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 Authority's 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 NO_y 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.