AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Measurements of Ice Nucleation in the Contact Mode by Mineral Dusts
Kristopher Bunker, Swarup China, Claudio Mazzoleni, Alexander Kostinski, WILL CANTRELL, Michigan Technological University
Abstract Number: 337 Working Group: Aerosols, Clouds, and Climate
Abstract What initiates ice formation in the atmosphere for temperatures greater than ~ -20 C? Mineral dusts are known to be the most prevalent ice nuclei, but recent laboratory studies have shown that they are not effective in the immersion/condensation mode for temperatures above approximately -25 C (see e.g. Niedermeier et al., 2010). Ice nucleation in the contact mode, where the aerosol particle initiates freezing at the air-water interface, has been suggested as a possible candidate for nucleation at high temperatures, as previous work has suggested that the contact mode is active at temperatures as much as five degrees higher than the immersion/condensation mode.
We will discuss measurements of ice nucleation in the contact mode by mineral dusts of selected electrical mobility diameters, which cast doubt upon contact nucleation as a pathway to primary ice production in the atmosphere at high temperatures. Specifically, our measurements show that less than one in a hundred Arizona Test Dust particles with a diameter of 1 micron catalyzes freezing of water in the contact mode at -18 C. By comparison, less than one in a thousand kaolinite particles of the same size catalyzes freezing at that temperature. Arizona Test Dust was active in the contact mode at -15 C, though the fraction of particles active at that temperature was almost a factor of 10 smaller than those active at -18 C. Kaolinite was not active at -15 C.
Our measurements also suggest that the smallest Arizona Test Dust particles we investigated (electrical mobility diameter of 62.5 nm) are more effective as contact nuclei. Differences in the morphology of the dust as a function of size may be responsible for the difference.