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. 2014 Apr 18;122(8):850–855. doi: 10.1289/ehp.1307240

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Flow diagram of the study period for each participant. Abbreviations: H0, immediately before 1st exposure (day 1); H0’, immediately after 1st exposure (day 1); H6, 6 hr after H0’ (day 1); H32, 32 hr after H0’ (day 2); H48, 48 hr after H0’ (day 3). The dose order was attributed randomly; so, series A, B, and C corresponds to clean air, 200-ppb NO₂, or 600-ppb NO₂ exposure.