[Chemical Composition Characteristics and Source Apportionment of PM_2.5 During Winter in Taiyuan]

To study the characteristics and sources of PM_2.5 pollution in Taiyuan urban area in winter, PM_2.5 and its chemical components (water-soluble ions, carbon components, and trace elements) and gaseous pollutants (SO₂, NO₂) were monitored by online instruments in January 2017. Combined with meteorological data, the characteristics of PM_2.5 and its chemical components were analyzed. Also, source apportionment of PM_2.5 was conducted by using positive matrix factorization (PMF). The results showed that the mean mass concentration of PM_2.5 on polluted days (239.92 μg·m^-3) was 5.70 times as much as that on clean days. The concentrations of the main chemical components of PM_2.5 on polluted days, SO₄^2-, NO₃^-, NH₄⁺, Cl^-, OC, and EC, were 7.04, 5.76, 6.51, 5.62, 4.06, and 4.70 times their respective values on clean days. The sulfur oxidation ratios (SOR) and the nitrogen oxidation ratios (NOR) on polluted days were 0.12 and 0.19, respectively, which were higher than those in clean days, indicating that secondary transformation was more significant on polluted days. The results of the PMF source apportionment showed that the contributions of secondary sources (35.06%), coal combustion (30.19%), and vehicle emissions (24.25%) were higher on polluted days than on clean days, with increases of 18.03%, 7.39% and 2.10%, respectively. Thus, air pollution control strategies should pay more attention to controlling secondary source precursors on the basis of controlling the primary emission sources on polluted days.