Comparison of ozone pollution levels at various sites in Seoul, a megacity in Northeast Asia

Concentrations of ozone were continuously measured at four urban monitoring sites (Gu Ro (G); No Won (N); Song Pa (S); and Yong San (Y)) in Seoul, Korea from 2009 to 2011. The annual mean concentrations of ozone (in ppb) at these sites were found on the order of N (21.8 ± 19.3) > S (21.4 ± 20.14) > G (20.9 ± 18.0) > Y (18.8 ± 17.4). During peak hours (12-6 pm), the ozone concentrations were significantly higher (75, 69, 67, and 64% at site S, Y, N, and G, respectively) than overall 24 hour mean values. Seasonal variations of ozone have quite similar patterns at every site with systematic increases during spring (March-May) and summer (June-August) with the summer daytime mean (12-6 pm) values of 40.7 (site Y)-49.3 ppb (site S). The concentrations of ozone exhibited strong inverse correlations with other criteria pollutants (e.g., oxides of nitrogen and carbon monoxide), while a significant positive correlation was observed with some meteorological parameters (e.g., ultraviolet ray and solar radiation). Evidence collected in this study confirm that the spatio-temporal distribution of ozone in the study areas should be affected by the anthropogenic sources (e.g., vehicles, residential, and industrial sources) in concert with such well-known variables as the NOx-VOC chemistry and a number of natural parameters (e.g., wind speed, geographic position, and solar radiation).