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Spatial distribution of the monthly relative rate of change (ROC) of ground-level PM2.5 concentration from January to June 2020. In the insets, the red bar charts show the distribution of cities with different ROCs, while the blue lines show cumulative frequencies. Please note, the global lockdown as identified in this analysis ranges from March to May 2020. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)
