Atmospheric fine particulate dicarboxylic acids and related SOA in winter at the background site of Yangtze River Delta: Implication for the long-distance transport of solid fuels burning

To identify the pollution characteristics of dicarboxylic acids in the background of the Yangtze River Delta (YRD) during winter, diurnal PM_2.5 samples were collected in Chongming Island, a background site of YRD nearby Shanghai and determined for organic compounds including dicarboxylic acids, organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), levoglucosan, and related inorganic ions. The total concentration of dicarboxylic acid organics was 433 ± 70 ng/m³, of which oxalic acid was the most abundant species, followed by phthalic acid (Ph), succinic acid (C₄), and malonic acid (C₃). Four typical pollution events occurred during the campaign (defined as Event 1, Event 2, Event 3, and Event 4) were identified. The organic matters in Event 1 and Event 2 mainly came from the transport of coal burning emissions derived from northern China with space heating such as Inner Mongolia and Shandong, while those in Event 3 and Event 4 periods came from the long distance transport of biomass burning in Anhui and Henan provinces. We found that aqueous phase oxidation, instead of gaseous phase oxidation, dominated the formation of dicarboxylic acids in the region. The dicarboxylic acids followed a mono-modal size distribution pattern in winter, obviously different from that in summer, mainly due to the dominant aerosol aqueous phase formation and the weak volatilization in winter with low ambient temperature. The result obtained by this study was expected to provide novel insight of source, pollution characteristics, and formation mechanism of secondary organic aerosols (SOA) in the background of YRD and benefit the pollutants control policy formulation.