Our group's research centers on the development and application of advanced instrumentation for real-time, quantitative measurements of the size, chemical composition, and morphology of submicron aerosols. We care about atmospheric aerosols for many reasons, including their effect on radiation balance (climate forcing), severe short-term and long-term effects on human health, reduced visibility, and acid deposition ("acid rain"). Most of these effects are not well understood, in good part due to the limitations of the instrumentation available. Advanced instrumentation can be used to make much faster progress in many of these areas. We also investigate the role of aerosols in the transmission of respiratory diseases such as COVID-19.