A number of investigations have been published on relationships involving particulate sulfate over regions of North America. Elevated concentrations of sulfate and ozone have been identified as occurring during the same periods in the summer months of the year in the United States. Particle sulfur and particle mass measurements obtained from the regional monitoring stations (RAMS) in and around St. Louis, Missouri, during the Regional Air Pollution Study (RAPS) have been discussed previously. Ozone measurements made in the RAPS study have received separate consideration. The large extended series of concurrent measurements of fine particle sulfur, fine particle mass and ozone at both urban and nonurban locations in the St. Louis area provides an opportunity to examine relationships among these species in detail. The emphasis in this work will be on the patterns of concentration of these species particularly during periods of especially high concentrations, episodic periods.