THE PRODUCTION OF O-3 IN AN URBAN PLUME - AIRBORNE SAMPLING OF THE ATLANTA URBAN PLUME

As part of the Southern Oxidant Study, The Tennessee Valley Authority' s instrumented helicopter made a series of air sampling flights over t he city of Atlanta. The flights were made during the summer of 1992 to investigate the evolution of the urban O-3 plume. Air samples were ta ken during morning and afternoon hours; the morning data were used to estimate background O-3 and the afternoon data were used to estimate O -3 production efficiency, i.e. the number of O-3 molecules produced pe r molecule of NOy emitted. Detailed data on O-3 production were availa ble for five afternoon flights. Within the radius sampled, three zones were identified: the source zone where afternoon levels were comparab le with the morning levels, the production zone where O-3 increased ra pidly within a short distance, and the dilution zone where both O-3 an d its precursors were diluted, at the same rate. O-3 peak levels, or t he transition from net production to dilution occurred at 20-40 km fro m the city center. O-3, production efficiency for the five afternoon f lights was between 4 and 10, in good agreement with previous surface m easurements.