Hygroscopic Properties of Microstructured Aerosols

During their life time ambient aerosols from various sources coagulate with other aerosols or cloud droplets, in addition to undergoing alteration through heterogeneous processes, such as condensation and reactions. These processes lead to the formation of aerosols with complex microstructures that include solid particles dispersed in liquid droplets, or layered particles. Aerosol microstructures playa significant role on climate by altering atmospheric physical and chemical processes, as well as the balance between the incoming and outgoing solar radiation. Currently, no technique is available for time and space-resolved physical and chemical characterization of micro structured aerosols. The objectives of the proposed study are to develop single particle optical tomography (SPOT) techniques based on optothermal spectroscopy and elastic and inelastic scattering for in-situ physical and chemical characterization of a particle whose physical property varies with position, and use these and other techniques to study physical and chemical processes in microstructured aerosols. Experiments will be conducted on single particles that will be suspended in electrodynamic balances under controlled environments. This project will be conducted in collaboration with Prof. Reinhard Niessner of Technische Universitaet Muenchen. As a part of the proposal, we propose to develop an opthermal absorption spectroscopy technique for radial profiling of aerosols. In addition, we will also focus on tomographic techniques based on elastic and inelastic light scattering. We will validate the techniques with data on well-defined tailored microstructured aerosols that will be generated using various techniques. We will apply the techniques to study reactions between acid droplets and NH3 gas, and hygroscopic properties of micro structured aerosols that contain insoluble nanoparticles coated with hydrophilic and hydrophobic compounds. Nucleation of solid sulfate in neutralization reactions can result in the formation of either polycrystalline solids with many open and liquid-filled cavities, or a solid polycrystalline shell with an embedded liquid core. Using light scattering techniques we will monitor how fast such a reaction proceeds with the evolving microstructure. The intellectual merits of the proposed project lie in the development of new tools for studying microstructured aerosols that play significant roles in atmospheric processes and climate. A successful outcome ofthe proposed research will provide critically needed understanding ofthe processes associated with microstructured aerosols, as well as on optical properties of such aerosols. The proposed research provides training of Ph.D. students in non-traditional chemical engineering aspects, as well as provides them with an international research experience. The research knowledge from the project will impact both undergraduate and graduate education. In addition, high school students will be exposed to the proposed research.