10.1371/journal.pone.0201364.g011 Tianhang Huang Tianhang Huang Yunjiang Yu Yunjiang Yu Yigang Wei Yigang Wei Huiwen Wang Huiwen Wang Wenyang Huang Wenyang Huang Xuchang Chen Xuchang Chen t<sub>1</sub>/t<sub>2</sub> oval plot. Public Library of Science 2018 agglomeration air pollution treatment impact factors BTH distribution characteristics Viable policy recommendations PM 2.5 data mg U-shaped variation pattern PM 2.5 pollution sulphur dioxide emission PM 2.5 concentrations road freight volume PM 2.5 concentration 2018-09-20 17:51:20 Figure https://plos.figshare.com/articles/figure/t_sub_1_sub_t_sub_2_sub_oval_plot_/7112543 <p>t<sub>1</sub>/t<sub>2</sub> oval plot.</p>