Estimating Mortality Risk Reduction and Economic Benefits from Controlling Ozone Air Pollution (2008)Board on Environmental Studies and Toxicology
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Ozone, a key component of smog, can cause respiratory problems and other health effects. Evidence of a relationship between short-term exposure to ozone and mortality has been mounting, but because interpretations of the evidence have differed, the U.S. Environmental Protection Agency asked the Research Council to analyze the ozone-mortality link and assess methods for assigning a monetary value to lives saved. The report concludes that short-term exposure to current levels of ozone in many areas contributes to premature deaths and that such deaths are more likely among individuals with pre-existing diseases and other susceptibility factors but not limited to people who are already within a few days of dying. The link is strong enough that the EPA should include ozone-related mortality in its health-benefit analyses for future ozone standards. The report also concludes that if ozone has a threshold -- a concentration of ozone below which exposure poses no risk of death--it is probably at a concentration below the current public health standard. To compare the costs and benefits of steps taken to mitigate ozone, EPA assigns a monetary value to the avoided deaths by using what is known as a value of a statistical life (VSL). However, EPA assigns the same value to all lives regardless of the age or health status of the population experiencing the change in mortality risk. The report concludes that current evidence is not sufficient to determine how EPA should shift the VSL but that such adjustments may be appropriate in the future. The committee that wrote the report was not asked to consider how evidence is used by EPA to set ozone standards, including the new public health standard set by the agency last month.
- Deaths related to exposure to ozone are not restricted to people who are at high risk of death within a few days.
- Distributed- lag analyses appear to capture the overall effects of ozone better than do single-day models, but there have been relatively few such analyses.
- If further confirmed, the weak current evidence from cohort studies of an association of premature mortality with longer-term exposure would support the notion that effects seen in time series studies reflect only a portion of the total effect.
- Preliminary results indicate that the effect of acute ozone exposure on mortality is likely to be larger than average in persons with pre-existing disease, especially lung and heart diseases.
- The association between short-term changes in ozone concentrations and mortality is generally linear throughout most of the concentration range, although uncertainties make it difficult to determine whether there is a threshold for the association at the lower end of the range.
- The committee concludes from its review of the health-based evidence that short-term exposure to ambient ozone is likely to contribute to premature deaths.
- The empirical evidence is insufficient to support a specific quantitative adjustment of WTP estimates to account for differences in remaining life expectancy, but it does not reject the general concept that such adjustments may be appropriate.
- The evidence is insufficient to support a specific adjustment of the aggregate willingness to pay for reduction in annual mortality risk on the basis of differences in remaining life expectancy.
- The weak current evidence from cohort studies of an association of premature mortality with chronic exposure to ozone suggests that risks may be larger than those observed in acute effects studies alone.
- There is a lack of observed association between ozone and mortality during periods when ozone is low, such as winter.