Air pollution indices and other environmental quality indicators have often been subjects of debate. This article presents a case study of the creation and criticism of an air pollution index in Pittsburgh, Pennsylvania. Long known for its industrial production and the resulting pollution, Pittsburgh was home to engineers, scientists, institutions and corporations that developed new air pollution monitoring technologies in the years after World War II. These newly automated instruments were used as a part of a computerized monitoring network built in the late 1960s by the Allegheny County Health Department. County engineers created a daily air pollution index to summarize the information from the network, leading to public debates over the intent, meaning, and representation of air quality data. This case study serves to illustrate the inherent complexity of creating accessible, understandable, and uniformly acceptable indices of environmental quality. It also emphasizes the importance of understanding the social and political context in which data is collected, organized, and interpreted.