Heterogeneous chemistry of individual mineral dust particles from different dust source regions: the importance of particle mineralogy

The heterogeneous chemistry of individual dust particles from four different dust source regions is investigated on a particle-by-particle basis using state-of-the-art scanning electron microscopy techniques including computer-controlled Scanning Electron Microscopy/Computer-Controlled energy dispersive X-ray (CCSEM/EDX) analysis. Morphology and compositional changes of individual particles as they react with nitric acid are observed. Clear differences in the reactivity of mineral dusts from these four different dust regions with nitric acid could be observed. Mineral dust from source regions containing high levels of calcium, such as those found in parts of China and Saudi Arabia, are found to react to the greatest extent. Calcium containing minerals, such as calcite (CaCO 3) and dolomite (CaMg(CO 3) 2), react to form nitrate salts whereas other calcium containing minerals such as gypsum (CaSO 4 2H 2O) do not react. The importance of particle chemical composition and mineralogy in the heterogeneous chemistry of mineral dust aerosol is definitively borne out in this study of individual dust particles.