1 UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C. 20460

OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD October 28, 2008

EPA-CASAC-09-001

The Honorable Stephen L. Johnson
Administrator U.S. Environmental Protection Agency 1200 Pennsylvania Avenue, N.W. Washington, D.C. 20460

Subject: Clean Air Scientific Advisory Committee’s (CASAC) Peer Review of Draft Chapter 8 of EPA’s Risk and Exposure Assessment to Support the Review of the NO 2 Primary National Ambient Air Quality Standard

Dear Administrator Johnson:

The Clean Air Scientific Advisory Committee (CASAC), augmented by subjectmatter-experts to form the CASAC Oxides of Nitrogen Primary National Ambient Air Quality Standards (NAAQS) Review Panel (herea fter referred to as the panel, roster provided in Enclosure A) held a public te leconference on October 22, 2008 to review draft chapter 8 of EPA’s Risk and Exposure Assessment (REA) to Support the Review of
the NO 2 Primary National Ambient Air Quality Standard. Chapter 8 is entitled "Exposure
Assessment and Health Risk Characterizati on." Additionally, CASAC offers comments on the schedule for NAAQS revision, prompt ed by the Staff’s presentation of the proposed outline for Chapter 10 of the REA.

Chapter 8 is critical to the REA because it provides a characterization of health
risk from NO 2 exposure based on the estimated numb er of exceedances obtained from a comprehensive personal exposure model for as thmatics in Atlanta. The CASAC panel was generally impressed with the careful work done over a short time with available tools and resources, but it has con cerns about the implications of certain model inputs and assumptions and about the general presentation of the approach and findings. The panel asks for changes in two main areas: in the interpretive presentation and in characterization of potential biases. The CA SAC plans to review the completed REA at its December 5, 2008 public teleconference and will provide recommendations for EPA's consideration in developing the Advance No tice of Proposed Rulemaking (ANPR) for

NO 2 during and immediately afte r that teleconference.2 Response to EPA Charge Questions

EPA requested CASAC’s responses to f our charge questions related to the exposure assessment and health risk characte rization of the draft chapter 8 provided for review. The charge questions and re sponses follow immediately below.

1. To what extent is the assessment, interp retation, and presentation of the results of the exposure analysis technically sou nd, clearly communicated, and appropriately characterized?

Staff has produced a solid application of the APEX model. While recognizing that there have been signif icant improvements since the fi rst draft of the REA and the update at the September CASAC meeting, th e panel still has c oncerns about the application of AERMOD. Staff should give serious consideration to improving AERMOD model performance in comparison to the concentrations measured by the monitors in Atlanta. For example, AERMOD output could be adjusted to better reflect observed peak values and di urnal profiles. Many factors influence the AERMOD predictions and the panel is concerned that the overall unc ertainty, reflective of the uncertainties from each of these factors, is no t appropriately characte rized. In particular, the tails of the exposure distribution could be strongly biased, notably with respect to onroad and near-road exposures. These exposures are particularly important, since they are the major contributors to the benchmark exce edances. On-road exposures may be biased high because receptors are in the middle of th e road; the exhaust is not diluted much; and observed data suggest that the on-road vs. background ratios are much more narrowly distributed than the AERMOD predictions. Near-road exposures may similarly be affected by biases in the on-road estimates. In addition, near-road exposures may not be appropriately weighted to the Atlanta populatio n because a greater proportion of residents may live closer to major roads than is repr esented by the assigned locations of model receptors at the census block centroids used in the AERMOD model.

In evaluating population exposure under altern ative standards, Staff elected to roll
back health benchmark values as a time -saving substitute for rolling up ambient concentrations. In view of the potential ly strong influence of this decision on the
numerical determination of benchmark ex ceedances, the chapter needs to provide a clearer justification for this approach and consideration need s to be given to validating the procedure.

2. The draft risk and exposure assessment document evaluates exposures in Atlanta. What are the views of th e Panel on the approach taken and on the interpretation of the results of this analysis?

The chapter needs to better evaluate the generalizability of findings for Atlanta. In particular, three aspects of the selection of Atlanta should be addressed more carefully. First, the selection of Atlant a should be reviewed with c onsideration of the extent to which the city represents exposures nationall y, since the model results are being used as the basis for setting a national ambient air qual ity standard. What ar e typical features of the population behaviors, building use (e.g., air conditioning), housing stock, and residential patterns that suggest similaritie s and differences with other major cities,3 particularly with respect to an ticipated high-end exposures to NO 2 ? As a minimum, the panel suggests that a table be a dded to describe variation of key parameters across cities. Ideally, a sensitivity analysis that assessed th e importance of such parameters would also be included. Second, is the model applied to Atlanta adequately reflecting the local population? In particular, in assigning model receptors to census tr act centroids, is the model systematically missing the fraction of the population who lives closest to roads and is consequently regularly exposed to high near-road exposures? The fraction of the Atlanta population that lives w ithin 50 meters of a major roadway could be much higher than the 1% figure represented by the census tr act centroids. We encourage EPA to seek an independent estimate of th is important quantity. Thir d, the application of AERMOD to Atlanta suggests a significant potential to predict concentrati ons that are biased upwards at the high end of the distributi on. This bias should be more thoroughly discussed, along with likely implications.

3. What are the views of the Panel regarding the ade quacy of the assessment of uncertainty and variability with respect to characte rization of exposures and health risks associated with those exposures?

A complete analysis of uncertainty is an essential component of a thorough exposure and risk assessment. The panel is c oncerned that there is the potential for more bias and uncertainty in the re sults than has been characterized in the current uncertainty and variability assessment and that no rationa le has been provided for assigning weight or priority to identified uncertainties. A bette r characterization of un certainty is needed, with attention to prioritizati on of the multiple sources of uncertainty, and where possible, quantification of their impact. Qualitative approaches that might be followed for this purpose can be found in other reports 1

In addition, previous suggestions made by individual panel members on this topic have not been explicitly considered; the conc erns raised should be addressed in the final report. More thorough characterization of the assumptions and model features that most strongly influence the estimated number of exceedances is ne eded. Most notably, the onroad and near-road exposures are important determinants of the number of exceedances of specified concentration levels experien ced by the population. In addition to on- and near-road characterization, and locations of r eceptors, assumptions about penetration into various microenvironments, particularly transportation environments, should be discussed. The implications of the significan t biases discussed in the application of
AERMOD need to be covered in this sect ion. Value-laden statements in Section 8.4.8 about the acceptability of AE RMOD over-predictions should be relocated to Section 8.10
and discussed in the context of variability and uncertainty.

4. To what extent is the assessment, interp retation, and presentation of health risk characterization included in Chapter 8 technically sound, clearly communicated, and appropriately characterized?

1 See, for example, U.S. EPA. Limitations in the 1996 National-Scale Air Toxics Assessment 1996 [cited 10/23/08. Available from http://www. epa.gov/ttn/atw/nata/natsalim2.html ] and World Health Organization International Programme on Chemical Safety. Part 1: guidance document on characterizing and Communicating uncertainty in exposure assessment. World Health Organization In Press. [cited 10/23/08. Available from http://www.who.int/ipcs/met hods/harmonization/areas/uncertainty%20.pdf].4 The overall presentation of the chapter needs to be improved in order to help
readers to understand the broa d framework of the modeling a nd to give a context for the
health risk characterization. In addition to expanding the overview section, several figures and tables should be added to show the relationships among the various models and to summarize the data inputs. Furthermore, this chapter needs to note that the health
risk characterization focuse s exclusively on exposure benchmark comparisons through additional discussion and/or cross-referencing to other sections of the REA. EPA should add a concluding section that summarizes the primary results and implications from the large number of models and analys es presented in the chapter.

Comments on the Schedule for NAAQS Revision

Staff provided an overview of plans for Chapter 10 of the REA, which will be critical for considering options for the NAAQS for NO 2 . The timeframe of the teleconference permitted only a brief exchange around the general appr oach that will be taken. The panel was told that time might not permit the EPA to respond to the CASAC recommendations concerning Chapter 10 and th e implications of that summary chapter for developing the ANPR, following the CA SAC public teleconference planned for December 5, 2008. The REA and the ANPR are cr itical parts of the new review process and the panel would find it unacceptable to be unable to provide advice on these
documents in an effective manner. Time fo r these essential CASAC review steps should be included in any revisions to th e timetable for completion of the NO

x review.

This is only one example of the implica tions of the rapid schedule for completion of the NAAQS revision process. EPA is pr oducing and revising analyses and documents at a pace that is compromising CASAC’s revi ew function and conseque ntly the quality of the scientific foundation for revising the NAAQ S. CASAC recognizes the drivers of the schedule for NAAQS revision but cautions th at there are now warnings that CASAC's review role, mandated by the Clean Air Act, is likely to be diminished by the compressed
schedule.

In closing, the panel noted the substantia l progress in the development of this chapter of the Risk and Exposure Assessment. We look forward to reviewing the final
version of the entire document later this year

.

Sincerely,

/Signed/

Dr. Jonathan M. Samet, Chair Clean Air Scientific Advisory Committee

cc: Marcus Peacock, Deputy Administrator5 

### NOTICE

This report has been written as part of the activities of the EPA's Clean Air Scientific Advisory Committee (CAS AC), a Federal advisory committee independently chartered to provide extramural scientific information and advice to the
Administrator and other offici als of the EPA. The CASA C provides balanced, expert
assessment of scientific matters related to issues and problems facing the Agency. This report has not been re viewed for approval by the Agency and, hence, the contents of this report do not necessarily represent the views and policies of the EPA, nor of other agencies within the Executiv e Branch of the Federal government. In addition, any mention of trade names or commercial products does not constitute a recommendation for use. CASAC reports are posted on the EPA Web site at: http://www.epa.gov/casac

.6 Enclosure A 

### U.S. Environmental Protection Agency Clean Air Scientific Advisory Committee Oxides of Nitrogen Prim ary NAAQS Review Panel

CHAIR
Dr. Jonathan M. Samet , Professor and Chair of the Depa rtment of Epidemiology, Bloomberg School of Public Health, Johns H opkins University, Baltimore, MD

CASAC MEMBERS Dr. Joseph Brain , Philip Drinker Professor of Envir onmental Physiology, Department of Environmental Health, Harvard School of Public Health, Ha rvard University, Boston, MA

Dr. Ellis B. Cowling , University Distinguished Professo r At-Large, Emeritus, Colleges of Natural Resources and Agricultur e and Life Sciences, North Caro lina State University, Raleigh,

NC

Dr. James Crapo , Professor of Medicine, Department of Medicine, National Jewish Medical and Research Center, Denver, CO

Dr. H. Christopher Frey , Professor, Department of Civ il, Construction and Environmental Engineering, College of Engineering, Nort h Carolina State University, Raleigh, NC, USA

Dr. Donna Kenski , Data Analyst, Lake Michigan Air Di rectors Consortium, Des Plaines, IL

Dr. Armistead (Ted) Russell , Professor, Department of Civ il and Environmental Engineering, Georgia Institute of Technology, Atlanta, GA

CONSULTANTS

Professor Ed Avol , Professor, Preventive Medicine, Keck School of Medicine, University of Southern California, Los Angeles, CA

Dr. John R. Balmes , Professor, Department of Medi cine, Division of Occupational and Environmental Medicine, University of California, San Francisco, CA

Dr. Douglas Crawford-Brown , Emeritus Professor and Director , Department of Environmental Sciences and Engineering, University of Nort h Carolina at Chapel H ill, Chapel Hill, NC

Dr. Terry Gordon , Professor, Environmental Medici ne, NYU School of Medicine, Tuxedo, NY

Dr. Dale Hattis , Research Professor, Center for Tec hnology, Environment, and Development, George Perkins Marsh Institute, Clark University, Worcester, MA7 Dr. Rogene Henderson , Scientist Emeritus, Lovelace Re spiratory Research Institute, Albuquerque, NM

Dr. Patrick Kinney , Associate Professor, Department of Environmental Health Sciences, Mailman School of Public Health , Columbia University, New York, NY

Dr. Steven Kleeberger , Professor, Lab Chie f, Laboratory of Resp iratory Biology, National Institute of Environmental Health Sciences, Na tional Institutes of Health, Research Triangle Park, NC

Dr. Timothy V. Larson , Professor, Department of Civ il and Environmental Engineering, University of Washi ngton, Seattle, WA, USA

Dr. Kent Pinkerton , Professor, Regents of the University of California, Center for Health and the Environment, University of California, Davis, CA

Dr. Edward Postlethwait , Professor and Chair, Department of Environmental Health Sciences, School of Public Health, Un iversity of Alabama at Birmingham, Birmingham, AL

Dr. Richard Schlesinger , Associate Dean, Department of Biology, Dyson College, Pace University, New York, NY

Dr. Christian Seigneur , Director, Atmospheric Environmen t Center, Université Paris-Est, Champs-sur-Marne, France

Dr. Elizabeth A. (Lianne) Sheppard , Research Professor, Biostatistics and Environmental & Occupational Health Sciences, Public Health and Community Medici ne, University of Washington, Seattle, WA

Dr. Frank Speizer , Edward Kass Professor of Medici ne, Channing Laboratory, Harvard Medical School, Boston, MA

Dr. George Thurston , Professor, Environmental Medi cine, NYU School of Medicine, New York University, Tuxedo, NY

Dr. James Ultman , Professor, Chemical Engineering, Bioengineering Program, Pennsylvania State University, University Park, PA

Dr. Ronald Wyzga , Technical Executive, Air Quality Health and Risk, Electric Power Research Institute, Palo Alto, CA

SCIENCE ADVISORY BOARD STAFF Dr. Angela Nugent , Designated Federal Officer8 Enclosure B: Compilation of Individua l Panel Member Comments on Chapter 8 of
EPA’s Risk and Exposure Assessment (REA) to Support the Review of the NO 2 Primary National Ambient Air Quality Standard

This enclosure contains final written comme nts of individual members of the Clean Air Scientific Advisory Committee (CASAC) Oxid es of Nitrogen Primary National Ambient Air Quality Standards (NAAQS ) Review Panel. The comm ents are included here to provide both a full perspec tive and a range of individua l views expressed by panel members during the review process. These comments do not represent the views of the
CASAC or the CASAC Panel.

Comments Received :

Comments from Prof. Ed Avol ........................................................................................... 9
Comments from Dr. John Balmes..................................................................................... 11 Comments from Dr. Joseph Brain .................................................................................... 13 Comments from Dr. James Crapo..................................................................................... 14 Comments from Dr. Dougl as Crawford-Brown ............................................................... 15 Comments from Dr.H. Christopher Frey .......................................................................... 19 Comments from Dr. Terry Gordon ................................................................................... 20
Comments from Dr. Dale Hattis ....................................................................................... 22 Comments from Dr. Rogene Henderson........................................................................... 26 Comments from Dr. Timothy Larson ............................................................................... 27
Comments from Dr. Kent Pinkerton................................................................................. 29
Comments from Dr. Armistead Russell............................................................................ 31
Comments from Dr. Jonathan Samet................................................................................ 33 Comments from Dr. Richard Schlesinger......................................................................... 34 Comments from Dr. Christian Seigneur ........................................................................... 35 Comments from Dr. Elizabeth “Lianne” Sheppard .......................................................... 36 Comments from Dr. Frank Speizer................................................................................... 38
Comments from Dr. Ge orge Thurston.............................................................................. 40
Comments from Dr. James Ultman .................................................................................. 429 Comments from Prof. Ed Avol

Comments on Second Draft NOx REA, Chapter 8
Ed Avol

General Comments:

My expertise is not in modeling, so I am not familiar with AERMOD and will have to defer to others regarding the appropriate application of it here. I did appreciate
that there was a considerabl e effort undertaken to lay out the modeling approach,
and Staff should be commended for those effo rts. Although a gr eat deal of detail was provided in the chapter, I did not feel it was properly synthesized or
summarized for the reader. A final few paragraphs asserting what it all means
would have been useful. There was consid erable discussion about uncertainty, but it, too, seemed almost philosophical in nature, rather than specific – can anything focused to the effort at hand be said regarding the magnitude or degree of uncertainty related to this modeling exercise?

Specific Comments: Table of Contents, Section 8.8 title, (t ypographical error), check font type size

P4, Section 8.3.1, line 21 – the statement that “...Atlanta was selected as the second-case study location...” is m ade, with no reference, comment, or explanation about the first study case (P hiladelphia), the reasons for going to a second, the generalizability of either of these selections, or the selection process...something needs to be said as to how these choices were made, even
if it is to a discussion deferred to the appendix (although the appropriateness of
this selection would seem to be an issue to be addressed in the main body of the document).

P5, Section 8.3.3, lines 5-7 – the asse rtion is made that 3 years of met data (2001-2003) are used to achieve a degree of stability in dispersion and exposure model estimates. Given recent fluct uations in meteorological patterns, how
“stable” or “usual” are t he 2001-2003 weather patterns fo r the area? Are they, for example, unusual drought years, wet years, hot years, or cold years? Is it reasonable (and credible) to use them to generalize for the air quality modeling?

P6, Section 8.3.4, lines 7 and 8 – specify units (years)

P6, Section 8.4.1, line 23 – change “are” to “were”

P6, Section 8.4.1, line 27 – typo at end of word “included”

P7, Section 8.4.2.1, line21 – insert “a irport” in Atlanta Hartsfield name.

P8, Section 8.4.2.4, line 16 – insert “was” after “10%”10 P11, Table 8.2 – Comment – the HDV fractions seem high (10%-25%) for a metropolitan area with commuters (mo st of whom will use LDV for transportation)...?

P19, Section 8.4.7, line 14-15 – how does assignment of receptors to a height of
0 meters make the model more efficient (let alone realistic)?

P21, Section 8.4.8.1, li nes 15-17 – does that observa tion that there were only two predicted exceedances of 150ppb NO 2 at one monitor and no estimated NO2 concentrations above 200ppb for 1hour say something about the modeling results, or the location of the samplers?

P29, Section 8.5, line 4 – 64,000 asth matics/500,000 children is about 13%; is this a high value or in conformanc e with other estima tes for the region?

P33, Section 8.7.2.1, li nes 5-18 – this discussion exclusively focuses on gas cooking as the only indoor source of NO2 interes t. What about un-vented or poorly-vented room or wall heaters or fireplaces?

P37, line 8 – change ”an” to “and”

P38, Section 8.9.1, lines 22-23 – This st atement is not necessarily true, so it would be better to just say the expos ure results focused on asthmatics.

P39, Section 8.9.2, line 13 – c hange “individual” to “individuals”

P39, Section 8.9.2, lines 18-21 – this is poorly phrased and confusing, since
these are two different t houghts. Suggest breaking in to two sentences: “...with most containing less than 30ppb.” “A bout 5% of these receptors...”

P53, Figure 8-17 – Why are there three Figure 8-17a illustrations? How can the first Figure 8-17a (> 100ppb) be so different from the rest?11 Comments from Dr. John Balmes

Characterization of Exposure and Health Risk s Associated with Exposure (Chapter 8 and Appendix B): John Balmes’ comments

GENERAL COMMENTS

The agency staff members responsible for th e work presented in Chapter and Appendix B
are to be commended for their hard work over a short timeframe.

1. To what extent is the assessment, interp retation, and presentation of the results of the exposure analysis technically sound, clearly communicated, and appropriately
characterized?

I do not have modeling expertise, but I found th e logic and results of the modeling efforts conducted to be presented clea rly. The discussion of assump tions and uncertainties was also clear. A general concern that I have is that the overa ll modeling exercise is complex and dependent on many sources of data with va rying quality and uncertainties. Multiple assumptions are required. Is it necessary to support the air quality standard setting with such a complex model. Put another way, c ould a simpler model with less assumptions and less data inputs be built that provides reasonable bounds to the likely population exposures to NO2 above the benchmark values, but that is also easier for non-modelers to understand? A specific concern that I have is that APEX apparently uses only one temperature value per day (p. 63, sub-secti on 8.10.3). Given the overall complexity of the exposure model, one would think that te mperature could be better parameterized.

2. The draft risk and exposure assessment document evaluates exposures in Atlanta. What are the views of the Panel on the appr oach taken and on th e interpretation of the results of this analysis?

Atlanta is a large metropolitan area that ha s both relatively good am bient air quality and
health effects data. Given lim itations of time and staff resour ces, I think the decision to focus Atlanta is reasonable. My major concer n about the decision is that because of its climate, the penetration of air conditioning is high (apparently almost 100%). This makes modeled NO2 exposures in Atlanta less re presentative of such exposures in areas with more temperate climates.

3. What are the views of th e Panel regarding the adequ acy of the assessment of uncertainty and variability with respect to characterization of exposures and health risks associated with those exposures?

The variability and uncertainty section of the chapter (sec tion 8.10) reads well, but there is no overall assessment of the impact of the sources of uncertainty on the exposure estimates presented in section 8.9.

4. To what extent is the assessment, interp retation, and presentation of health risk characterization included in Chapter 8 technically sound, clearly communicated,12 and appropriately characterized?

There is no presentation of health risk char acterization. In my view, presentation of the number of potential exposures to NO2 of the total population or persons with asthma
does not constitute sufficient health risk char acterization. The impact of the estimated exposures on the health of th e total and asthmatic populations should be discussed in the chapter.

SPECIFIC COMMENTS

p. 17, line 5 For what the abbreviation, SCC, st ands should be spelled out the first time
it is used..

p. 33, line 11 American Housing Survey shoul d be spelled out with its first use.

p. 33, lines 17-18 Should be “...CHAD diaries, stratified by hour of the day and normalized to the expected value of daily food preparation events, 1.4 (Table 8-11).

p. 39, line 29 Persons do not “contain” exposures to ambient exposures.

p. 41, lines 6-8 Ibid.

p. 42, line 12 Should be “...cooking fuel as an influential variable...”

p. 42, line 13 Should be “...of whom 13 had personal...”

p. 42, line 17 Should be “...an exposur e distribution was constructed for each individual,...”

p. 43, line 3 Should be “1999-20 00”.

p. 51, line 7 Should be “...the times spent...”

p. 51, line 12 Should be “...regarding the e ffect of indoor sources...”

p. 51, line 13 “...microenvironments, however, changes...”

p. 51, line 16 Delete “a” between “to” and “comprising”.

p. 56, lines 27-28 “Results for asthmatics when exposures were estimated...”

p. 66, line 15, line 26 For what the abbreviations, CMSA and CSA stand should be spelled out the first time they are used.13 Comments from Dr. Joseph Brain

Chapter 8 and other parts of the REA document rely heavily on analyses of Atlanta data. An essential question which dese rves much more attention is the extent to which these findings can be generalized. In terms of NOx levels and other aspects of exposure assessment, we need to know how A tlanta compares to other population centers throughout the United States, such as Los A ngeles, Houston, or Chicago. What is the range of NOx exposure in these other cities? Other critical parameters should also be compared? What is the prevalence of air conditioning? What do we know about human activity in different cities, e.g. time spent i ndoors vs. outdoors, and what about relevant confounders such as temperature and humidity?

I am sensitive to the limited time availabl e to address their issues. There may not be time to carry out what should be done – a sensitivity analysis. To what extent do the predictions and models change when we subs titute data from other cities? One could, however, even with the existing Atlanta model, change various parameters, and see what happens to the outcomes. Another approach w ould be to create a table which lists these parameters for selected US cities. That would reinforce the point that safety factors need to be built in because of uncertainty about the extent to which Atlanta is typical.14 Comments from Dr. James Crapo

Comments on Chapter 8, REA NO2 Document, dated October 2008

In general the EPA staff have done an excellent job in compiling a very complex model to predict the number of individuals in Atlanta who would be exposed to NO

2 levels above various potential Health Effect Benchmark Levels. The models are appropriate and the descriptions of how the data was used in the models, including the assumptions involved, are clearly described. This will provide a reasonable basis on which to estimate the population impact of conformance to various NO

x NAAQS. My concerns

are:

1. The model is extremely complex with a large number of assumptions at almost every aspect of the model. In most cases it is not known how these assumptions may aggregate to create a significant positive or negative bias in the results. Would a much simpler model provide estimates of populations at risk that would be of similar - or better - final accuracy? This complex model may create a false sense of accuracy. My point is that this model needs to be validated with experimental data. The model should be used to predict testable outcomes such as ER admissions for asthma, etc., which can then be compared to actual observations. This could be done in a prospective fashion or by applying the model to prior time periods not used to create the model, but where outcome data is already known.

2. The overview for the chapter states that the intent is to document the methodology and data used in the inhalation exposure assessment and in the associated health risk characterization for NO

2 . The chapter only models the temporally and spatially variable NO

2 concentrations and simulates the predicted human contact with those modeled NO

2 concentrations. The chapter needs to go on to use these simulations to predict health risk in terms of testable outcomes - i.e.: mortality, hospital admissions, ER admissions for asthma, exacerbation of respiratory symptoms, etc. This is the ultimate purpose in creating these models and will provide a means to eventually validate the utility
of the models.15 Comments from Dr. Do uglas Crawford-Brown

Comments on Risk and Exposure Assessmen t to Support the Review of the NO2

Primary National Ambient Air Qualit y Standard: Chapter 8 and Appendix

Doug Crawford-Brown

April 22, 2008-04-27

These comments focus on Chapter 8 and the appendix of the Risk and Exposure Draft.

My review is organized around the four charge questions.

1. To what extent is the assessment, interp retation, and presentation of the results of

the exposure analysis technically sound, clearly communicated, and appropriately

characterized?

I was in general quite pleased with by the an alysis and the way it was described both in

the text and in the appendix (which was, by the way, well written). There are a number of

important issues from the previous review th at have now been addr essed adequately, and

there has been an impressive amount of wo rk done in short order to provide these

improvements. I found it easy to understand the analytic steps, and the justification for

formulating them as the staff did.

The characterization of AERMOD could use a bi t more work. My sense is that it biases

results upwards, which would then bias upwar ds the predicted number of effects. This

aspect of the model is not adequately descri bed, nor is it reflected in the uncertainty

section. I also was never completely clea r as to how the percentiles of ambient

concentrations were being used in the A tlanta and Philadelphia examples, or whether

there even was consistency between the two cas e studies in regards to percentiles used.

There needs to be a concise paragraph or tw o explaining more clearly how the upper tails

of distributions were used a nd why these particular percentil es were selected. Otherwise,

it strikes me – if I were a first time reader – that there is a lot of conservatism built into16 the analysis, especially using parts of a di stribution (the upper tails) where I am less

confident in the results..

The discussion of receptor locations in Sect ion 8.4.7 could use improvement. I was never

clear in reading that section how the recep tor locations were related to the APEX

modelling, which can follow people through an act ual exposure field rather than through

representative locations of exposure. As I read the sect ion, it sounded to me as if a few

receptor locations were selected as representa tive of ambient concentrations associated

with a given activity, and I was not sure how that fit into the APEX approach based on

census tracts. I can imagine how it is done , but the section didn’t give me enough

description to understand the issue fully.

I repeat here a point I raised in previous drafts. I ge nerally approve the proportional rollup or roll-down methods based on current maxi mum concentration at a specific site. And

I agree that the adjustment of the benchmarks produces the same result mathematically.

But it continues to make no sense scientific ally, and. the savings in processing time don’t

appear to me sufficient to justify a met hod that people will fail to understand as

mathematically equivalent.

2. The draft risk and exposure assessment document evaluates exposures in Atlanta.

What are the views of the Panel on the appr oach taken and on th e interpretation of

the results of this analysis?

I agree with the approach taken, subject to the comments in Charge Question 1. It seemed

to me, however, that the analyses for Atlant a and Philadelphia were not quite the same,

making comparisons difficult. I particularly liked the genera tion of results on person-days

of effects in Atlanta, and wish the same had been done for Philadelphia.

I think the interpretation of results for A tlanta is appropriate, given the assumptions

made. However, as mentioned earlier, AERMOD appears to bias resu lts high, or at least

above the monitoring results. This should factor into the interpretation, or at least into the

uncertainty analysis, and I didn’t find that to be the case.17 I also didn’t know how the staff were interpre ting the results that di vide effects between

categories of with or withoutindoor sources included. In so me cases, the large majority

of effects appear to be from indoor (and hen ce uncontrolled) sources, while the results as

the ambient levels rise show the dominance of the ambient exposures. There should be a

better description of how the st aff believe these results should be interpreted. However, I

do agree with the results themselves, again given the assumptions and models employed.

The development of the longitudinal activity sequences is a sophisticated piece of work,

and is described adequately. The one comment I have here is that at one point, the staff

had to decide whether to use correlated da ily activities or uncorrelated. They used a

cluster approach, which I support. However, it was a bit difficult, reading the text alone,

to understand the cluster approach selected or why the authors believe it produces results

intermediate between the other two results. It might have been useful to present a

representative set of results under each of the three a pproaches and see how much

variation it produces (a kind of sensitivity analysis).

3. What are the views of th e Panel regarding the adequ acy of the assessment of

uncertainty and variability with respect to characterization of exposures and

health risks associated with those exposures?

The uncertainty analysis remains inadequate to produce any sort of confidence bounds on

the analytic results, although it improves w ith each iteration we have seen. And it now

gives the reader a sense of the contribution to variance from each component. I am not

pushing for a formal nested variability-uncertain ty analysis, but it does seem to me that

something akin to what went into NATA might be appropriate, where at least the overall

uncertainty was categorized. And there rema ins the issue of the influence of the

conservatism of AERMOD on whether final results should be seen as simply uncertain,

or biased upwards.18 On a minor point, there is an odd part of Pa ge 67 where the authors talk of a negative

value for the GSD and for the GM. I must be reading it incorrectly (since these negative

values are not possible), but I cannot understand these sentences.

4. To what extent is the assessment, interp retation, and presentation of health risk

characterization included in Chapter 8 technically sound, clearly communicated,

and appropriately characterized?

My comments are the same as in Charge Question 1, although I note here that the

presentation of health effects results was quite effective in this document. The analysis of

repeat effects is interesting scientifically, but the policy implications are not clear. I

would suspect that the person-days above the benchmark is more likely to inform any

final decision. Some clarification on the signi ficance of this analysis (of multiple effects

for an individual) would be useful

I am not convinced by the argument that the daily activity patterns for asthmatics and

non-asthmatics are the same, especially on high ozone days where an alert has been

issued. There is a passing comment about a study suggesting otherwise, but I don’t

believe that study examined the effect of air quality indices being published. I know RTI

were doing such a study at one time (Carol Mansfield was heading it), so perhaps the

staff might find the results of that stu dy and see if the conclusions are changed.

I end with a comment I have made in almost all similar cases reviewed by CASAC. The

modelling performed here is impressive and re presents state-of-the-science. But I worry

that it may be too elaborate for the purpos es of establishing a NAAQS. There are many,

many assumptions built into the assessment, fr om air modelling to activity patterns. And

all of these rest on spatial resolution of exposure fields and receptor locations. The

science is great, but I feel the current analysis is pushing the resolution of the results just

a bit. Some comments in the document mentioning this issue, and why the results still are

useful for a NAAQS determination, would be good.19 Comments from Dr.H. Christopher Frey

The following guidance document should be referenced and cited in Chapter 8:

"GUIDANCE DOCUMENT ON CHAR ACTERIZING AND COMMUNICATING
UNCERTAINTY IN
EXPOSURE ASSESSMENT"

http://www.who.int/ipcs/methods/harmoni zation/areas/exposur e/en/index.html

Also, , the assumption of 10% NO2 vers us total NO for source strength may be conservative for existing mobile and stationary sources. However, for diesel vehicles equipped with particle traps and other postcom bustion controls, there is evidence that the

NO 2 /NO
x ratio is higher than this. As such ve hicles penetrate the on road fleet, this may
have some effect on the overall ration of NO 2 /NO
x .

I recommend that EPA consider that one of the useful outputs of this study will be a prioritized list of key uncertainties, as disc ussed today. Such a list could be developed from qualitative weight of evidence approach es, and communicated in broad categories (e.g., low, medium, high uncertainty) or could be developed quantitatively (preferred where possible). One benefit of this informa tion is that it could help prioritize data collection or research to improve the state of knowledge for future reviews and revisions
of the NO 2 NAAQS.

However, my concern is that we don't want to imply that what can be done in a short
amount of time under a court-order is what SH OULD be done for the best science. The qualitative approach is a first step, but not (in my view) suffi cient. Along these lines, EPA should acknowledge any unresolved issues, possible uncertainties that are not fully characterized, and better met hodologies for dealing with thes e issues, in order to guide
future work.20 Comments from Dr. Terry Gordon

1. To what extent is the assessment, interp retation, and presentation of the results of the exposure analysis technically sound, clearly communicated, and appropriately
characterized?

Although my expertise does not allow me to evaluate whether the exposure analysis is technically sound, the analys is was clearly communicat ed and characterized. Explanations as to why certain decisions were made for the chosen methods were particularly clear. One minor communicati on suggestion would be to expand the figure legends and labeling for the figures.

2. The draft risk and exposure assessment document evaluates exposures in Atlanta. What are the views of the Panel on the appr oach taken and on th e interpretation of the results of this analysis?

The approach and interpretation were very good, but there still ex ists the potential problem or bias associated with using an analysis of one city in the Southeast (and Philidelphia) to encompass a risk analysis for the entire country. In particular, it appears
that 12 urban centers were us ed to estimate population expo sures for ozone (stated in Section 8.2, page 1, line 26). Perhaps this will be better addressed in the final REA chapter.

3. What are the views of th e Panel regarding the adequ acy of the assessment of uncertainty and variability with respect to characterization of exposures and health risks associated with those exposures?

The assessment of uncertainty and variability factors is very cl ear although a table delineating the direction of bias that each factor might introduce would be a good addition either in Chapter 8 or 9 (where I believe there may already be one).

4. To what extent is the assessment, interp retation, and presentation of health risk characterization included in Chapter 8 technically sound, clearly communicated, and appropriately characterized?

EPA did a great job under tight ti me constraints to finish this health risk characterization. It is technically sound and well communicated and characterized, although a conclusion section summarizing the relevance of the characterized exceedances/exposed asthmatics would solidify this chapter (rather than waiting until the final chapter).

Minor comments:

1. Table 8-1 – It would help the reader to define Fringe, Rural, Arterial, Freeway,
etc. below the table.

2. Table 8-5 – Again, please define FIPS, Major and Minor Links, and % Minor.

3. page 15, line 9 – Define NEI here and in Table 8-6.

4. page 26, line 8 – typo = lcocated.21 5. page 27, Table 8-7 – Define p0 to p100. Including ‘N’ as the first row is confusing as it’s not really On-Road H ourly NO2 (ppb) or Number of hours greater than x00 ppb.

6. page 29, line 2 – Given the use of 4 central counties, is it correct to look at the total population of Atlanta?

7. page 34, line 10 – typo = ‘ra te and the cooking...’.

8. page 68 – Should there be a discussion of th e uncertainty in applying 1 city (or 2)
to the rest of the U.S.?22 Comments from Dr. Dale Hattis Comments on the Treatment of Uncertainty and Variability in the Revised Chapter 8 Exposure Analysis

Dale Hattis, Clark University



### Over the course of reviewing the APEX and air quality modeling for past meetings, I and others have offered quite a few constructive suggestions for improving the modeling, the distributional assumptions (on such parameters as indoor air elimination rates and on road/off-road adjustment factors) and other issues. These include the following comments on the first draft REA reviewed in the May 2008 meeting:

“Air exchange distributions contingent on temperature and presence or absence of air conditioning. Overall the panel does not ha ve any objection to the idea of using lognormal distributions with very broa d limits (.1 and 10 air changes/hr).
However the detailed results seem to s how different patterns with temperature arbitrarily blocked into a few ranges. There does not appear to be any great consistency or overall theory for this analysis. A better description of the data as a whole might be produced by a more extensive regression study using temperature or some transform of temperat ure as a continuous variable and either fixed-effect or mixed effects modeling of differences among cities and for the air conditioner presence variable.

NO2 removal rate distribution--p. 101 . At least one pane list expressed an objection to the narrow fixed limits used for the removal rate distribution based on six values from Spicer et al (1993). The abstract to the Spicer paper makes it
clear that all six observations were made in a single house, and that there are additional complications from the presence of HONO, an apparently longer-lived NOx species:

p. 101—The same panelist also objected to the fixed limits used for the removal
rate distribution based on six values from Spicer et al (1993). The abstract reads.

Transformations, lifetimes, and s ources of NO2, HONO, and HNO3 in
indoor environments.

Spicer CW, Kenny DV, Ward GF, Billick IH.

Air Waste. 1993 Nov;43(11):1479-85.

Battelle, Columbus, OH 43201-2693.

Recent research has demonstrated that nitrogen oxides are transformed to nitrogen acids in indoor environments , and that significant concentrations23 of nitrous acid are present in indoor air. The purpose of the study reported in this paper has been to investigat e the sources, chemical transformations and lifetimes of nitrogen oxides and nitrogen acids under the conditions existing in buildings. An unoccupi ed single family residence was instrumented for monitoring of NO, NO2, NOy, HONO, HNO3, CO, temperature, relative humidity, a nd air exchange rate. For some experiments, NO2 and HONO were inj ected into the house to determine
their removal rates and lifetimes. Ot her experiments investigated the
emissions and transformations of nitr ogen species from unvented natural gas appliances. We determined that HONO is formed by both direct emissions from combustion processes and reaction of NO2 with surfaces present indoors. Equilibrium cons iderations influence the relative
contributions of these two sources to the indoor burden of HONO. We
determined that the lifetimes of trace nitrogen species varied in the order NO approximately HONO > NO2 > HNO3. The lifetimes with respect to reactive processes are on the order of hours for NO and HONO, about an hour for NO2, and 30 minutes or less for HNO3. The rapid removal of NO2 and long lifetime of HONO suggest that HONO may represent a significant fraction of the oxidized nitrogen burden in indoor air.

The uniform distribution with its fixe d boundaries (0% probability assumed for values outside of the defined limits) is pa rticularly inappropriate when the data are limited, as in this case. Use of the uni form distribution artificially reduces the
likelihood of more extreme values of th e modeled parameter than happen to be present in the limited available data. This in turn limits the model-predicted variability of NO2 concentrations, whic h critically determines the number of exceedances of the high hourly NO2 levels that are the focus of the risk assessment modeling. It would likely be fa r better to use a lognormal here as an initial hypothesis, but in the light of the f act that different houses with different internal materials might well destroy NO2 at different rates, expert judgment might well be needed to expand the li kely distribution beyond what can be derived from a simple data fit.

The same panelist also strongly objected to the use of uniform distribution of
concentrations of NO2 from use of gas stoves (p. 101). The very breadth of the bounds derived (4 – 188) ppb argues against a uniform distribution and in favor of something more skewed, such as a lognormal. The lognormal guarantees a positive contribution, and doesn’t have the unfortunate property of implying zero
chance that the indoor contribution w ill be above the derived maximum. Moreover, if a mass balance approach is being used to model indoor NO2, then the input per cooking event should be in terms of mass units of NO2, not concentration. Concentration will depe nd on house- and temperature specific factors such as air exchange rates, NO2 removal rates and residual contributions from HONO, among other things. Because these observations were from a single house in California, there must be extra allowance for variabi lity and uncertainty in these estimates that must clearly extend beyond the mass equivalent of the concentration range quoted.24 Finally the assumption that all cooking ev ents contributing to indoor NO2 last exactly one hour also artificially limits the variability in NO2 inputs and therefore exposures represented in the model.”



### In addition to these suggestions from the last meeting, earlier suggestions on the planning document for the REA included explicit modeling to deal with the fact that the air quality monitors are generally greater than people’s breathing zones, leading to a systematic underestimation of air concentrations to which people are exposed in the air quality characterizations.

My reading of the current chapter 8 is that the EPA authors have completely blown off all of these suggestions for revision of the uncertainty/variability analysis using the APEX modeling tool and the air quality modeling system. Not only that, the most recent version of the REA appears to omit sections of the previous exposure analysis draft that gave the reader a clue that improved quantitative characterization of the uncertainty and variability was possible. By not acknowledging these sources of uncertainty, and discussing the previous suggestions for improvement it seems to me they have not just been neglectful. It is fine if EPA wants to disagree with my/our previous review of their analysis on technical grounds. It is also fine if they want to say that they cannot make the improvements in their analyses that we suggested because of time and resource constraints. But to completely omit discussion of the previous critiques and suggestions for improvement of the analysis is unacceptable and could be interpreted as actively misleading. At the very minimum, the REA authors need to provide quantitative documentation and

discussion of:

• The height distributions for the air quality monitors, both nationally (as in earlier drafts of the REA and/or ISA appendices) and specifically for the case study cities (Philadelphia and
Atlanta),25 

### • The 30-odd values of the on-road/off-road ratios that the authors used for their empirical distribution of this key parameter,

• The six values for the indoor NO2 removal rate

distribution that underlies the calculations of

indoor air concentrations.

Documentation of the individual data are needed for these parameters in order for the committee to adequately review the conclusions of the final REA and the eventual comparative evaluations of alternative standards. The “margin of safety” language of the Clean Air Act, it seems to me, requires the

Administrator of EPA to consider in some detail the degree of confidence that can be achieved in conclusions that alternative NAAQS adequately protect public health. Therefore, absent a fair analysis and discussion of the likely quantitative effects of uncertainty and variability of these parameters on the estimates of population exposure under different regulatory scenarios, I would have the committee advise

the Administrator that the current document is so

deficient that it cannot be a reasonable basis for informed decision-making.26 Comments from Dr. Rogene Henderson Preliminary Comments on Chapter 8 of the NOx REA Submitted by Rogene Henderson, PhD October 16, 2008

My comments are given from th e viewpoint a non-modeler.

1.The details of the models for exposure were fully described and di scussed. I think it is important to compare the modeling values wi th actual measurements to see how well the models reflect reality. This was described we ll in Chapter 8. I am concerned that the diurnal comparisons showed the models overe stimated NO2 exposures at the beginning and ending of the day. Models can be useful when they are wrong because they tell us that we are not taking something( s) into account that influences , in this case, the diurnal variation in NO2. Has any thought b een given to what that might be?

2. Using only one city as the basis for the exposure analysis has the potential for not being representative of the total populati on of the US. However, from a practical viewpoint, limited resources prev ent one from analyzing more ci ties in depth. I think the
document describes the limitations of th e approach well and I agree with it.

3.The limitations of the models for e xposure are discussed in great detail.

4. I think of "health risk char acterization" as comparing what we know about the toxicity or hazard potential of the pollutant with wh at we know about exposures to come up with the potential health risk. But in this ch apter I only see the ex posure portion of the characterization discussed. Can you add a di scussion of the hea lth effects you might expect from the described exposures?27 Comments from Dr. Timothy Larson

Comments by Tim Larson on Chapter 8 of the NO 2 REA

General Comments

EPA is to be commended for the framework outlined in Chapter 8. The inclusion of deterministic approaches to spatial extrapol ation of measurements from sparse network for purposes of exposure estimation is a welcome addition. It is an improvement on simple interpolation schemes that ignore the spatial distribution of important sources.

My main concern with this analysis centers around the assumption that the census block
centroids describe the location of the exposed population. My reading of the chapter says that only 1% of the exposed population is a ssumed to be living within 100 meters of relatively small roadways (>15,000 vpd). If this is the underlying assumption in the final assignment of ambient NO 2 by AERMOD, then it does not re flect the reality in most urban areas. In fact, if this assumption is what was made, the exposed population in the
Atlanta assessment could underestimated that in most urban areas by at least an order of magnitude. While I agree that the AERM OD model probably overpredicts the on-road exposures by up to a factor of 2, this is outweighed by the exposure location assignment
bias.

Something should also be mentioned in the uncertainty se ction regarding the roll-up methods. There is an apparent correlation between the average NO2 concentrations at EPA sites and the peak to mean ratio. In the roll-up method used by EPA, the assumption is that these two quantities are not correlated and therefore the peak to mean ratio remains constant during roll-up. The data suggest otherwise. Therefore the peak values may be overpredicted for a scenario just meeting the current a nnual standard. This is important when drawing conclusions a bout how well the current standard protects against the exceedance of peak hourly benchmark values. The analysis presented by Paine in the September 26 public comments s uggests that the EPA approach is very
conservative. There needs to be acknowle dgement of this issue and/or a rebuttal
argument.

Specific Comments

P6 line 19 Strictly speaking, AERMOD is a bi-Gaussian model

P 7 line 8 clarify wording

P23 what about smaller NOx point soujrces wi th short stacks? Is emission rate the only
criterion?

P25 only 1% near roadways?

Fig 8-7 The overprediction of AERMOD could be the effect of ignoring vehicle induced turbulence as well as including too much fr esh ozone. Comparison of NOx predictions would be useful in assessing the pure dispersion estimates.28 P31 locally high values? Do you mean within 100 meters of the road? Table 8-8 How do you get asthma prevalence rate for a 0-1 year old?

P53 line 16 should read “spend more time”

Fig 8-16 the in-transit estimates are probabl y generous given the assumption of pen=1. Also, given that people spend most time in their homes, even if the pen=0.5 for homes near roads, this could be important. In Atla nta, only 1% of the population lives within 50 m of a major road??

P55 line 2 should read figure 8-19

P61 line 13 in travel exposures may be underestimated due to ignoring the communting
route on-road levels

P63 line 24 a bit optimistic- e .g. compare with line 20 on p64

P64 line 27 the vehicle wake effect is most pronounced for wind directions parallel to the road, where the wakes of multiple vehicles can reduced on-road concentrations more than a simple one-time adjustment factor (e.g. 1.7) applied to all wind directions (including cross-winds).

P66-67 discussion of between city variation in APEX results for ozone not necessarily applicable to NO2, given the proxim ity to road effect for NO2.

Other comments (including ma terial in Appendix B)

Discuss whether there any visu al check on the conflation of TDM links with the actual street map. Using an algorithm that is ba sed on closest road to the TDM node will not always put the link on the correct road (case of nearly para llel roads and also underpass links).

Add a few sentences about the use of segm ented lengths- discuss how much mismatch
there is with actual road locat ions. Could be large for curv ed roads and may affect both
on-road and off-road estimates from AERMOD.

Initial NO2 to NOx ratio from tailpipe em issions- include a few sentences about the effect of catalytic converters on newer heavy duty vehicles.

Add to the discussion of vehicle induced tu rbulence- initial sigma z values are not adjusted for wind path length along the road way, an effect most pronounced for near parallel wind directions.

Discuss the uncertainties of assuming a s uperimposed, steady state area source plume model for aggregated small ro adway area sources- if travel times are greater than one hour, then the steady stat e assumption breaks down.29 Comments from Dr. Kent Pinkerton

COMMENTS: Kent E. Pinkerton, Un iversity of California, Davis

CHARGE QUESTION #1: To what extent is the assessment, interpretation, and presentation of the results of the e xposure analysis technically sound, clearly communicated, and appropriately characterized?

REPLY: The authors of chapter 8 have done an incredible job to organize this chapter. The presentation of information within the chapter is extremely thorough and carefully described. The methodology and data used in inhalation expos ure assessment and health
risk characterization for NO 2 as a criteria pollutant is up to date and highly innovative in its application as presented in Chapter 8. Th e estimation of temporal and spatial variation
of NO 2 concentrations appears to be a highly complicated and comple x process, but the authors have done an reasonable job to provi de a sound description and rationale. The authors describe approaches taken using th e Air Pollutants Exposure Model (APEX) to estimate human population exposure, while AERM OD is used to characterize ambient air quality. The APEX model simulates exposure using 1) characterizat ion of the study area, 2) generation of simulated individuals, 3) construction of a seque nce of activities, 4) calculation of hourly concentratio ns in mcroenvironments and 5) estimation of exposure. Each step in Chapter 8 is systematically de scribed with potential c oncerns for potential error described. It is my evaluation that the assessment, interpretation, and presentation of the results of the exposure analysis in Ch apter 8 have been done in a technically sound, clearly communicated, and appropr iately characterized fashion.

CHARGE QUESTION #2: The draft risk a nd exposure assessment document evaluates exposures in Atlanta. What are the views of the Panel on the approach taken and on the interpretation of the results of this analysis?

REPLY: Atlanta appears to be an ideal location for crafting th is risk and exposure assessment, based on the historical richness for NO 2 concentrations in this region and the availability of an excellent database of information to use in creating this model. The
inclusion of four counties c overing much of urban and subur ban Atlanta seems to provide a reasonable base to model and to make pr edictions for risk and exposure assessment. However, it is critical that the authors fully justify the selection of a single city or region for making predictions for the enti re nation in the assessment of NO 2 for the REA for

NOx.

CHARGE QUESTION #3: What are the views of the Panel regarding the adequacy of the assessment of uncertainty a nd variability with respect to characterization of exposures
and health risks associated with those exposures?

REPLY: The authors have carefully laid ou t the parameters used for the modeling to
estimate NO 2 exposure risk to individuals. The authors acknowledge the limitations of their model that must use assumptions, but ha ve applied APEX which from the authors’ point of view provides the most power and flexibility to estimate exposure assessment
and risk characterization. The aut hors acknowledge CHAD (Consolidated Human Activity Database) used in their model is likel y to produce the greatest uncertainty. This30 concern is based on 1) the variability of hu man activity patterns and 2) much of the information used is over 20 years old. The au thors have attempted to correct for some of these uncertainties, but there appears to still remain potential errors and/or factors that may not be able to be accounted for a nd/or are unknown. Population and commuting data, meterological data, and ai r quality data are only a few of the many parameters that
must be factored into this model. Base d on these parameters as well as indoor and outdoor factors, air exchange ra tes and others, it is impressive that the authors can make any predictions at all with any degree of certainty!

CHARGE QUESTION #4: To what extent is the assessment, interpretation, and presentation of health risk characteriza tion included in Chapter 8 technically sound, clearly communicated, and a ppropriately characterized?

REPLY: The implementation of the exposure modeling and health risk characterization is very thorough, well documented and reasona bly explained. Howeve r, concern remains when multiple assumptions must be made in a model where minor errors or large variations in values are po ssible, can easily be compounde d, thus leading to a highly misleading exposure model or health risk ch aracterization. Again, the authors simply need to make these limitations of the model clearly evident for the reader.31 Comments from Dr. Armistead Russell

Review of Chapter 8:

EPA Staff and their contractor are to be complimented on the amount of work conducted, and how quickly, to address concerns discusse d at the last NOx-primary meeting. While they have reduced some of the largest di fferences between the modeled and observed NO2, some remain. Those, for the most part, can be explained by some of the assumptions made:

1. 10% NO2 in exhaust. This could be lower, and would, in particular, lower the early morning NO2 peak. It was c hosen to be conservative. This is fine, and should be recognized as lead ing to a possible bias, and the issue
observed.

2. The temporal NOx emissions patter n would show less hourly variation than is likely, and, in particular , the smoothing used will put more emissions before 6 am than is likely the case. I drive here. There are few on the road before 6 am, and it is ghostish before 5 am. They would have done better to use the hourly temporal distributions available in SMOKE. This, alone, might get rid of th e aberrant peak at 5 am.

3. They could choose greater initial mixing values, though this would be small except for on-road estimates.

On the other hand, I would actually think the way they did the NOx emissions estimation would be more accurate than the NEI, and the 28% is too big of an expected change (and would go in the other direction).

There is a major bias in the AERMOD results that can not be r eadily dismissed, that being that the on-road/non-road ratio gets much higher for AERMOD. There is a consistent tendency, in all of the approaches , for AERMOD to have higher on-road than might be indicated by the observations. Th is is discussed, but should be highlighted more, particularly later on when interpreting the APEX results. As you will note, most of the exposures to high levels come from on- and near-road activities.

The application of APEX appears solid, though the evaluation and interpretation is flawed. While I am glad to see the evaluati on performed, it is misleading. In particular, Fig. 8-11 should show maximums, not P97.5 fo r comparison with Fig. 8-10. Indeed, I suspect we will see that the maximums pr edicted by APEX (which drive the later analysis) are much higher than observed. I w ould actually like to see a figure where they bin the APEX results in deciles (e.g., cumula tive %ile deciles), and plot the min, median, 97.5%ile and max. They also might estimate the 97.5%ile of the observations from Suh et al., for comparison. Call Helen.

The reason all of the above is important (at least to me) is that we are compounding some apparently large biases at the upper end of the distri bution to the point that I think we are well overestimating the population that is bei ng exposed to greater than the benchmarks chosen. Remember, there has been one observation of over 200 ppb of NO2 over the three year period. What was the second high? Does that support th e distribution found?32 In the end, I am uncomfortable with the compounding of biases for factors leading to the upper tail of the NO2 exposure distribution. While they may have to work with this, they should be extremely cautious about ho w the results are communicated.33 Comments from Dr. Jonathan Samet

Comments: Draft Chapter 8 of EPA’s Risk and Exposure Assessment to Support the Review of the NO 2 Primary National Ambient Air Quality Standard

General Comments:

The draft Chapter 8 on Exposure Assessment and Health Risk Characterization is improved and now complete. The Staff made substantial progress in developing the chapter and it will prove useful as the basis for health risk characterization. As far as major concerns, I offer the following:

• The document is detailed and lengthy, and does not offer a sufficiently informative overview of the approach th at would be taken. It does have an introductory section, but the description is inad equate. I recommend the incorporation of appropriate diagra ms that would lay out the various
models that would be used and the data inputs for the modeling. This diagram would be useful for describi ng what has been done and also for describing the uncertainties that arise.

• At a number of points, judgments are made with regard to what evidence
shows and what determinations can be made. However, I find that the
criteria for these determinations ar e lacking. For example, on page 27, lines 7-9, the conclusion is reac hed that adjustment of model
concentrations to the ambient monito rs was not necessary. I cannot find a clear rationale. Similarly, on page 24, lines 1-3, “general agreement” is
said to be found between observed an d modeled values. Again, what is “general agreement?”34 Comments from Dr. Richard Schlesinger

I do not have expertise in the area of expos ure assessment. However, that said, the revised chapter did present material in a c oherent and understandable manner. As I have noted in prior types of analys es such as these, I am c oncerned about having one site
become the model site for all of the an alyses. Thus, there should be a more comprehensive justification for use of this one site.35 Comments from Dr. Christian Seigneur

Comments on Chapter 8 of the 2 nd draft of the REA

Christian Seigneur CEREA, Université Paris-Est

OAQPS has accomplished a large amount of work in a short time. Their overall methodology to calculate exposure and risk for Atlanta seems sound. However, I have some questions regarding the resu lts of the air quality modeling.

Section 8.4.2.4: It seems that the ozone limita tion techniques were applied to AERMOD by source category ((mobile sources, airport, et c.). Thus, if two source categories were to impact significantly a same location, would it be possible to double-count the ozone available for oxidizing NO to NO2?

Section 8.4.8: The report pr esents a thorough comparison of modeled and measured NO2
concentrations. Both the cumulative distribut ions and the diurnal profiles show that
AERMOD tends to overestimate the measured concentrations. Such results suggest that some adjustment of the modeled values is warranted to better reflect the actual concentrations. However, the document states th at “it was determined that adjustment of the modeled air quality based on the three mon itors was not necessary”. Such a statement could apply if the model show ed error with no or negligib le bias. However, the model shows a systematic bias (overestima tion) for concentrations above the 60 th percentile of the observed values (i.e., thos e concentrations of most in terest for health effects). Therefore, it seems that some adjustment is warranted to scale the modeled values down
toward the values observed at the monitors.

Section 8.10.4: The discussion of the uncertainti es associated with th e air quality values does not highlight the significant bias th at was shown in the AERMOD evaluation
section.36 Comments from Dr. Elizabeth “Lianne” Sheppard

General comments : I wish to complement EPA staff for comple ting so much work in a short time. The APEX model for NO2 is complex and requires more complex inputs than some previous APEX applications, particularly given the 1- hour averaging time and the need to capture strong spatial gradients in the ambient exposur e. Adequate spatio-temporal modeling of ambient pollutants is a new focus area for the ERA, and a strong effort has been made to apply available tools appropriately. While further improvements to the modeling and its assessment are desirable (and possibly necessa ry), significant revisions since the first draft REA have resulted in 1) better predictions and 2) a mo del assessment that is much better aligned with the modeling goals.

Important issues that need additional attention before the REA is finalized :

• Philadelphia vs. Atlanta . Make sure to bring out in se veral places in the report (intro to Appendix B (B-1), Appendix B case study descriptions (B-3 and B-4), intro to Chapter 8, and as added comments in conj unction with text references to the Philadelphia analysis (e.g. p 4, line 21)) the fact that these two modeling efforts were sequential and the improvements in Atlanta we re not applied to Philadelphia. While it is reasonable to include the Philadelphia analysis in the appendix, the presence of the two will mean some partie s will make an effort to compare the results. Since the modeling efforts were significantly different, th is is not appropriate. Readers need to
be told this.

• AERMOD application :

o On-road model assumptions : The strong discrepancy between the data and the model predictions plotted in Figure 8-7 suggest much more attention is
needed to this model featur e, particularly since it is an important driver of exceedances. Do the existing published data provide an adequate foundation for this direct comparison? Is the co mparison of ratios of AERMOD receptors fair (since there may be a large amount of variability in locations of AERMOD receptors relative to the empirical studies)?

o Census block centroids and the consequent impact on near-road exposures : The assumption that the Atlanta populati on resides at census block centroids must be evaluated more carefully si nce this could have a huge impact on estimation of exceedances. Exposure to high pollution falls off rapidly in the first 100 m from a road. The data show 1% of the simulated population (located at block centriods) is within 50m of a road. Since census block boundaries may not cross busy roads, th e fraction of population living near busy roads as defined by census block centr oids is most likely underestimated. For comparison, here are data from the 6 ci ties that are a part of the MESA air study. The percentages of 6,014 MESA Air study subjects living within 50 meters of a busy road (census class A1-A3) are approximately 16% (WinstonSalem), 18% (Baltimore, Los Angeles, Minneapolis-St Paul), 26% (Chicago), and 48% (New York City).

• Discussion and interpretation : Additional text is need ed to discuss the results, particularly in terms of the large fraction of the s imuated population experiencing
exceedances and the dominant locations/ac tivities where exceedances occur (which37 appear to me to be predominantly driven by near-road and on-road exposures). The main locations for exceedances are not only important from a policy perspective, but should also guide the discussion of uncertainty and variability.

• Uncertainty and variability : The key questions to addre ss with respect to uncertainty and variability are 1) what features are mo st influential in modeling the tails of the distributions, and 2) are there major sources of bias and uncertainty in these features. Both aspects need more attention. Make sure concerns about on-road and near-road exposures are addressed. One approach for structuring a revision may be to list every single assumption and model input (e.g. receptor height of 0 m) and discuss its possible contribution to bias a nd uncertainty. If more exte nsive analytical work were to be done in support of this REA, better quant ification of bias and variability is most likely where the bulk of the attention should be focused.

Specific comments :

• Appendix B-4.14: It is good to summarize the receptor location distribution. This should be compared to information about the Atlanta population residence
distribution.

• p 1 l 7: insert “ambient” before NO2.

• p 21 l19-21: Fix wording

• p 25 l 5: Replace “the same seasonal patte rn” with “similar seasonal relationships”.

• p 25 l 16-19: This statement need s more analysis to support it.

• Section 8.4.8.3: The value-laden statements in this section should be moved to the uncertainty and variability section.

• p 37 l 11 and others following: Improve nota tion. Why define b if b=1-a? Include indexes, at least for individuals and time, to reflect that the predictions are across
individuals and hours.

• p 47, 52: The fraction of the population expos ed to exceedances is huge and deserves further comment (most likely in the discussion section to be added).

• p 49: The evaluation of microenvironments to reflect locations of exceedances is
valuable.38 Comments from Dr. Frank Speizer

Comments on Chapter 8, REA NO 2 Document, dated October 2008

Submitted by : Frank E. Speizer, MD
Pre Conference Call submission. 10/15/08 In general I thought this chapte r reads rather well. Most of my comments are minor.

Charge Question 1: The first part of chapte r 8 does an excellent job of describing what was done to make the exposure estimates. Th e only question would be whether it would be worth reviewing and expanding on bot h the selection of Atlanta and the reasonableness of Atlanta as a place to derive estimates for the whole country. As I recall some of this is discussed in previous chap ter and there may be no need to repeat here except to reinforce the selection.

Page 10-11, Tables 8-1 and 8-2: It is not clear how Cent ral Business District (CBD) differs from Urban. May need an expanded footnote.

Charge Question 2: The logic us ed in developing the assessment is well laid out. In table 8.12 it might be worth constructing an addition set of figures for the 24 hour measure (or 8 hour), since in the end we will need to advise on one number and it would be good to be able to justify how that one number differs from or covers the same at risk groupings as other time periods. At 100ppb there appe ars to be little difference in the 98 th vs 99 th
percentiles. Only be dropping the level to 50ppb does the form appear to have an effect. Without additional calculations, it would appear that this argues strongly for a margin of safety for safety sake rather than as an estimate of uncertainty (see below).

Page 54, Figure 8-17: the labels on the figures need to be corrected. (a-a-a, should be ab-c).

Charge Question 3: Although there is an exce llent description of th e uncertainties that are associated with the various analyses presented, there appears to be no comment in either direction of the magnitudes of what these uncertainties do to the estimates provided. It seems clear that in some cases they would actually re duce the variance of the estimates and in other cases may increase it. As indicated on the top of page 66, by analogy with O3 may not be adequate, and th erefore some sensitivity analyses with NO2 need to be performed. By example, the sens itivity test performed that generally showed low variation helped to reinforce the findings as presented, and thus reduce the potential importance of some of the issues mentioned.

Page 68, section 8.10.8 is useful but raises an i ssue that is generic to the consideration of
Atlanta. This section states that almost 100 % households are air conditioned. Thus understanding both penetration from outdoors as well as indoor source contribution, although understood for this region, may not be adequate for ge neralizing beyond the Atlanta region, particularly to regions that are not so saturated by air conditioning.

Charge Question 4:Although the chapter does a reasonable job in characterizing the exposure of the at risk populat ion, it seems to fall short in estimation of outcomes from39 those exposures. For example it never goes on to provide estimates of asthma exacerbations, or hospitalizations based on the esti mates of exposure. This is particularly troublesome in that the lowest estimated exposur e result in substantia l numbers of at risk subjects. It would therefore be useful to in dicate what those at risk subject will suffer from, and the degree that true health impact s will occur from those exposures. I would think this next step is ne cessary and look forward to hearing it presented in the conference call (or seeing a few charts or tables before the conference call).

Section B-4.2.6. Supplemental Exposure Results It appears that there is little impact on the exposure results until the Air Quality Adjustment gets to 50 ppb for the form (98 vs 99 percentile) to make any difference. This would suggest that estimates ba sed on a lower bound of 100ppb are too high, and that they should be recalculated and pres ented as low as 50 ppb, if not lower.

In reviewing the rest of Appendix B it is clear that there is a repeat of the material from the first draft on Philadelphia, but because of the way that analysis was done and the way the current analysis of Atlanta was ch anged, they really are not comparable. I therefore am concerned that these two very different urban cent ers (eg. One warm and almost 100% air conditioned, and the other more typical of urban Northeast) can’t be judged side by side and therefor e cannot figure out how comforta ble to be with just using Atlanta. Right now it looks as if the estimates for Phili are done to a level of 200 ppb whereas for Atlanta they go down to 50 ppb. I would like to see similar analysis of what would be predicted exposures in Phili at the same levels seen for example in table B-50 on page B-114. (There may be a reason why this can’t be done---as l ong as it is not that there is just not enough time to do it, and if so, so be it.)40 Comments from Dr. George Thurston

Prof. George Thurston’s Initial Comments fo r CASAC on Chpt. 8 of the Second Draft of: Risk and Exposure Assessment to Support th e Review of the NO2 Primary National Ambient Air Quality Standard

1. To what extent is the assessment, inte rpretation, and presentation of the results of the exposure analysis technically sound, cl early communicated, and appropriately
characterized?

The EPA staff should be congratulated fo r their arduous effort at a formidable task to reach the ultimate goal of the chapter: to conduct a case study of an exposure and
health risk characterization fo r various alternative NO2 standards. While the approach is basically technically sound, it involved numerous challengi ng modeling steps, each with their own uncertainties and possible biases th at are potentially compounded from step to step. The populations consid ered and the 3 receptor classi fications considered in these analyses seem very appropriate, and the modeli ng applied is state-of-the art. One major concern I have with regard to the modeling, though, is the continuing overestimation of peak values, as displayed (for example) in Fi gures 8-5 and 8-6. I wonder if it is the fact that the roadway emissions are reportedl y modeled here using the Ozone Limiting Method (as noted on page 8, lines 10-12), an approach which I believe tends to give higher (more conservative) NO2 level estimates , since it is my understanding that this
model assumes all available ozone is reacted with NO to form NO2, which will not likely be met at peak times of the day, seemingly c onsistent with the resu lts in Figure 8-6. Is this the cause of these overestimates? If so, this assumption is fine for screening analysis, but may not be satisfactory for this application.

2. The draft risk and exposure assessment document evaluates exposures in Atlanta. What are the views of the Panel on the appro ach taken and on the interpretation of the results of this analysis?

The choice of Atlanta seems appropriate, given the existing pollution conditions and availability of modeling input information, bu t more discussion as to how these results might vary in other cities and regions would seem appropriate. Section 8.10.7.1 needs much further elaboration (e.g., sensitivity anal ysis of potentially varying conditions such as %AC, and discussion of the potential h ealth effects/policy implications of this variability).

3. What are the views of the Panel rega rding the adequacy of the assessment of uncertainty and variability with respect to ch aracterization of exposures and health risks associated with those exposures?

To me, this is the greatest weakness of the chapter as it is now written: no quantitative or qualitative pr opagation of errors by the sequential modeling steps is provided in Section 8.10. It is my belief that such a comprehensive uncertainty analysis would indicate large uncertainties in this ap proach to achieve the final estimates. A41 consideration of these uncertain ties would, I think, indicate th at, while a useful exercise, such a human exposure-health effects analysis is not sufficient to al one assess the health implications of alternative st andards, and that a consider ation of the results of an application of the 

### NO 2 -health effects epidemiology are al so required in each such REA (as is the case for this particular document) to obtain a fuller appreci ation of the health implications of various alternative standards.

4. To what extent is the assessment, in terpretation, and presenta tion of health risk characterization included in Chapter 8 t echnically sound, clearly communicated, and appropriately characterized?

Very little is provided in the way of an interpretation of the results (e.g., putting the numbers into a context useful for regulatory assessment). I suggest an additional Section 8.11 to provide just such information.42 Comments from Dr. James Ultman

Comments on Second Draft NOx REA, Chapter 8

James Ultman

General Comments

I commend staff on completing an extensive b ody of work in such a short time. The document is clearly written. It conveys th e methodology (including the description of computer models, sources of i nput data and assumptions) in as detailed a manner as is possible within the confines of a single chapte r. The results are also summarized in a logical fashion.

I do, however, feel somewhat overwhelmed by the complexity that emerges from the layering of different models, input data sets and accompanying assumptions that I feel are not always justified or validated. Moreover, lacking an integrated summary at the end of the chapter, it is not clear what key conclu sions should be drawn.

Specific Comments

I am skeptical that rolling back the health be nchmark values in the exposure analysis is equivalent to rolling up of ambient concentr ations (and visa versa). The document does not present clear evidence—either numerical or mathematical—that this is the case. Moreover, the equation that is used to justify a paralle l roll-back in indoor source concentration (pg 38, line 5) fails to recognize that C indoor is determined, in part, by
C ambient . In particular, if C ambient is rolled up by a fact or f (pg. 38, line 3), C indoor must also increase. Thus, its original value cannot be used to compute C thresh (see equation on pg. 38, line 3). Moreover, th e relationship between C indoor and C ambientis algebraically nonlinear when the mass balance model is used to determine C indoor

.

Given the importance of on-road exposures, I am also concerned with the discrepancy
between the AERMOD-based and data-based determination of the on-road/non-road concentration ratio. On the other hand, this is not surprising give n that the data was
measured in a number of locales where me teorology and emission patterns are different
than in Atlanta.

Finally, I believe that the document provide s an extensive discussion of areas of uncertainty, but it does not attempt to quantify the uncertainty. In retrospect, I feel that it would have been wiser to spend less time in the modeling/simulation effort and more time in analyzing those uncertainties that are judged to be the most important.