Figure 8 (a) Map showing the spatial distributions of the chemical production of sulfate from July 27 to 28 from WRF-Chem results. The pie charts show the average contributions of different aerosol species during the same time for different regions from multiple observation results. The city names of each measurement site are marked with different numbers corresponding to the city numbers in the right panel. (b) average contributions of different aerosol species, (c) average concentrations of different aerosol species, (d) sulfate-to-nitrate ratio of different cities. All these results are based on ground online measurements except for Baicheng. The aircraft measurement data on July 30 was used to calculate the average aerosol compositions in Baicheng.