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| Titel |
Do vibrationally excited OH molecules affect middle and upper atmospheric chemistry? |
| VerfasserIn |
T. Clarmann, F. Hase, B. Funke, M. López-Puertas, J. Orphal, M. Sinnhuber, G. P. Stiller, H. Winkler |
| 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 ; 10, no. 20 ; Nr. 10, no. 20 (2010-10-20), S.9953-9964 |
| Datensatznummer |
250008845
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| Publikation (Nr.) |
 copernicus.org/acp-10-9953-2010.pdf |
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| Zusammenfassung |
| Except for a few reactions involving electronically excited molecular
or atomic oxygen or nitrogen, atmospheric chemistry modelling usually
assumes that the temperature dependence of reaction rates is
characterized by Arrhenius' law involving kinetic temperatures.
It is known, however, that in the upper atmosphere the vibrational
temperatures may exceed the kinetic temperatures by several hundreds
of Kelvins. This excess energy has an impact on the
reaction rates.
We have used upper atmospheric OH populations and reaction
rate coefficients for OH(v=0...9)+O3 and OH(v=0...9)+O to estimate the
effective (i.e. population weighted) reaction rates for various atmospheric
conditions. We have found that the effective rate coefficient for
OH(v=0...9)+O3 can be larger by a factor of up to 1470 than that involving
OH in its vibrational ground state only. At altitudes where vibrationally
excited states of OH are highly populated, the OH reaction is a minor
sink of Ox and O3 compared to other reactions involving, e.g.,
atomic oxygen. Thus the impact of vibrationally excited OH on the ozone or
Ox sink remains small. Among quiescent atmospheres under investigation,
the largest while still small (less than 0.1%) effect was found
for the polar winter upper stratosphere and mesosphere. The contribution
of the reaction of vibrationally excited OH with ozone to
the OH sink is largest in the upper polar winter stratosphere (up to 4%),
while its effect on the HO2 source is larger in the lower thermosphere
(up to 1.5% for polar winter and 2.5% for midlatitude night conditions). For
OH(v=0...9)+O the effective rate coefficients are lower by up to 11%
than those involving OH in its vibrational ground state. The effects on
the odd oxygen sink are negative and can reach −3% (midlatitudinal nighttime
lowermost thermosphere), i.e. neglecting vibrational excitation overestimates
the odd oxygen sink. The OH sink is overestimated by up to 10%. After a solar
proton event, when upper atmospheric OH can be enhanced by an order of
magnitude, the excess relative odd oxygen sink by consideration of vibrational
excitation in the reaction of OH(v=0...9)+O3 is estimated at up to 0.2%,
and the OH sink by OH(v=0...9)+O can be reduced by 12% in the thermosphere
by vibrational excitation. |
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