10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Surface Chemistry of Ice Nucleating Mineral Dust Particles
ALEXEI KISELEV, Alice Keinert, Alexei Nefedov, Weijia Wang, Christof Woell, Thomas Leisner, Karlsruhe Institute of Technology
Abstract Number: 1191 Working Group: Unraveling the Many Facets of Ice Nucleating Particles and Their Interactions with Clouds
Abstract Heterogeneous ice nucleation on the surface of mineral dust particles is an important process responsible for the ice formation in atmospheric clouds. Recently, the surface topography and crystalline structure have been recognized as the two major factors defining the ice nucleation efficiency of K-feldspar, a very common aluminosilicate mineral abundant in the atmosphere as a universal component of airborne mineral dust particles. However, the chemistry of the mineral surface in contact with supercooled water or ice remains poorly characterized due to the lack of experimental methods sensitive to the water-mineral interface. Several questions have to be answered to complement the picture of heterogeneous nucleation, such as the importance of surface charge, the role of framework cations, protonation state of the mineral surface, and the role of ionic species dissolved in water.
In this contribution, we address some of these questions by conducting water freezing experiments on the well-defined surfaces (thin sections) of alkali feldspars with various crystallographic orientations. We show how their freezing efficiency can be predictably modified by treating the surface by argon plasma of different density. We further investigate the chemical composition of the samples in the environmental scanning electron microscope (ESEM) by means of X-ray energy and wavelength dispersive spectroscopy (EDS and WDS), as well as with ultra-high vacuum IR adsorption spectroscopy and X-ray photoelectron spectroscopy (XPS). The measurements conducted with these surface sensitive analytical methods allow us to make certain conclusions about the role of surface chemistry and the particular importance of hydroxyl groups in the nucleation of ice on mineral surfaces. Moreover, these findings offer a possibility of bridging the gap between the atomistic simulations and laboratory experiments, with the ultimate goal of creating a molecular dynamic model of heterogeneous ice nucleation on realistic substrates.