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| Titel |
Temperature thresholds for chlorine activation and ozone loss in the polar stratosphere |
| VerfasserIn |
K. Drdla, R. Müller |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 30, no. 7 ; Nr. 30, no. 7 (2012-07-13), S.1055-1073 |
| Datensatznummer |
250017244
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| Publikation (Nr.) |
 copernicus.org/angeo-30-1055-2012.pdf |
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| Zusammenfassung |
| Low stratospheric temperatures are known to be responsible for
heterogeneous chlorine activation that leads to polar ozone
depletion. Here, we discuss the temperature threshold below which
substantial chlorine activation occurs. We suggest that the onset
of chlorine activation is dominated by reactions on cold binary
aerosol particles, without the formation of polar stratospheric
clouds (PSCs), i.e. without any significant uptake of HNO3
from the gas phase. Using reaction rates on cold binary aerosol in
a model of stratospheric chemistry, a chlorine activation threshold
temperature, TACL, is derived. At typical stratospheric
conditions, TACL is similar in value to TNAT (within 1–2 K),
the highest temperature at which nitric acid trihydrate (NAT) can
exist. TNAT is still in use to parameterise the threshold
temperature for the onset of chlorine activation. However,
perturbations can cause TACL to differ from TNAT: TACL is
dependent upon H2O and potential temperature, but unlike
TNAT is not dependent upon HNO3. Furthermore, in contrast to
TNAT, TACL is dependent upon the stratospheric sulfate aerosol
loading and thus provides a means to estimate the impact on polar
ozone of strong volcanic eruptions and some geo-engineering
options, which are discussed. A parameterisation of TACL is
provided here, allowing it to be calculated for low solar elevation
(or high solar zenith angle) over a comprehensive range of
stratospheric conditions. Considering TACL as a proxy for
chlorine activation cannot replace a detailed model calculation, and
polar ozone loss is influenced by other factors apart from the initial
chlorine activation. However, TACL provides a more accurate
description of the temperature conditions necessary for
chlorine activation and ozone loss in the polar stratosphere
than TNAT. |
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