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Characterisation of ice particle residuals and aerosol particles in laboratory and field experiments by scanning electron microscopy during INUIT (Ice Nuclei research UnIT)

Eriksen Hammer, Stine (2019):
Characterisation of ice particle residuals and aerosol particles in laboratory and field experiments by scanning electron microscopy during INUIT (Ice Nuclei research UnIT).
Darmstadt, Technische Universität, [Online-Edition: https://tuprints.ulb.tu-darmstadt.de/8611],
[Ph.D. Thesis]

Abstract

Ice nucleating particles are necessary for formation of ice crystals in mixed-phase clouds, but there are still uncertainties regarding physico-chemical properties, variability and concentration of these particles in the environment. The ice nuclei research unit (INUIT), funded by the German research foundation (DFG), has thoroughly investigated ice nucleation in laboratory, model and field studies. This thesis contains research from a field study (Jungfraujoch, Switzerland) and a laboratory experiment (of coal fly ash) as well as a methodological part to study the performance of single particle techniques applied. Scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDX) was used as main technique in this thesis. The capability of SEM-EDX in ice nucleation research is demonstrated in the following chapters and in the corresponding papers to this thesis. Single particle analysis by SEM-EDX can be performed operator controlled (opSEM) or computer controlled (ccSEM). In this thesis, it is shown that the technique of choice is dependent on the research question and the particle composition. A comparison of the techniques for different types of aerosol samples provided valuable information about the differences and was further used as a guide to the technique of choice in the remaining studies. Ice particle residuals were studied in mixed-phase clouds at Jungfraujoch in February 2017. The results show that different silicate groups were the most important ice nucleating particles, consistent with previous literature. However, in our study, soot and complex secondary particles were not found in the ice particle residual fraction which is inconsistent with previous results. Furthermore, an upgraded sampling procedure gave the opportunity to determine enrichment and depletion of particle groups in the ice particle residual fraction relative to total aerosol, as well as to identify sampling artefacts. The ice nucleation properties of coal fly ash particles were investigated in a laboratory study. In this study, SEM-EDX was applied to characterise the fly ash particles before and after suspension in water. Anhydrite and CaO, in one of the fly ash samples, reacted to gypsum, calcium hydroxide and calcite needles after suspension. This change led to an overestimation of the ice nucleation active surface site density, which was later corrected for because of the morphological information from SEM. Last, a newly developed method for phase determination by single particle mass spectrometry (SP-MS) was tested and compared to SEM-EDX. Both techniques show the same differences in chemical composition of mineral dust from North-Africa. SP-MS could characterise the phase composition of the particles. Still, SP-MS was limited by matrix effects which was seen from a higher abundance of Ca- and Mg-rich silicates obtained by SEM-EDX. A better understanding of these matrix effects is needed to improve the application of the former method to ice particle research.

Item Type: Ph.D. Thesis
Erschienen: 2019
Creators: Eriksen Hammer, Stine
Title: Characterisation of ice particle residuals and aerosol particles in laboratory and field experiments by scanning electron microscopy during INUIT (Ice Nuclei research UnIT)
Language: English
Abstract:

Ice nucleating particles are necessary for formation of ice crystals in mixed-phase clouds, but there are still uncertainties regarding physico-chemical properties, variability and concentration of these particles in the environment. The ice nuclei research unit (INUIT), funded by the German research foundation (DFG), has thoroughly investigated ice nucleation in laboratory, model and field studies. This thesis contains research from a field study (Jungfraujoch, Switzerland) and a laboratory experiment (of coal fly ash) as well as a methodological part to study the performance of single particle techniques applied. Scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDX) was used as main technique in this thesis. The capability of SEM-EDX in ice nucleation research is demonstrated in the following chapters and in the corresponding papers to this thesis. Single particle analysis by SEM-EDX can be performed operator controlled (opSEM) or computer controlled (ccSEM). In this thesis, it is shown that the technique of choice is dependent on the research question and the particle composition. A comparison of the techniques for different types of aerosol samples provided valuable information about the differences and was further used as a guide to the technique of choice in the remaining studies. Ice particle residuals were studied in mixed-phase clouds at Jungfraujoch in February 2017. The results show that different silicate groups were the most important ice nucleating particles, consistent with previous literature. However, in our study, soot and complex secondary particles were not found in the ice particle residual fraction which is inconsistent with previous results. Furthermore, an upgraded sampling procedure gave the opportunity to determine enrichment and depletion of particle groups in the ice particle residual fraction relative to total aerosol, as well as to identify sampling artefacts. The ice nucleation properties of coal fly ash particles were investigated in a laboratory study. In this study, SEM-EDX was applied to characterise the fly ash particles before and after suspension in water. Anhydrite and CaO, in one of the fly ash samples, reacted to gypsum, calcium hydroxide and calcite needles after suspension. This change led to an overestimation of the ice nucleation active surface site density, which was later corrected for because of the morphological information from SEM. Last, a newly developed method for phase determination by single particle mass spectrometry (SP-MS) was tested and compared to SEM-EDX. Both techniques show the same differences in chemical composition of mineral dust from North-Africa. SP-MS could characterise the phase composition of the particles. Still, SP-MS was limited by matrix effects which was seen from a higher abundance of Ca- and Mg-rich silicates obtained by SEM-EDX. A better understanding of these matrix effects is needed to improve the application of the former method to ice particle research.

Place of Publication: Darmstadt
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Earth Science
11 Department of Materials and Earth Sciences > Earth Science > Environmental Mineralogy
Date Deposited: 28 Apr 2019 19:55
Official URL: https://tuprints.ulb.tu-darmstadt.de/8611
URN: urn:nbn:de:tuda-tuprints-86113
Referees: Weinbruch, Prof. Dr. Stephan and Kandler, Prof. Dr. Konrad
Refereed / Verteidigung / mdl. Prüfung: 29 March 2019
Alternative Abstract:
Alternative abstract Language
Für die Bildung von Eiskristallen in Mischphasenwolken ist die Anwesenheit von Partikeln notwendig. Es bestehen jedoch immer noch Unsicherheiten hinsichtlich der physikalisch-chemischen Eigenschaften, der Variabilität und der Konzentration dieser Partikel. Im Rahmen der DFG-Forschergruppe INUIT (Ice Nuclei reseach UnIT) wurde die Eiskeimbildung in Labor-, Modell- und Feldstudien detailliert untersucht. Die vorliegende Arbeit enthält Ergebnisse einer Feldstudie (Jungfraujoch, Schweiz), einem Laborexperiment (Flugaschen aus der Kohleverbrennung) sowie einen methodischen Teil zur Untersuchung der Leistungsfähigkeit der verwendeten Messtechniken. Als Hauptmethode wurde in dieser Arbeit Rasterelektronenmikroskopie (SEM) gekoppelt mit energie-dispersiver Röntgenmikroanalyse (EDX) verwendet. Das Potential von SEM-EDX in der Eisnukleationsforschung wird in den folgenden Kapiteln und in den entsprechenden Veröffentlichungen zu dieser Dissertation demonstriert. Die Einzelpartikelanalyse mit SEM-EDX kann bediener- (opSEM) oder computergesteuert (ccSEM) durchgeführt werden. In dieser Arbeit wird gezeigt, dass je nach Fragestellung und Partikelzusammensetzung beide Ansätze Vor- und Nachteile haben. Dementsprechend wurde in den nachfolgenden Studien die jeweilig beste Technik eingesetzt. In dem Feldexperiment auf dem Jungfraujoch (Februar 2017) wurden Eispartikelresiduen in Mischphasenwolken untersucht. Verschiedene Gruppen von Silikaten waren (in Übereinstimmung mit früheren Arbeiten) die wichtigsten Eiskeime. In unserer Studie wurden jedoch keine Ruß- und komplexen Sekundärpartikel bei den Eispartikelresiduen gefunden, was im Gegensatz zu früheren Veröffentlichungen steht. Ein verbessertes Probenahmeverfahren eröffnete die Möglichkeit, die An- bzw. Abreicherung von Partikelgruppen in der Eisresiduenfraktion relativ zum Gesamtaerosol zu bestimmen. Außerdem erlaubte dieses Probenahmeverfahren eine bessere Identifikation von Artefakten. Die Eiskeimfähigkeit von Flugaschepartikeln aus der Kohleverbrennung wurde in einer Laborstudie untersucht. Hierbei wurde SEM-EDX eingesetzt, um die Flugascheteilchen vor und nach der Suspension in Wasser zu charakterisieren. In einem Flugaschetyp reagierten Anhydrit und CaO zu nadelförmigem Gips, Calciumhydroxid und Calcit. Die Änderung der Morphologie während dieser Reaktion führte zunächst zu einer Überschätzung der Oberflächedichte aktiver Stellen für die Eisnukleation, die jedoch durch die SEM-Untersuchungen korrigiert wurde. Abschließend wurde eine neue Methode zur Phasenbestimmung mit Einzelpartikel-Massenspektrometrie (SP-MS) durch den Vergleich mit SEM-EDX überprüft. Beide Techniken zeigten die selben Unterschiede in der chemischen Zusammensetzung von nordafrikanischen Mineralstaubproben. SP-MS ermöglichte zusätzlich die Bestimmung der Phasenzusammensetzung. SEM-EDX konnte jedoch nachweisen, dass Ca und Mg-reiche Silikate in der SP-MS aufgrund von Matrixeffekten unvollständig detektiert wurden. Ein Verständnis der Matrixeffekte ist jedoch erforderlich, um die Anwendung dieser Methode in der Eispartikelforschung zu verbessern.German
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