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

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Study design for each of the three series of exposures separated by 2 weeks. 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). Participants were exposed at rest in a double-blinded, randomized, crossover design to clean air, 200-ppb NO₂, or 600 ppb NO₂ once for 30 min on day 1, and twice for 30 min on day 2. There was no exposure on day 3. Time of day is expressed in military form.