FIGURE 1-4 Comparison of growth areas and emission trends. Note that the trends in the graph (except for aggregate emissions) did not change substantially in 1995; only the scale of the graph changed. SOURCE: EPA 2002a.

EPA (1997) estimated that the benefits that have accrued in human health and welfare as a result of the aforementioned decreases in pollutant emissions have been substantial. The estimated benefits include about 100,000 to 300,000 fewer premature deaths per year and 30,000 to 60,000 fewer children each year with intelligence quotients below 70. However, these estimates are highly uncertain (OMB 1997). They require quantification of the air quality responses to pollutant emission changes and quantification of the human health and welfare responses to those air quality changes. Because it is difficult to isolate the effects of air pollution exposures from those of other risk factors that humans face daily, little direct empirical evidence is available to carry out the latter quantification. As a result, assessments of the benefits of pollution control often rely on complex models instead of direct empirical evidence.7 These models, in turn, tend to depend on a variety of estimated input parameters and assumptions.

Even more uncertainty is added when the benefits are compared with the costs of regulatory compliance by using a cost-benefit analysis, which


A notable exception is lead, for which blood lead concentrations are used as a relatively straightforward indication of human health impacts (Mendelsohn et al. 1998).

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