Chemical characteristics of acidic gas pollutants and PM2.5 species during hazy episodes in Seoul, South Korea

Abstract

Very high PM 2.5 concentrations have been observed, which were classified as hazy episodes, on several days in the fall of 2001 in the Seoul metropolitan area. It was the worst air pollution event ever seen in this area. In order to develop the scientific PM 2.5 control strategies for hazy episodes in this area, it is necessary to investigate the chemical characteristics of air pollutants during hazy episodes and evaluate where these high concentrations came from. All measurements were simultaneously taken using two sets of annular denuder system (ADS) to collect acidic gas pollutants and PM 2.5 species. To characterize chemical species for the hazy days, the data were divided into the hazy and non-hazy episodes. Atmospheric HNO 3 , HNO 2 , and SO 2 during the hazy episodes increased by a factor of about 1.6–2.1 compared to those during the non-hazy episodes. The NO 3 − , SO 4 2− , and NH 4 + during the hazy episodes increased by a factor of about 4.4–6.1 compared to those during the non-hazy episodes. In addition, ambient PM 2.5 concentrations for hazy days were a factor of 1.3–3.3 in excess of the 65 μg m −3 , which is the 24-h US PM 2.5 NAAQS. The mean concentrations of carbonaceous species during the hazy and non-hazy episodes were 29.26 and 11.76 μg m −3 for organic carbon (OC) and were 9.75 and 7.23 μg m −3 for elemental carbon (EC), respectively. Higher OC concentrations were observed in the hazy episodes, which may be influenced by biomass burning which occurred from the outside of the Seoul area rather than the local atmospheric formation of secondary OC. The results of the backward air trajectory analysis and weather charts reconfirmed the possibility of the effect of biomass burning. The highest contributors to the PM 2.5 mass during the hazy event were major ionic species such as: NO 3 − , SO 4 2− , and NH 4 + .