The Clean Air Act prevents visibility impairment - changes in visual range, contrast, and coloration caused by human activities - in three distinct programs: (1) national ambient air quality standards (NAAQS), (2) prevention of significant deterioration (PSD) in areas cleaner than the national standards, and (3) visibility protection in pristine areas such as National Parks. The 1970 amendments to the Act authorized the first program; the 1977 amendments made the second an express statutory requirement and authorized the third program.
Since the Clean Air Act drew attention to visual air quality, researchers have defined the various aspects of visibility, determined visibility trends in different regions of the country, described its value, identified regions where visibility has special significance and thus where it must receive immediate regulatory attention.
Regulators, moreover, have initiated the first phase of what will be a comprehensive visibility protection program for pristine parts of the country, mandatory Class I areas. This program extends some of the features found in the NAAQS and PSD programs and may have implications for visibility protection nationwide.
Joan Rae Hartmann, Analyst in Environmental Policy, Environment and Natural Resources Policy Division and Alison Holt, Intern, Environment and Natural Resources Policy Division.
CRS 85-736 ENR
May 8, 1985."
SuDoc# 14. 18/3
