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Despite frequent observations of high particulate matter (PM) concentrations in Seoul, Korea, the sulfate (SO42−) concentrations in PM with an aerodynamic diameter below or equal to 2.5 μm (PM2.5) in Seoul have been reduced during the 1990s. However, there has been no decreasing trend during the 2000s. Despite the very low ambient SO2 concentrations, high SO42− concentration episodes frequently occur in Seoul; however, the reasons for this remain poorly understood. In the present study, we sought to determine the major factors that enhance sulfur oxidation in Seoul by analyzing measurement data from an intensive air quality monitoring station in the Seoul metropolitan area acquired in 2015. Additionally, we aimed to distinguish the contributions of local sources and long-range transport to the elevated SO42− concentrations in PM2.5 in Seoul. In some cases in March and October 2015, the molar ratio of SO42− to SO2, which reflects sulfur partitioning between the particle and gas phases, showed an exponential increase with an increase of relative humidity (RH). However, despite the fact that the RH was high during August 2015, no statistically significant relationship was observed between RH and the molar ratio of SO42− to SO2 during this month. In August 2015, the molar ratio of SO42− to SO2 showed an exponential increase with increasing O3 concentration. Therefore, under sufficient RH, the concentrations of radical oxidants might be the most important factor that underlies the increase in ambient SO42− concentrations. No significant relationship was observed between the molar ratio of SO42− to SO2 and O3 in October. Furthermore, using Potential Source Density Function (PSDF) and backward trajectory analysis, the high SO42− concentrations in March 2015 were found to be caused by the transportation of air pollutants from China and local sources around Seoul. The high SO42− concentrations in August 2015 are concluded to have been greatly affected by these power plant emissions in the Taean area on the west coast of Korea. The high SO42− concentrations in October 2015 appear to have been caused by the transportation of air pollutants from North Korea. In summary, the high SO42− concentration in Seoul is affected by long-range transport from China and by the emissions from around the Seoul metropolitan area, such as Taean or North Korea.

Two approaches were applied for characterization of organic compounds in the atmospheric aerosols. These were chemical and statistical grouping analysis. We applied chemical group analysis as a new approach using the GC×GC data. Based on the principle of GC×GC, analytes in two dimensional data were divided into 6 chemical group depending on their volatility and polarity. Using this classification standards, all analytes were classified as one of 6 chemical groups, HP-VOC, LP-VOC, HP-SVOC, LP-SVOC, HP-NVOC and LP-NVOC. The relationship between the sum of the peak areas of each chemical group with other variables such as the concentrations of OC, EC, OCPOC, OC/EC and OCSOC were studied. However, no apparent relationship was observed. The principle component analysis (PCA) was carried out to find out the relationship among the analytes based on their sources. The OVOCs were dominant compounds in 3 out of 4 factors in summer. In winter, factor 1 was related to secondary organic aerosol and factor 3 was related to primary emission sources. The proposed approach looks promising in characterization of chemical groups but have limitations at current stage which are discussed.

Atmospheric volatile organic compounds (VOCs) in Seoul, the capital of South Korea, have attracted increased attention owing to their emission, secondary formation, and human health risk. In this study, we collected 24 hourly samples once a month at an urban site in Seoul for a year (a total of 288 samples) using a sequential tube sampler. Analysis results revealed that toluene (9.08 ± 8.99 μg/m

Five nitrosamines (nitroso-methyl-ethylamine (NMEA), nitroso-pyrrolidine (NPYR), nitrosodi-ethylamine (NDEA), nitroso-piperidine (NPIP), and nitrosodi-butylamine (NDBA)) in the atmospheric particulate matter with an aerodynamic diameter of less than or equal to a nominal 10 μm (PM10) at Seoul were identified and quantified by using a gas chromatography/mass spectrometry (GC/MS) in chemical ionization (CI) mode. The average ambient concentrations of the sum of the five nitrosamines showed a distinctive seasonal pattern, higher in winter (2.79 ± 1.41 ng/m3) than in summer (0.92 ± 0.29 ng/m3). Diurnal pattern showed slightly higher in night time (1.67 ± 1.47 ng/m3) than day time (1.57 ± 1.04 ng/m3) but it was not statistically significant. Possible contributors of nitrosamines were discussed based on various statistical analyses. Since BaP/BeP ratio and nitrosamines’ concentrations showed negative correlation, indicating aged aerosols containing more nitrosamines, it was suggested that nitrosamines might be produced by the atmospheric reactions. However, the correlations of nitrosamines with PAHs, CO, and SO2 were also good which were emitted from the primary emission sources, suggesting the particulate nitrosamines observed at Seoul could be also emitted from the primary emission sources. Primary emission sources were also identified by using the principal component analysis (PCA). It was concluded that NDBA could be mainly emitted from plastic and rubber combustions, release of landfill and tobacco smoke, and NPYR and NDEA might be emitted from the vehicular emission and cooking. The other nitrosamines, NMEA and NPIP, which were not included in both factors and showed relatively higher negative correlation with BaP/BeP ratios than other nitrosamines, could be produced from the atmospheric reactions.

Seven particulate oxygenated-polycyclic aromatic hydrocarbons (oxy-PAHs) were analyzed in atmospheric particulate matter with an aerodynamic diameter of less than or equal to a nominal 10 μm (PM10) for the period between September 2006 and August 2007 in Seoul, South Korea. The major contributors of oxy-PAHs production were identified based on statistical analyses such as correlation coefficient relationship, principal component analysis (PCA), and simple reaction kinetics calculation. The results show that (1) the average concentrations of seven oxy-PAHs were 7.63 ± 4.32 ng/m3, with distinctive seasonal variations, being higher in winter (8.70 ± 3.90 ng/m3) and lower in summer (1.47 ± 0.73 ng/m3), similar to PAHs; (2) there were mixed contributions of primary emissions (e.g., vehicular emissions, biomass burning, long-range transport) and atmospheric reactions to oxy-PAH production; and (3) primary emissions might affect more than atmospheric reactions to the oxy-PAHs levels.