Comparative decomposition of ozone in the nasopharynx of beagles: acute vs chronic exposure.

The mean tracheal concentration of ozone (O3) was measured in two groups of physiologically unaltered beagles. One group had been exposed to 03 for 18 months and consisted of four subgroups exposed to the following daily concentration × time regimens: 1 ppm × 8 hours, 2 ppm × 8 hours, 3 ppm × 8 hours, and 1 ppm × 24 hours. The control group consisted of previously unexposed beagles sampled similarly at either 1 ppm O3 or 3 ppm O3 following one hour of acclimatization. For groups receiving equal O3 concentrations, the chronically exposed subjects had statistically higher mean tracheal concentrations of O3. All dogs inspiring higher concentrations of O3 demonstrated significantly higher mean tracheal concentrations. Furthermore, the subgroup chronically exposed to 1 ppm × 24 hours had statistically higher mean tracheal concentrations than the chronically exposed subgroup receiving 1 ppm × 8 hours.