On Friday, EPA released its “Policy Assessment for the Review of the Ozone National Ambient Air Quality Standards.” EPA staff concluded:
that it is appropriate in this review to consider a revised primary O3 standard level within the range of 70 ppb to 60 ppb. A standard set within this range would result in important improvements in public protection, compared to the current standard, and could reasonably be judged to provide an appropriate degree of public health protection.
As staff noted, the Clean Air Science Advisory Committee made the same recommendation. I therefore think it’s game over for the current standard. Whatever the politics surrounding the ozone NAAQS, I just don’t think that a decision by EPA to retain the current standard would survive judicial review.
The real question, then, is how low EPA will actually go. Both CASAC and staff hedged their bets by recommending a range of 70 ppb to 60 ppb. Basically, a standard of 70 ppb would appear to provide a “margin of safety” for all impacts other than “the lowest exposure concentration demonstrated to result in lung function decrements and pulmonary inflammation (i.e., 60 ppb).”
It’s worth noting that, if Gina McCarthy wants to use lung function decrements as the basis for the NAAQS, even 60 ppb may not be enough, because it provides no margin of safety. Thus, if I were forced to bet, I’d predict a new NAAQS at 70 ppb. I don’t think it will save EPA from criticism on the right, but it’s a reasonable balancing act.
I think you are correct. In court it may become apparent that we tend to focus sharply on the individual numbers, e.g., 70 or 60 ppb, but tend to forget that these often are derived at least in part from controlled experiments where the exposure is limited to the pollutant of interest. In reality, ambient exposures are always “multi-parametric” including all other pollutants and lifestyle choices (e.g., smoking, commuting in heavy traffic, etc.). As such, the real damage thresholds are a function of some mix of additions, synergies and antagonisms that are not generally re-created in the lab. Hence, the “margin of safety” philosophy specified in the Clean Air Act.