Dresden 2020 – scientific programme

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UP: Fachverband Umweltphysik

UP 9: Aerosols

UP 9.1: Talk

Thursday, March 19, 2020, 14:00–14:20, HSZ 105

Ice nucleation efficiency of K-rich feldspar can be enhanced by K-Na cation exchange — •Tilia Gädeke¹, Corina Wieber¹, Alice Keinert¹, Reiner Abart², Thomas Leisner^1,3, and Alexei Kiselev¹ — ¹Karlsruhe Institute of Technology, KIT — ²University of Wien — ³University of Heidelberg

The efficiency of ice nucleation (IN) varies over orders of magnitude between different mineral aerosols in the atmosphere. Among all types of mineral dust, alkali feldspars have been found to be the most efficient ice nucleating particles. One of the major unanswered questions is how the spatial distribution of Na-rich and K-rich regions of alkali feldspar is related to its IN efficiency and what is the mechanism behind it. In this contribution, we report the results of a droplet freezing experiment conducted on the thin sections of feldspar which is artificially modified with respect to its chemical composition. Gem-quality K-feldspar crystals were chemically shifted towards a more Na-rich composition where K-rich and Na-rich regions split up into lamellae. Between those emerge highly anisotropic contraction of the crystal lattice, inducing a tensile stress which results in microscopic cracks, observable by optical and electron microscopy. We observe that ice nucleation is often associated with the crack appearance. We report a significant enhancement of the overall IN efficiency of the modified feldspar as compared to the initial natural sample. Finally, using the data of electron scanning microscopy, X-Ray microanalysis and the simulated crystalline structure of feldspar and ice, we discuss the possible mechanisms responsible for the observed behavior.