Fig. 8.

Daily mean NO₂ concentrations across all national stations from the January 1, 2020 (Day of the Year, DOY = 1) to the June 28, 2020 (DOY = 180). The red lines indicate the concentration of pollutants in 2020, while the blue lines indicate the average concentration of pollutants in the baseline (2015–2019), with standard deviations in the baseline in light blue. Gray rectangles show the duration of lockdown in each of the 12 study countries. The numbers in parentheses indicate the relative rate of change (ROC) of daily mean NO₂ concentration after the COVID-19 lockdown. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)