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It is shown that rapid vertical transport of air from urban plumes through deep convective clouds can cause substantial enhancement of the rate of O 3 production in the free troposphere. Simulation of convective redistribution and subsequent photochemistry of an urban plume from Oklahoma City during the 1985 PRESTORM campaign shows enhancement of O 3 production in the free tropospheric cloud outflow layer by a factor of almost 4. In contrast, simulation of convective transport of an urban plume from Manaus, Brazil, into a pristine free troposphere during GTE/ABLE 2B (1987), followed by a photochemical simulation, showed enhancement of O 3 production by a factor of 35. The reasons for the different enhancements are (1) intensity of cloud vertical motion; (2) initial boundary layer O 3 precursor concentrations; and (3) initial amount of background free tropospheric NO x . Convective transport of ozone precursors to the middle and upper troposphere allows the resulting O 3 to spread over large geographic regions, rather than being confined to the lower troposphere where loss processes are much more rapid. Conversely, as air with lower NO descends and replaces more polluted air, there is greater O 3 production efficiency per molecule of NO in the boundary layer following convective transport. As a result, over 30% more ozone could be produced in the entire tropospheric column in the first 24 hours following convective transport of urban plumes.
Pickering et al. (Fri,) studied this question.