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One form of air pollution, haze, degrades visibility in many American cities and scenic areas. Haze is caused when sunlight encounters tiny pollution particles in the air, which reduce the clarity and color of what we see. A national visibility goal was established in the federal Clean Air Act (CAA) as "the prevention of any future, and the remedying of any existing, impairment of visibility in 156 mandatory Federal Class I areas in which impairment results from manmade air pollution." The U.S. EPA developed the federal Regional Haze Rule, which requires all states to submit a State Implementation Plan (SIP) to mitigate their contribution to regional haze visibility impairment in Class I areas. Indiana does not have any Class I areas; however, Indiana sources have been determined to impact visibility in Class I areas in other states.
Indiana has been working to comply with all of the requirements of the Regional Haze Rule since its publication on July 1, 1999. Much work was done leading up to the creation of the following SIP documents, work that is now part of the IDEM Regional Haze Archive.