Infrared Interrogation of Atmospheric Aerosols

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9303058 Ewing Aerosols in a variety of sizes, shapes and compositions are found throughout the earth's atmosphere. Some are easily observed as clouds, haze, smog or smoke and they affect weather, climatology and the radiation energy balance. Some are nucleation sites or cloud formation. Others are sources of rich chemistry and photochemistry. With the obvious importance of aerosols, many techniques have been directed toward their study. This research advances the view that an understanding of important atmospheric aerosols will be enhanced by exploring the physical and chemical properties of their surfaces. A versatile analytical technique for this exploration is infrared spectroscopy. While many types of aerosols are amenable to infrared spectroscopic interrogation, salt particles are chosen as examples of the analytical techniques. These particles are of particular relevance. Sea salt aerosols generated over the oceans contribute one of the, if not the, most abundant particulate loads on the global atmosphere. Their composition is transformed by an intricate chemistry. Two methods for producing suspended salt particles in a temperature controlled chamber will be investigated. Since the optical path will be in excess of 100 m, infrared sensitivity allows interrogation of the size, shape and composition of the aerosols as well as molecules stuck to their surfaces. For solid salt aerosols the incorporation of OH- and other ions at the surface as well as water overlayers will be explored. Reactions of NO2 at the surface will also be monitored. Water, OH-, NO2 and other oxides have been targeted for laboratory studies of salt because similar surface chemistry is likely to occur in the atmosphere. Experiments to explore the properties of supported salt particles will also be performed and methods for interrogating surface defect concentrations will be explored. It is suggested that atmospheric chemistry is initiated at these surface defects . For ice particles spectroscopic interrogation will likely be able to characterize their interior structure (e.g. amorphous, ice I, or microporous) as well as their surface properties. It is the surface properties that dictate the type of heterogeneous chemistry that occurs in aerosols, whether in the laboratory or in the atmosphere. Preliminary experiments with both suspended and supported aerosols have already been successful in the laboratory of the Principal Investigator. These successes suggest the practically of the experiments. The infrared spectroscopic interrogation of these laboratory produced aerosols will reveal the feasibility for future experiments on aerosols in the atmosphere.