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| Titel |
How consistent are top-down hydrocarbon emissions based on formaldehyde observations from GOME-2 and OMI? |
| VerfasserIn |
T. Stavrakou, J.-F. Müller, M. Bauwens, I. Smedt, M. Van Roozendael, M. Mazière, C. Vigouroux, F. Hendrick, M. George, C. Clerbaux, P.-F. Coheur, A. Guenther |
| 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. 20 ; Nr. 15, no. 20 (2015-10-26), S.11861-11884 |
| Datensatznummer |
250120120
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| Publikation (Nr.) |
 copernicus.org/acp-15-11861-2015.pdf |
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| Zusammenfassung |
The vertical columns of formaldehyde (HCHO) retrieved from two satellite
instruments, the Global Ozone Monitoring Instrument-2 (GOME-2) on Metop-A and
the Ozone Monitoring Instrument (OMI) on Aura, are used to constrain global
emissions of HCHO precursors from open fires, vegetation and human activities
in the year 2010. To this end, the emissions are varied and optimized using
the adjoint model technique in the IMAGESv2 global CTM (chemical transport
model) on a monthly basis and at the model resolution. Given the different
local overpass times of GOME-2 (09:30 LT) and OMI (13:30 LT), the simulated diurnal cycle of HCHO columns
is investigated and evaluated against ground-based optical measurements at
seven sites in Europe, China and Africa. The modeled diurnal cycle exhibits
large variability, reflecting competition between photochemistry and emission
variations, with noon or early afternoon maxima at remote locations (oceans)
and in regions dominated by anthropogenic emissions, late afternoon or
evening maxima over fire scenes, and midday minima in isoprene-rich regions.
The agreement between simulated and ground-based columns is generally better
in summer (with a clear afternoon maximum at mid-latitude sites) than in
winter, and the annually averaged ratio of afternoon to morning columns is
slightly higher in the model (1.126) than in the ground-based measurements
(1.043).
The anthropogenic VOC (volatile organic compound) sources are found to be
weakly constrained by the inversions on the global scale, mainly owing to
their generally minor contribution to the HCHO columns, except over strongly
polluted regions, like China. The OMI-based inversion yields total flux
estimates over China close to the bottom-up inventory (24.6 vs.
25.5 TgVOC yr−1 in the a priori) with, however, pronounced increases in the northeast of China
and reductions in the south. Lower fluxes are estimated based on GOME-2 HCHO
columns (20.6 TgVOC yr−1), in particular over the northeast, likely reflecting
mismatches between the observed and the modeled diurnal cycle in this
region.
The resulting biogenic and pyrogenic flux estimates from both optimizations
generally show a good degree of consistency. A reduction of the global annual
biogenic emissions of isoprene is derived, of 9 and 13 % according to
GOME-2 and OMI, respectively, compared to the a priori estimate of 363 Tg in
2010. The reduction is largest (up to 25–40 %) in the Southeastern US, in
accordance with earlier studies. The GOME-2 and OMI satellite columns suggest
a global pyrogenic flux decrease by 36 and 33 %, respectively, compared to
the GFEDv3 (Global Fire Emissions Database) inventory. This decrease is especially pronounced over tropical
forests, such as in Amazonia, Thailand and Myanmar, and is supported by
comparisons with CO observations from IASI (Infrared Atmospheric Sounding
Interferometer). In contrast to these flux reductions, the emissions due to
harvest waste burning are strongly enhanced over the northeastern China plain
in June (by ca. 70 % in June according to OMI) as well as over Indochina in
March. Sensitivity inversions showed robustness of the inferred estimates,
which were found to lie within 7 % of the standard inversion results at the
global scale. |
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