The general effects of urban atmospheric pollutants on incoming solar radiation have been observed for many years. Estimates of shortwave depletion usually fall in the 15-20% range (Landsberg, 1956, p. 589), but only a few studies have concentrated on depletion across the spectrum. Such studies have generally been concentrated on absorptive effects of gases in the infrared and the ultraviolet (see Kondratyev, 1969 and Robinson, 1966 for examples). The visible spectrum has largely been ignored. Essential to a study of urban spectral depletion effects is a properly chosen rural background site for comparison purposes, free from urban influences. The results of this type of comparison would be of interest to many fields, including plant growth studies, architectural planners, animal husbandry, and others.
Bridgman, H.A. 1974. The Cedar-Sauk Field Station as a background site for urban-rural spectral comparisons of direct beam solar radiation in the visible. 7(2): 4-7.