Contaminated Character and Regional Source of PM_2.5 and Secondary Water-soluble Inorganic Ions in Wu'an City

Wu'an is a heavy industrial city based on steel industry. To study the change characteristics and regional source of PM_2.5 pollution in Wu'an city, it is necessary to collect the air environmental samples and test PM_2.5 components during non-heating period (October 2018) and heating period (January 2019). The simulation results of the CAMx-PSAT model were applied to analyze the regional source apportionment of PM_2.5 and secondary water-soluble inorganic ions(SO₄^2-, NO₃^-, and NH₄⁺) in Wu'an city. The test results show that Wu'an was seriously polluted by PM_2.5, and the average mass concentration of PM_2.5 during the sampling period was 113.5 μg/m³. The contamination of PM_2.5 during heating period was higher than that during non-heating period. SO₄^2-, NO₃^-, and NH₄⁺ were critical components of PM_2.5, and the average mass concentrations of them accounted for 41.1% of PM_2.5 concentration. The concentrations of SO₄^2-, NO₃^-, and NH₄⁺ during heating period were higher than that during non-heating period. Additionally, the average ration of NO₃^-/SO₄^2- was less than 1 during heating period and non-heating period, indicating that the stationary source was relatively important compared to other sources. The concentrations of SO₄^2-, NO₃^-, and NH₄⁺ obviously increased with the increasing of PM_2.5 pollution degree, and the mass concentrations of SO₄^2-, NO₃^-, and NH₄⁺ increased to the highest level in heavy pollution days. Simulation results show that formation of PM_2.5 pollution is the result of local pollutant emission and non-local pollutant emission transport. The local pollutant emission dominates the PM_2.5 pollution. Metallurgical source have the greatest impact on PM_2.5, NO₃^- and SO₄^2- concentrations in Wu'an. Agricultural source is the major source of pollution for NH₄⁺ concentration. Compared with non-heating period, the contribution of residential source to PM_2.5 concentration and secondary water-soluble inorganic ions concentration significantly increases in heating period. Industrial source and vehicle source of non-local source have made prominent contribution to PM_2.5 of Wu'an.