REGIONAL OZONE AND URBAN PLUMES IN THE SOUTHEASTERN UNITED-STATES - BIRMINGHAM, A CASE-STUDY

Aircraft measurements of ozone and the oxides of nitrogen have charact erized the horizontal and vertical extent of the urban plume downwind of Birmingham, Alabama. Derived NOx emission rate estimates of 0.6 x 1 0(25) molecules s(-1), with an uncertainty of a factor of 2, for this metropolitan area are in reasonable accord with the 1985 National Acid Precipitation Assessment Program inventory, which gives 1.2 x 10(25) molecules s(-1) for daytime emissions. These estimates are from two fl ights in 1992 when the urban plume was well separated from the plumes from two power plants northwest of the city. During three flights in 1 990 the plumes of the Birmingham metropolitan area and the two power p lants were combined; good agreement was found between the estimated fl uxes (2.0 to 5.5 x 10(25) molecules s(-1)) and the emission inventory (3.7 x 10(25) molecules s(-1)) for the combined sources. The enhanceme nt of O-3 in the urban plume indicates photochemical formation and sho ws that during the summertime, approximately seven O-3 molecules can b e formed per NOx molecule added by the urban and power plant emissions . This production efficiency applies both to the isolated urban plume and to the combined urban-power plant plumes and is similar to that de rived for rural areas from surface studies. Comparison of the results from several flights indicates the contribution of the regional ozone levels to the O-3 concentrations observed within the urban plumes. The aircraft measurements, in combination with surface measurements of oz one, show that the interaction of ozone concentrations entering the ur ban area, the photochemical formation of ozone during the oxidation of the urban emissions, and the wind speed and direction determine the l ocation and the magnitude of the peak ozone concentrations in the vici nity of this metropolitan area.