control to meet ambient SO2 air quality standards). Under the emissions control strategy, it is assumed that ambient levels of SO2 would not increase on the average, and would probably continue to decrease in urban areas. Under the dispersal strategy, the analysis in Chapters 6 and 7 suggests that there would be a small general increase in ambient SO2 levels in urban areas, a substantial increase in ambient SO2 levels in rural areas,* and a larger (40–175 percent) increase in the acidity of precipitation.

To place the problem in economic perspective, the dispersal strategy would result in an increase in annual emissions of about 20 109 pounds of sulfur (19 106 tons SOx) in the U.S., according to Table V in Chapter 6. Accordingly, an effect which leads to environmental costs of about $200 million per year would correspond to an average incremental cost of 1 cent per pound of sulfur emitted. Since other effects (e.g. those on human health and materials) are thought to involve costs substantially larger than 1 cent per pound of sulfur emitted (Chapter 13), the only tangible ecological effects that merit detailed consideration are those that involve nationwide economic costs of at least this amount.** To anticipate the results of this survey, none of the known tangible effects would involve costs of more than a few cents per pound of sulfur. However, some weight should be given

*  

It is assumed that a well-conducted dispersal strategy would relieve the damage now being caused by existing low-level point sources, but would lead to a general increase in ambient concentrations, roughly in proportion to the increase in emissions (i.e. by about 65 percent according to Table V in Chapter 6).

**  

This statement is not intended to deny the importance of intangible effects, such as effects on aesthetics, recreational opportunities, or unique natural assets; such effects need to be weighed together with tangible costs and benefits Nor is it intended to deny the importance of local damage around individual point sources, which may justify specific local measures to limit emissions or to provide compensation.



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