The overall purpose of this report is: - to continue the ongoing process of producing periodic evaluations of the global air pollution situation in urban areas; - to continue to develop and advance the techniques used for evaluating air pollution monitoring data with regard to human exposure and the associated risks implied; - to prepare a background document for consideration by the forthcoming meeting of Government Designated Experts on the GEMS Health Related Monitoring Programme which is scheduled to be held in Geneva in June 1988.