An analysis of the temporal variability in volatile organic compounds (VOCs) within megacity Seoul and an identification of their sources

In this study, the volume mixing ratio of 55 volatile organic compound (VOC) species was measured every hour using the online TD-GC-FID system during the period from January 2018 to December 2019 in Seoul. The most abundant species were ethane (10.0 ppbv) and toluene (4.1 ppbv), with alkanes and aromatics accounting for 57.5% and 31.5% of the total VOCs (TVOC), respectively. The mixing ratios of the TVOC were markedly higher in July and November, mainly owing to the presence of aromatics and alkanes, respectively, but were lower in other months, without any significant differences in other months. Of the aromatics, the maximum mixing ratios of xylene, benzene, and toluene were observed in summer, winter, and both seasons, respectively. Principal component analysis showed that emissions from traffic and solvent use were the main VOC sources, which were further categorized into liquefied natural gas/liquefied petroleum gas/gasoline, diesel fuel, mixed combustion, industrial solvents, and paint solvents. The two solvent sources were well represented by toluene and xylene, respectively. In addition, the distinct VOC composition of the air masses clustered by the back trajectory reveals the origin, seasonality, and transport characteristic of the five source categories. This study is the first report on multiyear variability of VOC mixing ratios in Seoul that highlights the contribution from evaporation sources and fugitive emissions and the potential impact of intercity transport from industrial areas near Seoul.