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| Titel |
On the depletion of HCl in the Antarctic polar vortex |
| VerfasserIn |
Tobias Wegner, Douglas Kinnison, Rolando Garcia, Sasha Madronich, Susan Solomon, Marc von Hobe |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250083798
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| Zusammenfassung |
| Satellite observations and numerical modeling are used to constrain the mechanisms that
deplete gas-phase HCl in the Antarctic vortex. Our analysis shows that current formulations
of heterogeneous chlorine activation cannot explain the observed loss of gas-phase HCl in
SD-WACCM. Uncertainties in photochemistry, transport and initial conditions are
investigated, and it is shown that ClONO2 formed after photolysis of condensed-phase nitrate
increases the loss of HCl through heterogeneous chemistry, especially in the sunlit edge of
the vortex. This process eventually produces sufficient NOx to completely deplete gas-phase
HCl but this occurs too late compared to observations. Our results suggest that the more
likely primary mechanism for decreases in gas-phase HCl from the beginning of the polar
night until about the middle of July is active partitioning between the gas and condensed
phase. Since the HCl taken up into particles is quickly released upon warming, it does not
represent irreversible loss of chlorine, only temporary removal from the gas-phase. With
HCl dissolved in STS particles, the associated decrease in gas-phase HCl is not an
indicator of chlorine activation. The solubility of HCl in STS is highly sensitive to
water vapor and temperature, such that accurate simulation of both is necessary to
reproduce the observed depletion of gas-phase HCl. With the reference setup of
SD-WACCM hardly any HCl is simulated to be sequestered in STS. A negative
offset has to be applied to model temperatures to achieve significant partitioning
of HCl into the condensed phase. While our results imply substantial changes in
chlorine partitioning during the polar night, the ozone loss is insensitive to them. |
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