Variation of the concentrations of the particulate chemical components in Seoul response to the changes of major emission sources in the region: emphasis on ambient heavy metals

This study analyzed the impact of air-mass transport via the Yellow Sea (YS) pathway on PM_2.5 concentrations and chemical composition in Seoul from 2016 to 2021, focusing on heavy metals while also considering inorganic and organic species. Using backward trajectories from the HYSPLIT model, the analysis showed that YS-pathway cases consistently showed higher concentrations PM_2.5 and most components compared to non-YS-pathway cases, indicating that the influence of transboundary air pollutants transported via the Yellow Sea persisted. This difference was also influenced by local meteorological conditions, such as lower planetary boundary layer heights and weaker wind speeds during YS-pathway cases in winter, which are unfavorable for pollutant dispersion. Vanadium (V) and nickel (Ni), markers of heavy oil combustion, showed similar trends, with significant declines in 2020 and 2021, likely due to the IMO 2020 regulation and reduced shipping activity during the COVID-19 pandemic. In contrast, arsenic (As) and selenium (Se), markers of coal combustion, showed different trends, suggesting variations in their emission sources. Elevated As levels observed in late 2020 were attributed to emissions from coal-fired power plants in North Korea and Liaoning Province, China. Meanwhile, lead (Pb) and As exhibited no significant differences between YS-pathway and non-YS-pathway cases, suggesting that their source distributions differ from those of other pollutants. These findings highlight the ongoing influence of transboundary air pollutants on air quality in Seoul and emphasize the need for international collaboration, sustained monitoring, and effective domestic and regional emissions controls.