Human Perception of Visual Air Quality

Abstract

The characterization of visibility should involve a selection of physical variables that (1) correlate with human perception, and (2) can be directly measured with appropriate instrumentation. To address these questions, the National Park Service in cooperation with US Environmental Protection Agency formulated a field program that involved a visitor survey. Visitors to Canyonlands National Park were asked to rate slides, on a scale of 1 to 10, that represented various levels of visual air quality of a pre-selected vista. In addition visitors rated on the same scale the visual air quality on the day that they visited the park. Objectives of the study included (1) evaluation of existing visibility indicators, such as visual range, contrast, etc. in their ability to characterize visual air quality, (2) formulate new physical variables that are better suited for characterization of visibility, and (3) establish the functional relationship between new and old physical variables and human perception.