We collected ambient PM10 and PM2.5 samples from six sites in Tian’jin, China, from February to March 2016, then analysed their chemical compositions and identified emission sources using the positive matrix factorization model. The mean concentrations of PM10 and PM2.5 were 98 and 71 μg m-3 with a mean PM2.5/PM10 ratio of 0.67. The average concentrations of the sum of SO42-, NO3- and NH4+ were 19.9–23.4 μg m-3, accounting for 72.4–77.1% of the total measured ions. The concentrations and percentages of NO3- and OC were significantly higher than those of other species. The SO42−/NO3− ratio showed a decreasing tendency with PM10 and PM2.5 concentrations increasing, implying the important influence of mobile sources. The mean OC/EC ratios for PM10 and PM2.5 were 3.1 and 3.2, with little spatial differences. Crustal elements were the most abundant elements, accounting for 73.2–84.2% of the total detected elements mass, mainly enriched in PM10. Optimal factors were selected for PM2.5 and PM10 by PMF analysis: the Q/Qexcept of PM10 and PM2.5 showed a smaller decrease when moving from five to six factors, indicating that five factors can be an optimal solution. All factors mapped in bootstrap (BS) in 100% of runs and no swaps occurring with displacement of factor elements (DISP) at five factors. Secondary inorganic aerosol, coal combustion, crustal dust, vehicle exhaust, and biomass burning contributed 28–30%, 20–21%, 18–21%, 17–20%, and 4%, respectively. The contributions of secondary inorganic aerosol showed less spatial difference than other sources. Backward trajectory and PSCF analysis showed that air masses affecting Tian’jin mainly originated in the northwest during the heating period, and the north-east of He’nan, south-western Shan’dong, Bei’jing, and Tian’jin itself were major potential source areas.