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| Titel |
Denitrification by large NAT particles: the impact of reduced settling velocities and hints on particle characteristics |
| VerfasserIn |
W. Woiwode, J.-U. Grooß, H. Oelhaf, S. Molleker, S. Borrmann, A. Ebersoldt, W. Frey, T. Gulde, S. Khaykin, G. Maucher, C. Piesch, J. Orphal |
| 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 ; 14, no. 20 ; Nr. 14, no. 20 (2014-10-31), S.11525-11544 |
| Datensatznummer |
250119134
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| Publikation (Nr.) |
 copernicus.org/acp-14-11525-2014.pdf |
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| Zusammenfassung |
| Vertical redistribution of HNO3 through large HNO3-containing
particles associated with polar stratospheric clouds (PSCs) plays an important
role in the chemistry of the Arctic winter stratosphere. During the RECONCILE
(Reconciliation of essential process parameters for an enhanced
predictability of Arctic stratospheric ozone loss and its climate
interactions) campaign, apparently very large NAT (nitric acid trihydrate)
particles were observed by the airborne in situ probe FSSP-100 (Molleker
et al., 2014). Our analysis shows that the FSSP-100 observations associated
with the flight on 25 January 2010 cannot easily be explained assuming compact
spherical NAT particles due to much too short growing time at temperatures
below the existence temperature of NAT (TNAT). State-of-the-art
simulations using CLaMS (Chemical Lagrangian Model of the Stratosphere;
Grooß et al., 2014) suggest considerably smaller particles. We consider
the hypothesis that the simulation reproduces the NAT particle masses in a
realistic way, but that real NAT particles may have larger apparent sizes
compared to compact spherical particles, e.g. due to non-compact morphology
or aspheric shape. Our study focuses on the consequence that such particles
would have reduced settling velocities compared to compact spheres, altering
the vertical redistribution of HNO3. Utilising CLaMS simulations, we
investigate the impact of reduced settling velocities of NAT particles on
vertical HNO3 redistribution and compare the results with
observations of gas-phase HNO3 by the airborne Fourier transform
spectrometer MIPAS-STR associated with two RECONCILE flights. The MIPAS-STR
observations confirm conditions consistent with denitrification by NAT
particles for the flight on 25 January 2010 and show good agreement with the
simulations within the limitations of the comparison. Best agreement is found
if settling velocities between 100 and 50% relative to compact
spherical particles are considered (slight preference for the 70%
scenario). In contrast, relative settling velocities of 30% result in
too weak vertical HNO3 redistribution. Sensitivity simulations
considering temperature biases of ±1 K and multiplying the
simulated nucleation rates by factors of 0.5 and 2.0 affect the comparisons
to a similar extent, but result in no effective improvement compared to
the reference scenario. Our results show that an accurate knowledge of the
settling velocities of NAT particles is important for quantitative
simulations of vertical HNO3 redistribution. |
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