The Health Benefits of Reduced Tropospheric Ozone in California

Abstract

Californians are exposed daily to concentrations of ozone (O₃) that are among the highest in the United States. Recently, the state adopted a new 8-hr ambient standard of 0.070 ppm, more stringent than the current federal standard. The new standard is based on controlled human studies and on dozens of epidemiologic studies reporting associations between O₃ at current ambient levels and a wide range of adverse health outcomes. Clearly, the new O₃ standards will require further reductions in the precursor pollutants and additional expenditures for pollution control. Therefore, it is important to quantify the incremental health benefits of moving from current conditions to the new California standard. In this paper, a standard methodology is applied to quantify the health benefits associated with O₃ concentration reductions in California. O₃ concentration reductions are estimated using ambient monitoring data and a proportional rollback approach in which changes are specific to each air basin, and control strategies may impact concentrations both below and above the standard. Health impacts are based on published epidemiologic studies, including O₃-related mortality and morbidity, and economic values are assigned to these outcomes based on willingness-to-pay and cost-of-illness studies. Central estimates of this research indicate that attaining the California 8-hr standard, relative to current concentrations, would result in annual reductions of 630 cases of premature mortality, 4200 respiratory hospital admissions, 660 pediatric emergency room visits for asthma, 4.7 million days of school loss, and 3.1 million minor restricted activity days, with a median estimated economic value of $4.5 billion. Sensitivity analyses indicate that these findings are robust with respect to exposure assessment methods but are influenced by assumptions about the slope of the concentration-response function in threshold models and the magnitude of the O₃-mortality relationship. Although uncertainties exist for several components of the methodology, these results indicate that the benefits of reducing O₃ to the California standard may be substantial and that further research on the shape of the O₃-mortality concentration-response function and economic value of O₃-related mortality would best reduce these uncertainties.