Characteristics of urban ground-level ozone in Korea

This study considers the characteristics of ground-level ozone (O-3) in fiv e Korean cities over a time period of 6-8 years. The focus of this study is daily maximum 1-hr and 8-hr concentrations. For all the study cities in th e period examined, the mean and most of the percentiles (5, 10, 25, 50, 75, 90, and 95) for the daily maximum 1-hr and 8-hr concentrations showed incr easing trends, although not all trends were statistically significant. The daily maximum 1-hr and 8-hr concentrations slowly increased during late win ter, and peaks were attained during the summer season (from May to Septembe r). All the selected cities exhibited a high degree of correlation between their daily maximum 8-hr and 1-hr concentrations. The daily maximum 8-hr co ncentrations, which were climatologically equivalent to the Korean 1 hr/100 parts per billion (ppb) standard, were higher than the current 8 hr/60 ppb by a difference of 8-16 ppb. Compared with other cities in Korea, Seoul re corded a substantially higher frequency of days and hours with concentratio ns above 1 hr/100 ppb, and a higher frequency of days with concentrations a bove 8 hr/60 ppb and 8 hr/80 ppb. Seoul also recorded a substantially highe r frequency of hours with concentrations above 1 hr/100 ppb than days with concentrations above 1 hr/100 ppb, implying that on some days severe exceed ances persisted for more than one hour per day. During multiple-day episode s a North Pacific High dominated Korea, which is quite typical in Korea dur ing the summer season.