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| Titel |
Heterogeneous chlorine activation on stratospheric aerosols and clouds in the Arctic polar vortex |
| VerfasserIn |
T. Wegner, J.-U. Grooß, M. Hobe, F. Stroh, O. Sumińska-Ebersoldt, C. M. Volk, E. Hösen, V. Mitev, G. Shur, R. Müller |
| 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 ; 12, no. 22 ; Nr. 12, no. 22 (2012-11-22), S.11095-11106 |
| Datensatznummer |
250011617
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| Publikation (Nr.) |
 copernicus.org/acp-12-11095-2012.pdf |
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| Zusammenfassung |
| Chlorine activation in the Arctic is investigated by examining different
parameterizations for uptake coefficients on stratospheric aerosols,
high-resolution in-situ measurements and vortex-wide satellite observations.
The parameterizations for heterogeneous chemistry on liquid aerosols are most
sensitive to temperature with the reaction rates doubling for every 1 K
increase in temperature. However, differences between the currently available
parameterizations are negligible. For Nitric Acid Trihydrate particles (NAT)
the major factors of uncertainty are the number density of nucleated
particles and different parameterizations for heterogeneous chemistry. These
two factors induce an uncertainty that covers several orders of magnitude on
the reaction rate. Nonetheless, since predicted reaction rates on liquid
aerosols always exceed those on NAT, the overall uncertainty for chlorine
activation is small. In-situ observations of ClOx from Arctic winters
in 2005 and 2010 are used to evaluate the heterogeneous chemistry
parameterizations. The conditions for these measurements proved to be very
different between those two winters with HCl being the limiting reacting
partner for the 2005 measurements and ClONO2 for the 2010 measurements.
Modeled levels of chlorine activation are in very good agreement with the
in-situ observations and the surface area provided by Polar Stratospheric
Clouds (PSCs) has only a limited impact on modeled chlorine activation. This
indicates that the parameterizations give a good representation of the
processes in the atmosphere. Back-trajectories started on the location of the
observations in 2005 indicate temperatures on the threshold for PSC
formation, hence the surface area is mainly provided by the background
aerosol. Still, the model shows additional chlorine activation during this
time-frame, providing cautionary evidence for chlorine activation even in the
absence of PSCs. Vortex-averaged satellite observations by the MLS instrument
also show no definite connection between chlorine activation and PSC
formation. The inter -and intra-annual variability of vortex-average
HCl and HNO3 based on MLS observations is examined for the Arctic
winters 2004/2005 to 2010/2011. These observations show that removal of HCl and
HNO3 from the gas-phase are not correlated. HNO3 loss exhibits great
inter-annual variability depending on prevailing temperatures while
HCl loss is continuous through December without considerable inter- or
intra-annual variability. Only the recovery of HCl in late winter depends on
the level of denitrification. Hence, the occurrence of HNO3 containing PSC
particles does not seem to have a significant effect on the speed of initial
chlorine activation on a vortex-wide scale. |
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