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

Adult male volunteers were exposed to ozone (O3) at 0.25, 0.37, or 0.50 ppm, and to O3 in combination with nitrogen dioxide (NO2) 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 O3, with 0.25 ppm 03 plus 0.30 ppm NO2, or when 30 ppm CO was added to the latter mixture. With 0.37 ppm O3, more symptoms were present and some subjects developed definite decreases in pulmonary function. With 0.50 ppm O3, 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.