EFFECTS OF PROLONGED, REPEATED EXPOSURE TO OZONE, SULFURIC-ACID, AND THEIR COMBINATION IN HEALTHY AND ASTHMATIC VOLUNTEERS

To evaluate effects of ''acid summer haze'' on individuals who exercis e extensively outdoors, we exposed 45 adult volunteers (15 normal or a topic, 30 asthmatic) in a chamber to a mixture of 0.12 ppm ozone (O-3) and approximately 100 mu g/m(3) of respirable sulfuric acid aerosol ( H2SO4). On separate occasions we exposed the same subjects to O-3 alon e, to H2SO4 alone, and to clean air. In exposures involving H2SO4, exc ess acid was generated to consume ammonia released by the subjects, an d the aerosol therefore contained ammonium salts in addition to H2SO4. Subjects were exposed to each atmosphere on two successive days, for 6.5 h/d, with six 50-min exercise periods at ventilation rates averagi ng 29 L/min. Exposures were conducted during four successive weeks, in random order. Lung function and symptoms were measured before exposur e and hourly during exposure. Bronchial reactivity to inhaled methacho line was measured just after the end of each exposure. Exposure to H2S O4 alone caused no significant changes in lung function, symptoms, or bronchial reactivity relative to clean air. Exposure to O-3 alone or O -3 + H2SO4 caused a progressive, statistically significant (p < 0.05) decline in forced expiratory function, smaller on the second day than the first, as previously found by others for O-3 exposure. Bronchial r eactivity increased significantly after exposure to O-3 with or withou t H2SO4. Changes in mean lung function and bronchial reactivity with O -3 + H2SO4 exposure were modestly larger than changes with O-3 exposur e, but the differences were nonsignificant or marginally significant. A minority of individual asthmatic and nonasthmatic subjects showed su bstantially greater declines in function with exposure to O-3 + H2SO4 relative to O-3 alone. Repeat exposure studies of these subjects again showed an excess response to O-3 + H2SO4 on the average, but there wa s no significant correlation between the excess responses of individua l subjects in the original and repeat studies. We conclude that for ty pical healthy or asthmatic adults heavily exposed to acid summer haze, O-3 is more important than H2SO4 as a cause of short-term respiratory irritant effects.