Characterization and Spatial Source Apportionments of Ambient PM_(10) and PM_(2.5) during the Heating Period in Tian'jin, China

Baoshuang Liu ； Xiaoyun Sun ； Jiaying Zhang ； Xiaohui Bi ； Yafei Li ； Liwei Li ； Haiyan Dong ； Zhimei Xiao ； Yufen Zhang ； Yinchang Feng

《Aerosol and Air Quality Research》 20卷1期 (2020/01) Pp. 1-13+ap1-26

https://doi.org/10.4209/aaqr.2019.06.0281

摘要

We collected ambient PM_(10) and PM_(2.5) 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 PM_(10) and PM_(2.5) were 98 and 71 μg m^(-3), respectively, with a mean PM_(2.5)/PM_(10) ratio of 0.67. The average concentrations of the combined SO_4^(2-), NO_3^-, and NH_4^+ were 19.9-23.4 μg m^(-3), accounting for 72.4-77.1% of the total measured ions. The concentrations and percentages were significantly higher for NO_3^- and OC than for other species. The SO_4^(2-)/NO_3^- ratio showed a decreasing tendency as the PM_(10) and PM_(2.5) concentrations increased, implying a strong influence from mobile sources. The mean OC/EC ratios for PM_(10) and PM_(2.5) 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 PM_(10). The optimal number of factors for PM_(2.5) and PM_(10) 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, Bei'jing, and Tian'jin itself were major potential source areas.

關鍵字

Chemical species ； Source apportionment ； Heating period ； Error estimation ； PMF