Abstract: Based on the Model 2001A thermal/photocarbon analyzer developed by the US Desert, the carbonaceous components （organic carbon （OC） and elemental carbon （EC）） and water soluble ions （NO₃^-, SO₄^2-, F^-, Cl^-, NO₂^-, NH₄⁺, K⁺, Ca²⁺, Mg²⁺, Na⁺） in PM2.5 during heavy pollution in 2016 winter in Xuzhou city were monitored by day and night sampling, and the secondary organic aerosol （SOC） content was optimized by the optimized MRS algorithm. The results showed that the average mass concentration of PM2.5 in Xuzhou city reached （129.7±37.0） μg/m³ during the sampling period. Through the OC/EC ratio analysis, the carbonaceous aerosol in Xuzhou city during the sampling period was mainly affected by the exhaust emissions of gasoline vehicles and diesel vehicles. The average mass concentration of SOC was 3.4 μg/m³, and the contribution to OC reached 44.3%, and the degree of secondary pollution at night was greater than that during the day. The average mass concentration of water-soluble ions in the heavy pollution period reached （126.0±24.0） μg/m³, and the three main water-soluble ions of NO₃^-, SO₄^2-, and NH₄⁺ existed in the form of NH₄NO₃ and （NH₄）₂ SO₄. Through the analysis of NO₃^- and SO₄^2- ratios, the fixed source of coal-burning contributed a lot to water-soluble ions. Using PMF model to analyze the mass concentration of atmospheric PM2.5 in heavy pollution period in Xuzhou city, there were mainly six, including traffic source （48.7%）, secondary inorganic aerosol pollution source （24.3%）, sea salt and coal combustion source （14.9%）, secondary chemical pollution sources （12.1%）, biomass combustion sources （0.9%）, and road dust sources （0.1%）. In general, the source of atmospheric PM2.5 in Xuzhou city is more multi-sourced, and the traffic source and secondary inorganic aerosol pollution source occupy a dominant position.

Key words: PM2.5, organic carbon, elemental carbon, MRS method, water-soluble ion, PMF model