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(a-c) Percentage difference in weekday median levels of PM2.5 in 2020 relative to the same period in reference years, 2017–2019. The data for April–June are listed in Table 1 for these sites. (d-f) The percentage in PM2.5 median values in 2020 and 2017–2019 relative to January of the same year(s). The vertical lines highlight the statistically significant percentage decreases based on the p-values for April–June.
