His primary area of interest focuses on urban air pollution, especially transportation emissions. Specifically, his research involves modeling and simulations of people's exposure to air pollution; comparing air pollution exposures among racial and socioeconomic subpopulations; the air quality and health impacts of urban planning; and, the use of geographic information systems (GIS) in modeling air pollution. Dr. Marshall also is actively involved in the study of sustainability engineering; energy and environment; and, the environmental impacts of development, especially in rapidly-developing Asian economies.