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

Abstract

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.