The research of the Jimenez group 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 deposition of acids, toxics, and nutrients to ecosystems and crops. 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. Aerosols are also important for other applications such as nanomaterials fabrication and pharmaceutical drug delivery.