CHARACTERIZATION OF THE NASHVILLE URBAN PLUME ON JULY 3 AND JULY 18, 1995

This paper reports results from the Southern Oxidants Study field camp aign designed to characterize the formation and distribution of ozone and related species in the Nashville urban region, Data from several a irborne platforms as well as surface observations on July 3 and 18 are examined to gain insight into the factors that control O-3 formation rates and concentrations in the regional plumes. On both days, well-de fined urban and power plant plumes were sampled. Utilizing both aircra ft and surface data, a detailed kinetic analysis of the chemical evolu tion of the urban plume is performed to derive NOx lifetime, ozone pro duction efficiency, OH concentration, HNO3 dry deposition rate, and th e relative importance of natural and anthropogenic hydrocarbons to O-3 production. Analysis of the urban plume data revealed a very active p hotochemical system (average [OH] similar to 1.2 x 10(7) molecules cm( -3)) which consumed 50% of the NOx within approximately 2 hours, at an ozone production efficiency of 2.5 to 4 molecules for each molecule o f NOx. Anthropogenic hydrocarbons provided approximately 44% of the fu el for ozone production by the urban plume. The dry deposition rate fo r HNO3 in the urban plume was estimated to be of the order of 5 to 7 c m s(-1).