The Ontario Air Pollution Study: identification of the causative agent.

Previously published data from the Ontario Air Pollution study are reviewed. It has been shown that there is a consistent association in summer between hospital admissions for respiratory disease in Southern Ontario, and daily levels of SO4, O3, and temperature. No association exists for a group nonrespiratory conditions. Multiple regression analyses are presented that show all environmental variables account for 5.6% of the variability in respiratory admissions and that if temperature is forced into the analysis first, it accounts for 0.89% of the variability only. Distribution plots of standardized residuals are presented. In June of 1983, there were an exceptional number of ozone episodes (defined as occasions when ozone was greater than 82 ppb for 3 or more hours in a calendar day) in this region. A separate analysis of hospital admissions for acute respiratory diseases for the month of June for several years shows no demonstrable excess in June of 1983; previously regional analyses have indicated that ozone is associated with increased levels in July and August over a 9-year period. It has also been found that daily SO4 data collected at one monitoring site in the center of the region are not correlated with respiratory admissions, whereas the SO4 values collected every sixth day, on different days of the week, at 17 stations in the region had the highest correlation with respiratory admissions.(ABSTRACT TRUNCATED AT 250 WORDS)