A candidate standard air pollution index has been developed for use by State and local air pollution control agencies in reporting daily air quality conditions to the news media and the public. The proposed index, which was developed in consultation with State and local agencies, is based on the National Ambient Air Quality Standards and the Federal Emergency Episode Criteria. The index is a segmented linear function which utilizes the highest observed concentrations of each pollutant for the daily calculation of nondimensional numerical index values. Index values are cross-referenced to descriptor words which reflect the health effects implications of the measured pollution levels. A flexible reporting scheme and methods for conveniently calculating the index are described.