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| Titel |
The application of the Modified Band Approach for the calculation of on-line photodissociation rate constants in TM5: implications for oxidative capacity |
| VerfasserIn |
J. E. Williams, A. Strunk, V. Huijnen, M. Weele |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1991-959X
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| Digitales Dokument |
URL |
| Erschienen |
In: Geoscientific Model Development ; 5, no. 1 ; Nr. 5, no. 1 (2012-01-06), S.15-35 |
| Datensatznummer |
250002290
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| Publikation (Nr.) |
 copernicus.org/gmd-5-15-2012.pdf |
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| Zusammenfassung |
| A flexible and explicit on-line parameterization for the calculation of
tropospheric photodissociation rate constants (J-values) has been integrated
into the global Chemistry Transport Model TM5. Here we provide a
comprehensive description of this Modified Band Approach (MBA) including
details of the optimization procedure employed, the methodology applied for
calculating actinic fluxes, the photochemical reaction data used for each
chemical species, the aerosol climatology which is adopted and the
parameterizations adopted for improving the description of scattering and
absorption by clouds. The resulting J-values change markedly throughout the
troposphere when compared to the offline approach used to date, with
significant increases in the boundary layer and upper troposphere.
Conversely, for the middle troposphere a reduction in the actinic flux
results in a decrease in J-values. Integrating effects shows that application
of the MBA introduces seasonal dependent differences in important trace gas
oxidants. Tropospheric ozone (O3) changes by ±10% in the
seasonal mean mixing ratios throughout the troposphere, especially over
land. These changes and the perturbations in the photolysis rate of O3
induce changes of ±15% in tropospheric OH. In part this is due to an
increase in the re-cycling efficiency of nitrogen oxides. The overall
increase in northern hemispheric tropospheric ozone strengthens the
oxidizing capacity of the troposphere significantly and reduces the lifetime
of CO and CH4 by ~5 % and ~4%, respectively. Changes
in the tropospheric CO burden, however, are limited to a few percent due to
competing effects. Comparing the distribution of tropospheric ozone in the
boundary layer and middle troposphere against observations in Europe shows
there are improvements in the model performance during boreal winter in the
Northern Hemisphere near regions affected by high nitrogen oxide emissions.
Monthly mean total columns of nitrogen dioxide and formaldehyde also compare
more favorably against OMI and SCIAMACHY total column observations. |
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