The primary focus of our group's research is to elucidate mechanisms by which volatile organic compounds emitted from biogenic and anthropogenic sources react in the atmosphere to form products that can create submicron-size organic aerosol particles. These reactions are complex and include photochemistry, gas-phase oxidation, and heterogeneous/multiphase reactions. The resulting particles affect global climate, visibility, and human health. We conduct experiments in large-volume environmental chambers under simulated atmospheric conditions and then identify and quantify organic gas and aerosol reaction products using a variety of analytical instruments and methods. This information is used to develop detailed, quantitative chemical reaction mechanisms for predicting organic aerosol formation, which can be used to improve air quality and global climate models. We also conduct laboratory, field, and modeling studies of indoor air chemistry.