing area and in Bujumbura are used for a more
detailed validation exercise. In both regions, we find an agreement better
than 15 % when MAX-DOAS profiles are used as a priori for the satellite
retrievals. Finally, regional trends in H2CO columns are estimated for
the 2004–2014 period using SCIAMACHY and GOME-2 data for morning conditions,
and OMI for early afternoon conditions. Consistent features are observed,
such as an increase of the columns in India and central–eastern China, and a
decrease in the eastern US and Europe. We find that the higher horizontal
resolution of OMI combined with a better sampling and a more favourable
illumination at midday allow for more significant trend estimates, especially
over Europe and North America. Importantly, in some parts of the Amazonian
forest, we observe with both time series a significant downward trend in
H2CO columns, spatially correlated with areas affected by deforestation. |
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