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Immersion and adhesion freezing influenced by charge and solutes

English title Immersion and adhesion freezing influenced by charge and solutes
Applicant Marcolli Claudia
Number 175716
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 01.04.2018 - 31.03.2022
Approved amount 288'964.00
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All Disciplines (3)

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

Keywords (5)

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

Lay Summary (German)

Lead
Wolken bestehen oft vollständig oder teilweise aus flüssigen Tröpfchen anstatt Eiskristallen, auch bei Temperaturen unter 0ºC. Flüssige Wolken können in etwa bis zu -38ºC auftreten. So starke Unterkühlungen sind bei grossen Wasservolumen nicht möglich, erklären sich jedoch dadurch, dass es eines Eiskeimes Bedarf, damit Wasser in diesem Temperaturbereich gefriert, und die Anzahl Aerosolpartikel, welche als Eiskeim wirken, gering ist. Gemäss Schätzungen wirkt weniger als ein Millionstel der Aerosolpartikel als Keim für die Eisbildung. Die Anzahl der Aerosolpartikel, welche als Eiskeime wirken, ist oft zu gering um die Anzahl der Eiskristalle in Wolken zu erklären. Ein möglicher Grund für diese Diskrepanz könnte darin liegen, dass zusätzliche Faktoren die Qualität eines Eiskeims beeinflussen. Solche Faktoren könnte die elektrische Ladung von Partikeln sein, oder Substanzen, die während des Transportes in der Atmosphäre auf die Partikel kondensieren und zu einer Beschichtung führen.
Lay summary

Inhalt und Ziel des Forschungsprojektes

Unser Ziel ist, den Einfluss von Ladungen und adsorbierten Substanzen auf die Eisnukleation von ausgewählten Eiskeimen zu untersuchen. Wir untersuchen den Effekt von Ladungen in einer Gefrierkammer deren Temperatur eingestellt werden kann. Durch diese Kammer werden positiv oder negative geladene Wassertropfen und positiv oder negative geladene Aerosolpartikel geleitet. Wir werden untersuchen, welchen Einfluss die Ladungen auf die Wahrscheinlichkeit einer Kollision und das Gefrieren der Wassertropfen hat. Wir werden solche Experimente mit Partikeln mit und ohne Beschichtungen durchführen.

Wissenschaftlicher und gesellschaftlicher Kontext des  Forschungsprojekts

Unsere Arbeit wird neue und wichtige Informationen zur Eisnukleation in der Atmosphäre generieren. Solche Daten sind wichtig zur Voraussage der Wolkendecke und von Niederschlag. Die Erkenntnisse können in globale Modelle zur Voraussage des Klimawandels implementiert werden, und so die Prognosen verbessern.

Direct link to Lay Summary Last update: 14.02.2018

Responsible applicant and co-applicants

Employees

Name Institute

Project partner

Associated projects

Number Title Start Funding scheme
138039 Ice Freezing on Clay Minerals (IFClaM) 01.01.2012 Project funding (Div. I-III)

Abstract

Glaciation of mixed-phase clouds occurs in the presence of ice-nucleating particles (INPs). INPs may represent less than 1 in a million particles of an atmospheric aerosol. Different types of particles are considered important as atmospheric INPs. Among these, mineral dust particles are probably best established, but most of them at temperatures below 255 K, which does not explain the occurrence of ice clouds and mixed-phase clouds at higher temperatures. The surface structure and therefore the ice nucleation ability of mineral dust can change due to interactions with organic or inorganic substances or the presence of electric charge. The effect of a coating depends on many different factors such as the mode of freezing, freezing temperature, and thickness and chemical composition of the coating. Charges and electric fields have been observed to induce ice nucleation when the droplets were in contact with a substrate. In most of these studies, the charge was generated by an externally applied electric field. Charge is a poorly constrained parameter in most studies on ice nucleation, although it may influence the ice nucleation ability of an INP. Moreover, droplets and particles in the atmosphere bear charges, which may increase their collision rate, in particular in electrified clouds.The proposed project requires two Ph.D. students, who will perform experiments under my supervision using instrumentation available in the Atmospheric Chemistry and Atmospheric Physics research groups of the ETH Zurich. Collaborations will require the students to make contacts with other researchers at the institute, at ETH and other institutions worldwide. Ph.D. student I will investigate the effect of electric charges on freezing for different INPs. CLINCH (CoLlision Ice Nucleation Chamber) experiments will be performed where charged particles come into contact with charged droplets. The collision efficiencies and the freezing efficiencies will be determined for different types of particles and particle sizes as a function of the charge on the droplet and particles. Freezing efficiencies for residence times of 2 s and 4 s in the chamber will be compared to assess whether freezing is immediate upon collision or delayed. Ph.D. student II will investigate effects of surface modifications due to solutes on the ice nucleation efficiencies of mineral dust. Suspensions of feldspars, clay minerals and quartz containing a solute will be exposed to repeated freezing cycles using a DSC (Differential Scanning Calorimeter) and a microscope. Such refreeze experiments allow to characterize the freezing characteristics of active sites. Among the investigated solutes will be ammonia, ammonium salts, amino acids, and proteins. The investigated mineral dust components will include feldspars with special focus on microcline, clay minerals and quartz.As a joint objective, the two Ph.D. students will assess the relative efficiencies of different INPs depending on the freezing modes. Selected particle types will be investigated with the instruments CLINCH, ZINC (Zurich Ice Nucleation Chamber), and IMCA-ZINC (Immersion Mode Cooling chAmber), and as droplets immersed in oil with the DSC or the microscope. Results from these various techniques will allow to assess the relative efficiencies of immersion, adhesion, collisional contact and condensation freezing of INPs. This study will be unique in combining results from different instrument types to shed light on how the ice nucleation efficiencies of INPs in different freezing modes are influenced by solutes and/or electric charge. The results will improve our understanding on how INPs induce ice nucleation and will be relevant for the parameterization of cloud glaciation in process-oriented, regional and global models.
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