Tag Archives: NAAQS

EPA’s New Ozone Rule: Part 22

The goal of our discussion is a cost-benefit analysis. What benefits would lower ozone bring us, how much would it cost, and do the benefits justify the costs? These questions are addressed in two EPA documents:

  • Final Ozone NAAQS Regulatory Impact Analysis (March 2008). To view, click here.
  • Regulatory Impact Analysis Final National Ambient Air Quality Standard for Ozone (July 2011), which is a supplement to the March 2008 document. To view, click here.

As these documents are at the heart of our discussion, I really should take the time to read and understand them thoroughly. But my time being short and the documents together totalling 645 pages, unfortunately I can’t do them justice. But you can read them, and I can point to certain highlights that can give us food for thought.

These papers can be challenged. But critics who would argue with their conclusions can’t just glibly dismiss their claims out of hand. They need to demonstrate that either their assumptions or their methods are wrong. They need to argue the issue with the same level of detail that these documents do.

What attracted my attention most were a few charts in the beginning of the July 2011 document. The first chart, Table S1.1 on page 6 of the document, lists the costs and benefits of ozone and PM2.5 (particles suspended in the air 2.5 microns in diameter and larger) reduction. Please open up the chart by clicking here.

Let’s describe the elements of the chart. There are three main rows, each row showing the costs and benefits of each of three possible limits on ground-level ozone: 0.075 ppm, 0.070 ppm, and 0.065 ppm. Each row is divided in half: the upper half for multi-city analyses, the lower half for meta-analyses, where the authors did not collect raw data but rather gathered data from other studies. Each half-row sites statistics from three studies: six studies in all. The studies, listed in order of appearance in the chart by author’s name are:

  • Bell, M.L. et al, 2004, Ozone and short term mortality in 95 US urban communities, Journal of the American Medical Association 292(19) 2372-2378. For the article, click here.
  • Schwartz, J., 2005, How sensitive is the association between ozone and daily deaths to control for temperature?American Journal of Respiratory and Critical Care Medicine, Vol. 171(6):627-631. For the article, click here.
  • Huang, Y., F. Dominici, M.L. Bell, 2005, Bayesian Hierarchical Distributed Lag Models for Summer Ozone Exposure and Cardio-Respiratory Mortality, Environmetrics, 16, 547-562. For the article, click here.
  • Bell, M.L., F. Dominici, J.M. Samet, 2005, A meta-analysis of time series studies of ozone and mortality with comparison to the national morbidity, mortality, and air pollution studies, Epidemiology, 16(4):436-445. For the abstract, click here.
  • Ito, K., S.F. DeLeon, M. Lippmann, 2005, Associations between ozone and daily mortality: analysis and meta-analysis, Epidemiology 16(4):446-457. For the article, click here.
  • Levy, J.L., S.M. Chemerynski, J.A. Sarnat, 2005, Ozone exposure and mortality: analysis and meta-analysis, Epidemiology 16(4):458-468. For the abstract, click here.

There are three major columns in the chart: total benefits, total costs, and net benefits (total benefits minus total costs). Total benefits and net benefits are divided into two half-columns: 3% discount rate and 7% discount rate. I don’t really understand what these are, but I can guess from what I’ve read. As I understand it, social discount rates are the rates of return one could expect if money spent on a social good was invested in financial markets instead. Let’s say you invested a large amount of money in 200 mutual funds chosen at random. Some funds would get a high rate of return, some a low rate of return, but over 10 years time, the rate of return would likely average out to some figure no matter what funds you chose. This rate of return is what we call the social discount rate.

Now the author prepared the chart showing amounts in 2006 dollars that would accrue in 2020. That suggests to me that the author is asking: if we go to a lower ozone standard in 2006, what are the costs and benefits we can expect in 2020? We can expect adopting a stricter ozone standard to cost us so much in 2007. If instead of adopting the stricter standard, we immediately invested that money instead at a 3% or a 7% rate of return, how much money would we get in 2020? We do the same for costs in 2008 and 2009 and so on. We would also see benefit in 2007. We can estimate the financial value of that benefit (harder to do than determining costs) and ask the same question: if we immediately invested that money at a 3% or 7% rate of return, how much money would we get in 2020? We do the same for benefits in 2008 and 2009 and so on. We sum up the financial returns from costs and benefits, and compare the results.

Now if you look at the numbers, you’ll see that for each combination of ozone limit, type of study (multi-city vs. meta-analysis) and cost/benefit column (for example, costs estimated for an ozone limit of 0.075 ppm, multi-city analyses) that the numbers in the combination are quite close to each other; the differences between the studies are not great. I took the average of each combination and put them into a condensed chart. I also calculated the size and midpoint of each net benefit range. Figures are in billions of 2006 dollars. A negative net benefit is a net cost.

Ozone Limit Study Type Total Benefits Total Costs Net Benefits Net Benefits Range Net Benefits Midpoint
0.075 ppm Multi-city 6.9 to 14.3 7.6 to 8.8 -1.9 to 6.7 8.6 2.4
0.075 ppm Meta-analysis 8.7 to 16.2 7.6 to 8.8 -0.20 to 8.4 8.6 4.1
0.070 ppm Multi-city 13.2 to 27.3 19.0 to 25.0 -11.8 to 8.3 20.1 -1.8
0.070 ppm Meta-analysis 18.7 to 33.2 19.0 to 25.0 -6.0 to 14.2 20.2 4.1
0.065 ppm Multi-city 22.2 to 44.8 32.0 to 44.0 -22.0 to 12.7 32.7 -4.6
0.065 ppm Meta-analysis 32.3 to 54.7 32.0 to 44.0 -11.7 to 23.0 34.7 5.6

What I found interesting about these numbers is that total costs are the same for each limit of ozone both for the multi-city studies and the meta-analyses. However, for total benefits and net benefits, the meta-analyses are consistently higher than the multi-city studies.

Also interesting is that the range of estimation of net benefits widens as the ozone limit gets lower. The range is $8.6 billion for 0.075 ppm, about $20 billion for 0.070 ppm, and about $33 billion for 0.060 ppm. That tells me that as the ozone limit gets lower, there is more uncertainty in estimating costs and benefits.

Now if you look at the midpoints of the ranges, the midpoints for the meta-analyses are fairly consistent: about $4 – $5 billion. But the midpoints of the ranges for the multi-city analyses go down as the ozone limit gets lower: from a net benefit of $2.4 billion for 0.075 ppm to a net cost of $1.8 billion for 0.070 ppm and then finally to a net cost of $4.6 billion for 0.065 ppm. But even the meta-analyses predict high net costs at the lower end of their ranges: up to $6 billion for 0.070 ppm and up to $11.7 for 0.065 ppm.

This tells me that as we choose lower limits for ozone, the uncertainty of estimating what the net benefit will be increases as well as the risk that the net benefit will be negative (i.e. really be a net cost). Of course, this evaluation depends on how much financial value we attach to a human life.

But it is also important to consider the benefits alone. If the benefits were purely financial, then it would make sense to be very utilitarian and forget about those benefits if they were outweighed by costs. But if those benefits are in a substantial number of lives saved and illnesses alleviated, then they become much more desirable, even urgent. Even if the economics dictate that it is wiser not to pursue those benefits now, they can remain in our sights as a goal we want to achieve eventually.

Following the table we just discussed is Table S1.2: Summary of Total Number of Ozone and PM2.5‐Related Premature Mortalities and Premature Morbidity Avoided: 2020 National Benefits, page 8 of the document. Please open the chart now by clicking here.

According to this chart, the number of lives that can be saved by both reducing ozone and particulate matter 2.5 microns and larger is substantial. To put it in perspecitve, on 9/11 2,753 New Yorkers were killed. Surely, if we were aware of a plot by Al Qaeda to kill 4000 Americans, we would expect our government to react. If we can save that many lives by protecting them from air pollution, shouldn’t we try?

There is one more topic we need to discuss on this subject, and that is compliance.

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 16

We are continuing our discussion in our last post about why the EPA felt it necessary to formulate a new secondary standard for ground-level ozone concentration. As we noted before, initially the EPA felt it adequate for the secondary standard to be identical to the primary standard, but then it reconsidered its position.

The EPA performed an evaluation comparing primary and secondary standards and found that high cumulative exposures were widespread. Below is a summary of what they found, taken from the document National Ambient Air Quality Standards for Ozone, Final Preamble, 2011. Note point #4 where EPA explains why it thinks the primary standard is insufficient (p. 201):

…The following key observations were drawn from comparing predicted changes in interpolated air quality under each alternative standard form and level scenario analyzed:

  1. The results of the exposure assessment indicate that then-current air quality levels could result in significant impacts to vegetation in some areas. For example, [bulleted list is my formatting — MHK]
    • For the base year (2001), a large portion of California had 12-hr W126 O3 levels above 31 ppm-hours, which has been associated with approximately up to 14% biomass loss in 50% of tree seedling cases studies.
    • Broader multi-state regions in the East (NC, TN, KY, IN, OH, PA, NJ, NY, DE, MD, VA) and West (CA, NV, AZ, OK, TX) are predicted to have levels of air quality above the W126 level of 21 ppm-hours, which is approximately equal to the secondary standard proposed in 1996 and is associated with biomass loss levels no greater than approximately 9% in 50% of tree seedling cases studied, and biomass loss levels greater than approximately 9% in the other 50%.
    • Much of the East and Arizona and California have 12- hour W126 O3 levels above 13 ppm-hours which has been associated with biomass loss levels no greater than approximately 7% biomass loss in 75% of tree seedling cases studied and biomass loss levels greater than approximately 7% in the remaining 25% of cases studied.
  2. When 2001 air quality was rolled back to meet the then current 8-hour secondary standard, the overall 3-month 12-hour W126 O3 levels were somewhat improved, but not substantially. Under this scenario, there were still many areas in California with 12-hour W126 O3 levels above 31 ppm hours. A broad multi-state region in the East (NC, TN, KY, IN, OH, PA, MD) and West (CA, NV, AZ, OK, TX) were still predicted to have O3 levels above the W126 level of 21 ppm-hours.
  3. Exposures generated for just meeting a 0.070 ppm, 4th-highest maximum 8-hour average alternative standard (the lower end of the proposed range for the primary O3 standard) showed substantially improved O3 air quality when compared to just meeting the then-current 0.08 ppm, 8-hour standard. Most areas were predicted to have O3 levels below the W126 level of 21 ppm-hr, although some areas in the East (KY, TN, MI, AR, MO, IL) and West (CA, NV, AZ, UT, NM, CO, OK, TX) were still predicted to have O3 levels above the W126 level of 13 ppm-hours.
  4. While these results suggested that meeting a proposed 0.070 ppm, 8-hour secondary standard would provide substantially improved protection in some areas, the Staff Paper recognized that other areas could continue to have elevated seasonal exposures, including forested park lands and other natural areas, and Class I areas which are federally mandated to preserve certain air quality related values. This is especially important in the high elevation forests in the western U.S. where there are few O3 monitors and where air quality patterns can result in relatively low 8-hour averages while still experiencing relatively high cumulative exposures.

Now the EPA will explain where in particular the lack of a separate secondary standard is a problem. It seems that ozone levels in high-elevation rural areas remain fairly constant during the day, so that the ozone concentration may be below the primary standard and yet deliver a large cumulative exposure. This is where attention to a cumulative-based secondary standard might be particularly useful. Note that the 8-hour average form refers to the primary standard, which depends on the average of ozone measurements taken during an eight-hour time period (p. 202):

To further characterize O3 air quality in terms of the 8-hour and alternative secondary standard forms, an analysis was performed in the 2007 Staff Paper to evaluate the extent to which county-level O3 air quality measured in terms of various levels of the 8-hour average form overlapped with that measured in terms of various levels of the 12-hour W126 cumulative, seasonal form. This analysis was limited by the lack of monitoring in rural areas where important vegetation and ecosystems are located, especially at higher elevation sites. This is because O3 air quality distributions at high elevation sites often do not reflect the typical urban and near-urban pattern of low morning and evening O3 concentrations with a high mid-day peak, but instead maintain relatively flat patterns with many concentrations in the mid-range (e.g., 0.05-0.09 ppm) for extended periods. These conditions can lead to relatively low daily maximum 8-hour averages concurrently with high cumulative values so that there is potentially less overlap between an 8-hour average and a cumulative, seasonal form at these sites. The 2007 Staff Paper concluded that it is reasonable to anticipate that additional unmonitored rural high elevation areas important for vegetation may not be adequately protected even with a lower level of the 8-hour form.

Then the EPA seems to reverse its position. Since we can’t be confident that the primary standard will be adequate, especially in rural areas and remote areas where data on ozone might be sparse, we may need to establish a secondary standard. Whereas before the EPA wanted to err on the side of less regulation, now they want to err on the side of more regulation (p. 203):

It continues to remain uncertain as to the extent to which air quality improvements designed to reduce 8-hour O3 average concentrations would reduce O3 exposures measured by a seasonal, cumulative W126 index. The 2007 Staff Paper indicated this to be an important consideration because:

  1. The biological database stresses the importance of cumulative, seasonal exposures in determining plant response;
  2. Plants have not been specifically tested for the importance of daily maximum 8-hour O3 concentrations in relation to plant response;
  3. The effects of attainment of a 8-hour standard in upwind urban areas on rural air quality distributions cannot be characterized with confidence due to the lack of monitoring data in rural and remote areas.

These factors remain important considerations in the Administrator’s reconsideration of whether the current 8-hour form can appropriately provide requisite protection for vegetation.

Question on point #3: If we can’t be sure of the effects of attainment of an 8-hour standard on rural areas because we don’t have enough monitoring data, how would we be any more sure of the effects of attainment of the secondary standard?

The EPA’s own CASAC (Clean Air Scientific Advisory Committee) was also very unhappy with the decision to make the secondary standard equal to the primary standard. We will see what they have to say in the next post.

EPA’ s New Ozone Rule: Part 15

A major innovation of EPA’s 2010 revision of the ozone standard was the introduction of what is called a secondary standard that is different from the primary standard. The secondary standard has existed before, but it was always set identical to the primary standard. To summarize the two standards:

  • The primary standard is intended to protect the public health. It is currently based on the fourth-highest 8-hour average ozone concentration reading in a year.
  • The secondary standard is meant to protect property, economic interests, and other concerns. It is based on a cumulative ozone concentration over time. Ozone readings are taken hourly between 8 a.m. and 7 p.m., adjusted by what is called the W126 rule, and then summed during a three-month period. Units are in ppm-hours. See what I wrote in this blog about the secondary standard in the post “EPA’s New Ozone Rule: Part 6.” To view, click here.

Now if one standard was consistently stricter than the other, the EPA could simply adopt the stricter standard. That it felt necessary to formulate two standards can only mean that in some places one standard will be harder to meet, and in other places the other standard will be the stricter. The EPA wants to meet both standards everywhere, a condition we Orthodox Jews call being machmir for both shitos.

What I don’t understand yet is why the primary standard, which is meant to safeguard public health, is based on a highest one-time average, whereas the secondary standard, meant to protect property, is based on a cumulative measure. A cumulative standard makes sense, because research shows that the extent of damage to plants caused by ozone depends on cumulative exposure. But perhaps damage to human health also depends on cumulative exposure, just as the damage caused by radiation to human health depends on cumulative exposure. Why not make the primary standard cumulative as well? Be that as it may, currently the primary standard remains based on a highest one-time average, while the secondary standard remains identical to the primary standard.

What I want to do in this post is quote EPA in its own words why it felt a new secondary standard was necessary, discussed in the document National Ambient Air Quality Standards for Ozone, Final Preamble, 2011.

From the outset, the EPA is clear that the secondary standard was formulated because of ozone’s effects on plants (p. 196):

…The 2006 Criteria Document concluded that O3 exposure indices that cumulate differentially weighted hourly concentrations are the best candidates for relating exposure to plant growth responses…

It is interesting that the EPA recognized the value of a secondary standard long before 2010 (p. 197):

At the conclusion of the 1997 review, the biological basis for a cumulative, seasonal form was not in dispute. There was general agreement between the EPA staff, CASAC, and the Administrator, based on their review of the air quality criteria, that a cumulative, seasonal form was more biologically relevant than the previous 1-hour and new 8-hour average forms (61 FR 65716).

The EPA also explained why, rather than summing up straight ozone concentrations, it chose to sum up modified values, referred to as the W126 form. Using W126 values gives more weight to higher concentrations and much less weight to lower concentrations that would exist either naturally without human activity, or from foreign sources beyond the control of the U.S. government (p. 198):

Regarding the first consideration, the 2007 Staff Paper noted that the W126 form, by its incorporation of a continuous sigmoidal weighting scheme, does not create an artificially imposed concentration threshold, yet also gives proportionally more weight to the higher and typically more biologically potent concentrations, as supported by the scientific evidence. Second, the index value is not significantly influenced by O3 concentrations within the range of estimated PRB [policy-relevant background, the level of ozone not caused by human activity in the U.S. — MHK], as the weights assigned to concentrations in this range are very small.

Nevertheless, the EPA retained a secondary standard identical to the primary standard until 2010. Initially, the EPA felt that if the primary standard was made more strict, it would be sufficient for the secondary standard were made identical to it. A separate secondary standard that was cumulative would provide no additional protection unless it was made very strict, which can’t be justified because our knowledge of the effects of low-level ozone on vegetation is so uncertain (the paragraph sign [¶] indicates a paragraph break that I inserted. P. 209):

In considering the appropriateness of establishing a new standard defined in terms of a cumulative, seasonal form, or revising the 1997 secondary standard by making it identical to the revised primary standard, … EPA first considered the 2007 Staff Paper analysis of the projected degree of overlap between counties with air quality expected to meet the revised 8-hour primary standard, set at a level of 0.075 ppm, and alternative levels of a W126 standard based on currently monitored air quality data. This analysis showed significant overlap between the revised 8-hour primary standard and selected levels of the W126 standard form being considered, with the degree of overlap between these alternative standards depending greatly on the W126 level selected and the distribution of hourly O3 concentrations within the annual and/or 3-year average period. On this basis, as an initial matter, EPA concluded that a secondary standard set identical to the proposed primary standard would provide a significant degree of additional protection for vegetation as compared to that provided by the then-current 0.084 ppm secondary standard.

¶ In further considering the significant uncertainties that remain in the available body of evidence of O3-related vegetation effects and in the exposure and risk analyses conducted for the 2008 rulemaking, and the difficulty in determining at what point various types of vegetation effects become adverse for sensitive vegetation and ecosystems, EPA focused its consideration on a level for an alternative W126 standard at the upper end of the proposed range (i.e., 21 ppm-hours). The 2007 Staff Paper analysis showed that at that W126 standard level, there would be essentially no counties with air quality that would be expected both to exceed such an alternative W126 standard and to meet the revised 8-hour primary standard – that is, based on this analysis of currently monitored counties, a W126 standard would be unlikely to provide additional protection in any monitored areas beyond that likely to be provided by the revised primary standard.

The EPA states again that with the lack of extensive monitoring in rural areas, it is unsure how much additional protection a separate secondary standard would provide. At this point, it decided to err on the side of less regulation. Note that the term “8 hour standard” refers to the primary standard, which averages readings over eight-hour periods (p. 210):

The EPA also recognized that the general lack of rural monitoring data made uncertain the degree to which the revised 8-hour standard or an alternative W126 standard would be protective in those areas, and that there would be the potential for not providing the appropriate degree of protection for vegetation in areas with air quality distributions that result in a high cumulative, seasonal exposure but do not result in high 8-hour average exposures. While this potential for under-protection using an 8- hour standard was clear, the number and size of areas at issue and the degree of risk was hard to determine. However, EPA concluded at that time that an 8-hour standard would also tend to avoid the potential for providing more protection than is necessary, a risk that EPA concluded would arise from moving to a new form for the secondary standard despite significant uncertainty in determining the degree of risk for any exposure level and the appropriate level of protection, as well as uncertainty in predicting exposure and risk patterns.

…EPA concluded at that time that establishing a new secondary standard with a cumulative, seasonal form would result in uncertain benefits beyond those afforded by the revised primary standard and therefore may be more than necessary to provide the requisite degree of protection.

Eventually, though, the EPA changed its mind. Why will be discussed in the next post.

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 13

The EPA did an assessment estimating how many children in general and asthmatic children in particular, living in 12 metropolitan areas, engaged in moderate and greater exertion in areas that reached a particular maximum level of ozone, would actually be exposed to specific levels of ozone or higher (called benchmarks). The results of the assessment are summarized in the document National Ambient Air Quality Standards for Ozone, Final Preamble, 2011 (pp. 51 – 52) as Table 1, which appears below. EPA’s table footnotes appear at the end of this post.

The caption in bold is taken directly from the document (p. 51). The table follows. EPA’s footnotes appear after the end of this post:

Table 1. Number and Percent of All and Asthmatic School Age Children in 12 Urban Areas Estimated to Experience 8-Hour Ozone Exposures At and Above 0.060 and 0.070 ppm While at Moderate or Greater Exertion, One or More Times Per Season Associated with Just Meeting Alternative 8-Hour Standards Based on Adjusting 2002 and 2004 Air Quality Data1,2

Benchmark Levels of Exposures of Concern(ppm) 8-Hour Air Quality Standards3 (ppm) All Children, ages 5-18
Aggregate for 12 urban areas
Number of Children Exposed (% of all children)
[Range across 12 cities, % of all children]
Asthmatic Children, ages 5-18 Aggregate for 12 urban areas Number of Children Exposed (% of group)[Range across 12 cities, % of group ]

2002 2004 2002 2004
0.074 770,000 (4%)
[0 – 13%]
20,000 (0%)
[0 – 1%]
120,000 (5%)
[0 – 14% ]
0 (0%)
[0 – 1%]
0.070 0.070 270,000 (1%)
[0 – 5%]
0 (0%)
[0%]
50,000 (2%)
[0 – 6%]
0 (0%)
[0 – 1%]
0.064 30,000 (0.2%)
[0 – 1%]
0 (0%)
[0%]
10,000 (0.2%)
[0 – 1%]
0 (0%)
[0%]
0.074 4,550,000 (25%)
[1 – 48%]
350,000 (2%)
[0 – 9%]
700,000 (27%)
[1 -51%]
50,000 (2%)
[0 – 9%]
0.060 0.070 3,000,000 (16%)
[1 – 36%]
110,000 (1%)
[0 – 4%]
460,000 (18%)
[0 – 41%]
10,000 (1%)
[0 – 3%]
0.064 950,000 (5%)
[0 – 17%]
10,000 (0%)
[0 – 1%]
150,000 (6%)
[0 – 16%]
0 (0%)
[0 – 1%

An example on how to read the chart: Look at the benchmark level of 0.070 ppm on the leftmost column of the chart, then at the 8-hour quality standard of 0.074 ppm in the next column. In 2002, 4% of all children ages 5 – 18 in areas whose maximum ozone reached 0.074 ppm were actually exposed to levels of 0.070 ppm or greater (the rest might have been indoors when the ozone level was so high and so escaped exposure). In 2004, less than 1% were so exposed. In 2002, 5% of asthmatic children were so exposed, but in 2004, less than 1% were so exposed. Within brackets are the ranges of minimum and maximum percents encountered in the survey. For example, regarding areas that reached a maximum level of 0.074 ppm in 2002, the lowest percentage encountered of all children exposed to ozone levels of 0.070 ppm or higher was less than 1%. The highest percentage encountered was 13%. The percentage of all children in the 12 cities was 4%.

Jackson explains how the exposure assessment results influenced her judgement (p.179):

In considering the exposure assessment results, the Administrator focused on the extent to which alternative standard levels within the proposed range of 0.060 to 0.070 ppm would likely limit exposures at and above the health benchmark levels of 0.070 and 0.060 ppm for all [school age children] and asthmatic school age children in the 12 urban areas included in the assessment… In particular, the Administrator notes that the 0.070 ppm benchmark level reflects the information that asthmatics likely have larger and more serious effects than healthy people at any given exposure level, such that studies done with healthy subjects may underestimate effects for susceptible populations. Thus, in considering the strong body of evidence from the large number of controlled human exposure studies showing O3-related respiratory effects in healthy people at exposure levels of 0.080 ppm and above, the Administrator concludes it is appropriate to give substantial weight to estimates of exposures at and above the 0.070 ppm benchmark level. With regard to the 0.060 ppm benchmark level, the Administrator notes that this benchmark reflects additional consideration of the evidence from the Adams studies at the 0.060 ppm exposure level. In considering the important but limited nature of this evidence, the Administrator concludes it is appropriate to give some weight to estimates of exposures at and above the 0.060 ppm benchmark level, while recognizing that the public health significance of such exposures is appreciably more uncertain than for the 0.070 ppm benchmark level.

Adopting a standard of 0.070 ppm ozone would be advantageous as it would limit exposure to the 0.070 ppm benchmark (p. 179).

Considering the exposure information shown in Table 1 above in light of these considerations, the Administrator observes that a standard set at 0.070 ppm would likely very substantially limit children’s exposures at and above the 0.070 ppm benchmark, considering both the year-to-year variability and the city-to-city variability in the exposure estimates across the 12 cities included in the assessment. In particular, for the more recent year in the assessment, which had generally better air quality, such exposures were essentially eliminated, whereas in the earlier year with generally poorer air quality, exposures at and above the benchmark level were limited to approximately 2% of asthmatic children in the aggregate across the 12 cities, ranging from 0% up to 6% in the city with the least degree of protection. In weighing this information and in judging the public health implications of these exposure estimates, the Administrator recognizes that only a subset of this susceptible population with exposures at and above the benchmark level would likely be at risk of experiencing O3-related health effects.

Even better, A standard of 0.070 ppm would be effective at limiting exposure down to the 0.060 ppm benchmark (p. 180):

With regard to the 0.060 ppm benchmark level, a standard set at 0.070 ppm would likely also limit exposures at and above this benchmark level, but to a lesser degree. For example, as shown above in Table 1, for the more recent year, exposures at and above the 0.060 ppm benchmark level were limited to approximately 1% of asthmatic children in the aggregate, whereas for the earlier year approximately 18% of asthmatic children were estimated to experience exposures at and above this benchmark level. In weighing this information and judging the public health implications of these exposure estimates, the Administrator recognizes that relative to the 0.070 ppm benchmark, an even smaller, but unquantifiable subset of this susceptible population with exposure at and above the 0.060 ppm benchmark would likely be at risk of experiencing O3-related health effects, and that there is greater uncertainty as to the occurrence of such effects based on the limited evidence available from the Adams studies. The Administrator also notes that these estimates are substantially below the exposures that would likely be allowed by the 0.075 ppm standard (which would be somewhat higher than the estimates in Table 1 for a 0.074 ppm standard).

But then again, adopting the lower 0.064 ppm standard would be even better, according to the assessment (p. 181):

In also considering exposure estimates for the lowest alternative standard level considered in the exposure assessment, 0.064 ppm, the Administrator notes that the estimates of exposures at and above both health benchmark levels are even lower than for a 0.070 ppm standard. For example, for all years in the assessment, exposures of asthmatic children at and above the 0.070 ppm benchmark were essentially eliminated for a 0.064 ppm standard; even in the year with generally poorer air quality and in the city with the least degree of protection, exposures at and above the benchmark level were very substantially limited to approximately 1% of asthmatic children. Further, exposures of asthmatic children at and above the 0.060 ppm benchmark were also essentially eliminated in the more recent year for a 0.064 ppm standard, while in the year with generally poorer air quality such exposures were appreciably limited to approximately 6% of asthmatic children.

Well, in that case, why not go for the 0.064 ppm standard? (p. 181)

In considering these results, the Administrator notes that in its most recent advice, CASAC considered the public health significance of reductions in exposures above these benchmark levels of concern. In so doing, CASAC observed that while the predicted number of exposures of concern increases at every standard level as the benchmark level of concern is reduced, the public health impact of this increase becomes less certain, and that the public health significance of such exposures is difficult to gauge (Samet, 2011, p. 13). The Administrator also notes that CASAC judged that in terms of exposures above the 0.060 ppm benchmark level of concern, a further reduction in the standard from 0.070 ppm is estimated to have a small public health impact, although, in the absence of a threshold at the benchmark level of concern, this analysis is likely to be an underestimate of the true public health impact.

Jackson comes to her final conclusion (p. 181):

Taken together, in weighing this exposure information and judging the public health implications of the exposure estimates for the alternative standard levels, the Administrator finds that a standard of 0.070 ppm appropriately limits exposures of concern relative to the 0.070 and 0.060 ppm benchmark levels for the susceptible population of asthmatic children, as well as for the broader population of all children. Particularly in light of the relatively more uncertain public health implications of exposure at and above the 0.060 ppm benchmark, the Administrator concludes the exposure assessment provides support for a standard no higher than 0.070 ppm, but does not warrant selecting a standard set below that level.


Table Footnotes as Published by the EPA:

  1. Moderate or greater exertion is defined as having an 8-hour average equivalent ventilation rate > 13 l-min/m2.
  2. Estimates are the aggregate results based on 12 combined statistical areas (Atlanta, Boston, Chicago, Cleveland, Detroit, Houston,Los Angeles, New York, Philadelphia, Sacramento, St. Louis, and Washington, D.C.). Estimates are for the ozone season which is all year in Houston, Los Angeles and Sacramento and March or April to September or October for the remaining urban areas.
  3. All standards summarized here have the same form as the 8-hour standard established in 1997 which is specified as the 3-year average of the annual 4th highest daily maximum 8-hour average concentrations must be at or below the concentration level specified. As described in the 2007 Staff Paper (EPA, 2007a, section 4.5.8), recent O3 air quality distributions have been statistically adjusted to simulate just meeting the 0.084 ppm standard and selected alternative standards. These simulations do not represent predictions of when, whether, or how areas might meet the specified standards. As shown in Table 1, aggregate estimates of exposures of concern for the 12 urban areas included in the assessment are considerably larger for the benchmark level of 0.060 ppm O3, comparedto the 0.070 ppm benchmark level. Substantial year-to-year variability is observed in the number of children estimated to experience exposures of concern at and above both the 0.060 and 0.070 ppm benchmark levels. As shown in Table 1, aggregate estimates of exposures of concern at and above a 0.060 ppm benchmark level.

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.