Improvement of a respiratory ozone analyzer

The breath-to-breath measurement of total respiratory ozone (O3) uptake requires monitoring O3 concentration at the airway opening with an instrument that responds rapidly relative to the breathing frequency. Our original chemiluminescent analyzer, using 2-methyl-2-butene as the reactant gas, had a 10% to 90% step-response time of 110 msec and a minimal detectable concentration of 0.018 parts per million (ppm) O3 (Ben-Jebria et al. 1990). This instrument was suitable for respiratory O3 monitoring during quiet breathing and light exercise. For this study, we constructed a more self-contained analyzer with a faster response time using ethylene as the reactant gas. When the analyzer was operated at a reaction chamber pressure of 350 torr, an ethylene-to-sample flow ratio of 4:1, and a sampling flow of 0.6 liters per minute (Lpm), it had a 10% to 90% step-response time of 70 msec and a minimal detectable concentration of 0.006 ppm. These specifications make respiratory O3 monitoring possible during moderate-to-heavy exercise. In addition, the nonlinear calibration and the carbon dioxide (CO2) interference exhibited by the original analyzer were eliminated. In breath-to-breath measurements in two healthy men, the fractional uptake of O3 during one minute of quiet breathing was comparable to the results obtained by using a slowly responding commercial analyzer with a quasi-steady material balance method (Wiester et al. 1996). In fact, fractional uptake was about 0.8 regardless of O3 exposure concentration (0.11 to 0.43 ppm) or ventilation rate (4 to 41 Lpm/m2).