Tag Archives: CASAC

EPA’s New Ozone Rule: Part 18

In our last post, we saw how EPA’s CASAC reacted strongly to its decision to make the secondary standard of ground-level ozone identical to the primary standard. That influenced EPA to reconsider its decision as reported in the document National Ambient Air Quality Standards for Ozone, Final Preamble, 2011 (p. 215):

In reconsidering the 2008 final rule in the 2010 proposal, the Administrator agreed with the conclusions drawn in the 2006 Criteria Document, 2007 Staff Paper and by CASAC that the scientific evidence available in the 2008 rulemaking continues to demonstrate the cumulative nature of O3 – induced plant effects and the need to give greater weight to higher concentrations. Thus, the Administrator concluded that a cumulative exposure index that differentially weights O3 concentrations represents a reasonable policy choice for a secondary standard to protect against the effects of O3 on vegetation during the growing season. The Administrator further agreed with both the 2007 Staff Paper and CASAC that the most appropriate cumulative, concentration-weighted form to consider is the sigmoidally weighted W126 form.

As EPA noted before, the amount of protection the primary standard would give to vegetation is uncertain, but the hint is that EPA is now prepared to err on the side of regulation. In this excerpt (p. 216), EPA argues that we can’t be sure that the primary standard can protect vegetation as well as the W126 standard. A comparison is hard to make because the results of such a comparison would likely differ from year to year, and because we don’t have enough data in the areas where the secondary standard might do the most good, in rural areas. (The paragraph sign [¶] indicates a paragraph break that I introduced that wasn’t there in the original text. The “8-hour average standard” is the primary standard, which averages ozone readings taken during an eight-hour period.):

The Administrator noted that… EPA proposed a second option of revising the then-current 8-hour average secondary standard by making it identical to the proposed 8-hour primary standard. The 2007 Staff Paper analyzed the degree of overlap expected between alternative 8-hour and cumulative seasonal secondary standards using recent air quality monitoring data. Based on the results, the 2007 Staff Paper concluded that the degree to which the current 8-hour standard form and level would overlap with areas of concern for vegetation expressed in terms of the 12-hour W126 standard is inconsistent from year to year and would depend greatly on the level of the 12-hour W126 and 8-hour standards selected and the distribution of hourly O3 concentrations within the annual and/or 3-year average period.

¶ The 2007 Staff Paper also recognized that meeting the then current or alternative levels of the 8-hour average standard could result in air quality improvements that would potentially benefit vegetation in some areas, but urged caution be used in evaluating the likely vegetation impacts associated with a given level of air quality expressed in terms of the 8-hour average form in the absence of parallel W126 information. This caution was due to the concern that the analysis in the 2007 Staff Paper may not be an accurate reflection of the true situation in non-monitored, rural counties due to the lack of more complete monitor coverage in many rural areas. Further, of the counties that did not show overlap between the two standard forms, most were located in rural/remote high elevation areas which have O3 air quality patterns that are typically different from those associated with urban and near urban sites at lower elevations. Because the majority of such areas are currently not monitored, there are likely to be additional areas that have similar air quality distributions that would lead to the same disconnect between forms. Thus, the 2007 Staff Paper concluded that it remains problematic to determine the appropriate level of protection for vegetation using an 8-hour average form. [emphasis mine — MHK]

Now here is the real rationale behind the secondary rule: cumulative exposure hurts plants more than it hurts humans. But why that should be? That question I can’t answer. The document continues (p. 217):

The Administrator also noted in the 2010 proposal that CASAC recognized that an important difference between the effects of acute exposures to O3 on human health and the effects of O3 exposures on welfare [of vegetation — MHK] is that vegetation effects are more dependent on the cumulative exposure to, and uptake of, O3 over the course of the entire growing season (Henderson, 2006c). The CASAC O3 Panel members were unanimous in concluding the protection of natural terrestrial ecosystems and managed agricultural crops requires a secondary O3 standard that is substantially different from the primary O3 standard in form, averaging time, and level (Henderson, 2007).

That concludes the EPA’s rationale in the document. Again, it seems to me that the decision was based on a judgement call. You may agree with me that there is less of a moral imperative to safeguard property and crops than there is safeguarding human life, so when evaluating the secondary standard, it makes even more sense to compare gains and losses. True, a secondary standard might improve agricultural crops, but is it worth the additional cost to industry to maintain that standard? That question is especially hard to answer when we don’t know exactly how much benefit the secondary standard would bring us above and beyond the primary standard. It’s a very tricky question. More about this in my final comments on the subject. In the meantime, let’s discuss how EPA standards are implemented.

EPA’s New Ozone Rule: Part 17

In our previous post, the EPA explained why it found a secondary standard necessary to protect vegetation Indeed, when EPA’s Clean Air Scientific Advisory Committee (CASAC) found out, they strongly objected. I can imagine that a journalist reporting on CASAC would use words like “furious”, “enraged”, “livid.” They let the EPA know in no uncertain terms how they felt as reported in the document National Ambient Air Quality Standards for Ozone, Final Preamble, 2011 (p. 212):

Following the 2008 decision on the O3 standards, serious questions were raised as to whether the standards met the requirements of the CAA [Clean Air Act — MHK]. In April 2008, the members of the CASAC Ozone Review Panel sent a letter to EPA stating “[i]n our most-recent letters to you on this subject – dated October 2006 and March 2007 – … the Committee recommended an alternative secondary standard of cumulative form that is substantially different from the primary Ozone NAAQS in averaging time, level and form — specifically, the W126 index within the range of 7 to 15 ppm-hours, accumulated over at least the 12 “daylight” hours and the three maximum ozone months of the summer growing season” (Henderson, 2008). The letter continued: “[t]he CASAC now wishes to convey, by means of this letter, its additional, unsolicited advice with regard to the primary and secondary Ozone NAAQS. In doing so, the participating members of the CASAC Ozone Review Panel are unanimous in strongly urging you or your successor as EPA Administrator to ensure that these recommendations be considered during the next review cycle for the Ozone NAAQS that will begin next year” (id.).

Now CASAC is going to really lay into the EPA!

The letter further stated the following views:

The CASAC was … greatly disappointed that you failed to change the form of the secondary standard to make it different from the primary standard. As stated in the preamble to the Final Rule, even in the previous 1996 ozone review, ‘there was general agreement between the EPA staff, CASAC, and the Administrator, … that a cumulative, seasonal form was more biologically relevant than the previous 1-hour and new 8-hour average forms (61 FR 65716)’ for the secondary standard. Therefore, in both the previous review and in this review, the Agency staff and its advisors agreed that a change in the form of the secondary standard was scientifically well-justified.

Unfortunately, this scientifically-sound approach of using a cumulative exposure index for welfare effects was not adopted, and the default position of using the primary standard for the secondary standard was once again instituted. Keeping the same form for the secondary Ozone NAAQS as for the primary standard is not supported by current scientific knowledge indicating that different indicator variables are needed to protect vegetation compared to public health. The CASAC was further disappointed that a secondary standard of the W126 form was not considered from within the Committee’s previously-recommended range of 7 to 15 ppm-hours. The CASAC sincerely hopes that, in the next round of Ozone NAAQS review, the Agency will be able to support and establish a reasonable and scientifically-defensible cumulative form for the secondary standard.” (Henderson, 2008)

Wow! You can almost feel the burning red-hot indignation behind this rhetoric which I suspect was toned down quite a bit. In our next post, we’ll see how the EPA reacted.

EPA’s New Ozone Rule: Part 14

In my previous post, we discussed the role of an assessment EPA had done estimating how many children from 12 metropolitan areas would be exposed to different levels of ozone. We’ll close this discussion of why the EPA chose the primary standard it did with these final comments from Jackson, taken from the document National Ambient Air Quality Standards for Ozone, Final Preamble, 2011. In this comment, she compares the exposure assessment we were discussing in the previous post to the assessment of risk of how many people are likely to experience health problems from ozone at different maximum levels. She still comes to the conclusion that a standard of .070 ppm is warranted but not lower than that (p. 182):

In considering the estimates provided by the risk assessment, the Administrator notes that significant reductions in health risks for lung function, respiratory symptoms, hospital admissions and mortality have been estimated to occur across the standard levels analyzed, including 0.084 ppm, the level of the 1997 standard, 0.080, 0.074, 0.070, and 0.064 ppm. In looking across these alternative standards, as discussed above in section II.A.2, the patterns in risk reductions are similar to the patterns observed in the exposure assessment for exposures at and above the health benchmark levels. In considering these results, the Administrator recognizes there is increasing uncertainty about the various concentration-response relationships used in the risk assessment at lower O3 concentrations, such that as estimated risk reductions increase for lower alternative standard levels so too do the uncertainties in those estimates. In light of this and other uncertainties in the assessment, the Administrator concludes that the risk assessment reinforces the exposure assessment in supporting a standard level no higher than 0.070 ppm, but it does not warrant selecting a lower standard level.

CASAC asserted that the ozone standard should be set between .060 and .070 ppm, but it preferred that the standard be set closer to 0.060. Jackson agreed with CASAC with its assertion but not with its preference, and she explains why (p. 183):

With regard to selecting a standard level from within that range, the Administrator observes that CASAC recognized that she must make a public health policy judgment to select a specific standard that in her judgment protects public health with an adequate margin of safety. The Administrator notes that CASAC found the relative strength of the evidence to be weaker at lower concentrations, and that their recommended range of 0.060 to 0.070 ppm allowed her to judge the appropriate weight to place on any uncertainties and limitations in the science in selecting a standard level within that range (Samet, 2011, p.9). The Administrator further notes that CASAC expressed the view that selecting a level below the current standard, closer to 0.060 ppm, would be “prudent,” in spite of the uncertainties (Samet, 2011, p.7-8), and that selecting a standard level at the upper end of their recommended range would provide “little” margin of safety (Samet, 2011, p.2).

In reaching her public health policy judgment, after carefully considering the available evidence and assessments, the associated uncertainties and limitations, and the advice and views of CASAC, the Administrator judges that a standard set at 0.070 ppm appropriately balances the uncertainties in the assessments and evidence with the requirement to protect public health with an adequate margin of safety for susceptible populations, especially children and people with lung disease. In so doing, she also concludes that a standard set at a lower level would be more than is necessary to protect public health with an adequate margin of safety for these susceptible populations. This judgment by the Administrator appropriately considers the requirement for a standard that is neither more nor less stringent than necessary for this purpose and recognizes 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. Further, this judgment is consistent with and supported by the advice and unanimous recommendation of CASAC to set a standard within a range that included but was no higher than 0.070 ppm.

So there you have it. The proposed standard of 0.070 ppm was not based on a mathematical equation or a set of rigid criteria. It was a judgement call, something with which reasonable people can disagree.

So far, we’ve been discussing the rationale of EPA’s primary ozone standard, meant to safeguard the pubiic health. Next, we’ll discuss the secondary standard, formulated to help preserve property and other economic interests.

EPA’s New Ozone Rule: Part 12

In my last post, we quoted the document National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, where the current Administrator of the EPA, Lisa Jackson (who recently announced she is leaving the agency) discusses why she decided to lower the maximimum ozone concentration limit from 0.075 ppm to between 0.060 and 0.070 ppm. Now she will explain to us how she chose the exact limit. Note that she tacitly acknowledges that she can’t demand more than is necessary. Choosing the optimal number won’t be easy, because the evidence doesn’t point to any such number (p. 174):

The Administrator next considered what standard level within the proposed range of 0.060 to 0.070 ppm would be requisite to protect public health, including the health of susceptible populations, with an adequate margin of safety — i.e., a level that is sufficient but not more than necessary to achieve that result. She recognizes that neither the health evidence nor the human exposure and health risk assessments provide any “bright line” for selecting a specific level within the proposed range.

She explains the difficulties: no laboratory studies in the range of .060 to .070 ppm, studies of people in the street indicate no particular threshold within this range, difficulty in extrapolating what we know about healthy people to people with asthma, and risk assessments made at only two levels: 0.070 ppm and 0.064 ppm. In short, no easy method of determining the best limit. Instead, she will need to base her judgement on many factors taken together (Note: The paragraph sign in brackets [¶] indicates a paragraph break that I introduced that isn’t in the original document. P. 174):

[¶]No controlled human exposure studies were conducted at intermediate levels between 0.070 and 0.060 ppm. Associations reported in epidemiological studies generally ranged from well above to well below this range, with no suggestion of a possible threshold within this range. While there is substantial evidence that asthmatics have greater responses than healthy, non-asthmatic people, there is uncertainty about the magnitude of the differences in their responses within this range. Moreover, within this range, exposure and health risk assessments estimated the exposures of concern and health risks only for standard levels of 0.070 and 0.064 ppm. Thus, there is a combination of scientific evidence and other information that the Administrator needs to consider as a whole in making the public health policy judgment to select a standard level from within the proposed range.

The Administrator declares the limit she selected (p. 175):

After weighing the strengths and the inherent uncertainties and limitations in the evidence and assessments, and taking into account the range of views and judgments expressed by the CASAC Panel, including CASAC’s most recent advice, and in the public comments, as discussed above, the Administrator finds the evidence and other information on the public health impacts from exposure to O3 warrant an 8-hour primary standard set at 0.070 ppm [emphasis mine — MHK]…

Jackson notes that the surest source of evidence, laboratory studies, offer scant evidence below the 0.080 ppm level other than the studies of Adams. In the interest of brevity I’m omitting that section. She goes on to discuss epidemiological studies, studies of people in the street. While they may not be as robust as laboratory studies, the large number of studies do offer enough evidence of a link between levels of ozone and bad health outcomes to make a judgement (p. 177):

With regard to epidemiological studies, the Administrator observes that statistically significant associations between ambient O3 levels and a wide array of respiratory symptoms and other morbidity outcomes, including school absences, emergency department visits, and hospital admissions, have been reported in a large number of studies. These associations occur across distributions of ambient O3 concentrations that generally extend from above to well below the proposed range, although the Administrator recognizes that there are questions of biological plausibility in attributing the observed effects to O3 alone at the lower end of the concentration ranges extending down to background levels.

However, Jackson does recognize that epidemiological studies have their drawbacks, as she discusses here. Samet assures her that although these studies are less reliable at concentrations that approach the natural ambient level, they are not less reliable at the 0.060 to 0.070 ppm range (p. 177):

[¶] The Administrator also recognizes the uncertainty inherent in translating information from such studies into the basis for selecting a specific level from within the proposed range. The Administrator notes that in its most recent advice, CASAC concluded that epidemiological studies are inherently more uncertain as ambient O3 concentrations decrease and effect estimates become smaller, although CASAC’s confidence in attributing reported effects on health outcomes to O3 did not change over the range of 0.060 to 0.070 ppm (Samet, 2011. p.10-11).

Now Jackson must make a value judgement. At what level concentration is the epidemiological evidence pointing to? (p. 178)

[¶]In weighing this evidence and the related uncertainties, the Administrator concludes that while the epidemiological evidence provides support for a standard set no higher than 0.070 ppm, it does not warrant selecting a lower standard level within the proposed range.

But what about people with respiratory problems? Perhaps they need a standard below 0.070 ppm. but she concludes that there is not enough information to choose a lower limit for that reason (p. 178).

The Administrator has also considered the evidence from controlled human exposure and epidemiological studies that children and adults with asthma and other lung diseases are likely to experience larger and more serious responses to O3 exposures than healthy, non-asthmatic people. … the Administrator recognizes that controlled human exposure studies conducted using healthy subjects likely underestimate effects in this susceptible population. The Administrator also recognizes, however, that there is uncertainty about the magnitude of any such differences in responses. Thus, the Administrator concludes that while this evidence supports taking into consideration the extent to which a standard would limit exposures of susceptible populations to concentrations at and above the 0.070 and 0.060 ppm benchmark levels, it does not further inform the translation of the available evidence of O3– related effects in healthy subjects into the basis for selecting any specific standard level from within the proposed range.

Perhaps some quantifiable data can shed some light on an appropriate level that will assist people with respiratory problems. That is the subject of my next post.

EPA’s New Ozone Rule: Part 11

In 2008, the EPA under Administrator Stephen Johnson revised the primary ozone standard to 75 ppb. He was succeeded the next year by Lisa Jackson, the appointee of the incoming Obama administration. Soon after, the EPA began its reconsideration of the new ozone standard, and Ms. Jackson decided to revise the standard, lowering it to 70 ppb.

Her rationale is recorded in the EPA document National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, pages 61 through 186. In this section, Jackson’s positions are summarized, then comments from interested parties appear together with EPA’s responses. A short piece summarizes the comments of the Clean Air Scientific Advisory Committee (CASAC), followed by the rationale for the final decision. A second section, pages 192 through 296, describes the rationale for the secondary standard, the standard meant to protect property and other interests.

It’s a lot to read, and I can’t say I read every word. However, the impression from what I did read was that Jackson wasn’t in possession of any evidence that Johnson didn’t have. Rather, she placed different weight on the evidence. What Johnson saw as sufficient to lower the primary standard to 75 ppb and no further, Jackson felt compelled to lower the standard down to 70 ppb. Here is the summary section “Conclusions on the Level of the Primary Standard”, page 167 ff., with my comments interspersed. The frequent references to Samet are to a 67-page letter written to Jackson in March 2011 from Dr. Jonathan M. Samet, chair of CASAC with the subject line Clean Air Scientific Advisory Committee (CASAC) Response to Charge Questions on the Reconsideration of the 2008 Ozone National Ambient Air Quality Standards. If you wish to read the letter, click here.

Note: The paragraph sign in brackets [¶] indicates a paragraph break that I introduced that isn’t in the original document.

To begin, let’s read what the Jackson set out to do in EPA’s own words:

As a result of the reconsideration, the Administrator has determined that a different level of the primary O3 standard than the 0.075 ppm level set in 2008 is requisite to protect public health with an adequate margin of safety. For the reasons discussed below, the Administrator has decided to set the level of the 8-hour primary O3 at 0.070 ppm…

What influenced her to make this decision?

In the 2010 proposal, the Administrator [Jackson — MHK] concluded it was appropriate to propose to set the primary O3 standard below 0.075 ppm. This conclusion was based on the evidence and exposure/risk-based considerations … and the Administrator’s determination that 0.075 ppm was a level at which the evidence provides a high degree of certainty about the adverse effects of O3 exposure on healthy people. The Administrator’s public health policy judgment on the proposed range for the level of the primary O3 standard was framed by the evidence and exposure/risk-based considerations discussed above in this notice and informed by the following key observations and conclusions on the controlled human exposure and epidemiological studies and the results of the human exposure and health risk assessments.

She will now state four reasons why the evidence suggests that the standard should be lowered (p. 168).

(1) There is a strong body of evidence from controlled human exposure studies evaluating healthy people at O3 exposure levels of 0.080 ppm and above that demonstrated lung function decrements, respiratory symptoms, pulmonary inflammation, and other medically significant airway responses. Newly available for the 2008 review, there is the limited but important evidence of lung function decrements and respiratory symptoms in healthy people down to O3 exposure levels of 0.060 ppm…

I believe Johnson had this same evidence. I suspect that if we sat the two administrators together, they would argue about the importance of limited evidence. When is limited evidence important evidence?

(2) A large number of epidemiological studies [studies that look at people in the street, not in the laboratory — MHK] have reported statistically significant associations between ambient O3 levels and a wide array of respiratory symptoms and other morbidity outcomes including school absences, emergency department visits, and hospital admissions. More specifically, positive and robust associations were found between ambient O3 concentrations and respiratory hospital admissions and emergency department visits… across distributions of ambient O3 concentrations that extend well below the 2008 standard level of 0.075 ppm…

The above is a powerful statement, which if true, would give good cause to lower the standard. But I would want to know what the contribution to morbidity outcomes is made by ambient O3 concentrations in the 0.075 – 0.070 ppm range. This is what we need to balance against any economic cost.

The next reason concerns people with respiratory problems and diseases. Note the concern that studies that look at only healthy people may be underestimating the effects of ozone on those with respiratory problems, although by how much is unknown:

(3) There is substantial evidence … indicating that children and adults with asthma and other preexisting lung diseases are at increased risk from O3 exposure… Evidence from controlled human exposure studies indicates that asthmatics are likely to experience larger and more serious effects in response to O3 exposure than healthy people. This evidence indicates that … controlled human exposure studies of lung function decrements and respiratory symptoms that evaluate only healthy, non-asthmatic subjects likely underestimate the effects of O3 exposure on asthmatics and other people with preexisting lung diseases. However, there is uncertainty about the magnitude of the differences in their responses such that we are not able to quantify the magnitude of any such differences.

Finally, a statement of confidence that lower ozone levels will improve public health:

(4) The assessments of exposures of concern and risks for a range of health effects indicate that important improvements in public health are very likely associated with O3 levels just meeting alternative standard levels evaluated in these assessments, especially for the alternative levels of 0.070 and 0.064 ppm, relative to levels at and above 0.075 ppm…

Now the following paragraph leads me to believe that Jackson did not base her decision on evidence that Johnson did not have. Rather, she interpreted the same evidence differently and was more accepting of CASAC’s recommendations (p. 171):

These observations and conclusions led the Administrator to propose to set the primary O3 standard at a level in the range of 0.060 to 0.070 ppm. In so doing she placed significant weight on the information newly available in the 2008 review that had been reviewed by CASAC, and took into consideration public comments that had been received during the 2008 review. She also placed significant weight on CASAC’s conclusion that important public health protections can be achieved by a standard set below 0.075 ppm, within the range of 0.060 to 0.070 ppm.

Here the document acknowledges the considerations that led Johnson to establish the 0.075 ppm standard, noting the value judgements he made (p. 171):

In reaching a final decision on the level of the primary O3 standard, the Administrator again considered whether the standard level of 0.075 ppm set in the 2008 final rule is sufficiently below 0.080 ppm to be requisite to protect public health with an adequate margin of safety. In considering this standard level, the Administrator looked to the rationale for selecting this level presented in the 2008 final rule… In that rationale, EPA observed that a level of 0.075 ppm is above the range of 0.060 to 0.070 ppm recommended by CASAC, and that the CASAC Panel appeared to place greater weight on the evidence from the Adams studies and on the results of the exposure and risk assessments, whereas EPA placed greater weight on the limitations and uncertainties associated with that evidence and the quantitative exposure and risk assessments. Additionally in 2008, EPA’s rationale did not discuss and thus placed no weight on exposures of concern relative to the 0.060 ppm benchmark level. Further, EPA concluded that “[a] standard set at a lower level than 0.075 ppm 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] is not prepared to make these assumptions.” (73 FR 16483).

Now Jackson is going to state where she disagrees with Johnson. This strengthens my impression that the decision to lower the limit was a judgement call about which reasonable people can differ (p. 172):

In reconsidering the entire body of evidence available in the 2008 rulemaking, including the Agency’s own assessment of the epidemiological evidence in the 2006 Criteria Document, the views of CASAC, including its most recent advice (Samet, 2011), and the public comments received on the 2010 reconsideration proposal, the Administrator finds no basis to change her conclusion that important and significant risks to public health are likely to occur at a standard level of 0.075 ppm. Thus, she judges that a standard level of 0.075 ppm is not sufficient to protect public health with an adequate margin of safety. In support of this conclusion, the Administrator finds that setting a standard that would protect public health, including the health of susceptible populations, with an adequate margin of safety should reasonably depend upon giving some weight to the results of the Adams studies and EPA’s analysis of the Adams’s data, and some weight to the results of epidemiological studies of respiratory morbidity effects that may extend down to levels below 0.060 ppm.

A limit of outdoor ozone concentration set at level X actually protects people from effects below X, since people spend much of their time indoors where ozone levels are naturally lower. Since they are likely to be indoors when the ozone level reaches X, their maximum exposure to ozone will probably be to levels much below X. Jackson’s argument here is that if setting the limit at 0.070 ppm will limit people’s exposure to ozone levels above 0.060 ppm:

[¶]Moreover, the Administrator concludes that, in setting such a standard, consideration should be given to how effectively alternative standard levels would serve to limit exposures of concern relative to the 0.060 ppm benchmark level as well as the 0.070 ppm benchmark level, based on EPA’s exposure and risk assessments…

So far, Jackson has explained why she feels that the limit of 0.075 ppm is inadequate. She wants to take CASAC’s recommendation of a limit between 0.060 and 0.070 ppm. But she needs to select an exact number. In my next post, she’ll explain how she did that.

EPA’s New Ozone Rule: Part 10

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.

EPA’s New Ozone Rule: Part 8

In 2008, the EPA under George W. Bush reduced the maximum allowable concentration of ground-level ozone from 80 ppb to 75 ppb1. Two years later, the EPA decided to reduce the limit still further to 70 ppb.2. What made the EPA decide to do so in only two years? This was unusual because the Clean Air Act only requires the EPA to review its policy on ozone once every five years, the next review required in 20133. What was the rush?

In April 2008, soon after the EPA lowered the standard, the Clean Air Scientific Advisory Committee (CASAC, EPA’s scientific advisory board on clean air4) sent the EPA a letter strongly disagreeing with the new standard, claiming that the new ozone standard was not low enough to provide a margin of safety. It wanted a primary standard between 60 and 70 ppb. In addition, CASAC felt that a different secondary standard should be established to protect property and the environment. This standard should be cumulative rather than be based on highest average readings5.

A month later, a number of groups challenged EPA’s standards in court. Some of them felt the standard went too far: business interests and some states. Other petitioners felt the standard did not go far enough: environmental organizations, public health organizations, and other states. These lawsuits were consolidated into one: State of Mississippi et al v. U.S. Environmental Protection Agency. In March 2009, the EPA filed an unopposed motion to hold the lawsuit in abeyance while it reviewed the new standard. 6 The revised standard, which lowered the maximum allowable concentration from 75 ppb to 70 pbb, was published in July 20117. In September 2011, the Obama administration requested that the EPA rescind its new standard8.

The document which lays out this new standard, National Ambient Air Quality Standards for Ozone, Final Preamble published July 7, 2011, lays out a detailed explanation of EPA thinking: why it didn’t think 75 ppb was a good enough standard, why 60 ppb was too low and 70 ppb was about right, and why it felt a new secondary standard to protect property and the environment was necessary9. I am going to try to summarize that thinking here.

Footnotes:

  1. U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, June 2012, p.lxxiii.
  2. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.6.
  3. United States Code, Title 42, Chapter 85, §7409 (d)(1). To view, click here.
  4. The Clean Air Act requires that an independent scientific body review the NAAQS at five-year intervals and make recommendations. CASAC currently fulfils this role. See United States Code, Title 42, Chapter 85, §7409 (d)(2). To view, click here.
  5. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.18.
  6. ibid.pp.29-30
  7. This is the National Ambient Air Quality Standards for Ozone, Final Preamble, 2011 that has been referred to above.
  8. Statement by the President on the Ozone National Ambient Air Qualities Standards. White House website. To view, click here.
  9. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011. The rationale for the primary standard (section II) starts on p. 34 and the rationale for the secondary standard (section III) starts on p. 192.

EPA’s New Ozone Rule: Part 6

Let’s look at EPA’s proposed ozone rule to see exactly what it entails. Unlike previous ozone rules, it has two distinct parts1:

  • A primary standard to protect human life and health.
  • A secondary standard to protect property, agriculture, and the environment.

Technically speaking, EPA rules always had primary and secondary standards, but up to now, the ozone primary and secondary standards were identical2. This is the first time that the two standards were made distinct, done at the urging of EPA’s Clean Air Scientific Advisory Committee (CASAC)3.

The two standards are different in character. The primary standard is based solely on averages4. If the average ozone concentration rises above a certain level, that location is in non-attainment. The secondary standard is based on cumulative exposure to ozone1. It is more focused on the effects caused by long-term exposure to ozone.

The new rule is making an interesting statement: it appears that with regards to human health we are more interested in the acute effects of high exposure. With property and agriculture, we seem more concerned with ozone’s long term effects. Yet the EPA is aware of that long-term exposure to ozone can degrade human health over time.

Now if a locale is to be in attainment, it presumably must meet both the primary and secondary standards. Sometimes one standard will be more stringent, sometimes the other. Consider locales which meet one standard and not the other. In one locale, ozone levels are usually very low. Occasionally, they peek to high levels, just often enough so that the locale does not meet the primary standard, yet the cumulative exposure to ozone remains low. In another locale, ozone levels are consistently high causing large cumulative exposure, but they fall just shy of breaking the primary standard. State and Federal authorities will need to keep track on two sets of numbers for each locale to enforce both standards.

The primary standard in the proposed rule is actually the same as in current rule, just a little stricter, the maximum concentration lowered from 75 ppb in the current rule to 70 ppb. The air is sampled frequently at a measuring station, and readings are averaged out over an eight-hour period. This yields 1,095 such averages in a calendar year (1,098 in a leap year). The three highest averages are thrown out and the fourth-highest average is used to represent the year’s maximum. The maximums from three consecutive years are then averaged together. If this composite average exceeds 70 ppb, that locale is considered in nonattainment1.

The secondary standard is a little more complicated but easily understandable if you remember your high school algebra. The values to be summed are not the ozone concentrations themselves but a calculation based on each reading of ozone concentration, called the W126 index5. To determine, the cumulative index, hourly readings of ozone concentrations are taken at an individual station 12 hours a day, starting at 8 a.m. and finishing at 7 p.m. A value Wi is then calculated as follows:

                                     Wi =        Ci                 
1 + 4403e –ACi

where:

Ci (read as “C sub i”) is the reading of ozone concentration measured in parts per million (ppm) taken at hour i. Because the W126 index is cumulative, Ci is in units of ppm-hours.

e is the base of natural logarithms, approximately equal to 2.71828.
A is a constant equal to 126/ppm-hour.

For example, suppose at 2:00 in the afternoon we measured an ozone concentration of .083 ppm. We would then calculate a W value for 2 pm this way:

             W2pm =                              .083 ppm-hours                   
                                1 + (4403)(e – (126/ppm-hour)(.083 ppm-hours))

This can easily be calculated with the help of a scientific calculator6 (note that the ppm-hours units cancel in the exponent as they should), yielding a value of 0.74 ppm-hours. This means that the ozone concentration at 2 pm will contribute slightly less to the cumulative total than if we did not use the formula (.074 ppm-hours versus .083 ppm-hours).

The Wi values are summed each day, giving a daily cumulative total:

Wdaily = ΣWi

summed from the first reading of the day at 8 am to the last reading at 7 pm.

The Wdaily values are themselves summed over a three-month period. As I understand it, these are running totals: January-February-March, February-March-April, March-April-May, and so on.

W126 = ΣWdaily

summed from the first day of each three-month period through the last day.

Thus, each calendar year produces ten W126 values, from January-February-March through October-November-December. The highest W126 value for the year is selected. This process is carried out for three consecutive years, producing three yearly maximum W126 values. The average of these three values is the final W126 value. If it is higher than 13 ppm-hours, then the area where the readings were taken is declared to be in non-attainment5.

For example, the following are fictitious highest W126 totals summed up during each of 2008, 2009, and 2010. All values are in ppm-hours:

Year Highest Value Period Summed
2008 15.2 Apr-May-Jun
2009 14.3 May-Jun-Jul
2010 12.9 Mar-Apr-May

The average of these three values is 14.1 ppm-hours. Since this is above the standard of 13 ppm-hours, the area from where these readings were taken is in non-attainment.

Why is the W126 index used? To quote A.S.L. & Associates, a Montana company whose founder developed the W126 index:

The W126 index is a cumulative exposure index that is biologically based. The W126 ozone index focuses on the higher hourly average concentrations, while retaining the mid- and lower-level values. By applying a continuous weighting, the W126 index has the advantage of not utilizing an artificial “threshold.”

In 1985, A.S. Lefohn proposed the use of the W126 ozone exposure index for predicting vegetation effects. The cumulative W126 exposure index uses a sigmoidally weighted function (i.e., “S” shaped curve) as described by Lefohn and Runeckles (1987) and Lefohn et al. (1988). The W126 index is a cumulative exposure index and not an “average” value. It is a biologically based index, which is supported by research results (i.e., under both experimental and ambient conditions) that show that the higher hourly average ozone concentrations should be weighted greater than the mid- and lower-level values. The W126 index is accumulated over a specified time period.7

Let’s look again at the equation that defined the individual hourly W126 values, designated as Wi:

                                     Wi =        Ci                 
1 + 4403e –ACi

Let’s plot the Wi values on a graph as a function of the original hourly ozone concentrations that generated them, Ci:

Graph of Wi values plotted against the ozone concentrations used to calculate the values.

As the graph shows, when the ozone concentration Ci is less than .035 ppm-hour, Wi values are negligible. As Ci increases, the Wi values quickly climb, but are still always less than Ci. As Ci increases beyond about .085 ppm-hour, the growth rate of Wi subsides somewhat until about .10 ppm-hour, when Ci nearly equals Wi (within 1%), and the graph becomes linear. This shows that for ozone concentrations less than 0.035 ppm, the W126 values contribute almost nothing to the cumulative total. For concentrations greater than than .100 ppm, the W126 values are almost identical to the ozone concentrations. In between 0.035 ppm and .100 ppm, the contribution varies, with larger concentrations contributing much more to the cumulative total than smaller concentrations.

You can also see this in a table that I prepared of oxygen concentrations in increments of .010 ppm and their corresponding W126 values:

Ozone   Percent of Ozone
Concentration (ppm) W126 Value Concentration
0.01 0.0000 0.08%
0.02 0.0001 0.28%
0.03 0.0003 0.99%
0.04 0.0014 3.39%
0.05 0.0055 11.01%
0.06 0.0182 30.36%
0.07 0.0424 60.59%
0.08 0.0675 84.42%
0.09 0.0855 95.03%
0.10 0.0985 98.54%

Footnotes:

  1. U.S. Environmental Protection Agency, National Ambient Air Quality Standards, 2010, pg. 1 and pg. 6
  2. U.S. Environmental Protection Agency website, Ozone (O3) Standards – Table of Historical Ozone NAAQS. To view, click here.
  3. U.S. Environmental Protection Agency, National Ambient Air Quality Standards, 2010, pg. 17.
  4. ibid., pg. 34
  5. ibid., pg. 193.
  6. It is even easier using Microsoft Excel® or similar spreadsheet program. If an ozone concentration in ppm is in cell A1, then this formula typed in cell B1 will give the corresponding W126 value:

    = A1 / (1 + 4403 * EXP(-126*A1))

  7. A.S.L. & Associates website, How the W126 Ozone Exposure Index Was Developed. To view, click here.