The purposes of this study are to evaluate the effects of local circulations on the ambient air quality and to study the control strategies for ozone in southern Taiwan. The characteristics of local circulations were studies by three-dimensional field observations and model simulations. Sea-land breeze and valley wind dominate the local circulation in southern Taiwan. Therefore, the vertical profile of wind field can be divided into three regions: the first region is from ground to 1200 m which is dominant by the local circulations, the second region is above the first one to 3000 m which is determined by the vortex eddy due to the effect of topography on seasonal northeastern wind, and the third and highest region is the prevailing western wind. Thus, the combined effect of local circulations and vortex eddy forms a convergent region around Kaoping area and air pollutants cumulate in this region to create bad air quality. The long-term trend analysis for the EPA monitored data showed that the ozone concentration increased at rates of 0.5 to 1.1 ppb per year, except for Pingtung station. However, the concentrations of NOx and NMHC, ozone precursors, decreased at rates of 0.5 to 1.8 ppb and 2 to 14 ppbC per year, respectively. The intensities of UVb at Douliu and Tainan stations increased gradually at rates of 0.55% and 0.43% per year, respectively; but those at Pingtung station decreased at rate of 0.41% per year. Therefore, the variations of ozone concentrations were highly correlated with those of UVb intensities; the increment of solar intensity may be one of the reasons causing the high ozone concentrations. The diurnal variations of vertical profiles of ozone concentrations can be classified into four groups based on the results of field observations and model simulations. The four types are the uniform vertical profile at inland region and the internal boundary layer at coastal region during daytime and the ozone residence layer and the ozone depletion layer at nighttime. The contributions of ozone residence layer on the ground ozone concentrations are on the average of 5 to 12 ppb and the peak hourly value is up to almost 30 ppb. Three-dimensional back trajectory analysis is conducted to evaluate the source and receptor relationship for each ozone episode event by using the MM5 simulation results. The back trajectory analyses show that the fractions of no circulated cross air basin transport, circulated flow cross Kaoping and Yuchianan air basins, and circulated flow within Kaoping air basin only are 14%, 26%, and 60%, respectively. Therefore, the ozone events in Kaoping air basin are predominantly due to its own emission. The sensitivity analyses for ozone control show site dependent results: VOCs-control at near downwind sites of urban and industry parks and NOx-control for aged air parcel at remote area. Therefore, emission for both NOx and NMHC should be reduced in order to control the ozone concentrations in Kaoping air basin. The suggestions of this projects include to setup an air quality monitoring site at Shinliuchow, to use three-dimensional back trajectory analysis to study the source and receptor relationship, to further analyze the causes for the increasing ozone concentration and to conduct more three dimensional field observation due to the complex air flow patterns in southern Taiwan.

sea-land breeze, internal boundary layer, ozone residence layer, ozone depletion