[Chemical Compositions and Sources of PM_2.5 in Weinan City]

Based on the PM_2.5 samples from Weinan City collected from December 16, 2020 to January 14, 2021, the contamination characteristics of the carbonaceous components and inorganic ions in PM_2.5 and the relationship between PM_2.5 and water-soluble ions were analyzed. Meanwhile, the sources and source areas were also analyzed by using the positive matrix factorization(PMF), potential source contribution factor(PSCF), and concentration weight trajectory(CWT) methods. The results showed that the night and daytime concentrations of PM_2.5, OC, EC, and TWSIIs during the winter in Weinan City were 119.08, 17.02, 6.20, and 34.30 μg·m^-3and 130.66, 18.09, 6.22, and 50.65 μg·m^-3, respectively. Ion concentrations followed the order of F^->NO₃^->Ca²⁺>SO₄^2->Na⁺>Cl^->NH₄⁺>K⁺>Mg²⁺ during the daytime and NO₃^->SO₄^2->Ca²⁺>NH₄⁺>F^->Na⁺>Cl^->K⁺>Mg²⁺ at night. PM_2.5 was acidic during the day and alkaline at night. SOR and NOR values were 0.20 and 0.09, respectively. The R² values of NH₄⁺ and SO₄^2- during the day and night were 0.04 and 0.09, respectively, and those of NH₄⁺ and NO₃^- during the day and night were 0.07 and 0.65, respectively. The PMF model analysis showed that the sources of PM_2.5 in Weinan City during the winter were mainly coal burning and industrial emission sources, dust sources, and secondary sources. Backward trajectory combined with the potential source analysis indicated that the PM_2.5 sources in Weinan City during the winter could be divided into two categories:the first was northwest to the remote source transmission, mainly affected by Gansu, Southern Inner Mongolia, and the Ningxia Hui Autonomous Region; the other category was local emissions, affected by the surrounding neighboring cities of Xianyang, Xi'an, and Tongchuan.