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Ice Freezing on Clay Minerals (IFClaM)

English title Ice Freezing on Clay Minerals (IFClaM)
Applicant Peter Thomas
Number 138039
Funding scheme Project funding (Div. I-III)
Research institution Institut für Atmosphäre und Klima ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Climatology. Atmospherical Chemistry, Aeronomy
Start/End 01.01.2012 - 28.02.2015
Approved amount 167'382.00
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All Disciplines (3)

Discipline
Climatology. Atmospherical Chemistry, Aeronomy
Other disciplines of Earth Sciences
Other disciplines of Environmental Sciences

Keywords (5)

ice nucleation; mineral dust; montmorillonite; kaolinite; illite

Lay Summary (English)

Lead
Lay summary

Cloud ice is an important factor in climate and in the atmospheric self-cleansing capacity because it affects precipitation and thus the lifetime of clouds and trace gases. Ice crystals in the atmosphere may form by homogeneous nucleation of cloud droplets and aqueous aerosol particles or by heterogeneous nucleation on surfaces of so-called ice nuclei (IN). Field measurements show that ice formation in cumulus and stratiform clouds begins at temperatures much warmer than those associated with homogeneous ice nucleation in pure water, and the partial glaciation of these clouds is ascribed to heterogeneous ice nucleation. Various insoluble particles such as mineral dust, soot, metallic particles, volcanic ash, or primary biological particles have been suggested as IN. In terms of the efficacy of individual particles, mineral dusts seem to play a predominant role. Mineral dust aerosols, e.g. from deserts, contain mainly the clay minerals kaolinite, montmorillonite, and illite, which have frequently been used as mineral dust surrogates in ice freezing experiments. All of these studies do report heterogeneous ice nucleation; however, there are large uncertainties in the observed freezing temperatures, prevalent modes of nucleation, and the influence of aging and coatings of mineral dust particles.

The objectives of the proposed project are:

(1) To perform experiments with emulsified and bulk suspensions of clay minerals using differential scanning calorimetry, where freezing is observed via the released latent heat. Experiments with emulsified suspensions reflect the IN activity of average clay mineral particles, while freezing in bulk experiments occurs on the best IN present in the solution.

 (2) To investigate how surface modifications and coatings influence the IN activity of the clay minerals. This part of the project aims at elucidating, which surfaces of the clay minerals are involved in the freezing process and how aging may influence the IN ability of airborne clay minerals.

(3) To observe crystal growth and the preferred location of nucleation of aqueous droplets deposited on hydrophobically coated slides with a high-speed camera attached to an optical microscope. This part of the project aims at resolving whether ice nucleation occurs preferentially surface close or in the volume of the droplet.

We will use the clay minerals kaolinite, montmorillonite, and illite for these investigations as well as natural desert dust samples. The results of this study can be cast into a form that can be used in numerical models of cloud formation and precipitation to parameterize the IN number concentration as a function of temperature and/or ice saturation (from box models to large-scale climate models).

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Name Institute

Publications

Publication
Ice nucleation efficiency of natural dust samples in the immersion mode
Kaufmann Lukas, Marcolli Claudia, Hofer Julian, Pinti Valeria, Hoyle Christopher, Peter Thomas (2016), Ice nucleation efficiency of natural dust samples in the immersion mode, in Atmospheric Chemistry and Physics, 16, 11177-11206.
Refreeze experiments of water droplets containing different types of ice nuclei interpreted by classical nucleation theory
Kaufmann Lukas, Marcolli Claudia, Luo Beiping, Peter Thomas (2016), Refreeze experiments of water droplets containing different types of ice nuclei interpreted by classical nucleation theory, in Atmos. Chem. Phys. Discuss., 1.

Collaboration

Group / person Country
Types of collaboration
ETHZ, IAC, Prof. U. Lohmann Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
U Mainz, Germany, Dr. Lothar Schütz Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
European Geosciences Union (EGU) General Assembly 2014 Poster Characterization of ice nucleation on different natural dust samples (poster). 27.04.2014 Vienna, Austria Kaufmann Lukas; Marcolli Claudia; Peter Thomas;
16th International Conference on Clouds and Precipitation (ICCP 2012) Poster Ice nucleation efficiency of clay minerals in the immersion mode 30.07.2012 Leipzig, Germany Peter Thomas; Marcolli Claudia;


Associated projects

Number Title Start Funding scheme
175716 Immersion and adhesion freezing influenced by charge and solutes 01.04.2018 Project funding (Div. I-III)
120175 Modelling Heterogeneous and Homogeneous Ice Nucleation and Growth at Cirrus Cloud Levels 01.03.2009 Project funding (Div. I-III)
125151 Physical states of mixed organic-inorganic aerosols 01.10.2009 Project funding (Div. I-III)
156251 Ice freezing on mineral dust samples 01.03.2015 Project funding (Div. I-III)

Abstract

Ice Freezing on Clay Minerals: Influence of Surface Modifications and Freezing Mode (IFClaM)Cloud ice is an important factor in climate and in the atmospheric self-cleansing capacity be-cause it affects precipitation and thus the lifetime of clouds and trace gases. Ice crystals in the atmosphere may form by homogeneous nucleation of cloud droplets and aqueous aerosol particles or by heterogeneous nucleation on surfaces of so-called ice nuclei (IN). Field measurements show that ice formation in cumulus and stratiform clouds begins at temperatures much warmer than those associated with homogeneous ice nucleation in pure water, and the partial glaciation of these clouds is ascribed to heterogeneous ice nucleation. Various insoluble particles such as mineral dust, soot, metallic particles, volcanic ash, or primary biological particles have been suggested as IN. In terms of the efficacy of individual particles, mineral dusts seem to play a predominant role. Mineral dust aerosols, e.g. from deserts, contain mainly the clay minerals kaolinite, montmorillonite, and illite, which have frequently been used as mineral dust surrogates in ice freezing experiments. All of these studies do report heterogeneous ice nucleation; however, there are large discrepancies between the observed freezing temperatures. Older studies from the 1960s and 1970s report freezing temperatures between -12? and -35?C for aqueous droplets containing kaolinite, montmorillonite, or illite particles. More recent studies report immersion freezing at the lower end of this broad range, mostly too low to explain the enhanced glaciation of clouds with cloud top temperatures of only -10°C to -20°C in air masses containing mineral dust. Possible explanations for this discrepancy could be that (i) contact instead of immersion freezing was the dominant pathway leading to ice crystals at the highest observed cloud glaciation temperatures; (ii) aging of mineral dusts changed their IN activity, e.g., by adsorption of semivolatile vapors during atmospheric transport; (iii) freezing between -10°C to -20°C was not initiated by average clay particles, but by a small number of very best IN present in a clay mineral sample.To improve our basic understanding of heterogeneous ice nucleation on mineral dusts, we intend to investigate how the location of heterogeneous freezing on clay minerals (surface-proportional or constrained to active sites), chemical modification of clay mineral surfaces, and the location of freezing in the droplet (near-surface versus in the free volume), influence the freezing temperatures. The objectives of the proposed project are:(1) To perform experiments with emulsified and bulk suspensions of clay minerals using differential scanning calorimetry, where freezing is observed via the released latent heat. Experiments with emulsified suspensions reflect the IN activity of average clay mineral particles, while freezing in bulk experiments occurs on the best IN present in the solution. (2) To investigate how surface modifications and coatings influence the IN activity of the clay minerals. Surface modifications will be achieved by protonation/deprotonation of surface hydroxyls, cation exchange or surface adsorption of organic molecules. This part of the project aims at elucidating, which surfaces of the clay minerals are involved in the freezing process and how aging may influence the IN ability of airborne clay minerals.(3) To observe crystal growth and the preferred location of nucleation of aqueous droplets deposited on hydrophobically coated slides with a high-speed camera attached to an optical microscope. This part of the project aims at resolving whether ice nucleation occurs preferen-tially surface close or in the volume of the droplet. Prevalent surface close nucleation in droplets consisting of clay mineral suspensions would hint to an important role of contact nucleation inside-out.We will use the clay minerals kaolinite, montmorillonite, and illite for these investigations as well as natural desert dust samples. An attribution of ice nucleation to certain surface proper-ties is better feasible for the structurally well defined clay minerals, whereas investigations on natural dust samples can better mimic the actual processes (including aging) in the atmos-phere. The results of this study can be cast into a form that can be used in numerical models of cloud formation and precipitation to parameterize the IN number concentration as a function of temperature and/or ice saturation (from box models to large-scale climate models).
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