HR: 1340h
AN: A53A-0148    [Abstracts]
TI: Heterogeneous Ice Nucleation During Ozonolysis of Organic Thin Films on Aqueous Solution Droplets
AU: * Wicks, G
EM: gwicks@eup.k12.mi.us
AF: Sault Area High School and Career Center, 904 Marquette Ave. , Sault Ste. Marie, MI 49783 United States
AU: Cantrell, W
EM: cantrell@mtu.edu
AF: Michigan Technological University, Dept. of Physics 1400 Townsend Dr., Houghton, MI 49931 United States
AB: The mechanism by which ice is created affects cloud properties and processes. Although homogeneous ice nucleation is reasonably well understood, both experimentally and theoretically, heterogeneous ice nucleation is not. Since deep convection in the tropics lofts organic materials high into the atmosphere, it is important to achieve an understanding of heterogeneous nucleation by these materials and how it affects cirrus cloud formation. Sources of atmospheric organic compounds include combustion, biomass burning, emissions from vegetation, and sea spray which contains organic material from the ocean's surface. Fatty acids such as stearic acid and oleic acid are common organic constituents. The reaction of oleic acid with atmospheric ozone has recently become a model for understanding how atmospheric oxidation processes affect organic particles. Over the past six years, more than twenty publications have described reactive uptake coefficients, primary products, secondary reactions, mechanisms, and other aspects of this oxidation. With this background information in mind, we built an ozonolysis apparatus in tandem with a solution drop freezer to study the freezing point of 10-microliter, 0.25 M sodium chloride solution droplets coated with thin layers of 18-carbon fatty acids or alcohols. We determined the freezing points before and after ozonolysis for solution droplets coated with stearic acid, oleic acid, cis-13-octadecenoic acid, oleyl alcohol, and 1-octadecanol. During the experiments, temperature cycling was controlled by a computer-driven temperature controller. Results showed little change in mean freezing temperature before and after ozonolysis for all of the organic compounds studied except oleyl alcohol. The lack of a significant temperature change for oleic acid may be good news for atmospheric modelers since the well-studied reaction of ozone with oleic acid is known to give a complex mixture of products.
DE: 0320 Cloud physics and chemistry
DE: 3311 Clouds and aerosols
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005