The production of O3 in an urban plume: Airborne sampling of the Atlanta urban plume

As part of the Southern Oxidant Study, The Tennessee Valley Authorityʹs instrumented helicopter made a series of air sampling flights over the city of Atlanta. The flights were made during the summer of 1992 to investigate the evolution of the urban O3 plume. Air samples were taken during morning and afternoon hours; the morning data were used to estimate background O3 and the afternoon data were used to estimate O3 production efficiency, i.e. the number of O3 molecules produced per molecule of NOy emitted. Detailed data on O3 production were available for five afternoon flights. Within the radius sampled, three zones were identified: the source zone where afternoon levels were comparable with the morning levels, the production zone where 03 increased rapidly within a short distance, and the dilution zone where both O3 and its precursors were diluted, at the same rate. O3 peak levels, or the transition from net production to dilution occurred at 20–40 km from the city center. O3 production efficiency for the five afternoon flights was between 4 and 10, in good agreement with previous surface measurements.