Characteristics of ground-level ozone distributions in Korea for the period of 1990-1995

General characteristics and trends of ground-level ozone were investigated by using observations from over 80 stations in Korea for the period of 1990 -1995. In general, seasonal ozone variations are characterized by a spring peak with decreased levels in the summer, followed by increases in the fall . In summer, owing to frequent precipitation, monthly average ozone levels notably decreased in most coastal areas, while a weak depression was observ ed in inland stations, sustained by photochemical ozone buildup under relat ively low wind speeds. Coupled with frequent precipitation in summer, with high ozone-forming potential, low wind speeds in inland areas play a signif icant role in local variations of ozone concentrations. Accordingly, ozone concentrations vary in a quite different maimer among monitoring stations i n the Greater Seoul Area, as well as among major cities nationwide. On the whole, monthly average ozone concentrations in major cities, whether locate d in island or coastal areas, are about 10-20 ppb lower than background lev els of 30-40 ppb typical of the Northern Hemisphere. These lower concentrat ions are likely due to the titration effect of local NO, emissions, which i s a clear indication of urban characteristics for most of the stations. Nex t, ozone concentration variations at 34-37 stations in the Greater Seoul Ar ea, characterized by typical photochemical air pollution, were closely inve stigated. Special efforts were made to clarify the effects of transport wit hin the Greater Seoul Area on the ozone concentration variations, a long-st anding question at: issue, by examining monthly variations of percentile va lues and frequency distributions of hourly ozone concentrations. It is beli eved that complex local variations across the nation are superimposed on un derlying effects from the Asian continent and the ocean, located to the wes t and northeast of the Korean Peninsula, respectively. Further research is needed to quantify the relative importance of these effects in controlling the nationwide distribution of ozone levels.