Nucleation modeling of the Antarctic stratospheric CN layer and derivation of sulfuric acid profiles
Recent analysis of long-term balloon-borne measurements of Antarctic stratospheric condensation nuclei (CN) between July and October showed the formation of a volatile CN layer at 21–27 km altitude in a background of existing particles. We use the nucleation model SAWNUC to simulate these CN in...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-06-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | http://www.atmos-chem-phys.net/17/7581/2017/acp-17-7581-2017.pdf |
| Summary: | Recent analysis of long-term balloon-borne measurements of Antarctic
stratospheric condensation nuclei (CN) between July and October showed the
formation of a volatile CN layer at 21–27 km altitude in a background of
existing particles. We use the nucleation model SAWNUC to simulate these CN
in subsiding air parcels and study their nucleation and coagulation
characteristics. Our simulations confirm recent analysis that the development
of the CN layer can be explained with neutral sulfuric acid–water nucleation
and we show that outside the CN layer the measured CN concentrations are well
reproduced just considering coagulation and the subsidence of the air
parcels. While ion-induced nucleation is expected as the dominating formation
process at higher temperatures, it does not play a significant role during
the CN layer formation as the charged clusters recombine too fast. Further,
we derive sulfuric acid concentrations for the CN layer formation. Our
concentrations are about 1 order of magnitude higher than previously
presented concentrations as our simulations consider that nucleated clusters
have to grow to CN size and can coagulate with preexisting particles.
Finally, we calculate threshold sulfuric acid profiles that show which
concentration of sulfuric acid is necessary for nucleation and growth to
observable size. These threshold profiles should represent upper limits of
the actual sulfuric acid outside the CN layer. According to our profiles,
sulfuric acid concentrations seem to be below midlatitude average during
Antarctic winter but above midlatitude average for the CN layer formation. |
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| ISSN: | 1680-7316 1680-7324 |