EFFECTS OF URBAN EMISSION CONTROL STRATEGIES ON THE EXPORT OF OZONE AND OZONE PRECURSORS FROM THE URBAN ATMOSPHERE TO THE TROPOSPHERE

An urban plume model is used to simulate the photochemistry of ozone ( O-3) precursors and the concomitant generation of O-3 within an urban plume as it advects and mixes with the background atmosphere. On the b asis of these calculations, we estimate the rates at which O-3 and its precursor compounds are exported to the background atmosphere and how these export rates are affected by various control strategies that mi ght be implemented to reduce maximum O-3 concentrations within the urb an plume. Two model cities with different chemical characteristics are considered: case 1, where peak O-3 concentrations during extreme air pollution episodes are more sensitive to nitrogen oxides (NOx = NO + N O2) and case 2, where peak O-3 concentrations during these episodes ar e more sensitive to volatile organic compounds(VOC). The model is firs t run for extreme meteorological conditions conducive to the generatio n of high O-3 concentrations to determine the most effective emission control strategies for reducing peak O-3 under these conditions. The m odel is then run for more typical meteorological conditions, to determ ine how these various emission control scenarios might affect the expo rt of O-3 and its precursors from the urban to the rural and backgroun d atmosphere. The export of O-3 from the urban atmosphere is found to be more sensitive to NOx emissions, even for case 2 where VOC emission controls more effectively reduced peak O-3 during pollution episodes. The impact of VOC and NOx emission reductions on the export of primar y and secondary O-3 precursor compounds is more complex, leading to re ductions in the export of some species and enhancements in the export of others.