Human exposure to sulfur dioxide and ozone in a high temperature-humidity environment

In order to examine the role of high temperature and humidity in the possible synergistic action of ozone and sulfur dioxide on human pulmonary function previously reported by some investigators and repudiated by others, we randomly exposed eight healthy young male nonsmokers to filtered air, 0.4 ppm SO2, 0.4 ppm O3, and 0.4 ppm SO2 plus 0.4 ppm O3 at 35 degrees C--85% rh for 2 hours. Subjects exercised for 15 minutes of each half hour at a workload sufficient to elicit a minute ventilation of 30 liters (BTPS). Pulmonary function tests were performed prior to, during, and following exposure. Observed alterations in pulmonary functions in the SO2 + O3 exposure reflected the changes occurring during the O3 exposure, clearly indicating that no synergistic effects related to the additional presence of SO2 were evident in this study. We considered factors suggested as causes for a potential synergism in comparing the conflicting studies on O3 and SO2, and suggest that factors other than temperature-humidity and/or sulfate aerosol production must be sought.