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| Titel |
Tropospheric methanol observations from space: retrieval evaluation and constraints on the seasonality of biogenic emissions |
| VerfasserIn |
K. C. Wells, D. B. Millet, L. Hu, K. E. Cady-Pereira, Y. Xiao, M. W. Shephard, C. L. Clerbaux, L. Clarisse, P.-F. Coheur, E. C. Apel, J. Gouw, C. Warneke, H. B. Singh, A. H. Goldstein, B. C. Sive |
| 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 ; 12, no. 13 ; Nr. 12, no. 13 (2012-07-12), S.5897-5912 |
| Datensatznummer |
250011305
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| Publikation (Nr.) |
 copernicus.org/acp-12-5897-2012.pdf |
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| Zusammenfassung |
| Methanol retrievals from nadir-viewing space-based sensors offer powerful
new information for quantifying methanol emissions on a global scale. Here
we apply an ensemble of aircraft observations over North America to evaluate
new methanol measurements from the Tropospheric Emission Spectrometer (TES)
on the Aura satellite, and combine the TES data with observations from the
Infrared Atmospheric Sounding Interferometer (IASI) on the MetOp-A satellite
to investigate the seasonality of methanol emissions from northern
midlatitude ecosystems. Using the GEOS-Chem chemical transport model as an
intercomparison platform, we find that the TES retrieval performs well when
the degrees of freedom for signal (DOFS) are above 0.5, in which case the
model:TES regressions are generally consistent with the model:aircraft
comparisons. Including retrievals with DOFS below 0.5 degrades the
comparisons, as these are excessively influenced by the a priori. The
comparisons suggest DOFS >0.5 as a minimum threshold for interpreting
retrievals of trace gases with a weak tropospheric signal. We analyze one
full year of satellite observations and find that GEOS-Chem, driven with
MEGANv2.1 biogenic emissions, underestimates observed methanol
concentrations throughout the midlatitudes in springtime, with the timing of
the seasonal peak in model emissions 1–2 months too late. We attribute this
discrepancy to an underestimate of emissions from new leaves in MEGAN, and
apply the satellite data to better quantify the seasonal change in methanol
emissions for midlatitude ecosystems. The derived parameters (relative
emission factors of 11.0, 0.26, 0.12 and 3.0 for new, growing, mature, and
old leaves, respectively, plus a leaf area index activity factor of 0.5 for
expanding canopies with leaf area index <1.2) provide a more realistic
simulation of seasonal methanol concentrations in midlatitudes on the basis
of both the IASI and TES measurements. |
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