Ozone fluxes obtained with the NOAA Twin Otter during the Southern Oxidants Study

During June and July of 1995, as part of the Southern Oxidants Study (SOS), the National Oceanic and Atmospheric Administration (NOAA) instrumented Tw in Otter research aircraft made meteorological and chemical measurements to characterize atmospheric conditions in and around the Nashville, Tennessee , area. In addition to these characterization studies, the aircraft measure d the vertical fluxes of ozone, water vapor, heat, and momentum in the stud y area, at altitudes between 100 and 2500 m above ground level (agl) along transects a few kilometers downwind of the urban area, and extending crossw ind well outside of the urban plume. During all low-level transects, fluxes were measured over short length scales in order to assess their spatial va riability. Several powerplant plumes impacted the local region, creating a complex scenario for analysis of ozone production and deposition processes. Deposition velocities derived from aircraft observations near the ground w ere found to be in reasonable agreement with values estimated by a depositi on velocity model applied along the transects. The results are difficult to reconcile with expectations unless it is assumed that the area of the meas urements was susceptible to considerable advection and/or effects of plume chemistry and spatial heterogeneity. Additional studies of this kind are no w planned, in situations that are less complex.