DO STRATOSPHERIC AEROSOL DROPLETS FREEZE ABOVE THE ICE FROST POINT

Citation
T. Koop et al., DO STRATOSPHERIC AEROSOL DROPLETS FREEZE ABOVE THE ICE FROST POINT, Geophysical research letters, 22(8), 1995, pp. 917-920
Citations number
12
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
00948276
Volume
22
Issue
8
Year of publication
1995
Pages
917 - 920
Database
ISI
SICI code
0094-8276(1995)22:8<917:DSADFA>2.0.ZU;2-9
Abstract
Laboratory experiments are presented which show that liquid stratosphe ric aerosol droplets under polar winter conditions do not freeze for t emperatures higher than the water ice saturation temperature (frost po int). Calorimetric measurements of the freezing of supercooled H2SO4/H NO3/H2O bulk solutions with concentrations typical of the polar strato spheric aerosol exhibit very small freezing rates, which excludes the possibility of homogeneous freezing of the droplets for temperatures a bove the frost point. Even heterogeneous formation of H2SO4 and HNO3 h ydrates at these temperatures is a very inefficient process unless the stratosphere offers nuclei better suited for nucleation than those pr esent in the laboratory experiments, which appears to be unlikely. Onl y ice was found to be a potential nucleus suited for the formation of the hydrates, which could cause the hydrates to freeze at temperatures below the frost point.