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Ice freezing on mineral dust samples

English title Ice freezing on mineral dust samples
Applicant Peter Thomas
Number 156251
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 01.03.2015 - 31.08.2018
Approved amount 206'287.00
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All Disciplines (3)

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

Keywords (4)

Surface Modification; Feldspars; Heterogeneous Ice Nucleation; Mineral Dust Aerosols

Lay Summary (German)

Lead
Wolken in der Atmosphäre bilden sich in Gegenwart von Aerosolpartikeln, an denen flüssige Tröpfchen kondensieren, wenn die relative Feuchte 100 % übersteigt, oder sich Eiskristalle bilden, wenn die Temperatur tief genug ist. Man versteht relativ gut, wie Aerosolpartikel beschaffen sein müssen, damit sich aus ihnen Wassertröpfchen bilden, viel unklarer ist jedoch, welche Aerosolpartikel für die Vereisung von flüssigen Wolken verantwortlich sind.
Lay summary

Viele Wolken bestehen immer noch aus flüssigen Wassertröpfchen, auch wenn die Temperatur tief unter 0°C gesunken ist. Wasservolumen von der Menge eines Woklentröpfchens können bis fast -40°C unterkühlt werden, ohne dass sie gefrieren. Wenn sie jedoch ein festes Aerosolpartikel enthalten, können Wolkentröpfchen gefrieren, sobald die Temperatur unter 0°C gesunken ist. Wenn die Eisnukleation an einem festen Einschluss wie einem Aerosolpartikel stattfindet, spricht man von heterogener Eisnukleation. Nur sehr wenige Aerosolpartikel haben die Eigenschaft, dass sie zum Gefrieren von Wassertröpfchen führen. Dazu gehören Mineralstäube, Russ, metallische Partikel, Vulkanasche und biologische Partikel wie zum Beispiel Pollen. Mineralpartikel haben ihren Ursprung meist in Wüsten wie der Sahara. Sie gelangen bei Sandstürmen in die Atmosphäre und können je nach Grösse weit transportiert werden. Wenn sie in eine Wolke gelangen, können sich an ihrer Oberfläche Eiskristalle bilden. Mineralstäube sind Gemische von verschiedenen Mineralien wie Quarz, Feldspate, Tonmineralien und Kalzit. Die genaue mineralogische Zusammensetzung der Mineralstäube und welche Bestandteile der Stäube für die Eisnukleation verantwortlich sind, ist jedoch immer noch unklar. Wir haben über die vergangenen Jahre Proben aus verschiedenen Wüstenregionen gesammelt (Sahara, Bolivien, Namibia, Botswana, Katar). Diese Proben wollen wir nun hinsichtlich ihres Gefrierverhaltens über einen weiten Temperaturbereich (-40°C bis 0°C) charakterisieren. Wir wollen zu  verstehen versuchen, welche mineralogischen Bestandteile bei welcher Temperatur zum Gefrieren führen und ob die Gefriereigenschaften verändert werden, wenn man die Oberfläche der Mineralstäube verändert.

Direct link to Lay Summary Last update: 16.02.2015

Responsible applicant and co-applicants

Employees

Publications

Publication
Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 2: Quartz and amorphous silica
Kumar Anand, Marcolli Claudia, Peter Thomas (2019), Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 2: Quartz and amorphous silica, in Atmospheric Chemistry and Physics, 19(9), 6035-6058.
Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 3: Aluminosilicates
Kumar Anand, Marcolli Claudia, Peter Thomas (2019), Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 3: Aluminosilicates, in Atmospheric Chemistry and Physics, 19(9), 6059-6084.
Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline
Kumar Anand, Marcolli Claudia, Luo Beiping, Peter Thomas (2018), Ice nucleation activity of silicates and aluminosilicates in pure water and aqueous solutions – Part 1: The K-feldspar microcline, in Atmospheric Chemistry and Physics, 18(10), 7057-7079.

Collaboration

Group / person Country
Types of collaboration
PSI, Prof. U. Baltensperger Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
Weizmann Institute, Prof. Y. Rudich Israel (Asia)
- in-depth/constructive exchanges on approaches, methods or results
KIT Karlruhe Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
ETHZ, IAC, Prof. U. Lohmann Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
- Exchange of personnel

Awards

Title Year
ETH Medal, Nomination of Dr. Anand Kumar 2018

Associated projects

Number Title Start Funding scheme
138039 Ice Freezing on Clay Minerals (IFClaM) 01.01.2012 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)
146760 Physical states of mixed organic-inorganic aerosols 01.09.2013 Project funding (Div. I-III)
125151 Physical states of mixed organic-inorganic aerosols 01.10.2009 Project funding (Div. I-III)

Abstract

Ice freezing on mineral dust samplesFreezing of liquid droplets and subsequent ice crystal growth affects optical properties of clouds and precipitation. Field measurements show that ice formation in cumulus and strati-form 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 hetero-geneous ice nucleation occurring on the foreign surfaces of ice nuclei (IN). IN are very rare and may represent < 1 in 10^6 of the aerosol population. Various insoluble particles such as mineral dust, soot, metallic particles, volcanic ash, or primary biological particles have been suggested as IN. Among these the suitability of mineral dusts is best established. Natural mineral dusts are mixtures of different minerals, with quartz, feldspars, clay minerals, and calcite being main mineral components. For a long time, clay minerals were considered as the components that determine the ice nucleation ability of mineral dusts. More recently, it was suggested that instead feldspar particles may account for a large proportion of the ice nuclei in Earth’s atmosphere that contribute to freezing at temperatures below about -15ºC.During the last years we succeeded in collecting and characterizing natural dust samples from important source regions of airborne mineral dusts namely from the central Sahara (Hoggar Mountains), Bolivia (Altiplano), Namibia (Etosha Pan), Botswana (Makgadikgadi Pans), and Qatar. We will further extend this collection. We intend to perform ice nucleation experiments on individual water droplets containing suspensions of these natural mineral dusts and reference samples with a differential scanning calorimeter (DSC) and an optical microscope equipped with a cooling cell to treat the following objectives: 1.Characterization of the ice nucleation activity of natural dust samples in the tempera-ture range from 236 - 273 K in terms of number of nucleation sites per unit surface area which are active at a given temperature (IN spectra).2.Relate the ice nucleation activity of natural mineral dusts to their mineralogical com-position to constrain the degree to which the ice nucleation activity of natural mineral dusts is determined by their mineralogical composition.3.Investigate how heating, surface modifications and coatings influence the IN activity of the components present in natural dust samples.4.Investigation of the freezing characteristics of individual sites on natural dust sam-ples to find out the relative importance of exposure time vs. temperature for ice nu-cleation on average and best sites. The results of this study will improve the basic understanding of the factors that determine the ice nucleation ability of natural mineral dusts and can be cast into a simple parameteriza-tion of the ice nuclei number concentration as a function of temperature and/or ice saturation that can be used in numerical models of cloud formation and precipitation (from box models to large-scale climate models).
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