Simulated-Photograph Technique as a Tool for the Study of Visibility Impairment

摘要

With the 1977 Clean Air Act amendment, visibility impacts of anthropogenic emissions in national parks and wilderness areas assume increased importance. Existing sources that produce visibility effects may be required to clean up, and proposed new sources may be faced with new siting and emission control constraints. Consequently it is important to develop visibility models that can translate emissions, meteorology, and topography into visibility impacts. Furthermore, because many of the key decision makers identified in the Act are resource managers without training in air dispersion or radiative transfer, it is important to produce visibility models with easily understood outputs. To meet these needs the reported visibility model and the simulated-photograph technique (SPT) were developed. The SPT transforms the results of visibility models into pictures that display the modification of a scene by air contaminants, thus producing outputs understandable to untrained persons. The SPT technique can be used to compare various models, identify important variables, and aid decision makers. The visibility model consists of several modules that compute light scattering by particles, air dispersion, and radiation transfer through a pollutant cloud. The features of the model, its limitations, and its uses along with those of the SPT are described. (ERA citation 05:007572)