Molecular Distributions and 13C Isotopic Composition of Dicarboxylic Acids, Oxocarboxylic Acids, and a-dicarbonyls in Wintertime PM2.5 at Three Sites Over Northeast Asia: Implications for Origins and Long-Range Atmospheric Transport

To investigate the spatial changes in origins and impact of long-range transported air masses on organic aerosols (OA) loading and composition over Northeast Asia, fine aerosols (PM2.5) were collected at three sites: Tianjin (TJ), North China and in Padori (PD), and Daejeon (DJ), South Korea, during winter 2019. We studied molecular distributions and compound-specific stable carbon isotopic composition (d(13)C) of dicarboxylic acids, oxocarboxylic acids and a-dicarbonyls, and carbonaceous and inorganic ionic components in PM2.5. Concentrations of organic carbon was drastically enhanced in haze period compared to that in clean period, but elemental carbon was almost comparable between the two periods. Concentrations of total diacids, oxoacids, and a-dicarbonyls were higher at TJ followed by DJ and PD during haze period and at DJ followed by TJ and PD during clean period. On average, oxalic acid (C-2) was the most abundant among measured species at all three sites, followed by methyl glyoxal (MeGly) and glyoxylic acid (?C-2) at TJ and DJ, and succinic acid (C-4) and ?C-2 were almost equal and second most abundant followed by MeGly at PD. Based on the mass ratios and linear relations of selected species together with d(13)C of diacids and related compounds, we found that contributions of OA from biomass burning/biogenic emissions and their aging were higher at TJ and PD, whereas at DJ, emissions from anthropogenic sources and in situ secondary formation were also important. Furthermore, this study implies that long-range atmospheric transport of aerosols from source regions to downwind regions are substantial over Northeast Asia.Plain Language Summary Fine atmospheric aerosols (PM2.5) collected at three sites: Tianjin (TJ), North China and in Padori (PD), and Daejeon (DJ), South Korea, during winter 2019 were studied for molecular distributions and compound-specific carbon isotopic composition (d13C) of dicarboxylic acids (diacids), oxocarboxylic acids (oxoacids), and a-dicarbonyls as well as the carbonaceous and inorganic ionic components. The results obtained from this study suggested that the contributions of organic aerosols from biomass burning/biogenic emissions and their photochemical secondary formation and transformations (aging) are higher at TJ and PD, whereas at DJ, the emissions from anthropogenic sources and in situ secondary formation are also important. This study also implies that contributions of long-range transported aerosols from source regions to downwind regions such as PD and DJ are substantial over Northeast Asia.