The heterogeneous chemistry of mineral dust and sea salt and their components with trace atmospheric gases.

摘要

Tropospheric aerosols can have a significant impact on the Earth's atmosphere, specifically through health effects, effects on the biogeochemical cycle and climate forcing. These aerosols react with trace atmospheric gases such as nitrogen oxides, sulfur oxides, and organics through heterogeneous chemistry which can alter their effect on the atmosphere. It is estimated that 1000--3000 Tg of mineral aerosols are emitted into the atmosphere annually. Calcite, CaCO3 and oxides such as MgO, Al2O 3 and SiO2 are all common components of aerosol particles in the troposphere. Sea salt is also a common aerosol found in the troposphere and has an estimated annual integrated flux on the order of 2800 Tg NaCl yr -1. Mineral dust and sea salt are both often represented as single entity aerosols. However, this is a poor representation of the rich mineralogy and varying chemical composition of mineral dust as well as the multi-component nature of sea salt.; In this dissertation research, several state of the art analytical techniques were used for the first time to study heterogeneous reactions. These techniques include scanning electron microscopy (SEM), computer-controlled SEM, environmental SEM and energy-dispersive X-ray (EDX) microanalysis. They were used to monitor and quantify phase transitions, morphology changes and compositional changes of individual particles of calcium carbonate, NaCl, sea salt and dust particles from 4 different dust source regions, as they are reacted with nitric acid and monitored as a function of time and relative humidity. Atomic force microscopy was also used to monitor the nanometer-scale changes in surface structures of freshly cleaved CaCO3(101¯4) and MgO(100) as they are allowed to age under ambient conditions as well as reacted with nitric acid. Finally, Fourier-transform infrared spectroscopy was used to investigate the adsorption of several gases (HNO3, CH3COOH, CH3OH and SO2) and chemical nature of adsorbed species on carbonate and oxide surfaces including CaCO3, alpha-Al2O3 and SiO2.