Catalyst Summer 2017
Got Science?

The Science Is Robust. So Why Is the EPA Delaying the Ozone Rule?

Photo: Davild Iliff/Creative Commons (Wikimedia Commons)
The EPA’s delay of a new rule on ground-level ozone pollution—the main ingredient in smog—will allow more days with unhealthy air quality in Los Angeles (above) and many other US locales.


By Gretchen Goldman

When Environmental Protection Agency (EPA) Administrator Scott Pruitt recently announced a one-year delay on a new rule limiting ground-level ozone pollution—the main ingredient in smog—he cited “insufficient information.” Really?

As an air quality scientist, I’ve closely studied the data on ground-level ozone pollution and health and I can assure you we are standing on solid ground when it comes to the ozone rule.

In keeping with a vast body of scientific evidence, the rule was tightened in 2015 to allow no more than 70 parts per billion (ppb) of ozone in the atmosphere (down from 75 ppb in 2008). Ozone has been linked to a variety of health effects including emphysema and asthma attacks, and cities across the country continue to experience unsafe levels—especially as temperatures rise from climate change.

Here’s a quick rundown of just how robust the science is on the public health threat posed by ground-level ozone pollution. As part of the update to the ozone standard, the EPA’s Integrated Science Assessment on the rule runs to 1,251 pages. This peer-reviewed document, produced by EPA scientists, surveys the current scientific literature on ozone (including one of my own papers) and finds several “causal” and “likely causal” relationships between ozone pollution and health impacts including cardiovascular problems, total mortality, and long-term respiratory effects. Of note, the report identifies “a very large amount of evidence spanning several decades [that] supports a relationship between exposure to O3 [ozone] and a broad range of respiratory effects.”

The Clean Air Science Advisory Committee (CASAC), a group of external experts the EPA relies on, concluded that the standard should be tightened. In CASAC’s letter to the EPA administrator, the science advisors recommended a range of 60 to 70 ppb for the standard, while also noting that 70 ppb—while included in the recommended range—would not provide an “adequate margin of safety,” as the Clean Air Act mandates. CASAC actually proposed that the ozone rule be tightened to this range back in 2007.

The bottom line is this: the law specifically requires the EPA to set an ozone standard that protects public health with an adequate margin of safety based on science and science alone. The agency is legally prohibited from considering economic arguments. So, Administrator Pruitt, I have to ask: What is your definition of “insufficient”? Because I have looked at the science, and I can tell you the evidence is clear that, contrary to what you claim, we have more than sufficient information to act.

Gretchen Goldman is an atmospheric scientist and the research director for the Center for Science and Democracy at UCS. Read more from Gretchen on our blog, The Equation.