Fast-responding chemiluminescent ozone analyzer for respiratory applications

Abstract

With the eventual goal of measuring ozone (O3 ) uptake distribution in human lungs, we developed a fast-responding chemiluminescent O3 analyzer. As the instrument will be used to sample gases respired by human subjects, it is necessary that the reacting species be nontoxic. We chose to test ten alternative alkenes known to be biologically inert. For each of the alkene reactants, we measured the effect of reacting species flow, reaction cell pressure, and ozone inlet fraction. At fixed ozone fraction, the analyzer output reaches a well-defined maximum value at an optimum reaction cell pressure and the signal reaches a plateau value at a critical reacting flow. Operating at the optimum pressure and critical alkene flow, the ozone calibration curve is nonlinear for seven of the alkenes. It appears, however, that the calibration curve can be made linear by operating at a pressure above the optimum value. Comparison of analyzer performance among the ten alkenes indicates that the most effective reacting species is 2-methyl-2-butene. Using this vapor, the analyzer exhibited a linear calibration curve with a resolution of 20 ppb O3 and a 90% step response of 200 ms at a sampling flow of 3 mℓ/s and a reaction cell pressure of 107 Torr. By increasing sampling rate, it may be possible to improve dynamic response further.