Comparison of chamber and face-mask 6.6-hour exposures to ozone on pulmonary function and symptoms responses

Because of increased interest in an 8-h ozone (O(3)) federal air quality standard, acute pulmonary function responses to prolonged square-wave O(3) exposure between 0.08 and 0.12 ppm have been examined in several U.S. Environmental Protection Agency (EPA) chamber studies. A low-cost face-mask O(3) exposure system was developed in this laboratory and found to produce closely similar pulmonary responses to those observed in prolonged exposures by U.S. EPA investigators. The primary purpose of the present study was to investigate the pulmonary function and subjective symptoms effects of 6.6-h square-wave exposure to 0.12 ppm O(3) by these two methods using the same group of subjects. In addition, further investigation of pulmonary function and symptoms responses upon 6.6-h exposures to lower levels of O(3) (0.04-0.08 ppm) were studied with the face-mask inhalation system. Thirty young adult subjects completed five 6.6-h exposures with six 50-min periods of exercise at an intensity requiring a minute ventilation rate (V(E)) of ~20 L/min/m2 of body surface area, each followed by 10 min of rest, except following 3 h when the rest period was lengthened for a lunch break. The total O(3) doses for the chamber and face-mask exposures to 0.12 ppm O(3) were not significantly different from each other, since the additional O(3) dose during the 35 min lunch break in the chamber exposure was offset by a slightly lower average exercise V(E) (i.e., 19.1 L/min/m2). The data convincingly demonstrated that the two methods of exposing young adults to nearly identical total inhaled O(3) doses at 0.12 ppm produce very similar pulmonary function, symptoms, and exercise ventilatory pattern responses. On the other hand, results of the 6.6-h face-mask exposures to 0.08 ppm O(3) in the present study, compared to similar U.S. EPA exposure study results, revealed several incongruities that may be due primarily to high individual subject variability in responses to a relatively low O(3) exposure. Thus, a comparison of chamber exposure responses to those elicited via face-mask exposure to 0.08 ppm O(3) in the same subject group seems warranted.