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O 3 production in the Nashville urban plume during the O 3 episode that occurred on July 11–July 13 1995, is examined to characterize the factors that control the ozone production rate and efficiency, and to examine the relative importance of natural and anthropogenic sources of hydrocarbons to ozone production in the urban center and outlying areas. The analysis focuses on data collected during aircraft flights on July 11 when the Nashville area was sampled more or less continuously from about 1000 to 1800 LT. The instantaneous ozone production rate P(O 3 ) in the downtown area from late morning through midafternoon on July 11 ranged between 10 and greater than 30 ppbv/h depending on location. After 1700 local time, production rates dropped to a few ppbv/h owing to the diminished solar intensity. Instantaneous production efficiencies with respect to NO x in the downtown area ranged between 2.5 and 8, linearly depending on the ratio of the hydrocarbon to NO x , OH reactivity. Integral O 3 production efficiencies corrected for NO z losses ranged between 1.5 and 4. The lowest efficiency was observed in the downtown area in the morning where NO x concentrations were high and hydrocarbon to NO x reactivity ratios were the lowest. Throughout the day, P(O 3 ) in the downtown area was limited by the availability of hydrocarbons. Anthropogenic hydrocarbons and CO contributed about 66% of the total hydrocarbon OH reactivity in the downtown area. In the mature urban plume downwind of Nashville, P(O 3 ) dropped to 6–9 ppbv/h at midafternoon and was controlled by the availability of NO x . Integral O 3 production efficiencies in the mature urban plume ranged between 3.5 and 4. When present in large quantities (1–3 ppbv), isoprene significantly increased both the rate and efficiency of ozone production as long as the photochemical system was not strongly NO x ‐limited.
Daum et al. (Sat,) studied this question.