Ice nucleation by different types of soil dusts under mixed-phase cloud conditions: Laboratory studies and atmospheric implications

Wednesday, 17 December 2014
Yutaka Tobo1,2, Paul J DeMott2, Thomas Christopher James Hill2,3, Anthony J Prenni2,4, Norbert G Swoboda-Colberg3, Gary D Franc3 and Sonia M Kreidenweis2, (1)NIPR National Institute of Polar Research, Tokyo, Japan, (2)Colorado State University, Fort Collins, CO, United States, (3)University of Wyoming, Laramie, WY, United States, (4)National Park Service Lakewood, Lakewood, CO, United States
It has been suggested that ice nucleation by desert soil dusts composed largely of minerals plays an important role in forming ice crystals in mixed-phase clouds and subsequent precipitation. More recently, several studies have suggested that soil dusts having higher contents of soil organic matter (SOM) may also contribute significantly to atmospheric ice nucleation. In this study, we examine the ice nucleation properties of soil dusts derived from different locations in the world. Our results show that the ice nucleating ability of agricultural soil dusts derived from the largest dust source regions in North America is almost comparable to that of desert soil dusts at temperatures colder than about −15°C. We also confirm that the agricultural soil dusts can serve as effective ice nuclei (IN) at much warmer temperatures. On the other hand, our results indicate that the ice nucleating ability of the agricultural soil dusts is significantly reduced after H2O2 digestion, while the reduction is not significant for the desert soil dusts. In this regard, based on single particle analysis, we demonstrate that such a significant reduction observed in the agricultural soil dusts is mainly attributable to the removal of organic-rich particles (namely, SOM particles), which have much higher ice nucleating ability than mineral particles. Moreover, we discuss the potential contributions of these soil dusts to atmospheric IN populations.