Congress enacted a special "visibility protection" measure for the statutory Class I areas where visibility is an "important value." In the PSD title of the CAA, "Congress declares as a national goal the prevention of any future, and the remedying of any existing, impairment of visibility in mandatory Class I federal areas which impairment results from manmade air pollution." In this provision, Congress expressed the national desire to preserve the ability to see long distances, entire panoramas, and specific features associated with the statutory Class I areas.
EPA is still developing the regulatory program to assure "reasonable progress" toward the national visibility goal. Prodded by lawsuits, EPA issued so-called "Phase I" visibility regulations (40 C.F.R. 51.302, 40 C.F.R. 51.305, 40 C.F.R. 51.306) that address "plume blight" and other visibility impairment "reasonably attributable" to a specific source or sources. "Phase II" visibility regulations (40 C.F.R. 51.308, 40 C.F.R. 51.309) to address visibility impairment from "regional haze" were promulgated in 1999.
The visibility regulations attempt to protect visibility in mandatory Class I areas in several ways. Through "new source review," (40 C.F.R. 51.307) major new and modified sources may not receive an air quality permit if they will have an adverse impact on visibility within the Class I area. States must establish a monitoring strategy (40 C.F.R. 51.305 ) for evaluating visibility conditions, baselines, and trends and develop a long-term (10 to 15 years) strategy (40 C.F.R. 51.306) for making "reasonable progress" toward eliminating all manmade visibility impairment from mandatory Class I areas. Existing sources found to impair Class I visibility may have to retrofit pollution controls as a result of an analysis to determine best available retrofit technology (BART) (40 C.F.R. 51.302).
EPA's visibility regulations also allowed the federal land managers until December 31, 1985 , to identify "integral vistas," (40 C.F.R. 51.304 ) but the Secretary of the Interior declined to do so. "Integral vistas" are views from inside a mandatory Class I area looking outward to specific important panoramas or landmarks beyond the Class I area's boundaries, which views have scenic, scientific, or cultural importance to the Class I area. The National Park Service issued a preliminary list of integral vistas for its Class I areas on January 15, 1981 . Had these vistas been promulgated as final regulations, they would have become mandatory factors for the states to consider in the review of development activities that might impair the vistas. States would not have had to protect these vistas, but would have had to consider vista protection along with energy, economic, and other factors in the decision-making process. As a policy matter, the Department of the Interior has nevertheless encouraged the park service to seek protection of these park-related resources on a case-by-case basis in individual permit and SIP proceedings.
Implementing regulations for this provision are at 40 C.F.R. 51.300 through 40 C.F.R. 51.309.
More information can be found on EPA's Visibility web page.