Characteristics of PM2.5 and Assessing Effects of Emission–Reduction Measures in the Heavy Polluted City of Shijiazhuang, before, during, and after the Ceremonial Parade 2015

The measurement of PM2.5 was conducted from 15(th) August to 17(th) September, 2015 in Shijiazhuang, China, covering the period of a ceremonial parade. The PM2.5 concentrations and the major chemical components were analyzed. The concentrations of PM2.5 was 26.5 mu g m(-3) during control, which were 57.0% and 51.1% lower compared to before and after control, respectively. The lowest concentrations of elements and water-soluble ions were also found during control with a decreasing tread of 31.1%-44.2%, and 57.1%-64.2%, respectively. Two typical pollution episodes characterized by significantly elevated PM2.5 concentration were found during no control due to the combination of no emission-reduction measures and unfavorable weather conditions. The mass percentage of secondary inorganic ions was larger during no control ( 38.1%-40.3%), pointing to the strong contribution of atmospheric chemical processes. The NO3-/SO42- ratios were 0.85, 0.94, and 0.85 before, during, and after control, respectively, and the elevated ratios during control indicate a greater proportion of the PM2.5 originated from vehicle exhaust. The WRF-CMAQ modeling system was also used to assess the effectively of emission reduction measures and weather conditions. The results indicated that the PM2.5 concentration increased by 21.6% and 32.1% if no emission-reduction measures were taken and weather conditions in 2014 were used.