Visibility has improved dramatically in the US, due largely to the Clean Air Act and Regional Haze Rule.

Our National Parks and Wilderness Areas possess many stunning vistas and scenery. Unfortunately, these scenes are diminished by uniform haze causing discoloration and loss of texture and visual range. Layered hazes and plume blight also detract from the scene.  Recognizing the importance of visual air quality, congress included legislation in the 1977 Clean Air Act to prevent future and remedy existing visibility impairment in Class I areas.  To aid in the implementation of this legislation, the IMPROVE program was initiated in 1985.  This program implemented an extensive long term monitoring program to establish the current visibility conditions, track changes in visibility and determine causal mechanism for the visibility impairment in the National Parks and Wilderness Areas.

As the result of reduced emissions due to the Clean Air Act and Regional Haze Rule, as well as the ongoing efforts of IMPROVE and other state, regional and national programs, visibility has improved dramatically in the US.  However, new sources related to climate change and oil and gas development are expected to impact all aspects of air quality in the US, including visibility, and continued efforts are needed to ensure that impacts from new and existing sources are well understood and controlled.