Fig. 1.

Experimental design and exposure regimen. Animals (N = 24, 4/group at each age) were assigned at 1 mo of age to 2 age groups, 2 or 6 mo, and then designated to 1 of 3 exposure subgroups: filtered air (FA), FA + acute ozone (O₃) challenge (AO: exposure at 0.5 ppm O₃ 8 h/day × 2 days), or episodic biweekly O₃ exposure cycles + acute O₃ challenge (EAO). Each 14-day cycle consisted of 0.5 ppm O₃ × 8 h/day × 5 days of exposure, followed by 9 days of filtered air, repeated over a 14-day cycle, and/or 2 consecutive, overnight acute O₃ exposures (0.5 ppm × 8 h/day × 2 days) just prior to necropsy at 2 or 6 mo of age. For EAO groups, the 2-day acute overnight challenge took place on days 14 and 15 of the last cycle, immediately followed by necropsy. All exposures took place overnight. EAO 2- and 6-mo animals completed 1 or 11 cycles, respectively.