Critical factors in computing externalities for electricity resources

The New York State Environmental Externalities Cost Study and computerized externality model (EXMOD) are used to examine the specification of methods design and application facts in the computation of electricity externalities. The sensitivity is reported of externality estimates with alternative specifications for 15 different factors in the analysis, including the selection of facility type, site, and operating characteristics; air emission assumptions and air modeling procedures; dose-response assumptions; economic valuation assumptions and other modeling procedures and assumptions. Many factors influencing externality computations can be well specified in the analysis. Significant scientific uncertainty remains in the selection and application of air dispersion models, selection of air pollution thresholds for health impacts, reduced life span risks associated with ozone exposure and with long-term exposure to PM10, values for CO2 damages, and the value to be applied to increased risks of reduced life span for individuals age 65 or older. 44 refs., 11 tabs