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).