Tag Archives: 0.070 ppm

EPA’s New Ozone Rule: Part 22

Posted on February 5, 2013 | 2 comments

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.

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EPA’s New Ozone Rule: Part 20

Posted on January 31, 2013 | 1 comment

Had the EPA succeeded in lowering the primary standard to 70 ppb and introducing a secondary standard of 13 ppm-hours, how much would that have cost industry? Would the benefits of a stricter standard justify that cost?

Here I must confess that I am at a considerable disadvantage. I do not know how to estimate industry costs, although I can report on other people’s claims. If I had all the time I needed, I would interview as many businesspeople I could on how tighter ozone restrictions imposed in 1998 affected them. In particular, I would want to know what new equipment they needed to buy to comply with the new standards. Did the new standards affect their decisions to buy equipment they were going to buy anyway and in what manner? How much more did they feel obliged to spend because of the new standards? Alas, time is short, I’m not getting paid to do this, I have no training in estimating costs, and I feel the need to move on to new topics. But these are still very important questions.

What I really would like is to compare three versions of one state’s State Implementation Plan (SIP). The first version would be designed to comply with the 0.084 ppm standard, the second with the 0.075 ppm standard, and the third to comply with the 0.070 ppm standard. Where are they the same? Where are they different? What are businesses expected to do differently to comply with the stricter standards? What kind of equipment are they expected to acquire under the three standards?

Do the benefits of a stricter standard justify the costs? Critics didn’t think so, such as the organization Americans for Tax Reform quoting a report by Oklahoma Senator James Inhofe:

EPA itself estimated that its ozone standard would cost $90 billion a year, while other studies have projected that the rule could cost upwards of a trillion dollars and destroy 7.4 million jobs.1

A couple of comments on this. The $90 billion a year figure and the trillion dollar figure are not contradictory. If the rule would cost us $90 billion a year for a dozen years, that will cost us more than a trillion dollars. Both figures are the upper limits of ranges, so that $90 billion a year and $1 trillion overall may be worst-case scenarios. According to a chart produced by the EPA which I will present in a later post, going to a 0.070 ppm standard would cost between $19 and $25 billion 2006 dollars by 20202. It is important to note that nobody can know for sure just how much the rule will cost either in money or in jobs. What experts do is estimate a range wide enough so that they think they will be right 95% of the time (95% confidence interval). That is to say, if an expert made an estimate of a range in twenty circumstances, in 19 times the true numbers will fall somewhere within those ranges.

Also, it should be pointed out that lowering ozone limits brings economic benefits in terms of lower medical costs and increased worker productivity (mainly because employees are out sick less). This is brought home by another EPA chart which estimates that if we had gone to a 0.070 ppm standard in 2011, we could have saved 170,000 sick days from work and eliminated 6,600 visits to the hospital and emergency rooms2. That all needs to be subtracted from the economic cost.

And what is the meaning of the destruction of 7.4 million jobs? Does that mean 7.4 million layoffs or 7.4 million people not hired who otherwise would be, or is it a combination of both? How does one determine how many jobs will be lost? (Note that Senator Inhofe is claiming two-digit accuracy: 7.4 million jobs, not 7.3 million or 7.5 million, so he is claiming more accuracy than a mere rough estimate. That kind of accuracy comes from a calculation and not just from a guess.) Do we need to balance that figure against jobs that might be created by the new rule, for example if companies that produce antipollution equipment saw an upsurge in business?

I am not an economist, but I think that the cost to business needs to be put into two categories. There are purchases that companies must make to comply with the new rule. The money doesn’t disappear; it merely goes somewhere else. If businesses buy American pollution control equipment, that is not a loss to the U.S. economy. Then there is the loss of productivity or efficiency that can come with compliance. That really could mean destroyed wealth, although it may be justified by the health and other benefits of the new rule.

Also, it is important to distinguish between capital expenditures, money spent on equipment, and operating expenses, money spent on operating that equipment. Money spent on equipment is a one-time investment, whereas money spent on operating that equipment is an ongoing commitment.

The EPA produced two very important documents that do a thorough cost-benefit analysis: Final Ozone NAAQS Regulatory Impact Analysis, March 2008, and its updated addendum, Regulatory Impact Analysis Final National Ambient Air Quality Standard for Ozone, July 2011. We will discuss these two documents in the next post.

Footnotes

  1. Website of Americans for Tax Reform, EPA Regulation of the Day: Ozone Rule. To view, click here.
  2. See my post in this blog EPA’s New Ozone Rule: Part 22.

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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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