[Pollution Characteristics of Water-soluble Inorganic Ions in Chengdu in Summer and Winter].

ABSTRACT

The water-soluble inorganic ions (WSIIs) in PM2.5 and gaseous precursors of Chengdu were continuously observed by a gas and aerosol collector combined with ion chromatography (GAC-IC) in the summer and winter of 2017, and both their pollution characteristics and a typical pollution process in winter were analyzed. It was found that the concentration of PM2.5 in winter (100.2 µg·m-3) was significantly higher than that in summer (34.0 µg·m-3). WSIIs were important components of PM2.5 and their total contributions to PM2.5 were 52.9% and 53.3% in summer and winter, respectively. Secondary ions (SNA) accounted for 73.2% and 87.6% of WSIIs in summer and winter, respectively. SO42- and NO3- dominated the SNA in summer and winter, and the contributions to SNA were 37.7% and 59.7%, respectively. The NO3-/SO42- ratio (2.7) in winter was significantly higher than that in summer (0.8), reflecting the important contribution of mobile sources (especially motor vehicles) to PM2.5 in this season. The diurnal variation of SNA in the two seasons was obviously different due to the differences in sources and meteorological conditions. In winter, with the aggravation of pollution, the concentrations of WSIIs and gaseous precursors increased significantly, and NO3- was the key component in causing heavy pollution. Backward trajectory analysis revealed that the air masses in the two seasons in Chengdu differed significantly from each other. The WSIIs in summer and winter were dominated by SO42- and NO3-, respectively. The short-distance and low-altitude transmission from the east and south of Chengdu contributed significantly to PM2.5 pollution in Chengdu.