Examples of diurnal variation can be seen for the 3 largest cities in Korea, Seoul Pan40, Busan Pan17, and Gwangju Pan26. For Seoul, the amounts of NO2 during the morning (1 DU at 10:00) are much less than later in the afternoon (over 2 -3 DU at 16:00) on almost every day, and occasionally reaching 6 DU. Even early in the day, there is significant pollution levels . Seoul is unusual, since the NO2 levels occasionally reach 6 DU and the peak values occur in the late afternoon. Busan, a large city in the south of Korea near the eastern coast (see KORUS-AQ MAP) also has high values of NO2 reaching 3 DU in the afternoon. Busan also has relative low values of NO2 in the morning, reaching a peak in the mid-afternoon and declining in the late afternoon. Gwangju, located in the southwest, is a smaller city with less pollution (peak values = 1.6 DU) also has a minimum in the morning.
Taewha, Yeoju, and Anmyeondo show regions well outside the Seoul metropolitan area that still show substantial amounts of NO2. The Taewha site was semi-rural with only a small amount of car traffic in the immediate area. However, there are major highways about 6 km from the site. All of the sites showed a tendency to have peak NO2 occur in the late afternoon. Anmyeon island on the west central coast of Korea has pollution levels that are relatively low with occasional plumes arriving from the north from Inchon and Seoul.
Total column ozone variation during KORUS-AQ and Busan and Seoul. Given the narrow range of latitudes and longitudes, ozone is similar at all of the sites. The apparent decrease in O3 is just part of the annual cycle. However, the diurnal variation for Seoul is larger than for Busan.
