28 



anthropogenic light extinction among source types. 



Reducing emissions for visibility improvement could help alleviate other air- 

 quality problems, just as other types of air-quality improvements could help 

 visibility. 



Emissions that contribute to regional haze also contribute to a variety of 

 other undesireable effects on the environment and human health. S0 2 and N0 X 

 are precursors of acid deposition. N0 X and VOCs are precursors of ground- 

 level ozone. Fine particles are a respiratory hazard, and can influence 

 climate by interacting with incoming solar radiation and by modifying cloud 

 formation. Policy makers should consider the linkages between visibility and 

 other air-quality problems when designing and assessing control strategies. 



In summary, any effective visibility protection program must be aimed at 

 preventing and reducing regional haze. An effective program must, therefore, 

 control a broad array of sources over a large geographic area. Such a program 

 would mark a considerable break from the present approach of focusing on 

 visible plumes from nearby sources and of attempting to determine the effects 

 of individual sources on visibility impairment. 



Although visibility impairment is as well understood as any other air 

 pollution effect, gaps in knowledge remain. Filling these gaps will require 

 an increased national commitment to visibility protection research. With 

 major shifts projected in present patterns of pollutant emissions, the 

 committee believes that the time has come for Congress, EPA, and the states to 

 decide whether to make that commitment. 



