Annual and seasonal variations in atmospheric PCDDs/PCDFs and dioxin-like PCBs levels in satellite cities of Seoul, Korea during 2003-2009

Long-term measurements of atmospheric polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (dl-PCBs) were conducted in six satellite cities of Seoul, the capital of South Korea, from January 2003 to December 2009. Of the six sites, three were located in residential areas (Suwon, Anyang, and Seongnam) and the other three were in industrial areas (Ansan, Bucheon, and Siheung). For the 7 years, the average concentrations of PCDDs/PCDFs and dl-PCBs were higher at industrial sites than those at residential sites, and their lowest and highest concentrations were 0.113±0.073pg international toxicity equivalency quantity (I-TEQ)m^-3 and 0.0071±0.0040pg World Health Organization (WHO)-TEQm^-3 at Seongnam and 0.625±0.597pg I-TEQm^-3 and 0.0376±0.0285pg WHO-TEQm^-3 at Ansan, respectively. The annual averages of these compounds tended to decrease from 2003 to 2009, with the most apparent change in 2006 when the regulation of dioxin emission standard was reinforced for flue gas from incineration facilities. Complying with the reinforced standard, the concentrations of PCDFs were reduced more effectively than those of PCDDs, leading to increase in ratios of PCDDs to PCDFs since 2006. Additionally, a seasonal tendency was observed for PCDDs/PCDFs with higher concentrations in winter than summer, which was opposite for dl-PCBs. This seasonal difference suggests their sources such as combustion processes and volatilization and the influence of synoptic-scale circulation. The congener profiles indicated that 1,2,3,4,6,7,8-HpCDF, OCDF, OCDD, and 1,2,3,4,6,7,8-HpCDD were the most abundant, comprising 65.0% of the 17 toxic 2,3,7,8-substituted PCDDs/PCDFs mass. The three congeners of 2,3',4,4',5-PeCB, 2,3,3',4,4'-PeCB, and 3,3',4,4'-TeCB comprised 75.9% of the 12dl-PCBs.