Abstract: During the ‘13^th Five Year Plan’ period, the overall air quality in the Yangtze River Delta (YRD) region improved, significantly. However, the atmospheric environment situation in the northern area of YRD is still severe. In addition, the frequently occurrence of haze in winter has become a weakness in winning the battle to protest the blue sky. This study focuses on a typical agricultural city in the northern part of YRD region. Local PM_2.5 samples were collected manually at the Suzhou Environmental Protection Monitoring Station from December of 2020 to February of 2021, and the chemical components of the samples were analyzed. The results showed that the average PM_2.5 concentration in winter was (80±31) μg/m³, and 49% of the sampling days exceeded the standard limit of level Ⅱ (75 μg/m³) of Ambient Air Quality Standards (GB 3095-2012). The seasonal average concentration of water-soluble inorganic ions was (38.6±24.8) μg/m³, accounting for 48% of PM_2.5. The average concentration of secondary inorganic ions was (33.8±20.3) μg/m³, accounting for 42% of PM_2.5. The average concentration of NH₄⁺ in Suzhou was relatively high, and the emission intensity of NH₃ from local agricultural sources may be the key to reducing ion and even PM_2.5 concentrations in Suzhou. The seasonal average concentrations of total carbon, organic carbon (OC) and elemental carbon (EC) were (19.0±7.3), (16.3±6.2) and (2.7±1.2) μg/m³, respectively, and OC and EC accounted for 17% and 2.8% of PM_2.5, respectively. The seasonal average concentrations of crustal elements and trace inorganic elements were (8.5±7.8) and (0.23±0.11) μg/m³, respectively, accounting for 10.5% and 0.3% of PM_2.5, respectively. According to the PMF results, the local atmospheric PM_2.5 mainly came from traffic (22%), combustion (21%) and secondary inorganic (21%) sources. In addition, it was also affected by dust (18%), industrial (15%) and fireworks burning (3%) sources. Therefore, it is necessary to strengthen the emission regulations of traffic sources, combustion sources, and secondary inorganic precursors (NOx, SO₂ and NH₃) to reduce the secondary generation of PM_2.5. In addition, it is also essential to increase publicity and control efforts to forbid fireworks during the intensive fireworks period of the Spring Festival to further improve the ambient air quality.