RESUMEN
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.
RESUMEN
TSP and 9-stage size-segregated samples were simultaneously collected in Xi'an during the spring of 2013 and analyzed for organic aerosols (OA) on a molecular level. n-Alkanes were the dominant compound class during the whole campaign, followed by fatty acids. High molecular weight (HMW) n-alkanes and fatty acids dominated in the coarse mode particles (>1.1⯵m) during the dust event, indicating they were mostly originated from surface soil and plants in the upwind regions. Low-volatile anthropogenic compounds such as benzo(e)pyrene (BeP) and bisphenol A (BPA) dominated in the fine mode particles during the whole campaign. In contrast, semi-volatile anthropogenic compounds such as phenanthrene (Phe) and di-n-butyl phthalates (DBP) showed a bimodal size distribution with a significant increase in the coarse mode during the dust event due to their vaporization from the fine mode particles and the subsequent adsorption on the dust surface. Secondary organic aerosols (SOA) in Xi'an during the dust storm period were predominantly enriched on the coarse particles, which can be ascribed to the adsorption and subsequent oxidation of gas-phase hydrophilic organics on the aqueous-phase of hygroscopic dust surface (e.g., mirabilite). Our work suggested an important role of multiphase reaction in evolution of aerosol chemistry during the dust long-range transport process.
