Ozone absorption into excised porcine and sheep tracheae by a bolus-response method

The absorption of ozone (O3) into excised porcine and sheep tracheae was characterized by a bolus-response experiment in which a bolus with a peak O3 concentration of 1 ppm was rapidly injected into a steadily flowing airstream entering the trachea. Using a fast-responding chemiluminescent analyzer of our design, the O3 concentration curves at the proximal end (i.e., the bolus input) and at the distal end (i.e., the response) of the trachea were monitored. Each concentration curve was numerically integrated, and the fraction of O3 absorbed in the trachea was obtained by subtracting from unity the ratio of the response integral to the bolus input integral. Average values of ozone-absorbed fraction decreased from about 0.50 to 0.15 at increasing airflows from 50 to 200 ml/sec. A diffusion theory that includes the effects of bulk convection, axial dispersion, and first-order absorption was developed to relate the fractional absorption to an overall mass transfer coefficient (K). The results indicate that K is independent of airflow, suggesting that the diffusion resistance in mucus is much greater than that in the gas phase. The time-weighted integrals of the concentration curves were also computed, allowing the mean residence time of O3 in the trachea (delta tau) to be determined. As predicted by the diffusion theory, delta tau was inversely related to the rate of O3 absorption.