Before discussing how the EPA established its ground-level ozone standards in 2010, let’s look at for the standards it established in 2008 under the second Bush administration. I found the following excerpt very informative: I took it from the EPA document National Ambient Air Quality Standards for Ozone (Final Preamble, 2011), from the section “2008 Decision on the Level of the Primary Standard”, and it starts on page 57. I copied and pasted the entire section, edited down the length, then interspersed the text with my comments. Paragraph breaks not in the original text are marked with a paragraph sign in brackets [¶].
First, the EPA explains why it couldn’t leave the standard as it was. There was too much evidence that ozone causes harm at then present concentration of 84 ppb. Notice how much seems to depend on personal judgement rather than on objective criteria. In other words, you can’t program a computer to set ozone standards.
This section presents the rationale for the 2008 final decision on the primary O3 standard as presented in the 2008 final rule (73 FR 16475). EPA’s conclusions on the level of the standard began by noting that, having carefully considered the public comments on the appropriate level of the O3 standard, EPA concluded that the fundamental scientific conclusions on the effects of O3 reached in the 2006 Criteria Document and 2007 Staff Paper remained valid. … In considering the available scientific evidence, EPA concluded that a focus on the proposed range of 0.070 to 0.075 ppm was appropriate in light of the large body of controlled human exposure and epidemiological and other scientific evidence. The 2008 final rule stated that this body of evidence did not support retaining the then current 0.084 ppm 8-hour O3 standard, as suggested by some commenters, nor did it support setting a level just below 0.080 ppm, because, based on the entire body of evidence, such a level would not provide a significant increase in protection compared to the 0.084 ppm standard. Further, such a level would not be appreciably below the level in controlled human exposure studies at which adverse effects have been demonstrated (i.e., 0.080 ppm).
On one hand, the EPA couldn’t be satified with the current standard: there was too much scientific research proving that 84 ppb harmed people’s health. Lowering the standard a little bit wasn’t worth it; that would help too little. On the other hand, as we will see below, the EPA did not want to go overboard. Setting the level at 60 ppb was going too far; it had no evidence that going that far would increase protection for human health. This left the EPA with a range between 70 and 75 ppb, but the evidence in itself didn’t point to a specific level within this range (p. 58):
[¶] The 2008 final rule also stated that the body of evidence did not support setting a level of 0.060 ppm or below, as suggested by other commenters. In evaluating the information from the exposure assessment and the risk assessment, EPA judged that this information did not provide a clear enough basis for choosing a specific level within the range of 0.075 to 0.070 ppm.
But now EPA must explain why it is going against the recommendations of its own advisory committee, CASAC (Clean Air Scientific Advisory Committee). What EPA seems to saying here is that CASAC wasn’t influenced by scientific considerations alone but also by their opinions about policy. The EPA Administrator Stephen Johnson, however, asserted his policy perogative, used his own judgement, and overruled CASAC (p. 58).
In making a final judgment about the level of the primary O3 standard, EPA noted that the level of 0.075 ppm is above the range unanimously recommended by the CASAC (i.e., 0.070 to 0.060 ppm). The 2008 final rule stated that in placing great weight on the views of CASAC, careful consideration had been given to CASAC’s stated views and the scientific basis and policy views for the range it recommended. In so doing, EPA fully agreed that the scientific evidence supports the conclusion that the current standard was not adequate and must be revised.
With respect to CASAC’s recommended range of standard levels, EPA observed that the basis for CASAC’s recommendation appeared to be a mixture of scientific and policy considerations. While in general agreement with CASAC’s views concerning the interpretation of the scientific evidence, EPA noted that there was no bright line clearly directing the choice of level, and the choice of what was appropriate was clearly a public health policy judgment entrusted to the EPA Administrator. This judgment must include consideration of the strengths and limitations of the evidence and the appropriate inferences to be drawn from the evidence and the exposure and risk assessments.
The EPA Administrator will now explain that his judgement differed from CASAC’s because he put different weight on the available evidence. The Adams studies which indicated health effects on healthy sujuects at 60 ppb in the laboratory were too limited. The exposure and risk assessments done by CASAC were too uncertain (p. 59).
[¶] In reviewing the basis for the CASAC Panel’s recommendation for the range of the O3 standard, EPA observed that it reached a different policy judgment than the CASAC Panel based on apparently placing different weight in two areas: the role of the evidence from the Adams studies and the relative weight placed on the results from the exposure and risk assessments. While EPA found the evidence reporting effects at the 0.060 ppm level from the Adams studies to be too limited to support a primary focus at this level, EPA observed that the CASAC Panel appeared to place greater weight on this evidence, as indicated by its recommendation of a range down to 0.060 ppm. … However, EPA more heavily weighed the implications of the uncertainties associated with the Agency’s quantitative human exposure and health risk assessments. Given these uncertainties, EPA did not agree that these assessment results appropriately served as a primary basis for concluding that levels at or below 0.070 ppm were required for the 8-hour O3 standard.
Now comes EPA’s final explanation for setting the ozone standard at 75 ppb. Note the interesting argument that if the standard is set at 75 ppb, most people will not be exposed to more than 70 ppb, probably because ozone levels are always lower indoors, and people are not always outdoors when ozone levels are at their highest. EPA also explains what would have convinced it that a standard lower than 75 ppb carried enough additional public health protection to justify itself (p. 60).
The 2008 final rule stated that … EPA decided to revise the level of the primary 8-hour O3 standard to 0.075 ppm. EPA judged … that a standard set at this level would be requisite to protect public health with an adequate margin of safety, including the health of sensitive subpopulations, from serious health effects including respiratory morbidity, that were judged to be causally associated with short-term and prolonged exposures to O3, and premature mortality. EPA also judged that a standard set at this level provides a significant increase in protection compared to the 0.084 ppm standard, and is appreciably below 0.080 ppm, the level in controlled human exposure studies at which adverse effects have been demonstrated.
[¶] At a level of 0.075 ppm, exposures at and above the benchmark of 0.080 ppm are essentially eliminated, and exposures at and above the benchmark of 0.070 are substantially reduced or eliminated for the vast majority of people in susceptible populations. A standard set at a level lower than 0.075 would only result in significant further public health protection if, in fact, there is a continuum of health risks in areas with 8-hour average O3 concentrations that are well below the concentrations observed in the key controlled human exposure studies and if the reported associations observed in epidemiological studies are, in fact, causally related to O3 at those lower levels. Based on the available evidence, EPA was not prepared to make these assumptions.
[¶] Taking into account the uncertainties that remained in interpreting the evidence from available controlled human exposure and epidemiological studies at very low levels, EPA noted that the likelihood of obtaining benefits to public health decreased with a standard set below 0.075 ppm O3, while the likelihood of requiring reductions in ambient concentrations that go beyond those that are needed to protect public health increased.
[¶] EPA judged that the appropriate balance to be drawn … was to set the 8-hour primary standard at 0.075 ppm. EPA expressed the view that a standard set at 0.075 ppm would be sufficient to protect public health with an adequate margin of safety, and did not believe that a lower standard was needed to provide this degree of protection. EPA further asserted that this judgment appropriately considered the requirement for a standard that was neither more nor less stringent than necessary for this purpose and recognized that the CAA [Clean Air Act — MHK] does not require that primary standards be set at a zero-risk level, but rather at a level that reduces risk sufficiently so as to protect public health with an adequate margin of safety.
So we see that the 2008 standard of 75 ppb was clearly a judgement call. There is no sure way of determining where exactly the costs of reducing ozone outweigh the health benefits. From reading the section, it seems almost like a gut decision what risks are acceptable and how much evidence is necessary to prove harm. I think it is no more than an educated guess where the balance lies, and in 2008, the EPA thought it lay at 75 ppb. Why did its opinion change in 2010? That is the subject of the next post.
The Environmental Analyst 
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