A spectroscopic study of heterogeneous reactions of nitrogen oxides and sulfur oxides on solid particles of atmospheric relevance

The purpose of the research described in this thesis is to survey whether nitrogen oxides and sulfur oxides react with mineral dust (SiO₂, Al₂O₃, MgO, CaO, CaCO₃, Fe₂O ₃ and TiO₂) and sea salt (NaCl) particles. FT-IR and Diffuse Reflectance UV/Vis spectroscoples were the primary techniques used to probe these reactions.; In Chapter III, spectroscopic data show that the reaction between NO ₂ and water adsorbed on SiO₂ particles yields surface-bound HNO₃ and gas-phase HONO.; In Chapter IV, spectroscopic data show that HNO₃ reacts with CaCO₃ Particles to produce surface nitrate and gas-phase CO ₂ and H2LO. Under dry conditions, the reaction is limited to the surface of the CaCO₃ particles; only the exterior of the CaCO₃ particles reacts with HNO₃ to form surface nitrate. In the presence of water, bulk reactivity was found showing that the entire particle, both the exterior and interior, is available for reaction with HNO₃. Transmission electron microscopy studies revealed that the physiochemical properties of CaCO₃ particles change as the particle is processed from CaCO₃ to Ca(NO₃)₂ upon reaction with HNO₃ and H₂O vapor.; The studies in Chapter V are an outgrowth of Chapter IV in that the heterogeneous reaction of HNO₃ is investigated on oxide particles (SiO₂ , Al₂O₃, TiO₂) Fe₂O ₃, CaO and MgO). Spectroscopic data reveal that HNO₃ weakly adsorbs on SiO₂ particles, while HNO₃ reacts with the other particles to form surface nitrate. In the presence of water, reaction of HNO₃ on MgO and CaO particles was similar to reaction on CaCO ₃ particles because bulk reactivity was found. Reaction kinetic measurements show that the HNO₃ reaction probability on the oxide particles is enhanced two orders of magnitude when water vapor is present.; In the last two chapters, heterogeneous reactions of SO₂ (Chapter VI) and photochemical reactions (Chapter VII) are investigated. Spectroscopic data show that SO₂ reacts with Al₂O₃ and MgO to form surface sulfite and weakly adsorbed SO₂. Upon adsorption of gas-phase water on sulfite coated MgO particles, surface sulfate is converted to surface sulfate. Heterogeneous, thermal, and photochemical reactions of nitrogen oxides on NaCl, TiO₂ and Al₂O₃ particles are reported in Chapter VII.