- Exposure sessions: The 0.4 ppm ozone exposure will be conducted in an ozone exposure chamber. Each subject will be exposed to 0.4 ppm ozone for 2 hours. During exposures, subjects will perform four 15 minute bouts of moderate exercise (minute ventilation or VE = 30 40 L/min) on a treadmill, each separated by 15 minutes of seated rest. Minute ventilation is measured for 2 to 3 minutes after about 4 minutes of exercise during the first exercise period, and again at about 12 minutes of exercise. It is then measured at about 12 minutes into each exercise period. Two subjects may be exposed simultaneously, in which case the exercise/rest periods will be alternated.