Airborne lidar characterization of power plant plumes during the 1995 Southern Oxidants Study

One of the objectives of the 1995 Southern Oxidants Study was to assess the extent to which fossil fuel power plants contribute to high ozone episodes that often occur in the Nashville area during summer. Among other instruments, the National Oceanic and Atmospheric Administration airborne ozone and aerosol lidar was used to investigate power plant plumes in the vicinity of Nashville, Tennessee. Owing to its ability to characterize the two-dimensional structure of ozone and aerosols below the aircraft, the airborne lidar is well suited to document the evolution of the size and shape of a power plant plume as well as its impact on ozone concentration levels as the plume is advected downwind. We report on two case studies of the Cumberland power plant plume that were conducted on July 7 and 19, 1995. The meteorological conditions on these 2 days were distinctly different and had a significant impact on the plume characteristics. On July 7, the Cumberland plume was shaped symmetrically and confined to the boundary layer, while on July 19 the plume had an irregular shape and showed two cores, one above and the other within the boundary layer. Close to the Cumberland power plant, we found that ozone in the plume was destroyed at a rate of 5 to 8 ppbv h(-1) due to titration at high NO levels. Farther downwind, where plume NOx reacts with ozone precursor gases to form ozone, we measured plume-averaged ozone production rates of 1.5 to 4 ppbv h(-1). The results of these two case studies are compared to aircraft in situ measurements of the same power plant plume.