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EVALUATION OF WHITED · 15 currently require BART only when visibility impairment is Reasonably attribut- able. to an existing major stationary source (U.S. EPA, 1980~. EPA preliminarily attributed haze in the GCNP to NGS (U.S. EPA, 1989~. This is the first attempt by EPA to regulate an existing source under Section 169A. The agency is in the process of deciding whether to make its attribu- tion final and, if so, determining what level of control of air pollution from NGS would constitute BART, as defined in Section 169A(g) of the act. The agency placed ~ the public docket (EPA Docket No. A-89-02-A) a draft notice of proposed rule making pursuant to Section 110(c) of the Clean Air Act. The proposal would require that NGS reduce emissions to 0.1 Ib SO2/ million btu, which would reduce the level of allowable emissions by 90%. EPA believes that an approximately 90% reduction in emissions would be re- quired to meet the emission limit reliably. THE NRC COMMITTEE STUDY The Committee, Its Charge, and Its Approach This evaluation of WHITEX was prepared by the Committee on Haze In National Parks and Wilderness Areas, which was convened in February 1990 by the National Research Council's Board on Environmental Studies and Toxicology in collaboration with the Board on Atmospheric Sciences and Climate of the Commission on Geosciences, Environment, and Resources. The committee comprises members appointed for expertise In meteorology, atmospheric chemistry, atmospheric aerosols, air pollution monitoring and modeling, statistics, environmental engineering, control technology, and env~- ronmental law and public policy. The committee's overall charge is: to develop working principles for assessing the relative importance of anthropogenic emission sources that contribute to haze in Class I areas and for assessing alternative source control measures; and to recommend strategies for improving scientific understanding and technical information on relative source contributions to haze formation, regional and seasonal factors affecting haze, relevant air quality models, and various emission control measures. The committee's work is sponsored by the U.S. Department of the Interior (National Park Service, Bureau of Reclamation, and Office of Environmental