Abstract
In order to study the seasonal variations in the chemical composition of atmospheric particulate matter with diameters less than 2.5 μm (PM2.5) and its influence on visibility in background areas, atmospheric PM2.5 samples were collected in spring, summer, autumn, and winter 2016 at Qixingtai in Ji'nan. The pollution characteristics of water-soluble ions components, organic carbon (OC), and elemental carbon (EC) were analyzed, and their regional transmission contributions were studied. The results show that NH4+, SO42-, and NO3- were the main components of water-soluble ions, accounting for 90.24% of the annual total ion concentration. The secondary water soluble inorganic ions were polluted severely. NO3-/SO42- presented obvious seasonal variations of high (low) levels in winter (summer). In each season, SO42- and NH4+ existed mainly in the form of (NH4)2SO4. The value of secondary OC (SOC)/OC ranged from 21.17% to 54.21%, indicating the presence of relatively severe secondary organic pollution in this area. The sulfur oxidation ratio (SOR) value in all seasons was greater than 0.1, indicating that the secondary generation of SO42- occurs in all seasons in this region, and the value of nitrogen oxidation ratio (NOR) in all seasons was higher than the SOR value. The secondary transformation of NO2 in the Qixingtai region was stronger than that of SO2. The range of atmospheric extinction coefficient (Bext) was 172.68-320.61 Mm-1, with an annual mean of 256.48 Mm-1. The atmospheric extinction coefficient showed an obvious seasonal trend of the lowest (highest) in summer (winter). The backward airflow trajectory shows that the Qixingtai was affected mainly by the long-distance transmission from Northwest China and the ocean in spring and summer and by local sources in autumn and winter. A comparison of the characteristics of atmospheric PM2.5 pollution in Ji'nan in 2008 revealed that the influence of motor vehicles on the atmospheric environment has been significantly improved.
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