Characteristics of roadside air pollution in Korean metropolitan city (Daegu) over last 5 to 6 years: Temporal variations, standard exceedances, and dependence on meteorological conditions

The present study performed a roadside data analysis to provide baseline data for exploring associations between environmental exposure to four gaseous pollutants and health effects on residents living near roadways. The yearly roadside concentrations of CO and SO2 showed a well-defined decreasing trend, whereas those of NO2 and O-3 exhibited the reverse trend. In most cases, the diurnal trends of the roadside concentrations were well-defined for all seasons, plus the daytime concentrations were higher than the nighttime concentrations. In contrast to the other target pollutants, the daytime O-3 concentrations observed at the roadside sites were lower than those observed at the residential site, likely due to high-levels of fresh NO from traffic emissions that rapidly react with O-3, thereby reducing the O-3 roadside level. The Sunday roadside concentrations of CO, NO2, and SO2 were similar to or somewhat lower than the weekday concentrations. Conversely, for O-3, the Sunday roadside concentrations were similar to or somewhat higher than the weekday concentrations. The higher O-3 concentrations on Sunday may be due to the reduced titration from a decrease in NOx emissions under VOC-limited conditions (low VOC/NOx conditions). The monthly averages of O-3 concentrations exhibited the reverse seasonal variation to the other target compounds, with peak O-3 concentrations between April and June, and the second peak between August and October. It is also suggested that for O-3, the 8-h standard is more stringent than the 1-h standard, while for NO2 and SO2, the 1-h standard is more stringent than the 24-h standard. The multiple regression equations obtained from the relationship between the concentrations and five meteorological parameters indicated that the number and type of meteorological variables in the equations varied according to the pollutant, monitoring station, or season. (c) 2005 Elsevier Ltd. All rights reserved.