Characterization of volatile organic compounds (VOCs) in megacity Seoul from multiyear observation

Volatile organic compounds (VOCs) are the key precursors of O­₃ and secondary organic aerosols in urban atmosphere. This study investigates the variations and emission sources of 55 VOCs observed in central Seoul between 2013 and 2019. VOCs were continuously measured every hour using an online gas chromatography system by the Seoul Metropolitan Government Research Institute of Public Health and Environment (SIHE). The lower limit of detection was 0.1 ppbC and outliers were removed by applying Chauvenet’s criterion.

Of the 55 VOCs, the most abundant species was ethane, followed by propane and toluene and their average concentrations were 6.6 ppbv, 5.9 ppbv and 4.6 ppbv, respectively. In terms of TVOCs, toluene was the most abundant with the average concentration of 32.1 ppbC and comprises about the half of the aromatic VOCs. Alkane and aromatics showed different seasonal, diurnal and weekly variations, and dependence on meteorological variables. In addition, the toluene to benzene ratio was greater in summer than in winter with the average of 11.0. These results indicate the additional sources for VOCs to traffic related emissions in megacity Seoul. The PSCF (Potential Source Contribution Function) and cluster analysis of backward trajectories of air masses indicate that while alkanes are chiefly emitted from vehicles, aromatic concentrations are greatly influenced by fugitive emission from neighboring cities of Seoul. There is also chance for some VOCs with relatively long lifetime to be transported from nearby countries.