[Pollution Characteristics and Source Apportionment of PM₂.₅, in Lanzhou City]

In order to understand the characteristics and sources of PM₂.₅ pollutant in Lanzhou City, two PM₂.₅ sampling sites were set up in Chengguan district and Xigu district, respectively. Samples were sampled during October (non-heating period) and December (heating period) 2013, and mass concentrations of PM₂.₅ and its 16 kinds of chemical components were analyzed. The results showed that the average mass concentration of PM₂.₅ during the sampling period was 129 µg · m⁻³. The sequence of mass concentrations of inorganic elements was: S > Ca > Fe > Al > Mg > Pb > Zn > Mn > Ti > Cu, while the mass concentrations of S, Ca, Fe, and Al, which were the major element compositions, exceeded 1 µg · m⁻³. The mass concentration of inorganic elements during heating period was higher than that during non-heating period, meanwhile, the mass concentration in Chengguan district was higher than that in Xigu district. The sequence of mass concentrations of water-soluble ions was: SO₄²⁻ > NO₃⁻ > NH₄⁺ > Cl⁻ > K⁺ > Na⁺, while the mass concentrations of SO₄²⁻, NO₃⁻, NH₄⁺, which were the main ion components, exceeded 10 µg · m⁻³. The mass concentration of water- soluble ions during heating period was higher than that during non-heating period, meanwhile, the mass concentration in Xigu district was higher than that in Chengguan district. The result of enrichment factor (EF) analysis showed that the EF values of Al, Ca, Mg and Ti were lower than 1, indicating the contribution of natural source, while the EF values of Cu, Pb, S and Zn were higher than 10, indicating the contribution of anthropogenic pollution. The result of principal component analysis showed that the sources of PM₂.₅ were mainly derived from traffic emission, biomass burning, soil and secondary particles.