Abstract:  The overall air quality in the Yangtze River Delta (YRD) region has significantly improved during the ‘13^th Five Year’ Plan period. However, the atmospheric environment situation in the northern area of YRD is still severe. Additionally, the frequently occurred winter hazes has become a weakness in winning the battle for Blue Sky Defense. This study focuses on a typical agricultural city in the northern part of YRD region, and the local PM_2.5 collection was conducted manually at the Suzhou Environmental Protection Monitoring Station from December of 2020 to February of 2021, and then chemical components were analyzed. The research results indicate that the winter seasonal PM_2.5 average concentration 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 the water-soluble inorganic ions was (38.6±24.8)μg/m³, accounting for 48% of PM_2.5, while 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 could be the critical in reducing ionic 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, with OC and EC accounting 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, accounting for 10.5% and 0.3% of PM_2.5, respectively. Based on the PMF results, it is shown that the local atmospheric PM_2.5 was mainly 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 on traffic sources, combustion sources, and secondary inorganic precursors (NOx, SO₂, and NH₃) to help reduce the secondary generation of PM_2.5. In addition, it is also essential to enhance publicity and control efforts to forbid fireworks during the intensive firework-burning period of the Spring Festival to help further improve ambient air quality.