Experimental studies on human health effects of air pollutants. II. Four-hour exposure to ozone alone and in combination with other pollutant gases

Adult male volunteers were exposed to ozone (O/sub 3/) at 0.25, 0.37, or 0.50 ppm, and to O/sub 3/ in combination with nitrogen dioxide (NO/sub 2/) and carbon monoxide (CO), with secondary stresses of heat, intermittent light exercise, and repeated exposure. Few important physiological changes, and only mild symptoms, were found with 0.25 ppm O/sub 3/, with 0.25 ppm O/sub 3/ plus 0.30 ppm NO/sub 2/, or when 30 ppm CO was added to the latter mixture. With 0.37 ppm O/sub 3/, more symptoms were present and some subjects developed definite decreases in pulmonary function. With 0.50 ppm O/sub 3/, most subjects had symptoms and about half showed substantial pulmonary function decrement. In reactive subjects exposed on two successive days, changes were usually greater the second day, indicating that effects of successive exposures were cumulative.