Aerosol PM₁₀ of different sizes was collected the whole day in the northern suburb of Nanjing in winter 2009.This paper analyzes the distribution characteristics of water-soluble anions in PM₁₀ by using the ion chromatograph.Results show that the average total mass concentration of anions in PM₁₀ (PM_2.1) are 658.21 and 622.84 μg/m³ (337.86 and 319.97 μg/m³) in daytime and nighttime,respectively,and anions dominate in the fine particles.SO₄^2- are mainly water-soluble anions,and sea salt has little effect on the mass concentration of SO₄^2- in PM₁₀ and PM_2.1 in the northern suburb of Nanjing.The size distributions of SO₄^2-,Cl^- and F^- show bimodal nature,while those of NO₃^- and NO₂^- show single mode.Correlation coefficients between SO₄^2- and NO₃^-,F^- and NO₃^-,SO₄^2- and Cl^- are all greater than 0.8,which are significant,indicating that these anions are homologous.The average NO₃^-/SO₄^2- in daytime and nighttime are 0.0582 and 0.0484,respectively,indicating that the air pollution in northern suburb of Nanjing mainly comes from the stationary sources.Analysis of transformation of NO₃^- and SO₄^2- precursors shows that the average SOR and NOR during the sampling period are more than 10%.It is show that SO₄^2- in PM₁₀ is partially come from the second photochemical transformation of SO₂,rather than a single source of primary pollutants.