Measurements of atmospheric concentrations of CS2 were made at Philadelphia, PA and Wallops Island, VA. In relatively unpolluted air the mean CS2 level was approximately 38 pptv. At the Wallops Island site a CS2 level of 30 pptv was found in air that had spent an extended period of time over the Atlantic Ocean. Thus we estimated that the background CS2 level in the northern hemisphere is less than 30 pptv. In air which has been obviously influenced by anthropogenic sources, CS2 concentrations of 65 to 339 pptv were observed, the average being 150 pptv. This estimate of the CS2 background level and the published rate data for reactions of OH with CS2, OCS and SO2 revealed that CS2 can account for a maximum of 20 percent of the atmospheric QCS concentration and an upper limit of 33 percent of the background SO2 level.