Effects of Local Atmospheric Circulation on the Formation of High Ozone Concentration in Confined Area - A Case Study in Southern Taiwan

[[abstract]]This study aimed to investigate an air pollution episode case in southern Taiwan associated with high ozone concentration in the ambient air occurring on 25 October 2001. The relationships between local circulation and accumulation of ozone in confined area were investigated. The synoptic pattern during the investigated period was weak northeasterly. A local circulation was formed on west side of the mountains which had an average height of about 2000 m. During that period, it was dominated by a low pressure circulation. The wind system blew southwesterly at daytime but it turned to northwesterly at night. For determining the formation of local circulation in the atmosphere, the vertical structure of the atmosphere was established by collecting vertical meteorological information through intensive observation with sounding and pible in this study. Investigation results show that the ozone reached its maximum concentration around mid-noon and afternoon. The high-ozone area was confined at the place where low pressure circulation formed. The field results also indicated that the diurnal variation in wind and temperature was significant. Based on the estimated Froude number equal to 0.2 while the weak approaching to the mountains from the northeast, it indicated the weak flow northeasterly was unable to climb over the Mountains and a low pressure circulation formed behind the mountain. The weak wind and fare weather was favored for accumulating ozone within the are