Research Interests: Multidisciplinary areas of atmospheric chemistry air pollution, climate, and global biogeochemical cycles. His research group, composed of chemists and meteorologists, develops analytical instruments (for NOx, NOy, NH3, CO, SO2, CO2, CH4 and aerosols including black carbon), employs these instruments in the laboratory, field, and on ships and aircraft, and interprets the results in terms of photochemistry and atmospheric physics. They study convection, as well as the budget of tropospheric ozone and greenhouse gases in the Baltimore-Washington area, New York City, and on the large scale. In situ and satellite observations are compared to calculations from computer models.