Journal zyxwvutsrq of Environmental Psychology zyxwvu (1983) 3. zyxwv 129-145 URBAN VISUAL AIR QUALITY JUDGMENTS: RELIABILITY AND VALIDITY THOMAS R. STEWART, PAULETTE MIDDLETON AND DANIEL ELY Environmental and Societal Impacts Group, National Center for Atmospheric Research,* Boulder, Colorado 80307, U.S.A. Abstract A procedure based on judgments of human observers for measuring visual air quality in urban areas is described, and its reliability and validity are examined using the results of several studies conducted in a metropolitan area. It is concluded that the procedure provides a measure that is sufficiently reliable and valid to warrant its use in studies of the causes and consequences of changes in visual air quality. Substan- tial agreement was found among individuals with regard to judgments of visual air quality, but the possibility of differences between experienced and inexperienced observers requires further investigation. The paper provides an example of methods that can be used, and issues that should be addressed, in the development of perceived environmental quality indices. Introduction The protection of visual air quality (VAQ) is an emerging concern in the evaluation of policies, projects, and other actions that affect air quality. The Clean Air Act, for example, provides for the preservation of visual air quality in pristine areas in the United States of America. In urban areas air quality policy has dealt primarily with the health-related effects of air pollution. Visual air quality, however, is likely to become an important concern, particularly in western U.S. cities which have a tradition of relatively clear air and mountain vistas. Since woodburning for home- heating and sale of diesel automobiles, both of which lead to higher emissions of visibility-reducing pollutants, have been increasing, the likelihood of significant change in visual air quality is growing. Since visual air quality is one of the primary sources of information that people use to evaluate air pollution (Barker, 1976), changes in visual air quality can have significant political implications. Studies of urban visual air quality that will provide the scientific basis for urban planning or regulation require the development of a sound measure or ‘perceived environmental quality index’ (Craik and Zube, 1976) for VAQ. Daniel (1976) discussed the importance of demonstrating the reliability, validity, and usefulness of such indices. Despite the importance of VAQ, procedures for measuring VAQ in urban areas and for predicting the impact of policies on VAQ have not yet been established. Visual air quality depends upon the effect of the atmosphere on the visual experience of a person viewing an outdoor scene. It is distinct from other non-visual impacts of air quality, such as health effects or economic effects. A judgment of visual air quality is an aesthetic judgment based on those visually perceived elements of scenes *The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research and is sponsored by the National Science Foundation. 02724944/83/020129 zyxwvutsr + 17 $03.00/0 zyxwvut 0 1983 Academic Press Inc. (London) Ltd