| Mineral dust aerosol impacts the Earth's climate through the scattering and absorption of solar and thermal radiation (direct climate forcing) and the nucleation of clouds (indirect climate forcing). Through heterogeneous chemistry it can also impact the chemical balance of the atmosphere, affecting both gas-phase species and the particles themselves. An issue that arises when quantifying the impact of mineral dust on atmospheric chemistry and climate is in assessing how its physicochemical properties change as it is transported, reacted, and aged in the atmosphere. Although recognized as being important, this issue is poorly understood and little quantitative data available linking mineral dust aerosol chemistry and climate. Carbonates, such as calcite (CaCO 3) and dolomite (CaMg(CO3)2) are a considerably reactive component of mineral dust aerosol, forming nitrate salts as a result of reactions with nitrogen oxides such as HNO3, These salts can have properties that are significantly different than those of the original aerosol, resulting in an aerosol that will dramatically differ in its chemical reactivity, potential impact on climate forcing, and photoreactivity. In this thesis, the heterogeneous reactivity of carbonate minerals with nitric acid and the resulting changes in the physicochemical properties of the aerosol particles are analyzed. As a measure of reactivity, the heterogeneous uptake coefficient for the reaction of HNO3 on CaCO3 and CaMg(CO 3)2 is determined. To thoroughly characterize the changes that occur as mineral dust aerosol is entrained in the atmosphere and undergoes heterogeneous reactions with nitrogen oxides, a multi-analysis aerosol reactor system (MAARS) has been developed. MAARS has been designed, constructed and implemented to carryout measurements of aerosol hygroscopicity, cloud condensation nuclei (CCN) activity, and FTIR extinction spectra as a function of relative humidity (RH). The measurements presented here are focused primarily on the differences between carbonate minerals found in freshly emitted mineral dust aerosol and the nitrate salts that form as a result of heterogeneous chemistry. The measurements present in this work provide a first quantitative assessment of the correlation between mineral dust aerosol chemistry and climate, and lend insight to the impact processing of mineral dust aerosol has on its climate forcing capability. |
