Effects of urban emission control strategies on the export of ozone and ozone precursors from the urban atmosphere to the troposphere

Abstract

An urban plume model is used to simulate the photochemistry of ozone (O3) precursors and the concomitant generation of O3 within an urban plume as it advects and mixes with the background atmosphere. On the basis of these calculations, we estimate the rates at which O3 and its precursor compounds are exported to the background atmosphere and how these export rates are affected by various control strategies that might be implemented to reduce maximum O3 concentrations within the urban plume. Two model cities with different chemical characteristics are considered: case 1, where peak O3 concentrations during extreme air pollution episodes are more sensitive to nitrogen oxides (NOx = NO + NO2) and case 2, where peak O3 concentrations during these episodes are more sensitive to volatile organic compounds (VOC). The model is first run for extreme meteorological conditions conducive to the generation of high O3 concentrations to determine the most effective emission control strategies for reducing peak O3 under these conditions. The model is then run for more typical meteorological conditions, to determine how these various emission control scenarios might affect the export of O3 and its precursors from the urban to the rural and background atmosphere. The export of O3 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 O3 during pollution episodes. The impact of VOC and NOx emission reductions on the export of primary and secondary O3 precursor compounds is more complex, leading to reductions in the export of some species and enhancements in the export of others.