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Publication type: Article in scientific journal
Type of review: Open peer review
Title: The role of contact angle and pore width on pore condensation and freezing
Authors: David, Robert O.
Fahrni, Jonas
Marcolli, Claudia
Mahrt, Fabian
Brühwiler, Dominik
Kanji, Zamin A.
et. al: No
DOI: 10.5194/acp-20-9419-2020
Published in: Atmospheric Chemistry and Physics
Volume(Issue): 20
Issue: 15
Page(s): 9419
Pages to: 9440
Issue Date: 12-Aug-2020
Publisher / Ed. Institution: Copernicus
ISSN: 1680-7316
Language: English
Subject (DDC): 551: Geology and hydrology
Abstract: It has recently been shown that pore condensation and freezing (PCF) is a mechanism responsible for ice formation under cirrus cloud conditions. PCF is defined as the condensation of liquid water in narrow capillaries below water saturation due to the inverse Kelvin effect, followed by either heterogeneous or homogeneous nucleation depending on the temperature regime and presence of an ice-nucleating active site. By using sol–gel synthesized silica with well-defined pore diameters, morphology and distinct chemical surface-functionalization, the role of the water–silica contact angle and pore width on PCF is investigated. We find that for the pore diameters (2.2–9.2 nm) and water contact angles (15–78°) covered in this study, our results reveal that the water contact angle plays an important role in predicting the humidity required for pore filling, while the pore diameter determines the ability of pore water to freeze. For T>235 K and below water saturation, pore diameters and water contact angles were not able to predict the freezing ability of the particles, suggesting an absence of active sites; thus ice nucleation did not proceed via a PCF mechanism. Rather, the ice-nucleating ability of the particles depended solely on chemical functionalization. Therefore, parameterizations for the ice-nucleating abilities of particles in cirrus conditions should differ from parameterizations at mixed-phase clouds conditions. Our results support PCF as the atmospherically relevant ice nucleation mechanism below water saturation when porous surfaces are encountered in the troposphere.
Fulltext version: Published version
License (according to publishing contract): CC BY 4.0: Attribution 4.0 International
Departement: Life Sciences and Facility Management
Organisational Unit: Institute of Chemistry and Biotechnology (ICBT)
Published as part of the ZHAW project: Untersuchung der Eisbildungsmechanismen in der Atmosphäre
Appears in collections:Publikationen Life Sciences und Facility Management

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