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a Mobility index (MI) of different human activities before (light grey-shaded area), during (yellow-shaded area), and after (dark grey-shaded area) the lockdown being put into effect. b Daily average (24 h) concentrations of the three contaminants from 15 February to 31 August 2018 (blue), 2019 (green), and 2020 (red). Observe that concentration values in y-axes are different depending on contaminant and station
