Respiratory effects of mixed nitrogen dioxide and sulfur dioxide in human volunteers under simulated ambient exposure conditions

Abstract

Normal and asthmatic volunteers ( N = 24 and 19, respectively) were exposed to mixed nitrogen dioxide (NO 2) and sulfur dioxide (SO 2) in purified background air in an environmental chamber under conditions simulating an ambient pollution episode. The NO 2 concentration was 0.5 ppm; the SO 2 concentration was 0.5 ppm for normals and 0.3 ppm for asthmatics. Exposures lasted 2 hr and included intermittent exercise and heat stress. Control studies consisted of similar exposures to purified air alone. The mixed pollutant gases may have reacted chemically in the exposure chamber, but no appreciable amounts of sulfate or nitrate aerosol were detected there. Group mean lung function changes during exposure generally were not significantly different from control for normals or for asthmatics. Symptoms reported by the normal group showed a small significant overall increase during pollutant exposure and later the same day relative to the corresponding control periods; the asthmatics showed a small significant increase later in the day but not during exposure. The increased symptom reporting showed little consistency from subject to subject: there were small increases for most individual symptom categories evaluated, none of them statistically significant. The results are not sufficient to establish whether this slight and nonspecific clinical response should be attributed to the pollutant mixture or to some other aspect of the exposure protocol.