The primary research effort was in the development and evaluation of air quality simulation models using numerical and physical techniques supported by field studies. Work on the description and modeling of the planetary boundary layer continued. Major emphasis was on modeling photochemical oxidant dispersion and dispersion in complex terrain. In addition, climatic studies were conducted, including the analyses of the relationships between pollutant concentrations and meteorological parameters. A flow visualization field study of small hill impaction was conducted at Cinder Cone Butte, Idaho as part of the study of dispersion in complex terrain. This was complemented by towing tank studies in the Fluid Modeling Facility. The second Northeast Regional Oxidant Study field program was conducted during July-August 1980 to investigate physical and chemical processes important to long-range transport of oxidants and oxidant precursors. Four photochemical air quality models were evaluated using data for ten carefully selected high ozone days from the Regional Air Pollution Study in St. Louis. The European Model for Air Pollution (EURMAP), which predicts SO2 and SO4 concentrations and deposition rates as well as interregional sulfur transport, was adapted for use over eastern North America (ENAMAP).