In the sixth step, EPA estimated the human health benefits resulting from implementation of the proposed or alternative standards for each county in the continental United States and then summed across counties to give the national estimates. EPA estimated the reductions in the incidences of a number of human health effects (see Table 2-1). Although EPA indicated that a few additional health effects were quantified, the results were not included in the analysis. Human health effects that could not be quantified but were associated with exposure to the pollutants were also listed. The human health benefits were estimated on the basis of the differences in pre- and post-control air-quality data and quantitative concentration-response functions derived from the epidemiological literature. The Pope et al. (1995) study was used to determine mortality reductions resulting from PM reductions. For ozone, a meta-analysis of nine epidemiological studies was used to determine mortality reductions resulting from ozone decreases. Clinical studies were used to support data for effects of ozone exposure. One important assumption made in this analysis was that the health benefits were realized in the year in which the exposure reductions occurred. The benefits were monetized to derive a total benefits estimate that could be compared with the cost estimate.

The analytical uncertainty was partially reflected by providing a plausible range of benefits estimates.3 For the high-end estimates, an effects threshold of 12 µg/m3 was assumed for PM2.5-related long-term mortality, mortality benefits (deaths avoided) were estimated for reductions in ozone concentration using a meta-analysis of nine epidemiological studies, ancillary PM benefits were included in the ozone benefits estimates,4 and an approach based on the value of a statistical life (VSL) was used to monetize the mortality benefits. For the low-end estimate, an effects threshold of 15 µg/m3 was assumed for all PM2.5-related health outcomes, no mortality benefits were estimated for reductions in ozone concentration, no ancillary PM benefits were included in the ozone benefits analysis, and an approach based on the value of a statistical life year (VSLY) was used to value the

   

tions and emissions are proportionally related, and a quadratic rollback assumes a quadratic relationship between emissions and concentrations.

3  

EPA noted that the plausible ranges provided were not equivalent to upper and lower statistical confidence bounds.

4  

Reduction in precursors resulting from measures to control ozone formation will also result in reduction of PM. The benefits derived from the reduction in PM in this case are referred to as ancillary PM benefits.



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