According to press reports, EPA is preparing to ignore possible deaths caused by concentrations of pollutants occurring below the national ambient air quality standards (NAAQS). This is a key issue in a lot of decisions about pollution reduction. For instance, there is no NAAQS for mercury, but pollution controls on mercury would, as a side benefit, reduce pollution levels of harmful particulates. According to EPA’s prior cost-benefit analyses, those reductions could save many lives even in areas where current levels of particulates are below the NAAQS. Scientists see no reason to think that particulates in those areas are harm-free. But EPA now seems poised to ignore those saved lives. There’s a seeming logic behind that stance, but it’s fundamentally wrong.

The logic is simple — as simple as a magician pointing out she has nothing up her sleeves. The NAAQS is supposed to be set at a level that will protect human health with an ample level of safety. Hence, there must be no risk if the pollution level is below the NAAQS, or at least no risk that the Clean Air Act recognizes. So when EPA is passing rules to reduce mercury or carbon dioxide, it can …