The aim of my research efforts is to further the understanding of the chemical and physical properties of atmospheric secondary organic aerosols (SOAs). A large fraction (80–90% in some locations) of atmospheric organic aerosol is secondary in origin. The effects of SOA impact issues of climate change and human health, which in turn have implications for weather, the hydrogeological cycle, and changes in ecosystem stability. My program seeks to directly address important questions in SOA formation mechanisms and chemical composition, and to relate chemical properties to the optical properties of atmospheric aerosols.