Figure 1.

Schematic of face mask exposure of human subjects to ¹⁸O₃ with measurement of breathing airflow and O₃ uptake.

Notes: Subjects breathed into a modified silicone face mask. Inspired and expired flow rates and times as well as breath-by-breath O₃ removal from breathing air were measured for brief intervals during a 2 hour exposure to ¹⁸O₃ at a concentration of 0.4 ppm. ¹⁸O₃ concentration was maintained manually by adjusting the flow rate of an ¹⁸O₂-argon mixture through a silent arc O₃ generator (rate was 3–10 mL/min). Cylinder air maintained at 50% relative humidity flowed past the face mask at a rate of 60 L/min.