Analysis of air pollution in two major Korean cities: trends, seasonal Tvariations, daily 1-hour maximum versus other hour-based concentrations, and Tstandard exceedances

This study considers the characteristics of carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3) and sulfur dioxide (SO2) in two major South Korean cities, including the capital city of Seoul, over a time period of 7-8 years. Changes in the annual mean and percentiles of the daily 1-h maximum and other hour-based concentrations varied according to the compound and city type. Seasonal variations varied according to the compound, yet not with the city type. Both Seoul and Taegu exhibited lower O3 concentrations in July compared to other summer months. There was a high degree of correlation between the daily 1- and 8-h maximum or daily mean concentrations of all compounds in both cities, with an R2 of 0.66-0.90 at p<0.0001. It was indicated that for CO and O3, the 8-h standard was more stringent than the 1-h Astandard, while for NO2 and SO2, the 1-h standard was more stringent than the 24-h standard. The correlation coefficients between the daily 1-h maximum and daily mean concentrations decreased as the maximum concentration values of NO2, O3 , and SO2 increased in the two cities. For all the target compounds, Seoul recorded a substantially higher frequency of days with concentrations above the relevant 1-, 8-, and 24-h standards compared to Taegu.