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| Titel |
Formation of large NAT particles and denitrification in polar stratosphere: possible role of cosmic rays and effect of solar activity |
| VerfasserIn |
F. Yu |
| 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 ; 4, no. 9/10 ; Nr. 4, no. 9/10 (2004-11-23), S.2273-2283 |
| Datensatznummer |
250001412
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| Publikation (Nr.) |
 copernicus.org/acp-4-2273-2004.pdf |
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| Zusammenfassung |
| The formation of large nitric acid trihydrate (NAT) particles has important
implications for denitrification and ozone depletion. Existing theories have
difficulty in explaining the formation of large NAT particles at temperatures
above the ice frost point, which has been observed recently over wide Arctic
regions. Our analyses reveal that high-energy comic ray particles might
induce the freezing of supercooled HNO3-H2O-H2SO4
droplets when they penetrate these thermodynamically unstable droplets. The
cosmic ray-induced freezing (CRIF) appears to be consistent with the
observed, highly selective formation of NAT particles. We suggest a possible
physical process behind the CRIF mechanism: the reorientation of polar
solution molecules into the crystalline configuration in the strong
electrical fields of moving secondary ions generated by passing cosmic rays.
A simple formula connecting the CRIF rate to cosmic ray flux is derived with
an undefined parameter constrained by observed NAT formation rates. Our
simulations indicate that strong solar proton events (SPEs) may
significantly enhance the formation of large NAT particles and
denitrification. The CRIF mechanism offers a possible explanation for the
observed high correlations between the thin nitrate-rich layers in polar ice
cores and major SPEs, and the observed enhancement in the aerosol backscattering
ratio at PSC layers shortly after an SPE and the significant precipitation
velocity of the enhanced PSC layers. The key uncertainty in the CRIF
mechanism is the probability (P) of freezing when a CR particle hits a
thermodynamically, unstable STS droplet. Further studies are needed to either
confirm or reject the CRIF hypothesis. |
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