Aerosols are generated by a variety of natural and anthropogenic sources. I am interested in the processes that emit, transform and deposit particulate matter. A current focus of my research is how particles in the atmosphere directly modify the surface radiation balance of the Earth. This is of importance to the climate of the Earth, as well as plant growth and visibility. We have conducted studies at a variety of polluted urban sites as well as pristine remote sites to understand the contrast between clean and dirty locations. Another interest is the past impacts of aerosols on climate through interpretation of paleorecords archived in ice cores. My work involves a combination of lab and field studies as well as the development of relatively simple mathematical models.