Heterogeneous reactions of atmospheric gases on oxide, carbonate and soot surfaces

This thesis presents several fundamental studies of heterogeneous reactions of atmospheric gases with soot, oxide, and carbonate surfaces at the molecular level. Experimental techniques employed are reviewed in Chapter II. They include a Knudsen cell reactor and infrared spectroscopy for kinetic and spectroscopic measurements, respectively. Characterization of those surfaces includes BET surface area measurements, morphology and particle size measurements using transmission electron microscopy (TEM), surface elemental composition using Auger electron spectroscopy (AES), and surface topography and roughness using atomic force microscopy (AFM).; The study presented in Chapter III is the first to correct the uptake coefficient of NO₂ on soot for the surface area of freshly prepared soot samples. In addition, the production of HONO is quantified where it was concluded that other pathways or different conditions contribute more significantly to the observed high concentrations of HONO, for example the presence of adsorbed water on the surface of the particle.; In Chapter IV, different factors affecting the uptake coefficient and the diffusion constant of gases on powder samples are investigated. Specifically, changes in the area of the orifice size in Knudsen cell is found to cause a great shift in the calculated uptake coefficients for molecules such as HNO₃ due to surface saturation effects. It is emphasized that such observations may be more complicated in the presence of adsorbed water.; Due to its ubiquitous existence and role in enhancing the uptake of some gases on solid surfaces, water adsorption on oxide and carbonate surfaces has been investigated in Chapters V through VIII. The nature of water adsorption on alumina surfaces is discussed in Chapter V. The study presented in Chapter VI highlights the effect of water adsorption and desorption cycles on the conversion of the top-most layer of MgO to Mg(OH)₂. Changes in the properties of nitrate thin films supported on single crystal oxide and carbonate surfaces as a function of relative humidity are presented in Chapters VII and VIII. The studies highlight the role of water in enhancing the uptake of HNO₃ on ionic single crystal surfaces and in changing the physicochemical properties of surfaces coated with nitrate layers.