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| Titel |
Development and characterisation of a state-of-the-art GOME-2 formaldehyde air-mass factor algorithm |
| VerfasserIn |
W. Hewson, M. P. Barkley, G. González Abad, H. Bösch, T. Kurosu, R. Spurr, L. G. Tilstra |
| 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 ; 8, no. 10 ; Nr. 8, no. 10 (2015-10-05), S.4055-4074 |
| Datensatznummer |
250116624
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| Publikation (Nr.) |
 copernicus.org/amt-8-4055-2015.pdf |
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| Zusammenfassung |
| Space-borne observations of formaldehyde (HCHO) are frequently used to
derive surface emissions of isoprene, an important biogenic volatile
organic compound. The conversion of retrieved HCHO slant column
concentrations from satellite line-of-sight measurements to vertical
columns is determined through application of an air mass factor (AMF),
accounting for instrument viewing geometry, radiative transfer, and
vertical profile of the absorber in the atmosphere. This step in the
trace gas retrieval is subject to large errors. This work presents the
AMF algorithm in use at the University of Leicester (UoL), which
introduces scene-specific variables into a per-observation full
radiative transfer AMF calculation, including increasing spatial
resolution of key environmental parameter databases, input variable
area weighting, instrument-specific scattering weight calculation, and
inclusion of an ozone vertical profile climatology. Application of
these updates to HCHO slant columns from the GOME-2 instrument is
shown to typically adjust the AMF by ±20 %, compared to a
reference algorithm without these advanced parameterisations.
On average the GOME-2 AMFs increase by
4 %, with over 70 % of locations having an AMF of 0–20 % larger than originally,
largely resulting from the use of the latest GOME-2 reflectance product.
Furthermore, the new UoL algorithm also incorporates a full radiative
transfer error calculation for each scene to help characterise AMF
uncertainties. Global median AMF errors are typically 50–60 %, and
are driven by uncertainties in the HCHO profile shape and its vertical distribution relative to clouds and aerosols.
If uncertainty on the a priori HCHO profile is relatively small (< 10 %) then
the median AMF total error decreases to about 30–40 %. |
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