Modern society is facing a number of pressing global environmental challenges ranging from stratospheric ozone depletion to large-scale biomass burning to climate change. In each of these cases, the component of the Earth system on which the impact of human activities is most directly and acutely felt is the atmosphere. In order to develop strategies for mitigating current and preventing future damage to the atmosphere, an in depth understanding of this highly complex dynamic system is required. My research focuses on elucidating the biological, physical, and chemical mechanisms that control the composition and reactivity of the atmosphere. We currently are working to understand two specific issues: the role of biogenic volatile organic compounds in regional to global scale air quality, aerosol production, and climate and the atmospheric transport and fate of mercury from combustion sources.