Characterization and Spatial Source Apportionments of Ambient PM10 and PM2.5 during the Heating Period in Tian'jin, China

We collected ambient PM10 and PM2.5 samples from six sites in Tian'jin, China, from February to March 2016 and then analyzed their chemical compositions and identified the emission sources using the positive matrix factorization model. The mean concentrations of the PM10 and PM2.5 were 98 and 71 mu g m(-3), respectively, with a mean PM2.5/PM10 ratio of 0.67. The average concentrations of the combined SO42-, NO3-, and NH4+ were 19.9-23.4 mu g m(-3), accounting for 72.4-77.1% of the total measured ions. The concentrations and percentages were significantly higher for NO3- and OC than for other species. The SO42-/NO3- ratio showed a decreasing tendency as the PM10 and PM2.5 concentrations increased, implying a strong influence from mobile sources. The mean OC/EC ratios for PM10 and PM2.5 were 3.1 and 3.2, respectively, with small spatial differences. The most abundant elements were crustal, accounting for 73.2-84.2% of the total detected elemental mass, and mainly enriched in the PM10. The optimal number of factors for PM2.5 and PM10 was selected via PMF analysis: the decrease in the Q/Q(except) values of these two fractions lessened when choosing six instead of five factors, indicating that five factors may be optimal All the factors were mapped in bootstrap (BS) for 100% of the runs, and no swaps occurred with the displacement of factor elements (DISP) for 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. Secondary inorganic aerosol displayed less spatial heterogeneity than the other sources in its contributions. Backward trajectory and PSCF analysis showed that air masses affecting Tian'jin mainly originated in the northwest during the heating period, and northeastern He 'nan, southwestern Shan' dong, Beijing, and Tianjin itself were major potential source areas.