[Pollution Characteristics and Sources of Wintertime Atmospheric Brown Carbon at a Background Site of the Yangtze River Delta Region in China].

To investigate the pollution characteristics and sources of atmospheric brown carbon (BrC) in Chongming Island, a background site of the Yangtze River Delta (YRD) region in China, PM2.5 samples collected from December 2018 to January 2019 were analyzed to determine their chemical compositions and optical properties. The results showed that the light absorption coefficient (Abs365,M) of BrC extracted by methanol at 365 nm was (5.39±3.33) M-1·m-1, which was 1.3 times of the water extracted BrC. Both increased significantly with the increase of pH values, suggesting that less acidic conditions can enhance the light absorption ability of BrC. In winter, both Abs365 and MAE365 (mass absorption efficiency) were higher in the nighttime than in the daytime. A strong linear correlation observed between Abs365 and levoglucosan (R2=0.72) indicated that many light absorbing substances in Chongming Island were derived from biomass burning emissions. During the campaign, nitro-aromatic compounds (NACs) and PAHs accounted for (1.5±1.1) ng·m-3 and (8.3±4.7) ng·m-3, respectively, contributing to 0.1% and 0.067% of the absorption of the total BrC at 365 nm, respectively. Positive matrix factorization (PMF) analysis further showed that biomass and fossil fuel combustions were the main sources of BrC in Chongming Island in winter, accounting for 56% of the total BrC, followed by secondary formation, accounting for 24% of the total BrC, with road dust contributing only 6%.

[Pollution Characteristics and Source Apportionment of n-Alkanes and PAHs in Summertime PM2.5 at Background Site of Yangtze River Delta].

To investigate the pollution characteristics and sources of organic aerosols at a background site of the Yangtze River Delta, day- and night- PM2.5 samples were collected from May 30th to August 15th, 2018 in Chongming Island, China and measured for their normal alkanes (n-alkanes) and polycyclic aromatic hydrocarbons (PAHs) content employing a GC-MS technique. Concentrations of PM2.5, n-alkanes, and PAHs during the entire sampling period were (33±21) µg·m-3, (26±44) ng·m-3, and (0.76±1.0) ng·m-3, respectively. During the entire campaign, 35% of the collected PM2.5 samples were of a particle loading larger than the first grade of the China National Air Quality Standard (35 µg·m-3), suggesting that further mitigation with respect to air pollution in Chongming Island remains imperative. In the period with a PM2.5 concentration higher than 35 µg·m-3, which was classified as the pollution period, concentrations of n-alkanes and PAHs were one order of magnitude higher than those in the period with PM2.5 less than 15 µg·m-3, which was classified as the clean period. During the entire campaign, OC was higher in the daytime than in the nighttime, mainly due to the daytime photooxidation that enhanced the formation of secondary organic aerosols. During the pollution period, concentrations of EC and other pollutants were higher in the nighttime than in daytime, mainly due to the transport of the inland pollutants by the nighttime land breeze. Such a diurnal difference was not observed for the pollutants in clean periods, mainly due to the relatively clean breeze from East China Sea that diluted the air pollution. Diagnostic ratios showed that 67% of n-alkanes in PM2.5 was derived from fossil fuel combustion. PMF analysis further showed that during the pollution period, vehicle exhausts and industrial emissions were the largest sources of PAHs, both accounting for 51% of the total in PM2.5. In contrast, during the clean periods ship emissions were the largest source, contributing about 45% of the total PAHs, exceeding the sum (38%) of vehicle and industrial emissions.