Yesterday, EPA formalized its decision to leave the ozone NAAQS unchanged, at 70 ppb. I don't think that this decision is in the same category of egregiousness as EPA's recent decision not to reduce the PM2.5 NAAQS. After all, only one decision can be the single worst environmental policy of an entire administration.
I'm not that close to the science on the ozone NAAQS, but I have the sense that the ozone evidence is just more of the same in the past four years; it's nothing like the seeming flood of evidence we've seen concerning the risks of PM2.5 at sub-NAAQS exposures. We do need to remember that there was some substantial evidence in 2015, when EPA adopted the 70 ppb standard, that there are risks at concentrations below 70.
The real question is what we mean by an "adequate margin of safety." As I have previously noted, this is really a policy question, not a scientific question. On the other hand, it's not an infinitely malleable concept and it's pretty clear that questions of background or the cost-effectiveness of the controls necessary to get to a level below 70 ppb are not relevant to whether a NAAQS set at an particular level in fact attains an "adequate margin of safety." The adequate margin of safety is what it is; whether we as a society want to spend the money necessary to ensure that there is an adequate margin of safety is a different question.
Conceptually, I understand why Congress made the choice that it did. Let's first answer the scientific question regarding what level is "safe." Then we can figure out how we get to that "safe" level and whether society is prepared to spend the money to do so. Unfortunately, the structure of the Clean Air Act - not to mention the state of our politics in 2020 - doesn't permit a rational discussion regarding the policy choices that flow from the "how safe is safe" decision.
And so we end up with what's supposed to be a scientific question becoming infected with implicit policy questions, which perverts the answer to the scientific question. From a legal point of view, it's the conservative justices, who say that they care about what words Congress actually uses in writing legislation, who should be the quickest to reverse both Trump NAAQS decisions. From a purely etymological point of view, it's difficult to conclude that either the PM2.5 NAAQS or the ozone NAAQS currently protect the public health with an adequate margin of safety when there is substantial - even if not definitive - evidence that there is significant morbidity and mortality associated with exposures below the current NAAQS.
Do I expect the current conservative Supreme Court majority to do as I suggest? No, but it would not be a bad litigation strategy for the public health advocates who will inevitably challenge both decisions to focus really sharply on just how much flexibility there can be in the definitions of the words in the phrase "adequate margin of safety".
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