Estimating the Potential Health Benefits of Air Quality Warnings.

National, state, and local air quality authorities issue warnings urging residents to stay indoors or to take other precautions when pollutant levels are expected to exceed defined thresholds. Previous work explores the impact of warnings on specific activities but not the health improvements that might result if individuals fully responded to the recommendations. We estimate these potential health impacts using recent pollution data in three U.S. locations: Denver, Colorado; Los Angeles, California; and Pittsburgh, Pennsylvania. We focus on mortality risks among the elderly, who are particularly vulnerable. Under the strong assumptions of no infiltration and no offsetting indoor sources, we estimate that the benefits associated with avoiding ambient ozone and fine particle exposure are generally less than $14 per person for one additional hour spent indoors on days when air quality thresholds are exceeded. These estimates are sensitive to assumptions regarding the relationship between decreased exposure and mortality risks. Individuals' decisions to stay indoors likely depend on the value of the health benefits compared with the value of forgone work and leisure activities. While the national warning system provides flexibility and allows individuals to tailor their responses to personal circumstances, our analysis suggests that its benefits under typical conditions are small. The benefits of warnings under wildfire or other extreme conditions may be much greater.