Heterogeneous atmospheric chemistry of mineral dust and its components – carbonates, clays and oxides

It has become increasingly clear that all kinds of particles – including ice, sea salt and mineral dust – are present in the Earth’s atmosphere and that the surfaces of these particles play a role in the chemistry of the atmosphere. The ozone hole is one example of how heterogeneous chemistry involving chlorine-reservoir species on ice particles can decrease ozone levels in the stratosphere. In the troposphere, the region closest to the Earth’s surface, there are many more particles and the heterogeneous chemistry of these particles with trace gases such as NO₂, HNO₃, SO₂, O₃ and organics is not well understood. Heterogeneous reactions that take place on mineral dust in the troposphere may provide the “missing link” for some reaction schemes that cannot be explained solely by gas-phase reactions. Reactions on surfaces may provide additional pathways and the high loading of mineral aerosol into the troposphere during dust events may provide an important surface for these reactions. Exposure to reactive inorganic or organic chemical species or exposure to varying amounts of water vapor in the atmosphere may influence the chemical nature of mineral dust. These reactions cause “weathering or aging” of the aerosol and will result in a particle whose, reactivity and mineralogy may be very different from that of the original dust. In the Grassian research group, we are using a combination of surface spectroscopy, microscopy and particle analysis to gain an understanding of kinetics and mechanisms involvedin these important reactions. Reaction rate data measured in our laboratory for heterogeneous reactions of trace gases with mineral dust and its components (CaCO₃, alpha-Fe₂O₃, aluminum silicates…) are currently being incorporated into global chemistry models. We are collaborating with atmospheric modeler (Professor Gregory Carmichael, Chemical and Biochemical Engineering) on this project.