Abstract：To explore the characteristics of air pollutants， we collected 227 TSP samples in the center of Lanzhou in northwest China from May 2020 to April 2021. The major water-soluble ions and mass concentration of elemental carbon （EC） and organic carbon （OC） were measured by the ion chromatography and thermal-optical carbon analyzer. The results exhibited that the mean TSP concentration was （376.7±974.8） μg·m-3 in Lanzhou， which was higher than that of the 2th National Ambient Air Quality Standard （NAAQS）. The air pollutants also exhibited higher values in the nighttime than that in the daytime， which may resulted in the accumulation processes due to the stable meteorological condition in the nighttime. The average concentrations of ionic abundances exhibited a trend of NO3-＞SO42-＞Cl- for anions， and Ca2+＞NH4+＞Na+＞K+＞Mg2+ for cations. The fractional secondary ions （NO3-， SO42- and NH4+） accounted for 62.68% of the total water-soluble ions， which were mainly dominated by the local meteorological conditions in different seasons. The ratio of NO3-/SO42- （> 1） indicated that the air pollutants in Lanzhou mainly originated from local traffic sources. In contrast， the OC/EC ratios （> 2） exhibited significant SOC formation processes during the entire sampling period. Finally， we used a positive matrix factorization （PMF） model to explore the potential sources of air pollutants in Lanzhou. The results indicated a six-factor/sources solution， which mainly included traffic source， biomass burning， road dust， soil dust， coal burning， and secondary aerosol formation processes. The road dust and secondary aerosol formation processes were significantly dominant in the spring and winter seasons.