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. 2020 Jun 5;739:140000. doi: 10.1016/j.scitotenv.2020.140000

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Fig. 1 — Differences in the main chemical species and source contributions of PM_2.5 derived from PMF model for the two periods. A and B are the main PM_2.5 chemical compositions. C and D are PMF source contribution results. BB, CC, FW, IP, RD, SIA, and VE represent biomass burning, coal combustion, firework burning, industrial processes, road dust, secondary inorganic aerosol, and vehicle emissions, respectively.