Laboratory Studies of Ice Nucleation Using Optical and Raman Microscopy

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New laboratory techniques will be developed and used to probe ice nucleation and improve our understanding of ice formation in the upper troposphere. Optical microscopy to detect ice nucleation from individual particles, Raman microscopy to determine the chemical composition, and a cryogenic hygrometer will be combined in a single apparatus to gain insight into how the chemical and physical properties of the particles affect their ability to nucleate ice. First, ice nucleation on ammonium sulfate will be reexamined. Past work has indicated a wide spread in the supersaturation needed for homogeneous nucleation from aqueous ammonium sulfate. The combination of optical and Raman microscopy will be used to determine if this is due to the presence of different phases of ammonium sulfate. Second, a comprehensive study of ice nucleation on organics mixed with inorganics will be carried out. Field observations have shown large water supersaturations in the upper troposphere, and have suggested that organics may be underrepresented in particles that nucleate ice. Experiments will be performed to separate the size dependence of nucleation from the composition dependence. Finally, ice nucleation on mineral and dust aerosols will be examined. The Raman probe will provide insight into the role of chemically complex particles in atmospheric ice nucleation. The results will be useful in understanding cirrus cloud formation and its climatic impact. 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.