Category Archives: EPA’s New Ozone Rule

EPA’s New Ozone Rule: Part 14

Posted on January 10, 2013 | 1 comment

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.

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EPA’S New Ozone Rule: Part 13

Posted on January 6, 2013 | 2 comments

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.

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EPA’s New Ozone Rule: Part 12

Posted on January 3, 2013 | 1 comment

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.

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EPA’s New Ozone Rule: Part 11

Posted on September 13, 2012 | 1 comment

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.

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EPA’s New Ozone Rule: Part 10

Posted on September 6, 2012 | 1 comment

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.

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EPA’s New Ozone Rule: Part 9

Posted on July 26, 2012 | 1 comment

Exactly what was the EPA’s reasoning behind lowering the maximum ground-level ozone concentration from 75 ppb to 70 ppb? This is the opening paragraph of the discussion in EPA’s National Ambient Air Quality Standards for Ozone, 2011, page 35.

This section presents the rationale for the Administrator’s final decision that the O3 primary standard, which was set at a level of 0.075 ppm in the 2008 final rule, should instead be set at 0.070 ppm. In developing this rationale, the Administrator recognizes that the CAA [Clean Air Act — MHK] requires her to reach a public health policy judgment as to what standard would be requisite to protect public health with an adequate margin of safety, based on scientific evidence and technical assessments that have inherent uncertainties and limitations. This judgment requires making reasoned decisions as to what weight to place on various types of evidence and assessments, and on the related uncertainties and limitations. Thus, in selecting a final level, the Administrator is seeking not only to prevent O3 levels that have been demonstrated to be harmful but also to prevent lower O3 levels that may pose an unacceptable risk of harm, even if the risk is not precisely identified as to nature or degree.

What the EPA is saying is that it isn’t enough for the maximum concentration of ground-level ozone allowable to be set just below the minimum known to cause harm. Rather, the limit must be low enough so that even if the harm is not certain but only possible, the risk of harm is low enough to be acceptable. Question is, how low must the risk be to considered acceptable? The document itself states that risk must be taken into consideration even when it can’t be precisely identified. But does that mean that any level of risk, no matter how low, is unacceptable? That would be setting a very high standard indeed. And if that is not so, what is the maximum level of risk that is acceptable? What is the cutoff point?

Unspoken is the realization that it is politically unwise to try to impose tougher rules on the public than is necessary to achieve the objective. To do so is to impose unnecessary economic hardship that could provoke a backlash. And indeed, we saw that backlash in September 2011. The EPA can’t admit that fact, but it is nevertheless true.

There have been a number of controlled studies examining human exposure to ozone, but most have been at the 80 ppb level1. However, studies by William C. Adams, researcher (now retired) at the University of California at Davis did expose humans to ozone at average concentrations as low as 40 ppb2. Besides exposing his subjects to steady concentrations, Adams attempted to mimic the natural environment by slowly increasing and then decreasing the ozone concentration, much as the ambient ozone concentration grows in the morning, peaks in midday, and then declines toward evening. Adams found no statistically significant difference in lung function compared to breathing filtered (ozone-free) air at the 40 ppb and 60 ppb levels. However, a later analysis of Adam’s data by the EPA did find a small statistical difference at the 60 ppb level3. EPA finds this of concern, because a small statistical drop of lung function among healthy adults could manifest itself much more forcefully among those with lung disease4.

Still, most controlled studies on ozone exposure do not test beneath the 80 ppb level. Yet the EPA notes that there is no evidence that the harmful effects of ozone stop at the 80 ppb level (start with a very high concentration of ozone and slowly lower it. The concentration level where harmful effects would stop is known as the threshold). In fact, it can be inferred that such effects extend well below that level, because of the variability of responses of the test subjects5. I believe this means that if 80 ppb was the threshold level, then if you exposed test subjects to that concentration, you would see a number of small responses, but they would all be roughly equal to each other. If, on the other hand, some test subjects experience effects much more than others, even though the effects are still small, that indicates that the effects occur well below the 80 ppb level. And small effects for healthy people can mean big effects for those with respiratory disease.

The above concerned controlled studies of subjects of laboratory experiments. EPA also looked at epidemiological studies, studies of what is happening to populations in their day-to-day lives6. Some found thresholds between 25 and 50 ppb. Other studies never found a threshold because the damage that ozone inflicted seemed linear with the concentration. As I understand this, this means that if the concentration was reduced by a specific percentage (for example, a 20% reduction), measureable effects are reduced by the same percentage multiplied by fixed factor (say a 2% reduction in concentration results in a 3% decrease in effects, a 4% reduction results in a 6% decrease in effects, and so on). On the other hand, you might expect that at a concentration near the threshold level, a further reduction would result in a greater decrease of effects (say a 2% reduction results in a 3% in effects, but a 3% reduction results in a 25% decrease in effects, and a 4% reduction results in a 95% decrease in    effects)6. These studies never saw this sort of effect, so they could not conclude there was any threshold for ozone.

The EPA also looked at studies that did subset analysis looking only at days whose ozone concentration did not exceed certain ozone concentrations (such as 80 ppb and 61 ppb), and still found associations between those concentrations and lung function decrements)6.

Regarding the existence of a threshold for the effects of ozone, the EPA concluded:

Based on the above considerations, the 2007 Staff Paper recognized that the available evidence neither supports nor refutes the existence of effect thresholds at the population level for morbidity and mortality effects, and that if a population threshold level does exist, it would likely be well below the level of the then current standard and possibly within the range of background levels. Taken together, these considerations also support the conclusion that if a population threshold level does exist, it would likely be well below the level of the 0.075 ppm, 8-hour average, standard set in 2008.7

But if the EPA needed to pick the lowest allowable concentration, should it have chosen the lowest threshold found by the studies, 25 ppb? That would not be possible, because the background level of ground-level ozone (the concentration of ozone in the U.S. that is either naturally occurring or coming from outside the U.S. and over which the U.S. government has no control. The background level varies with location and season8.) is often above that level of 25 ppb9. This being the case, setting the standard at 25 ppb would have been an impossible demand. (In fact, the 2007 Staff Paper found that below 35 ppb, it was difficult to tell effects from ozone from effects from other air pollutants9.) Even 50 ppb would be an extremely difficult and expensive goal to meet.

Footnotes:

  1. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.38
  2. Adams,W.C., Comparison of chamber 6.6-h exposures to 0.04-0.08 ppm ozone via square-wave and triangular profiles on pulmonary responses Inhalation Toxicology vol. 18: pp. 127-136. For the abstract, click here.
  3. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.38
  4. ibid.p.39
  5. ibid.p.40
  6. ibid.p.42
  7. ibid.p.43
  8. For a detailed discussion of background ozone levels, see U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, June 2012, Section 3.4, “Background Ozone Concentrations”, p.3-32ff.
  9. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.42, p.107

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EPA’s New Ozone Rule: Part 8

Posted on July 23, 2012 | Leave a comment

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.

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EPA’s New Ozone Rule: Part 7

Posted on July 19, 2012 | 1 comment

Before discussing why EPA should lower the limit on maximium ground-level ozone concentration from 75 ppb to 70 ppb, we need to explain why EPA needs to regulate ozone in the first place. Just to clarify, we are not dealing with stratospheric ozone high above the earth’s surface 10 miles up that protects us from harmful ultraviolet radiation from the sun. Rather, we are strictly speaking about ground-level ozone, the only ozone that people have direct exposure to.

Ozone is a highly corrosive chemical, one of the most chemically active known (reaction potential = 2.07 volts in an acid solution at 25°C)1. When breathed in, it attacks the upper respiratory tract and the lungs2. Breathing 100% ozone is quickly fatal, in fact, breathing air with as little as 50 ppm (50,000 ppb) ozone will likely kill a human within a half-hour3. It has been observed that people inhaling 9 ppm ozone along with other air pollutants developed pulmonary edema3.

Ozone at much lower concentrations can also cause problems. To quote EPA’s Integrated Science Assessment:

…short-term O3 exposures induced or were associated with statistically significant declines in lung function. An equally strong body of evidence from controlled human exposure and toxicological studies demonstrated O3-induced inflammatory responses, increased epithelial permeability, and airway hyperresponsiveness. Toxicological studies provided additional evidence for O3-induced impairment of host defenses. Combined, these findings from experimental studies provided support for epidemiologic evidence, in which short-term increases in O3 concentration were consistently associated with increases in respiratory symptoms and asthma medication use in children with asthma, respiratory-related hospital admissions, and ED [emergency department – MHK] visits for COPD [chronic obstructive pulmonary disease, including chronic bronchitis and emphysema – MHK] and asthma. Additionally, recent evidence supports the range of respiratory effects induced by O3 by demonstrating that short-term increases in ambient O3 concentrations can lead to respiratory mortality. The combined evidence across disciplines supports a causal relationship between short-term O3 exposure and respiratory effects4.

The decrease in lung function caused by short-term exposure to ozone quickly fade when the ozone is removed5. However, repeated exposure to ozone over a long period of time may cause more chronic problems such as reduced lung function6. Ozone has also been implicated in causing problems to the cardiovascular, central nervous, and reproductive systems, although these have not been conclusively proven. 6. There is not enough evidence to suggest that ozone causes cancer6.

The EPA’s National Ambient Air Quality Standards 2011 document on ozone states these concerns with some passion:

These physiological effects [inflammation and damage to the respiratory system and impaired host defense capabilities – MHK] have been linked to aggravation of asthma and increased susceptibility to respiratory infection, potentially leading to increased medication use, increased school and work absences, increased visits to doctors’ offices and emergency departments, and increased hospital admissions. Further, pulmonary inflammation is related to increased cellular permeability in the lung, which may be a mechanism by which O3 exposure can lead to cardiovascular system effects, and to potential chronic effects such as chronic bronchitis or long-term damage to the lungs that can lead to reduced quality of life. These are all indicators of adverse O3-related morbidity effects, which are consistent with and lend plausibility to the adverse morbidity effects and mortality effects observed in epidemiological studies.7

Ozone has also been shown to injure plants and reduce their growth. This reduces agricultural yields and the productivity of ecosystems8. Ozone is a significant greenhouse gas, and is probably contributing to global warming9. However, I would think that it would be less than a threat than carbon dioxide, because ozone tends to quickly decompose into oxygen whereas carbon dioxide can linger in the atmosphere for a century or more10. Nevertheless, if society is constantly generating more ozone, the contribution to climate change could be significant. If it reduced its ozone production, this contribution would fade almost instantaneously.

To demonstrate the extent of scientific research documenting the effects of ozone on human health, I excerpted the reference section of Chapter 6 of EPA's Integrated Science Analysis, the chapter that discusses the health effects of short-term ozone exposure. This reference section lists some 500 scientific papers on the effects of ozone. I have not read these papers except for one, so I cannot vouch for them; nevertheless, the list taken together is formidable. Take a look yourself by clicking on the link below. You can click on any reference in the list to see the paper’s abstract.

Reference Section of Chapter 6

The next question we must discuss is: Granted that trace amounts of ozone in the ground-level atmosphere is injurious to human welfare, how do we know that 75 ppb (the former limit) is still injurious? Why wasn’t that level good enough? Why did the EPA think it should lower it?

Footnotes

  1. Rein Munter, Ozone: Science and Technology,Encyclopedia of Life Support Systems. To view, click here.
  2. U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, Section 6.2: Respiratory Effects, p. 6-1ff.
  3. Ozone Levels and Their Effects, edited by Den Rasplicka, OzoneLab Instruments website. To view, click here.
  4. U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, Chapter 1: Executive Summary, p.1-6.
  5. Ibid., Chapter 6: Integrated Health Effects of Short-Term Ozone Exposure, pp. 6-14, 6-27, 6-165.
  6. Ibid., Table 1-1: Summary of ozone causal determinations by exposure duration and health outcome, p. 1-5. Table 2-2: Summary of evidence from epidemiologic, controlled human exposure, and animal toxicological studies on the health effects associated with short- and long-term exposure to ozone, pp 2-25 — 2-26.
  7. U.S. Environmental Protection Agency, National Ambient Air Quality Standards for Ozone, Final Preamble, 2011, p.40.
  8. U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Third External Review Draft, Table 1-2: Summary of ozone causal determination for welfare effects, p. 1-8. Table 2-3: Summary of ozone causal determination for vegetation and ecosystem effects, p.2-40.
  9. Ibid., Section 2.7.1: Tropospheric Ozone as a Greenhouse Gas, pp. 2-49 — 2-50.
  10. I don’t have a single source for this. Wikipedia quotes M.Z. Jacobson in a 2005 letter to the Journal of Geophysical Research, 110 pp. D14105, as estimating the atmospheric lifetime of carbon dioxide as 300 years (click here to view the Wikipedia article). David Archer, in his article Fate of Fossil Fuels in Geologic Time, Journal of Geophysical Research, Volume 110 C09S05, argues, “A better approximation of the lifetime of fossil fuel CO2 for public discussion might be ‘300 years, plus 25% that lasts forever.'” He claims that when additional carbon dioxide is added to the atmosphere, some of it lingers for tens of thousands of years. To see the article, click here. See also Archer, David et al, Atmospheric Lifetime of Fossil Fuel Carbon Dioxide, Annual Review Earth Planet Sci. 2009 37:117-34 (click here to view). For a lively discussion of the topic, see the Skeptical Science website, which you can read by clicking here.

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EPA’s New Ozone Rule: Part 6

Posted on July 11, 2012 | 2 comments

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.

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EPA’ s New Ozone Rule: Part 5

Posted on July 2, 2012 | Leave a comment

On September 2, 2011, the Obama administration rescinded an EPA proposal to tighten standards on ozone in the atmosphere at ground level1.   This proposal would have:

  • Lowered the maximum allowable concentration of ground-level ozone from 75 parts per billion (ppb) to 70 ppb2. This is the primary standard whose purpose is to safeguard human health.
  • Introduced a secondary standard based on a cumulative total of ozone exposure, 13 parts per million-hours (ppm-hour) in a three month period2. One ppm-hour is the exposure one receives from breathing an atmosphere of 1 ppm ozone for one hour. Two ppm-hours is the exposure of 1 ppm for 2 hours or 2 ppm for 1 hour. The purpose of the secondary standard is to protect property, quality of life, and wildlife habitat.

The question we want to consider is: Did it serve the public interest to rescind the proposed regulation or would it have been better to allow the regulation to become law? Does the benefit that the regulation provides the public outweigh the costs or vice versa?

Some might argue that a regulation that is shown to save lives offers a benefit that outweighs all costs, but that isn’t necessarily true. We put a finite price on human life all the time: insurance companies, the courts, the medical profession, governments. To show why we must do this, ask yourself this question: suppose a single person was in grave danger but could be rescued for a billion dollars. Should the government pay a billion dollars to rescue that individual? There is a raging debate how about much money to spend on medical care for the poor at a cost much less than a billion dollars per life. There are limits to how much we can spend to rescue people, especially when the costs can affect the business and economic climate3.

Another example: suppose we want to institute environmental regulation X. X will save the lives of 1000 people but will cause 10,000 people to be laid off from their jobs. Is it worth it? What if it will save the lives of 5,000 people? 10,000 people? 100,000 people? What if X will reduce tax revenues needed for schools, sanitation, police and fire services? When the question is phrased as a matter of extremes (X will save a million lives at an economic cost of ten million dollars, or X will save a handful of lives but will wreak economic havoc), most of us would find the question easy to answer. But when the costs and benefits are more balanced, that’s when it becomes tricky.

Of course, saving lives are not the only benefits of environmental regulations4. Tougher ozone standards promise to reduce the amount and severity of respiratory illness5, even to increase general wellness, helping to keep our lung function from deteriorating over long periods of time. The atheletes among us will be able to retain their abilities longer, but even ordinary people may be able to retain their vigor longer into their old age.

Lower ozone levels could particularly benefit those with pre-existing respiratory conditions, such as asthma, chronic bronchitis, and emphysema5. While people with these conditions represent just a fraction of the population, they still deserve our consideration. We have a legislative precedent: the Americans with Disabilities Act (ADA) has made life easier for millions of people6. If we demand accommodations for the blind, the deaf, and wheelchair-bound, we should also make accommodation for those with breathing difficulties.

There are also economic benefits from tougher ozone standards. If even low concentrations of ozone make some people ill, then maintaining lower concentrations will mean less illness. That means lower health care costs, less productivity lost at work, less absences at school. Ozone also damages plant life7; lower ozone levels will benefit agriculture as well as protect other forms of property (ozone is murder on certain types of rubber8). Less tangible is the damage that can be prevented to our national parks and other wildlife habitat.

On the other hands, there could be substantial costs. Ozone is not emitted directly by industry but is formed from other chemicals released into the air9. To reduce ozone, industry (as well as private cars and trucks) must curtail these emissions, and that can be expensive. If the costs are too great, companies will become less profitable, will need to cut back on hiring, will yield less tax revenue, may be tempted to move to other jurisdictions with less onerous regulation. The EPA is prohibited by law from allowing cost considerations to influence its decision to impose new and stricter regulations10. But we are not so prohibited, and we need to weigh costs against benefits to determine how society’s interests are best served.

Footnotes:

  1. Statement by the President on the Ozone National Ambient Air Qualities Standards. White House website. To view, click here.
  2. U.S. Environmental Protection Agency, National Ambient Air Quality Standards, 2010, p. 1. To view the document, click here.
  3. A related concept is the value of statistical life (VSL), which is a measure of how much people are willing to pay for reduction of danger to life. For a discussion on determining VSL in three provinces in China, see the paper The Value of Statistical Life by Jie He and Hua Wong, World Bank eLibrary, which you can view by clicking here. See also the Wikipedia article Value of Life which you can view by clicking here.
  4. For discussions of mortality associated with ozone exposure, see the U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Second External Draft, September 2011, Sections 2.6.2, 6.6, 7.4.10, and 7.7. To view the document, click here, then click the button “Get the Report.”
  5. For discussions of health conditions associated with ozone exposure, see the U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Second External Draft, September 2011, Sections 2.6, 6.2 through 6.5, and 7.3 through 7.6. To view the document, click here, then click the button “Get the Report.”
  6. For discussions of the effect of ozone on lung health, see the U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Second External Draft, September 2011, Sections 6.2 and 7.2. To view the document, click here, then click the button “Get the Report.”
  7. The U.S. Equal Employment Opportunity Commission maintains a website with a good summary of the ADA, which you can view by clicking here.
  8. For discussions of the effect of ozone on vegetation and the environment, see the U.S. Environmental Protection Agency, Integrated Science Assessment for Ozone and Related Photochemical Oxidants, Second External Draft, September 2011, Sections 2.7 and 9. To view the document, click here, then click the button “Get the Report.”
  9. See my post “EPA’s New Ozone Rule, Part 4” which you can view by clicking here.
  10. U.S. Environmental Protection Agency, National Ambient Air Quality Standards, 2010, p. 9. To view the document, click here.

    Actually, this prohibition is not actually stated by the Clean Air Act, but has been inferred by the courts. It is based on Section 109 of the Clean Air Act (United States Code, Title 42, Section 7409, which you can read by clicking here) which states in subsection (b)(1): “National primary ambient air quality standards…based on such criteria and allowing an adequte margin of safety, are requisite to protect the public health.” Similarly, it states in subsection (b)(2): Any national secondary ambient air quality standard…is requisite to protect the public welfare from any known or anticipated adverse effects associated with the presence of such air pollutant in the ambient air.” The Supreme Court in its ruling in the case Whitman v. American Trucking Associations, Inc. (which you can read by clicking here) inferred from the lack of mention of cost as a criteria in determining NAAQS that cost was excluded. This is because in other places, the Clean Air Act explicitly does allow cost as a criteria. As an Orthodox Jew, I take great pleasure from this argument — it could have come straight from the Talmud.

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