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Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are of increasing interest due to their high toxicity. Thirteen particulate PAHs and ten particulate OPAHs were analyzed by Gas Chromatography/Mass Spectrometry (GC/MS) in atmospheric particulate matter with aerodynamic diameters less than or equal to a nominal 2.5 μm (PM 2.5) for the period between May 2020 and January 2021 in Seoul, Republic of Korea. The mean concentration ten OPAHs (5.49 ± 2.40 ng/m3) was higher than that of thirteen PAHs (3.96 ± 3.36 ng/m3), respectively. The concentration of total OPAHs was high in winter (9.40 ± 2.50 ng/m3) and low in summer (3.58 ± 0.78 ng/m3), showing the same trend with PAHs (9.16 ± 3.30 ng/m3 in winter and 0.62 ± 0.15 ng/m3 in summer). When comparing this study results with the measurement results on 2006 in Seoul, PAHs concentration dropped by 68% while only 22% was reduced for OPAHs. It suggests either improvement of combustion technology, i.e., high temperature combustion process in the region or higher ambient oxidation reaction rates on 2020 than 2006. Major sources and their contributions of PAHs and OPAHs were identified based on correlation analysis and Positive Matrix Factorization (PMF) modeling. Two cases were carried. Case 1 is for source apportionment for PM 2.5 and case 2 is for OPAHs and PAHs. The number of factors or sources in the two cases was determined as 7 and 4, respectively. The results of the PMF modeling using diagnostic ratios (DRs) in case 1 identified 7 factors; secondary nitrate (23%), secondary sulfate (21%), vehicles (20%), biomass burning (16%), coal combustion (12%), waste incineration (5%), and OPAHs (5,12-NAQ) emission-related (3%). The PMF modeling results in case 2 revealed 4 factors; vehicles (36%), coal combustion (30%), biomass burning (25%), and OPAHs (5,12-NAQ) emission related (9%). Significant correlation between OPAHs and indicators of primary emission sources, and high contribution from sources with emission characteristics implied that most sources of OPAHs were heavily influenced by primary emissions rather than secondary formation. • 13 particulate PAHs and 10 OPAHs were analyzed in Seoul, Korea for four seasons. • The mean concentration of 10 OPAHs was higher than that of 13 PAHs. • OPAHs were heavily influenced by primary emissions rather than secondary formation. • OPAHs reduction ratios were lower than PAHs from 2006 to 2020. [ABSTRACT FROM AUTHOR]

Aromatic volatile organic compounds (VOCs) including benzene, toluene, ethylbenzene, xylene, and trimethylbenzene (BTEX) are known to contribute the most to the formation of ozone and secondary organic aerosols (SOA) in an urban atmosphere and their representation in chemical transport models (CTM) is still uncertain. In this study, we evaluated the model representation of BTEX concentrations and their seasonal difference at Beijing and Seoul using the GEOS-Chem CTM and ground observations from the Fine particle Research Initiative in East Asia considering National Differences (FRIEND) project in winter and summer. The model captured different levels of observed BTEX at Beijing and Seoul, where benzene (BENZ) was comparable and toluene + ethylbenzene (TOLU) and xylenes + trimethylbenzenes (XYLE) were higher at Seoul. The observed seasonal variations of BTEX were similar at both sites, with benzene being higher in winter and TOLU and XYLE being higher in summer. However, the magnitude and seasonal variation of TOLU at Seoul and BENZ at Beijing were not reproduced by the model. TOLU was underestimated in both seasons at Seoul especially in summer due to the underestimation of emission rates and evaporative emission being not included in the current emission inventory. At Beijing, BENZ was underestimated especially in winter and showed no seasonal variation which was different from the observations. Underestimated benzene emission rates or missing sources of it cause discrepancies between observed and modeled benzene concentrations at Beijing. • The observed toluene and xylenes were higher in summer while benzene was higher in winter at Beijing and Seoul. • The evaporative emission of toluene at Seoul needs to be considered in the model to reproduce the observed seasonal variation of toluene. • Benzene concentration at Beijing is underestimated likely due to a low bias in emissions from Beijing's own or upwind region. [ABSTRACT FROM AUTHOR]