ABSTRACT
Impairment of a visual resource that results from air pollution can manifest itself in two distinct ways: as layered or uniform haze. Quantification of visual impairment resulting from either layered or uniform haze can be separated into two categories: the establishment of the amount of pollution that causes just noticeable differences in the appearance of a visual resource and a determination of the functional relationship between air pollution and perceived visual air quality. Judgments of visual air quality are examined as a function of position of plume in the scene, plume color and plume size. The chapter investigates how plumes and layered hazes affect peoples' judgments of visual air quality. Plume centerline contrast or AE can provide only partial indications or predictions of the impact that plumes will have on a scenic resource. The classic example of layered haze is a tight vertically constrained coherent plume.
