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To investigate the characteristics and sources of atmospheric fine particulate matter (PM2.5) in the medium-sized cities in East China, continuous observation of PM2.5was conducted in Huai’an City from April 18th to May 11st, 2021. During the observation process, the average mass concentration of PM2.5was 58.5 ± 26.9 µg/m3, with a low-to-high trend for observation periods: midnight and early morning < night < morning < afternoon. The composition of PM2.5remained consistent across all sampling periods, with the highest content being water-soluble ions, followed by carbonaceous components. The total concentration of water-soluble ions in PM2.5accounted for 43.4% of PM2.5, and the secondary inorganic components (NH4+, NO3-, and SO42-) were the main ion components, accounting for 36.1%, 33.6%, and 18.2% of the total ion concentration, respectively. The organic carbon (OC) and element carbon (EC) were 11.5 ± 5.0 µg/m3and 1.4 ± 0.9 µg/m3, with OC/EC ratio more than 2 in all periods, indicating a significant presence of secondary pollution throughout the observation process. The positive matrix factorization (PMF) model results indicate that the atmospheric PM2.5in Huai’an was influenced by vehicle exhaust (29.6%), other sources (19.0%), dust sources (18.5%), and secondary sources (13.9%). The sources of PM2.5were mainly secondary sources during midnight and early morning (18.0%), soil dust during morning and night (21.7% and 20.0%), and motor vehicle exhaust in the afternoon (21.8%), respectively. The results of this study have significance for the scientific prevention and control of atmospheric PM2.5in East China.