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. 2020 Aug 27;17(17):6208. doi: 10.3390/ijerph17176208

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© 2020 by the authors.

Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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Time series of the daily mean PM_2.5 concentration during pre-SD and SD in 2020. The horizontal dashed lines indicate the 30 day mean values for pre-SD (blue) and SD (red), respectively. The green horizontal solid line marks the threshold level of PM_2.5 concentration (35.0 μg m⁻³, “high” if >35.0 μg m⁻³). The period of social distancing (SD) is indicated by the shaded area.