Seasonal variations of acidic air pollutants in Seoul, South Korea

The annular denuder system (ADS) was used to characterize seasonal variations of acidic air pollutants in Seoul, South Korea. Fifty- four 24 h samples were collected over four seasons from October 1996 to September 1997. The annual mean concentrations of HNO3, HNO2, SO2 and NH3 in the gas phase were 1.09, 4.51, 17.3 and 4.34 μg m-3, respectively. The annual mean concentrations of PM2.5(dp≤2.5 μm in aerodynamic diameter, 50% cutoff), SO2-4, NO-3 and NH+4 in the particulate phase were 56.9, 8.70, 5.97 and 4.19 μg m-3, respectively. All chemical species monitored from this study showed statistical seasonal variations. Nitric acid (HNO3) and ammonia (NH3) exhibited substantially higher concentrations during the summer, while nitrous acid (HNO2) and sulfur dioxide(SO2) were higher during the winter. Concentrations of PM2.5, SO2-4, NO-3 and NH+4 in the particulate phase were higher during the winter months. SO2-4, NO-3 and NH+4 accounted for 26–38% of PM2.5. High correlations were found among PM2.5, SO2-4, NO-3 and NH+4. The mean H+ concentration measured only in the fall was 5.19 nmole m-3.