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.