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| Titel |
Sensitivity of top-down CO source estimates to the modeled vertical structure in atmospheric CO |
| VerfasserIn |
Z. Jiang, D. B. A. Jones, H. M. Worden, D. K. Henze |
| 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. 3 ; Nr. 15, no. 3 (2015-02-11), S.1521-1537 |
| Datensatznummer |
250119406
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| Publikation (Nr.) |
 copernicus.org/acp-15-1521-2015.pdf |
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| Zusammenfassung |
| We assessed the sensitivity of regional CO source estimates to the modeled
vertical CO distribution by assimilating multi-spectral MOPITT (Measurements of Pollution In The
Troposphere) V5J CO
retrievals with the GEOS-Chem model. We compared the source estimates
obtained by assimilating the CO profiles and the surface layer retrievals
from June 2004 to May 2005. Because the surface layer retrievals are less
sensitive to CO in the free troposphere, it is expected that they should
provide constraints in the CO source estimates that are less sensitive to
the vertical structure of CO in the free troposphere. The inferred source
estimates all suggest a reduction in CO emissions in the tropics and
subtropics, and an increase in the extratropics over the a priori estimates.
The tropical decreases were particularly pronounced for regions where the
biogenic source of CO was dominant, suggesting an overestimate of the a
priori isoprene source of CO in the model. We found that the differences
between the regional source estimates inferred from the profile and surface
layer retrievals for 2004–2005 were small, generally less than 10% for
the main continental regions, except for estimates for southern Asia, North
America, and Europe. Because of discrepancies in convective transport in the
model, the CO source estimates for India and southeastern Asia inferred from
the CO profiles were significantly higher than those estimated from the
surface layer retrievals during June–August 2004. On the other hand, the
profile inversion underestimated the CO emissions from North America and
Europe compared to the assimilation of the surface layer retrievals. We
showed that vertical transport of air from the North American and European
boundary layers is slower than from other continental regions, and thus air in
the free troposphere from North America and Europe in the model is more
chemically aged, which could explain the discrepancy between the source
estimates inferred from the profile and surface layer retrievals. We also
examined the impact of the OH distribution on the source estimates and found
that the discrepancies between the source estimates obtained with two OH
fields were larger when using the profile data, which is consistent with
greater sensitivity to the more chemically aged air in the free troposphere.
Our findings indicate that regional CO source estimates are sensitive to the
vertical CO structure. They suggest that diagnostics to assess the age of
air from the continental source regions should help interpret the results
from CO source inversions. Our results also suggest that assimilating a
broader range of composition measurements to provide better constraint on
tropospheric OH and the biogenic sources of CO is essential for reliable
quantification of the regional CO budget. |
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