华山山腰和山脚点大气 PM_2.5中非极性有机化合物污染特征及来源

To investigate the distribution characteristics and sources of atmospheric PM_2.5 at Mt. Hua in Guanzhong Basin, PM_2.5 samples with a 4 h-time resolution were simultaneously collected on a mountainside site and a mountain foot site in summer 2016, and analyzed for non-polar organic compounds (NPOCs), namely, n-alkanes and polycyclic aromatic hydrocarbons(PAHs). In this paper, we focus on the concentration, molecular composition of n-alkanes and PAHs to quantify the source of organic matter (OM) in PM_2.5. The results showed that the differences in the concentrations of n-alkanes and PAHs between the mountain side ((42.4±29.1) ng·m^-3, (3.5±3.4)ng·m^-3) and mountain foot ((197.8±121.0)ng·m^-3, (39.2±27.3)ng·m^-3) during the observation period were significant with the concentrations at the mountain foot being 4~10 times higher than those at the mountain side, suggesting a significant gradient of OM in vertical abundances in the troposphere. In addition, due to the boundary layer uplift and air mass vertical transport, n-alkanes and PAHs at the mountain side showed higher concentrations during daytime and lower concentrations during nighttime, which is opposite to that at the mountain foot. The concentrations of n-alkanes and PAHs in the polluted period at both sites were significantly higher than those in the clean period, which was attributed to increased fossil fuel combustion during the polluted period at Mt. Hua. Diagnostic ratio and PMF source apportionment further suggest that the origins of OM at the two sites are different, of which OM at the mountain foot are more influenced by fossil fuel combustions, accounting for 52% of the total. In contrast, OM at the mountain side are mainly from plant emissions and atmospheric photochemical oxidation, which contributed up to 62% of the total OM, indicating a significant formation of secondary organic aerosols in the upper boundary layer over the Guanzhong Basin.