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. 2021 Feb 17;413:125445. doi: 10.1016/j.jhazmat.2021.125445

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Fig. 5 — Box plots of CO levels during weekdays (24-h average) per month at Hamilton Downtown (urban), Ottawa Downtown (urban), Toronto West (urban) and Windsor Downtown (urban). Median values from these weekdays data were used to calculate percentage difference in CO levels in 2020 relative to 2017–2019 as described in the text. Number below each data box corresponds to the calculated p-value. See text for details.