25 



plant only 25 km from the Grand Canyon National Park (GCNP) boundary, 

 Illustrates the difficulty of quantifying individual source contributions. 

 The WHITEX report by the National Park Service, cited during your 1990 

 hearings as state-of-the-art information, attributed to NGS specific levels of 

 visibility impairment within GCNP. Based on qualitative reasoning, our 

 committee's interim report concluded that NGS did contribute significantly to 

 haze in GCNP at some times during the study period. Our report noted that the 

 standard of proof required by the Clean Air Act (§169A) was only that a source 

 emit a pollutant that "may reasonably be anticipated" to contribute to 

 impairment of visibility in such a Class I area. However, our report rejected 

 WHITEX' quantitative determination of the haze fraction attributable to NGS 

 emissions, citing weaknesses in both data and data analyses. Moreover, it 

 found no consensus on the availability of quantitative apportionment methods 

 that might be more appropriate. 



Assessing individual source contributions to haze will remain useful in some 

 situations. For example, a regional emissions management approach to haze 

 might be combined with a strategy to assess whether locating a new source at a 

 particular location would have especially deleterious effects on visibility. 



Visibility policy and control strategies might need to be different in the 

 Vest than in the East. 



Typical visibilities in the East are much lower than those in the West because 

 of the much higher pollution levels there, exacerbated by higher humidities. 

 The East contains a large population to enjoy the everyday benefits of any 

 improvement in visibility in that region, while the West contains most of the 

 nation's large national parks and wilderness areas. Many western views can be 

 fully appreciated only when visibility is excellent, and such views are 

 particularly vulnerable to increases in pollution levels. 



In the East, sulfates derived from the S0 2 emissions of coal-fired power 

 plants account for about one-half of all anthropogenic light extinction. 

 Reductions in these emissions are expected to occur in the next two decades as 

 a result of the 1990 Clean Air Act Amendments' acid rain control program. The 

 acid rain controls alone should yield a reduction of almost one quarter in 

 average anthropogenic light extinction. 



In the West, no single source category dominates. An effective western 

 visibility strategy will therefore have to address many source types, such as 

 electric utilities, gasoline- and diesel-fueled vehicles, petroleum and 

 chemical industry sources, forest-management burning, and fugitive dust. 

 Present rapid population growth in the West is projected to continue during 

 the coming decades, bringing with it the potential for increases in many 

 categories of emissions. 



