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Wuhan was the first city to adopt the lockdown measures to prevent COVID-19 spreading, which improved the air quality accordingly. This study investigated the variations in chemical compositions, source contributions, and regional transport of fine particles (PM 2.5 ) during January 23-February 22 of 2020, compared with the same period in 2019. The average mass concentration of PM 2.5 decreased from 72.9 μg m -3 (2019) to 45.9 μg m -3 (2020), by 27.0 μg m -3 . It was predominantly contributed by the emission reduction (92.0%), retrieved from a random forest tree approach. The main chemical species of PM 2.5 all decreased with the reductions ranging from 0.85 μg m -3 (chloride) to 9.86 μg m -3 (nitrate) (p < 0.01). Positive matrix factorization model indicated that the mass contributions of seven PM 2.5 sources all decreased. However, their contribution percentages varied from -11.0% (industrial processes) to 8.70% (secondary inorganic aerosol). Source contributions of PM 2.5 transported from potential geographical regions showed reductions with mean values ranging from 0.22 to 4.36 μg m -3 . However, increased contributions of firework burning, secondary inorganic aerosol, road dust, and vehicle emissions from transboundary transport were observed. This study highlighted the complex and nonlinear response of chemical compositions and sources of PM 2.5 to air pollution control measures, suggesting the importance of regional-joint control., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)