Comparison of Chamber 6.6-h Exposures to 0.04–0.08 PPM Ozone via Square-wave and Triangular Profiles on Pulmonary Responses

Abstract

It has become increasingly well realized that laboratory simulations of air pollution risk assessment need to employ O₃ concentration profiles that more accurately mimic those encountered during summer daylight ambient air pollution episodes. The present study was designed to compare the pulmonary function and symptoms of breathing discomfort responses to a 6.6-h square-wave 0.08-ppm O₃ chamber exposure to those observed in a triangular O₃ exposure profile (mean of 0.08 ppm), as well as to both a 0.06-ppm square-wave and triangular mean 0.06-ppm exposure, and to those observed during a triangular mean 0.04-ppm exposure and to a filtered air (FA) square-wave exposure. Thirty young adults (15 of each gender) served as subjects, each completing all exposures. While the 6.6-h postexposure responses to the acute triangular exposure to a mean O₃ concentration of 0.08 ppm did not differ significantly from those observed in the square-wave exposure, forced expiratory volume in 1 s (FEV)_1.0 and total symptoms severity (TSS) were significantly different from preexposure at 4.6 h (when O₃ concentration was 0.15 ppm) in the triangular exposure, but not until 6.6 h in the square-wave exposure. Thus, significant pulmonary function and symptoms responses were observed over a longer period in the triangular exposure protocol at a mean O₃ concentration of 0.08 ppm. These results support previous evidence that O₃ concentration has a greater singular effect in the total inhaled O₃ dose than do V_E and exposure duration. Subtracting pulmonary function effects consequent to O₃ exposure to existent 8-h average background levels (e.g., ∼0.04 ppm, rather than those observed in FA exposures) from those observed at higher concentrations (e.g., ∼0.08 ppm) represents a means of focusing the regulatory effort on effects that can be controlled. The greatest pulmonary function and symptoms responses observed for a 0.04-ppm triangular exposure were nearly the same as those for the FA square-wave exposure. Thus, results of the present study show that calculating the net pulmonary function effect of exposure to 0.08 ppm with “correction” for FA response, or for that incurred for 0.04 ppm O₃, does not result in any statistically significant difference.