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Marmara University (2004)

Sahara toz parçacıklarının buz çekirdekleme özelliklerinin incelenmesi - NUCLEATION PROPERTIES OF SAHARAN DUST PARTICLE

Fersiz, Necdet

Titre : Sahara toz parçacıklarının buz çekirdekleme özelliklerinin incelenmesi - NUCLEATION PROPERTIES OF SAHARAN DUST PARTICLE

Auteur : Fersiz, Necdet

Université de soutenance : Marmara University

Grade : Master Thesis 2004

Résumé
An estimated amount of 60-200 million tons of Saharan dust is released into the atmosphere per year. Observation of red rain events in Europe and in the Middle East indicates very effective scavenging processes are taking place. Most of the research on Saharan dust has been devoted to transport pathways and estimation of the dry/wet deposition fluxes. Fluxes are related to the removal rates. History of the particles may affect their nucleation characteristics as in the case of sulfate coated desert particles. However, laboratory studies on the nucleation and other scavenging processes of the Saharan dust are too limited. Furthermore, in spite of the nutrient characteristic of the minerals contained in Saharan dust most of the research was focused on the determination of the chemical composition and any biological process is not included on the ice nucleating ability. In this work, we investigated ice nucleation properties of the Saharan dust in the laboratory. Dust particles were placed on a temperature controlled substrate in a cold box. Supersaturation was obtained by maintaining temperature difference between the inner walls of the cold box and the substrate. Three sets of supersaturations were obtained this way : 10, 20 and 30% ( ± 1) with respect to ice, being underwater saturation, around water saturation and above water saturation respectively. Particles were monitored via a computer connected microscope-camera. Temperature of the substrate was determined with the first observation of the ice crystals. The number of nucleated particles were also recorded.In all supersaturations studied, at temperatures below -12°C natural Saharan dust particles were effective ice nuclei. In the case of irradiated particles, the critical temperature below water saturation was four degrees lower (Tc=-16°C). Results suggest that, bacterial activity may be playing a role in the enhancement of the ice nucleation ability of the Saharan dust particles.

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Page publiée le 29 avril 2022