I am a senior research fellow in the Atmospheric Chemistry Modeling Group at Harvard. The goal of my research is to understand how short-lived gases and particles in the atmosphere interact with climate. For example, I study how 21st-century climate change could affect the intensity or duration of smog episodes. I also examine how the projected decline in particle concentrations over the United States could amplify the warming due to greenhouse gases. I investigate changes in atmospheric composition during the last ice age and how these changes could account for the observed trends in methane. In all these studies, I use global models of the atmosphere together with observations.