Experimental results are presented from field studies of smoke plume diffusion and pollution-layer structure in both rural and urban areas, using the Mark VIII mobile lidar (laser radar) system. This new system was first applied to study the behavior of smoke plumes from the 250-m stacks of a large coal-burning power plant, the Homer City Generating Station, in western Pennsylvania. Examples from the Homer City study of characteristic changes in plume diffusion and low-level aerosol structure resulting from time-varying meteorological conditions are presented in the form of vertical plume cross sections. Helicopter-measured SO2 cross sections and the lidar-obtained smoke cross sections are compared on a case-study basis. The mobile lidar observations in urban areas (San Jose, California, and St. Louis, Missouri) reveal significant variabilities in the pollution-layer structure associated with urban effects, transitional meteorological conditions, and apparent convective influences. An analysis of the eye-safety aspects of lidar use in the atmosphere is also included.