Laboratory studies will examine heterogeneous ice nucleation and provide fundamental data to improve understanding of ice formation in the atmosphere. First, ice nucleation will be probed on particles relevant for the climate sensitive tropical tropopause layer (TTL) where recent work has identified particles composed mainly of sulfate and organic compounds as the main type responsible for ice nucleation. A range of organic compounds with different water solubility will be studied to probe how they influence ice nucleation. New studies on organic compounds that form glassy solids will provide additional insight into chemistry in the cold TTL. Next, heterogeneous ice nucleation on mineral particles representative of atmospheric dust will be studied. While dust is a well-known atmospheric ice nucleus, there is uncertainty about how coatings that form on the dust as it ages affect its ability to nucleate ice. Raman microscopy will be used to determine how the chemical composition, thickness and morphology of the coatings influence ice nucleation. Finally, experiments using Raman microscopy will characterize the ice nucleating ability of aerosols collected in the field. Ice nucleation on atmospheric samples will be used to select the particles most amenable to ice nucleation for detailed study using Raman spectroscopy and mapping.
Cirrus clouds, composed of water ice, cover up to 30% of the Earth's surface at any time and sub-visible cirrus are almost always present in the TTL. These clouds play an important role in the climate system as well as in controlling the amount of water entering the stratosphere. While the net effect of cirrus clouds on climate is usually a warming at the surface, the microphysical properties of the clouds dictate their overall climatic impact. The microphysical properties depend, in turn, on the nucleation mechanism of ice in the atmosphere. In addition to performing fundamental research on ice nucleation, this project will give students, particularly women, the opportunity to gain skills in research and teaching that will further their scientific careers in atmospheric chemistry and physics. The project will provide an opportunity to integrate research and teaching at the University of Colorado by bringing undergraduates and graduate students into the laboratory to work side-by-side with more senior researchers. The experience they gain will help widen their perspective and give them valuable research experience that will be useful to them in a variety of future careers.
