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Media type:
E-Article
Title:
Immersion Freezing Ability of Freshly Emitted Soot with Various Physico-Chemical Characteristics
Contributor:
Falk, John;
Korhonen, Kimmo;
Malmborg, Vilhelm B.;
Gren, Louise;
Eriksson, Axel C.;
Karjalainen, Panu;
Markkula, Lassi;
Bengtsson, Per-Erik;
Virtanen, Annele;
Svenningsson, Birgitta;
Pagels, Joakim;
Kristensen, Thomas B.
Published:
MDPI AG, 2021
Published in:
Atmosphere, 12 (2021) 9, Seite 1173
Language:
English
DOI:
10.3390/atmos12091173
ISSN:
2073-4433
Origination:
Footnote:
Description:
The immersion freezing ability of soot particles has in previous studies been reported in the range of low/insignificant to very high. The aims of this study were to: (i) perform detailed physico-chemical characterisation of freshly produced soot particles with very different properties, (ii) investigate the immersion freezing ability of the same particles, and (iii) investigate the potential links between physico-chemical particle properties and ice-activity. A miniCAST soot generator was used to produce eight different soot samples representing a wide range of physico-chemical properties. A continuous flow diffusion chamber was used to study each sample online in immersion mode over the temperature (T) range from −41 to −32 °C, at a supersaturation of about 10% with respect to liquid water. All samples exhibited low to no heterogeneous immersion freezing. The most active sample reached ice-activated fractions (AF) of 10−3 and 10−4 at temperatures of 1.7 and 1.9 K , respectively, above the homogeneous freezing temperature. The samples were characterized online with respect to a wide range of physico-chemical properties including effective particle density, optical properties, particle surface oxidation and soot maturity. We did observe indications of increasing immersion freezing ice-activity with increasing effective particle density and increasing particulate PAH fraction. Hence, those properties, or other properties co-varying with those, could potentially enhance the immersion freezing ice-activity of the studied soot particle types. However, we found no significant correlation between the physico-chemical properties and the observed ice-nucleating ability when the particle ensemble was extended to include previously published results including more ice-active biomass combustion soot particles. We conclude that it does not appear possible in general and in any straightforward way to link observed soot particle physico-chemical properties to the ice-nucleating ability using the online instrumentation included in this study. Furthermore, our observations support that freshly produced soot particles with a wide range of physico-chemical properties have low to insignificant immersion freezing ice-nucleating ability.