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| Titel |
What can 14CO measurements tell us about OH? |
| VerfasserIn |
M. C. Krol, J. F. Meirink, P. Bergamaschi, J. E. Mak, D. Lowe, P. Jöckel, S. Houweling, T. Röckmann |
| 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 ; 8, no. 16 ; Nr. 8, no. 16 (2008-08-29), S.5033-5044 |
| Datensatznummer |
250006349
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| Publikation (Nr.) |
 copernicus.org/acp-8-5033-2008.pdf |
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| Zusammenfassung |
| The possible use of 14CO measurements to constrain hydroxyl radical
(OH) concentrations in the atmosphere is investigated. 14CO is mainly
produced in the upper atmosphere from cosmic radiation. Measurements of
14CO at the surface show lower concentrations compared to the upper
atmospheric source region, which is the result of oxidation by OH. In this
paper, the sensitivity of 14CO mixing ratio surface measurements to the
3-D OH distribution is assessed with the TM5 model. Simulated 14CO
mixing ratios agree within a few molecules 14CO cm−3 (STP) with
existing measurements at five locations worldwide. The simulated cosmogenic
14CO distribution appears mainly sensitive to the assumed upper
atmospheric 14C source function, and to a lesser extend to model
resolution. As a next step, the sensitivity of 14CO measurements to OH
is calculated with the adjoint TM5 model. The results indicate that
14CO measurements taken in the tropics are sensitive to OH in a
spatially confined region that varies strongly over time due to
meteorological variability. Given measurements with an accuracy of 0.5 molecules 14CO cm−3 STP,
a good characterization of the cosmogenic
14CO fraction, and assuming perfect transport modeling, a single
14CO measurement may constrain OH to 0.2–0.3×106 molecules OH cm−3 on time scales of 6 months and spatial scales of
70×70 degrees (latitude×longitude) between the surface and
500 hPa. The sensitivity of 14CO measurements to high latitude OH is
about a factor of five higher. This is in contrast with methyl chloroform
(MCF) measurements, which show the highest sensitivity to tropical OH,
mainly due to the temperature dependent rate constant of the MCF–OH
reaction. A logical next step will be the analysis of existing 14CO
measurements in an inverse modeling framework. This paper presents the
required mathematical framework for such an analysis. |
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