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. Theircomposition 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 surfacewill 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 alsobe 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.In this project, tropospheric aerosols will be studied using infrared spectroscopy. Sea salt aerosol particles will be generated and studied in the laboratory under conditions that mimic those in the troposphere both in high and mid-latitudes. Chemical transformation of these aerosols by nitrogen oxides and acids of nitrogen oxides will be followed by infrared spectroscopy. The object is to unravel the temperature and humidity dependent mechanisms by which aerosols containing sodium chloride are transformed into sodium nitrate with the release of chemically active chlorine. Adsorbed layers of water influence the chemistry on salt particle surfaces even under arid conditions. The properties of the salt-water interface will be studied. Aerosol salt solution droplets, common to the marine boundary layer, will also be investigated. Spectroscopic experiments to study the uptake of sulfur dioxide in aerosols of water and ice particles are planned.In this project sponsored by the Experimental Physical Chemistry Program, Professor George Ewing of Indiana University will use infrared and fluorescence spectroscopy to map patterns of energy flow for small molecules weakly adsorbed on single crystal insulator surfaces. This includes developing techniques for growing well-ordered monolayers on well-defined surfaces, and studies of two dimensional phase transitions as well as obtaining rates of vibrational dephasing, radiation, phonon excitation, and photodetachment. The work is important because it illustrates differences between insulator surfaces which bind intact molecules weakly, and more commonly studied conducting (metallic) surfaces which involve much stronger atom-surface interactions. Moleculesbound to metal surfaces are often destroyed by the strong bonding forces. By focussing attention on molecules bound to insulators, Professor Ewing (Indiana University) is able to learn how energy flows between a surface and intact, weakly bound molecules. This provides a unique glimpse into the chemistry of fundamental processes involved in friction and lubrication.In this project in the Experimental Physical Chemistry Program, George Ewing of Indiana University, Bloomington, will study the spectroscopy, dynamics, and reactivities of diatomic and polyatomic molecules adsorbed on ionic insulator surfaces. Infrared spectroscopic techniques will be used to explore molecular structures and motions, energy transfer mechanisms between the adlayer and the substrate, and bonding within the adlayer and between the adlayer and substrate. Using pulsed ultraviolet laser excitation, photochemical reactions on the surface will be initiated and monitored by fluorescence. Systems to be investigated include hydrogen, sulfur dioxide, and methane on lithium fluoride, sodium chloride, and potassium bromide. A major objective of this research is to influence current theoretical models of monolayer photochemistry and energy transfer, and to observe and understand chemical reactions which are unique to surface environments. Surfaces can influence chemical reactions in a variety of ways, including energy transfer to or from the surface, changing the strength of chemical bonds, and altering the energetics of chemical reactions. Professor Ewing's work will clarify some of the issues involving energetics and chemical reactions on relatively inert substrates such as sodium chloride and potassium bromide. The study of these systems will also contribute to our theoretical understanding of more complex systems.
Atmospheric science, thin film water, the physics and chemistry of ice
Atmospheric Chemistry, Atmospheric Sciences, Chemical Physics, Chemistry, Chemistry, Physical, Lasers and Masers, Spectroscopy, Structure and Reactivity, Surface Chemistry
