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| Titel |
Numerical analysis of the chemical kinetic mechanisms of ozone depletion and halogen release in the polar troposphere |
| VerfasserIn |
L. Cao, H. Sihler, U. Platt, E. Gutheil |
| 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 ; 14, no. 7 ; Nr. 14, no. 7 (2014-04-15), S.3771-3787 |
| Datensatznummer |
250118586
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| Publikation (Nr.) |
 copernicus.org/acp-14-3771-2014.pdf |
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| Zusammenfassung |
The role of halogen species (e.g., Br, Cl) in the troposphere of
polar regions has been investigated since the discovery of their importance
for boundary layer ozone destruction in the polar spring about 25 years ago.
Halogen species take part in an auto-catalytic chemical reaction cycle, which
releases Br2 and BrCl from the sea salt aerosols, fresh sea
ice or snowpack, leading to ozone depletion. In this study, three different
chemical reaction schemes are investigated: a bromine-only reaction scheme,
which then is subsequently extended to include nitrogen-containing compounds
and chlorine species and corresponding chemical reactions. The importance of
specific reactions and their rate constants is identified by a sensitivity
analysis.
The heterogeneous reaction rates are parameterized by considering the
aerodynamic resistance, a reactive surface ratio, β, i.e., the ratio of
reactive surface area to total ground surface area, and the boundary layer
height, Lmix. It is found that for β = 1, a substantial
ozone decrease occurs after five days and ozone depletion lasts for 40 h for
Lmix = 200 m. For about β ≥ 20, the time required for
major ozone depletion ([O3] < 4 ppb) to occur becomes
independent of the height of the boundary layer,
and for β = 100 it approaches two days, 28 h of which are attributable to the
induction and 20 h to the depletion time.
In polar regions, a small amount of NOx may exist, which stems from
nitrate contained in the snow, and may have a strong
impact on the ozone depletion. Therefore, the role of nitrogen-containing
species on the ozone depletion rate is studied. The results show that the
NOx concentrations are influenced by different chemical reactions
over different time periods. During ozone depletion, the reaction cycle
involving the BrONO2 hydrolysis is dominant. A critical value of
0.0004 of the uptake coefficient of the BrONO2 hydrolysis reaction at
the aerosol and saline surfaces is identified, beyond which the existence of
NOx species accelerates the ozone depletion event, whereas for lower
values, deceleration occurs. |
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