 |
| Titel |
High variability of the heterogeneous ice nucleation potential of oxalic acid dihydrate and sodium oxalate |
| VerfasserIn |
R. Wagner, O. Möhler, H. Saathoff, M. Schnaiter, T. Leisner |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 10, no. 16 ; Nr. 10, no. 16 (2010-08-16), S.7617-7641 |
| Datensatznummer |
250008708
|
| Publikation (Nr.) |
 copernicus.org/acp-10-7617-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
| The heterogeneous ice nucleation potential of airborne oxalic acid dihydrate
and sodium oxalate particles in the deposition and condensation mode has
been investigated by controlled expansion cooling cycles in the AIDA aerosol
and cloud chamber of the Karlsruhe Institute of Technology at temperatures
between 244 and 228 K. Previous laboratory studies have highlighted the
particular role of oxalic acid dihydrate as the only species amongst a
variety of other investigated dicarboxylic acids to be capable of acting as
a heterogeneous ice nucleus in both the deposition and immersion mode. We
could confirm a high deposition mode ice activity for 0.03 to 0.8 μm
sized oxalic acid dihydrate particles that were either formed by nucleation
from a gaseous oxalic acid/air mixture or by rapid crystallisation of highly
supersaturated aqueous oxalic acid solution droplets. The critical
saturation ratio with respect to ice required for deposition nucleation was
found to be less than 1.1 and the size-dependent ice-active fraction of the
aerosol population was in the range from 0.1 to 22%. In contrast, oxalic
acid dihydrate particles that had crystallised from less supersaturated
solution droplets and had been allowed to slowly grow in a supersaturated
environment from still unfrozen oxalic acid solution droplets over a time
period of several hours were found to be much poorer heterogeneous ice
nuclei. We speculate that under these conditions a crystal surface structure
with less-active sites for the initiation of ice nucleation was generated.
Such particles partially proved to be almost ice-inactive in both the
deposition and condensation mode. At times, the heterogeneous ice nucleation
ability of oxalic acid dihydrate significantly changed when the particles
had been processed in preceding cloud droplet activation steps. Such
behaviour was also observed for the second investigated species, namely
sodium oxalate. Our experiments address the atmospheric scenario that
coating layers of oxalic acid or its salts may be formed by physical and
chemical processing on pre-existing particulates such as mineral dust and
soot. Given the broad diversity of the observed heterogeneous ice
nucleability of the oxalate species, it is not straightforward to predict
whether an oxalate coating layer will improve or reduce the ice nucleation
ability of the seed aerosol particles. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|