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Characterization of water soluble inorganic ions and their evolution processes during PM2.5 pollution episodes in a small city in southwest China
- Qiao, Baoqing, Chen, Yang, Tian, Mi, Wang, Huanbo, Yang, Fumo, Shi, Guangming, Zhang, Leiming, Peng, Chao, Luo, Qiong, Ding, Shimin
- The Science of the total environment 2019 v.650 pp. 2605-2613
- aerosols, ammonium, basins, emissions, inorganic ions, nitrates, nitrogen content, particulates, pollutants, pollution, sulfates, summer, water solubility, weather, winter, China
- PM2.5 samples were collected in four segregate one-month periods, each representing one season, for analyzing their contents of water soluble inorganic ions (WSIIs) in a small city inside Sichuan Basin. Daily PM2.5 concentrations ranged from 23.2 to 203.1 μg m−3 with an annual mean of 66.9 ± 33.6 μg m−3. Annual mean concentrations of WSIIs was 28.8 ± 20.3 μg m−3, accounting for 43.1% of PM2.5. Seasonal mean concentrations of WSIIs ranged from 17.5 ± 9.3 μg m−3 in summer to 46.5 ± 27.6 μg m−3 in winter. Annual mean mass ratio of NO3−/SO42− was 0.49, demonstrating predominant stationary sources for secondary inorganic aerosols (SNA, including SO42−, NH4+ and NO3−); whereas annual mean molar ratio of [NH4+]/[NO3−] was 3.5, suggesting dominant agriculture emissions contributing to the total nitrogen. During a severe and long-lasting (13 days) winter pollution period when mean PM2.5 concentration reached to 132.5 μg m−3, PM2.5 concentration was enhanced by a factor of 2.6 while that of SNA by a factor of 2.9 compared to those before the pollution event, and the fraction of SNA in PM2.5 only increased slightly (from 46.7% to 50.6%). Thus, local accumulation of pollutants under poor diffusion conditions played a major role causing the extremely high PM2.5 concentration, besides the contributions from the enhanced SNA formation under specific weather conditions.