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| Titel |
Homogeneous nucleation rates of nitric acid dihydrate (NAD) at simulated stratospheric conditions – Part II: Modelling |
| VerfasserIn |
O. Möhler, H. Bunz, O. Stetzer |
| 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 ; 6, no. 10 ; Nr. 6, no. 10 (2006-07-24), S.3035-3047 |
| Datensatznummer |
250004014
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| Publikation (Nr.) |
 copernicus.org/acp-6-3035-2006.pdf |
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| Zusammenfassung |
| Activation energies ΔGact for the nucleation of nitric acid
dihydrate (NAD) in supercooled binary HNO3/H2O solution droplets
were calculated from volume-based nucleation rate measurements using the AIDA
(Aerosol, Interactions, and Dynamics in the Atmosphere) aerosol chamber of
Forschungszentrum Karlsruhe. The experimental conditions covered temperatures
T between 192 and 197 K, NAD saturation ratios SNAD between
7 and 10, and nitric acid molar fractions of the nucleating sub-micron
sized droplets between 0.26 and 0.28. Based on classical nucleation
theory, a new parameterisation for ΔGact=A×(T ln SNAD)−2+B is fitted to the experimental data with A=2.5×106 kcal K2 mol−1
and B=11.2−0.1(T−192) kcal mol−1.
A and B were chosen to also achieve good agreement with literature data
of ΔGact. The parameter A implies, for the temperature and
composition range of our analysis, a mean interface tension
σsl=51 cal mol−1 cm−2 between the growing NAD germ and
the supercooled solution. A slight temperature dependence of the diffusion
activation energy is represented by the parameter B. Investigations with a
detailed microphysical process model showed that literature formulations of
volume-based (Salcedo et al., 2001) and surface-based (Tabazadeh et al., 2002) nucleation rates
significantly overestimate NAD formation rates when applied to the conditions
of our experiments. |
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