Demonstration of long-term increases in tropospheric O3 levels: causes and potential impacts.

Ground-level ozone (O3) is a well-known atmospheric pollutant with its adverse impacts on the environment and human health. Here, the tropospheric O3 concentrations monitored in seven major cities in Korea at monthly intervals over a 22-year period (1989-2010) are presented, and their long-term variability examined. The analysis of annual mean values of O3 (in nmolmol(-1), or ppb) showed a noticeable increase of 118±69% in all seven cities over the two decades (p<0.01). Changes in O3 levels are closely associated with both environmental (e.g., NOx (NO+NO2), SO2, CO, and total suspended particles (TSPs) (p<0.01), temperature, and sunshine hours) and common anthropogenic variables (e.g., population density and number of vehicles). Evidence collected in this study suggests that the atmospheric conditions in most major cities of Korea should be volatile organic compounds (VOCs) sensitive or NOx saturated with respect to O3 formation. As such, establishment of a proper management strategy seems a sensible approach to control tropospheric ozone concentrations in densely populated cities.