Laboratory studies of atmospheric particles: Heterogeneous reactions and phase transition.

摘要

This thesis presents several fundamental studies of the heterogeneous reactions of trace atmospheric gases with calcium carbonate and several oxides. Experimental techniques used are discussed in chapter 2. Infrared spectroscopy was used for kinetic and spectroscopic measurements. Characterization of the surfaces employed was done by the BET technique for surface area measurements and Scanning Electron Microscopy (SEM) was used to study morphological changes after reactions. Samples synthesized were identified for elemental composition by X-Ray Diffraction (XRD) technique.; In Chapter 3, the adsorption and reaction of sulfur dioxide and nitric acid on the surface of calcium carbonate is presented. This was the first study to identify the formation of carbonic acid, an important intermediate in the surface reactions of calcium carbonate. Chapter 4 presents the investigation of the surface reaction of formic acid and acetic acid on the surface of calcium carbonate. Carbonic acid is also shown to be a product of the reaction. Due to its ubiquitous nature, the role of water in enhancing the uptake of these gases on the surface of calcium carbonate was investigated and results presented.; The rates of reaction of nitric acid and acetic acid on the surface of calcium carbonate were also investigated and are represented in Chapter 5. Chapter 6 highlights an important phenomenon in atmospheric aerosols, namely phase transition as a function of relative humidity. This study investigated important difference and/or similarities between the phase transitions occurring in pure crystals as compared to phase transition occurring on thin films, of similar composition, on the surface of calcium carbonate.; The study presented in Chapter 7 investigates the adsorption of atmospheric gases on the surface of oxide particles. Among the highlights of this chapter is the reporting of a new reaction pathway for the production of sulfate from sulfur dioxide and experimental proof of the proposed theory that the formation of ammonium nitrate occurs via chemisorption of nitrates on the surface of oxides. Chapter 8 reports the study of water and nitric acid uptake on corn dust. This chapter shows that ATR-FTIR spectroscopy can be used to study particulates related to bioaerosols.