On July 31, 1997, the U. S. Environmental Protection Agency proposed regulations for Regional Haze in the Federal Register (FR Vol. 62, No. 147). As drafted, the proposed regulation would severely impact future industrial development in areas near Class I areas, or at a minimum be very costly. Facilities located within 150 kilometers of a Class I area may also be affected as part of New Source Review or Prevention of Significant Deterioration permit applications for new operations or modifications to existing facilities. As part of the proposed regulation, EPA introduced the deciview (dv) metric to be used as part of visibility improvement and degradation evaluations. This metric will be more restrictive to industry than the newly promulgated National Ambient Air Quality Standards for particulate matter. This paper examines current dv calculation methodologies and presents examples of the extreme conservatism of the results. The relationship between variables in the methodologies and calculated dv changes are also examined. In addition, the paper presents a comparison of calculated dv values and visibility and meteorological parameters measured in the Bridger Wilderness Area. Based on these comparisons, threshold emission limits for dv changes are derived for a hypothetical facility. Finally, a comparison of industrial facility and prescribed burning visibility impacts is presented.
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