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The role of contact angle and pore width on pore condensation and freezing
ETH Zürich, Switzerland; University of Oslo, Norway.
RISE Research Institutes of Sweden, Bioeconomy and Health, Biorefinery and Energy. Zürich University of Applied Sciences, Switzerland; .ORCID iD: 0000-0003-2396-6687
ETH Zürich, Switzerland.
ETH Zürich, Switzerland; University of British Columbia, Canada.
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2020 (English)In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 20, no 15, p. 9419-9440Article in journal (Refereed) Published
Abstract [en]

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<span classCombining double low line"inline-formula">ĝ</span>) 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 <span classCombining double low line"inline-formula"><i>T</i>>235</span> 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. © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.

Place, publisher, year, edition, pages
Copernicus GmbH , 2020. Vol. 20, no 15, p. 9419-9440
Keywords [en]
cirrus, cloud microphysics, condensation, freezing, ice mechanics, nucleation, saturation
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:ri:diva-50120DOI: 10.5194/acp-20-9419-2020Scopus ID: 2-s2.0-85090533941OAI: oai:DiVA.org:ri-50120DiVA, id: diva2:1497173
Note

Funding details: Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, SNF, 200021_156581; Funding details: National Science Foundation, NSF, 200021_156581; Funding text 1: Acknowledgements. We would like to thank Hannes Wydler for all of his technical assistance during this project. We would also like to thank Lukas Huber at EMPA Dübendorf for performing the water sorption measurements. Robert O. David, Zamin A. Kanji, Dominik Brühwiler and Jonas Fahrni acknowledge support for this work from SNF grant no. 200021_156581.; Funding text 2: Financial support. This research has been supported by the Swiss; Funding text 3: National Science Foundation (grant no. 200021_156581).

Available from: 2020-11-04 Created: 2020-11-04 Last updated: 2023-05-22Bibliographically approved

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