UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

 WASHINGTON D.C. 20460 

 

OFFICE OF THE ADMINISTRATOR 

SCIENCE ADVISORY BOARD 

June 12, 2008 

EPA-CASAC-08-013 

The Honorable Stephen L. Johnson 

Administrator 

U.S. Environmental Protection Agency 

1200 Pennsylvania Avenue, N.W.

Washington, D.C. 20460 

Subject: Consultation on EPA’s Draft Plan for Review of the Primary NAAQS for 

Carbon Monoxide (March 2008) 

Dear Administrator Johnson: 

The Clean Air Scientific Advisory Committee (CASAC) Carbon Monoxide (CO) Primary 

NAAQS Review Panel met on April 8, 2008, and has completed its consultation on EPA’s Draft 

Plan for Review of the Primary NAAQS for Carbon Monoxide (March 2008). The CASAC uses a 

consultation as a mechanism for individual technical experts to provide comments on the Agency’s 

draft plan for developing technical assessments as the basis of the review of the primary NAAQS 

for CO. Written comments provided by the individual Panelists are enclosed. Areas of concern 

emphasized by panelists included (but were not limited to): 1) the need for a multi-pollutant 

approach in considering CO standards; 2) the need to consider both a secondary and a primary 

standard; 3) the inadequacy of current monitoring data; and 4) the requirements related to the new 

NAAQS review process. 

As this is a consultation, we do not expect a formal response from the Agency. We thank 

the Agency for the opportunity to provide advice early in the NAAQS review process, and look 

forward to the review of the draft Integrated Science Assessment in April 2009. 

Sincerely, 

 /Signed/ 

Dr. Rogene Henderson, Chair 

Clean Air Scientific Advisory Committee 

Enclosures
U.S. Environmental Protection Agency 

Clean Air Scientific Advisory Committee 

CO Primary NAAQS Review Panel Roster 

CASAC MEMBERS 

Dr. Rogene Henderson (Chair), Scientist Emeritus, Lovelace Respiratory Research Institute, 

Albuquerque, NM 

Dr. Ellis B. Cowling, University Distinguished Professor At-Large Emeritus, Colleges of 

Natural Resources and Agriculture and Life Sciences, North Carolina State University, Raleigh, 

NC 

Dr. James D. Crapo, Professor, Department of Medicine, National Jewish Medical and 

Research Center, Denver, CO 

Dr. Douglas Crawford-Brown, Professor Emeritus and Director Emeritus, Department of 

Environmental Sciences and Engineering and UNC Institute for the Environment, University of 

North Carolina at Chapel Hill, Chapel Hill, NC

Dr. Donna Kenski, Data Analysis Director, Lake Michigan Air Directors Consortium, 

Rosemont, IL 

Dr. Armistead (Ted) Russell, Professor, Department of Civil and Environmental Engineering, 

Georgia Institute of Technology, Atlanta, GA 

Dr. Jonathan Samet, Professor and Chairman, Department of Epidemiology, 

Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD

PANEL MEMBERS 

Dr. Thomas Dahms, Professor and Director, Anesthesiology Research, Department of 

Anesthesiology and Critical Care, Saint Louis University School of Medicine, St. Louis, MO 

Dr. Russell R. Dickerson, Professor and Chair, Department of Atmospheric and Oceanic 

Science, University of Maryland, College Park, MD 

Laurence Fechter, Ph. D., Research Scientist and Professor, Loma Linda VA Medical Center 

and Loma Linda University School of Medicine, Loma Linda, CA 

Dr. Milan Hazucha, Professor, University of North Carolina at Chapel Hill, Chapel Hill, NC 

Dr. Michael T. Kleinman, Professor, University of California – Irvine, Irvine, CA 

Dr. Arthur Penn, Professor, Louisiana State University, Baton Rouge, LA 

Dr. Beate Ritz, Professor, University of California – Los Angeles, Los Angeles, CA 
Dr. Paul T. Roberts, Executive Vice President and Chief Scientific Officer, Sonoma 

Technologies, Inc., Petaluma, CA 

Dr. Stephen R. Thom, Professor and Chief of Service, Institute for Environmental Medicine, 

University of Pennsylvania, Philadelphia, PA 

SCIENCE ADVISORY BOARD STAFF 

Ms. Kyndall Barry, Designated Federal Officer, 1200 Pennsylvania Avenue, NW 

1400F, Washington, DC, Phone: 202-343-9868, Fax: 202-233-0643, (barry.kyndall@epa.gov)
Compilation of Individual Panel Member Comments on EPA’s Draft Plan for Review of the 

Primary NAAQS for Carbon Monoxide (March 2008) 

Comments received:

Dr. Ellis B. Cowling ...................................................................................................................... 5 

Dr. James Crapo ......................................................................................................................... 12 

Dr. Douglas Crawford-Brown ................................................................................................... 13

Dr. Thomas Dahms..................................................................................................................... 16 

Dr. Russell R. Dickerson ............................................................................................................ 19 

Dr. Milan Hazucha...................................................................................................................... 21 

Dr. Rogene Henderson................................................................................................................ 24 

Dr. Donna Kenski........................................................................................................................ 25 

Dr. Michael T. Kleinman............................................................................................................ 26 

Dr. Arthur Penn.......................................................................................................................... 28 

Dr. Beate Ritz .............................................................................................................................. 30 

Dr. Paul T. Roberts..................................................................................................................... 31 

Dr. Armistead Russell................................................................................................................. 33 

Dr. Jonathan M. Samet .............................................................................................................. 35 

Dr. Stephen R. Thom.................................................................................................................. 36 

4 
Dr. Ellis B. Cowling 

Individual Comments on the March 2008 Draft Plan for Review of the 

Primary National Ambient Air Quality Standard for Carbon Monoxide

Very General Comments on these NAAQS Review Processes 

Before dealing with the details of my specific assignment during the April 8, 2008 CASAC 

Consultation on the Primary (public-welfare based) NAAQS for Carbon Monoxide (CO), I 

would like to offer a few general comments about these periodic NAQQS Review processes and 

the changes that are being made in both the organization and focus of these reviews. 

As described on pages 1-2 of the “Draft Plan” for review of the primary NAAQS for CO, the 

Clean Air Act of 1970 established two general goals for management of air quality in the United 

States -- protection of human health and protection of public welfare. Section 108 of the CAA 

directs the Administrator of EPA to identify and list “air pollutants” that “in his judgment may 

reasonably be anticipated to endanger public health and welfare” and to issue air quality criteria 

for those that are listed – hence the term “Criteria Pollutants.” 

Section 109 of the CAA further directs the Administrator of EPA to propose and promulgate 

“Primary” National Ambient Air Quality Standards to protect public health and “Secondary” 

National Ambient Air Quality Standards to protect public welfare. 

A secondary standard, as defined in Section 109, must “specify a level of air quality the 

attainment and maintenance of which, in the judgment of the Administrator, based on such 

criteria, is required to protect the public welfare from any known or anticipated adverse effects 

associated with the presence of [the] pollutant in the ambient air ...” The welfare effects of 

concern include, but are not limited to “effects on soils, water, crops, vegetation, man-made 

materials, animals, wildlife, weather, visibility and climate, damage to and deterioration of 

property, and hazards to transportation, as well as effects on economic values and on personal 

comfort and well-being.” 

So far, the several Administrators of EPA since 1970 have: 

1) Identified six specific “Criteria Pollutants” – carbon monoxide, ozone and other 

photochemical oxidants, sulfur dioxide, oxides of nitrogen, particulate matter, and lead – 

which have thus been designated officially as requiring development and implementation 

of National Ambient Air Quality Standards; 

2) Emphasized protection of public health as the principal (and overwhelmingly important) 

de facto focus of concern within the Agency, and public welfare as a (rarely openly 

acknowledged) but distinctly less important de facto focus of concern; 

3) Established Secondary (public-welfare-based) NAAQS standards for all six criteria 

pollutants that almost always were identical in form (including level, indicator, statistical 

5 
form, and averaging time) to the Primary (public- health based) NAAQS standards for 

each of these six criteria pollutants;

4) Developed a long-standing tradition of dealing with these six specific air pollutants 

mainly on a “one-at-a-time” basis rather than collectively – i.e., without strong attention 

to the frequent interactions and simultaneous occurrence of some of these pollutants as 

mixtures within the air in various parts of our country; 

5) Maintained a reluctant attitude about the concepts of ecologically based “Critical Loads 

and Critical Levels” developed in Europe as possible alternative or additional approaches 

to air-quality management in the US; and 

6) Maintained a long-standing general focus on the related concepts of: 

a) “attainment counties and non-attainment counties,” 

b) “attainment demonstrations” based on mathematical modeling of a limited number of 

exceedance events under extreme weather conditions, and 

c) “local anthropogenic sources” as opposed to “both local and regional biogenic and 

anthropogenic sources of emissions.” 

In recent years, in contrast to several of the six ideas listed above, EPA has shown increased 

willingness to think more holistically – and in more fully integrated ways – about both the 

policy-relevant science and the practical arts of air quality management aimed at protection of 

both public welfare and public health. These shifts in both emphasis and approach have 

included: 

1) Participation with other federal agencies and international bodies in discussions about the 

“One Atmosphere,” “Critical Loads–Critical Levels,” and “Multiple-Pollutant–Multiple 

Effects” concepts; 

2) Adoption of the “NOx SIP Call” in 1999 and both the “Clean Air Interstate Rule” (CAIR) 

and the “Clean Air Mercury Rule” (CAMR) in 2005 with their more balanced 

perspectives about both regional (interstate) and local sources of emissions and 

interactions among NOx, SOx, VOCs, “air toxics,” and mercury in the formation, 

accumulation, and biological effects of “ozone and other photochemical oxidants,” and 

fine, coarse, thoracic, and secondary aerosol particles; 

3) Recognition of both fine and coarse PM as complex and geographically variable mixtures 

of sulfate-, nitrate-, and ammonium-dominated aerosols; natural biogenic and 

anthropogenic organic substances; heavy metals including cadmium, copper, zinc, lead, 

and mercury; and some other miscellaneous substances; 

4) More frequent discussion about of the occurrence and both ecologically-important and 

public-health impacts of mixtures of air pollutants; and, most recently 

5) Making the unprecedented decisions (at least in the case of the NAAQS reviews for 

oxides of nitrogen and sulfur) to: 

A) Separate the preparation and review of documentation, the required CASAC and 

public reviews, and the final decision-making processes for the Secondary (public6 
welfare-based) National Ambient Air Quality Standards from the (previously always 

dominating) Primary (public-health-based) NAAQS review processes, and 

B) Prepare and publish a single draft plan for integrated [simultaneous] of two different 

criteria pollutants (NOx and SOx), and 

6) Identify in advance a set of Key Policy-Relevant Questions that will be the primary focus 

of attention in the design and completion of all four major components of the new 

NAAQS review processes: 

A) An Integrated Review Plan (IRP), 

B) An Integrated Science Assessment (ISA), 

B) A Risk/Exposure Assessment (REA), and 

C) A Policy Assessment/Rulemaking document developed in the form of an Advanced 

Notice of Proposed Rule Making (ANPR). 

All six of these adjustments in focus of attention, documentation requirements, and sequential 

procedures are being undertaken with the intention to:” 

“... improve the efficiency of the process while ensuring that the Agency’s decisions are 

informed by the best available science and timely advice from CASA and the public” ... 

and 

“... help the agency meet the goal of reviewing each NAAQS on a 5-year cycles as 

required by the Clean Air Act without compromising the scientific integrity of the 

process.” 

Need for Policy Relevancy as the Dominant Concern in NAAQS Review Processes

In a May 12 2006 summary letter to Administrator Johnson, CASAC Chair, Dr. Rogene 

Henderson, provided the following statement of purpose for these periodic NAAQS review 

processes. 

“CASAC understands the goal of the NAAQS review process is to answer a critical 

scientific question: “What evidence has been developed since the last review to indicate 

if the current primary and/or secondary NAAQS need to be revised or if an alternative 

level or form of these standards is needed to protect public health and/or public 

welfare?” 

During the past 18 months, CASAC has participated in reviews of three of the existing six 

criteria pollutants – particulate matter, ozone, and lead. CASAC has also joined with senior EPA 

administrators in a “top-to-bottom review” and the resulting recently-completed revision of the 

NAAQS review processes. These two experiences have led to a seemingly slight but important 

need for rephrasing and refocusing of this very important “critical scientific question:” 

“What scientific evidence and/or scientific insights have been developed since the last

review that either support or call into question the current public-health based and/or the 

7 
8 

current public-welfare based NAAQS, or if alternative levels, indicators, statistical forms, 

or averaging times of these standards are needed to protect public health with an 

adequate margin of safety and to protect public welfare?” 

With regard to the important distinction in purpose of the primary (public health) and secondary 

(public welfare) NAAQS standards, it is noteworthy that in all five cases in which a secondary 

NAAQS standard has been established, the secondary standard has been set “Same as Primary.” 

Thus, a second very critical scientific question that needs to be answered for CO as well as the 

other criteria air pollutants is: 

 “What scientific evidence and/or scientific insights have been developed since the last 

review to indicate whether, and if so, what particular ecosystem components or other airquality-related public welfare values, are more or less sensitive than the populations of 

humans for which primary standards are established and for this reason may require a 

different level, indicator, statistical form, or averaging time of a secondary standard in 

order to protect public welfare.” 

I hope these two “critical scientific questions” will be borne in mind carefully as CASAC joins 

with the various relevant parts of the Environmental Protection Agency in completing the 

upcoming reviews of both the primary and secondary National Ambient Air Quality Standards 

for CO, NOx, SOx, PM, ozone, and lead. 

We now have the considerable advantage that a much more complete focus can be achieved in 

the Integrated Science Assessment than has historically been achieved in the encyclopedic 

Criteria Documents that have been prepared during the years since 1970. 

Thus, I recommend that every chapter of the soon to be completed Integrated Science 

Assessment, the Risk/Exposure Assessment, and the Policy Assessment/Rule Making 

documents for CO contain a summary section composed almost entirely of a series of very 

carefully crafted statements of Conclusions and Scientific Findings that: 

1) Contain the distilled essence of the most important topics covered in each chapter, 

and 

2) Are as directly relevant as possible to the two Critically Important Scientific 

Questions written in bold italic type above. 

In this connection, I call attention once again to the attached “Guideline for Formulation of 

Statements of Scientific Findings to be Used for Policy Purposes.” These guidelines were 

developed and published in 1991 by the Oversight Review Board for the National Acid 

Precipitation Assessment Program. They are the best guides that I know of for formulation of 

scientific findings to be used for policy purposes.
GUIDELINES FOR FORMULATION OF SCIENTIFIC FINDINGS 

TO BE USED FOR POLICY PURPOSES 

The following guidelines in the form of checklist questions were developed by the NAPAP Oversight Review 

Board to assist scientists in formulating presentations of research results to be used in policy decision processes. 

1) IS THE STATEMENT SOUND? Have the central issues been clearly identified? Does each statement contain 

the distilled essence of present scientific and technical understanding of the phenomenon or process to which it 

applies? Is the statement consistent with all relevant evidence – evidence developed either through NAPAP 

research or through analysis of research conducted outside of NAPAP? Is the statement contradicted by any 

important evidence developed through research inside or outside of NAPAP? Have apparent contradictions or 

interpretations of available evidence been considered in formulating the statement of principal findings? 

2) IS THE STATEMENT DIRECTIONAL AND, WHERE APPROPRIATE, QUANTITATIVE? Does the 

statement correctly quantify both the direction and magnitude of trends and relationships in the phenomenon or 

process to which the statement is relevant? When possible, is a range of uncertainty given for each quantitative 

result? Have various sources of uncertainty been identified and quantified, for example, does the statement include 

or acknowledge errors in actual measurements, standard errors of estimate, possible biases in the availability of 

data, extrapolation of results beyond the mathematical, geographical, or temporal relevancy of available 

information, etc. In short, are there numbers in the statement? Are the numbers correct? Are the numbers relevant 

to the general meaning of the statement? 

3) IS THE DEGREE OF CERTAINTY OR UNCERTAINTY OF THE STATEMENT INDICATED 

CLEARLY? Have appropriate statistical tests been applied to the data used in drawing the conclusion set forth in 

the statement? If the statement is based on a mathematical or novel conceptual model, has the model or concept 

been validated? Does the statement describe the model or concept on which it is based and the degree of validity of 

that model or concept? 

4) IS THE STATEMENT CORRECT WITHOUT QUALIFICATION? Are there limitations of time, space, or 

other special circumstances in which the statement is true? If the statement is true only in some circumstances, are 

these limitations described adequately and briefly?

5) IS THE STATEMENT CLEAR AND UNAMBIGUOUS? Are the words and phrases used in the statement 

understandable by the decision makers of our society? Is the statement free of specialized jargon? Will too many

people misunderstand its meaning?

6) IS THE STATEMENT AS CONCISE AS IT CAN BE MADE WITHOUT RISK OF 

MISUNDERSTANDING? Are there any excess words, phrases, or ideas in the statement which are not necessary

to communicate the meaning of the statement? Are there so many caveats in the statement that the statement itself 

is trivial, confusing, or ambiguous? 

7) IS THE STATEMENT FREE OF SCIENTIFIC OR OTHER BIASES OR IMPLICATIONS OF SOCIETAL

VALUE JUDGMENTS? Is the statement free of influence by specific schools of scientific thought? Is the 

statement also free of words, phrases, or concepts that have political, economic, ideological, religious, moral, or 

other personal-, agency-, or organization-specific values, overtones, or implications? Does the choice of how the 

statement is expressed rather than its specific words suggest underlying biases or value judgments? Is the tone 

impartial and free of special pleading? If societal value judgments have been discussed, have these judgments been 

identified as such and described both clearly and objectively?

8) HAVE SOCIETAL IMPLICATIONS BEEN DESCRIBED OBJECTIVELY? Consideration of alternative 

courses of action and their consequences inherently involves judgments of their feasibility and the importance of 

effects. For this reason, it is important to ask if a reasonable range of alternative policies or courses of action have 

been evaluated? Have societal implications of alternative courses of action been stated in the following general 

form?: 

 "If this [particular option] were adopted then that [particular outcome] would be expected." 

9) HAVE THE PROFESSIONAL BIASES OF AUTHORS AND REVIEWERS BEEN DESCRIBED OPENLY? 

Acknowledgment of potential sources of bias is important so that readers can judge for themselves the credibility of 

reports and assessments.

9 
My Assignment in this CASAC Consultation on the Draft Plan for 

Review of the NAAQS Primary Standard for Carbon Monoxide 

My specific assignment in preparation for the April 8, 2008 CASAC Consultation on the Draft 

Plan for review of the NAAQS for CO, as outlined in Chairman Rogene Henderson’s memo of 7 

March 2008, is -- Key Policy-Relevant Issues. Rogene also asked Jim Crapo to deal with these 

same issues. Thus, I am very much looking forward to comparing notes with Jim during our 

Consultation on April 8 – especially since he knows so much more than I do about public health 

effects of CO and other Criteria Pollutants. 

These Key Policy-Relevant Questions are summarized on pages 3-1 through 3-3 in Section 3.2 

and are presented as a series of thirteen major policy-focused “Issues to be considered in the 

current review”. In addition, several other detailed questions are presented in the several Subsections of Chapter 4. In most cases, however, these more detailed questions are focused mainly 

on scientific issues rather than policy issues and, I presume, will be dealt with adequately by 

other members of our CASAC Carbon Monoxides Panel. 

I see the decision to develop “Key Policy-Relevant Policy Questions” as a part of these Draft 

Plans for NAAQS reviews as a major step forward. I am also very satisfied with the particular 

set of 13 such questions listed in Chapter 3 of this Draft Plan. Of course they all relate to the 

effects of CO on public health – which is the principal focus of this NAAQS review. 

In addition, however, I also note that Section 1.3 – History of Reviews of the NAAQS for CO -- 

indicates that identical primary and secondary NAAQS standards for CO were promulgated in 

1971 and that the decision was made in 1985 to revoke the secondary standard. The rationale for 

this decision was not included in this “History” section, 

But Section 1.4 – Scope of the Review – also indicates that 

“ ... relevant scientific information on human exposures and health effects associated 

with exposures to ambient concentrations of CO will be assessed. The possible influence 

of other atmospheric pollutants on the interpretation of the role of CO in health effects 

studies will e considered. This will include other pollutants with the potential to co-occur 

in the environment (e.g., NO2, SO2, O3, and PM). The review will also assess any 

relevant scientific information associated with known or anticipated public welfare 

effects that may be identified.” 

Thus, because of my keen scientific interest in the welfare effects of criteria pollutants, I believe 

it is essential that both current and past scientific literature be examined closely to determine if: 

A) The 1985 decision to revoke the secondary NAAQS standard for CO is valid in the 

context of current scientific knowledge --especially about the effects of CO on the 

health of both domestic and wild animals, and perhaps also on crop, forest, and 

ornamental plants, insects, and microorganisms as well. 

10
B) There are significant interactions of ambient concentrations of CO with other cooccurring Criteria Pollutants in terms of their potential to cause either additive, 

competitive, or no significant interactions with regard to the effects of CO on both 

public health and public welfare, and 

C) There are significant times and places in the US where ambient concentrations of

CO are adding to the total oxidative capacity of the atmosphere and thus increase

the rate of accumulation of ozone near the ground in urban, suburban, rural, and 

even remote parts of the United States. Although CO is not a very reactive volatile 

organic compound, when present in high concentrations, as often occurs in the 

vicinity of municipal waste incinerators and in the plumes of wild fires in grasslands 

and forests, CO can be a very significant precursor of tropospheric ozone. 

I suggest this last issue for inclusion in the First Draft Integrated Science Assessment for CO as a 

result of the discovery by Wotawa and Trainer during the 1994 and 1995 Nashville-Middle 

Tennessee Ozone Study by the Southern Oxidants Study -- where a coherent plume containing 

extraordinarily high concentrations of CO were observed for several days about 50 miles east of 

Nashville and could be traced to wild fires in the Northwest Territories of Canada that persisted 

over a six-week period. 

Wotawa, G. and M. Trainer. 2000. The influence of Canadian forest fires on pollutant 

concentrations in the United States. Science 288:324-328. 

Other important sources of insight about the influence of CO emissions from wild fires include 

the following important references: 

Forster, C., U. Wandingrer, G. Wotawa, P. James, I. Mattis, D. Althausen, P. Simmonds, S. 

O’Doherty, S. G. Jennings, C. Kleefeld, J. Schneider, T. Trickly, S. Kreipl, H. Jäger and 

A. Srohl. 2001. Transport of boreal forest fire emissions from Canada to Europe. J. 

Geophys. Res. 106(D19)12,887-22,906. 

McKeen, S. A., G. Wotawa, D. D. Parrish, J. S. Holloway, M., G. Hübler, F. C. Fehsenfeld, and 

J. F. Meagher. 2002. Ozone production from Canadian wildfires during June and July of 

1995. J. Geophys. Res. Vol. 107, NO. D14,4192, 10.1029/2001JD000697. ACH 7-1 to 

ACH 7-25. 

Westerling, A. L., H. G. Hidalgo, D. R. Cayan, and T. W. Sweetman. 2006. Warming and 

Earlier Spring Increase Western U. S. Forest Wildfire Activity. Science 313:940-943. 

Wotawa, G., P. C. Novelli, M. Trainer, and C. Granier. 2001. Inter-annual variability of 

summertime CO concentrations in the Northern Hemisphere explained by boreal forest 

fires in North American and Russia. Geophys. Res. Lett. 28:4575-4578. 

11
Dr. James Crapo 

The basic plan laid out by EPA staff for review of the primary National Ambient Air Quality 

Standard (NAAQS) for carbon monoxide is appropriate. The work in implementing this plan 

should focus primarily on new data (studies carried out and published since the last CO review) 

and both on low level effects of CO that are relevant to the NAAQS and on sensitive populations 

who may be at risk. 

 

For this review process to be effective, it is important that the EPA staff and administration 

provide a clear policy assessment document that gives the range of opinions the agency will 

consider as well as the scientific basis for those decisions. Advance notice of proposed rulemaking documents needs to include the material that would have been included in staff papers 

for prior NAAQS reviews and needs to include an assessment of realistic options that could be 

considered for the CO NAAQS as well as the rigorous scientific justification for those options. 

CASAC can be of greatest assistance to the EPA administration if open dialogue on these topics 

is engaged in as early as possible in the review process. 

 

It will also be important to carry out a rigorous review of the value of an independent secondary 

standard for CO. 

 

A primary limitation of review of single pollutants is the absence of detailed consideration of the 

effects of complex pollutant interactions. The proposed review process is appropriate for 

consideration of the NAAQS for CO; however, the EPA should consider moving in the future to 

an analysis of multiple pollutants and their interactions, with the consideration of setting 

NAAQS based not only on individual pollutant levels but also on multiple pollutant interactions. 

12
Dr. Douglas Crawford-Brown

Review of EPA’s Draft Plan for Review of the Primary NAAQS for Carbon Monoxide 

The document is intended solely to provide the general structure of a review, rather than details 

as to how this will be carried out. As a result, the following comments are general in nature and 

may change as the actual plan is formalized. 

My most general comment is that the draft plan contains all of the relevant sections that must be 

completed to produce a full review. The authors have therefore not left out any major 

considerations. However, throughout the document, the authors raise a series of questions that 

will be addressed in each section without providing a succinct statement as to the role the 

answers to these questions will play in specific policy considerations. As a result, the reader is 

left unclear as to how any specific answer to any specific question might push the discussion of a 

NAAQS decision in any particular direction. Perhaps this was intentional on the part of the 

authors: trying not to judge how a particular answer might inform a final decision. But it leaves 

the reader unclear as to the intent behind specific questions, other than providing a scientific base 

on which any manner of decision might be based. 

The authors raise the issue of co-pollutants, which will be important in using epidemiological 

studies. It is not clear, however, how these co-pollutants will be analyzed. Is the plan to treat 

them as confounders and then work to extract this confounding from any slope factors 

developed? Is the intent to examine the effect of CO exposures on the sensitivity of individuals 

to the co-pollutants, and the effect of the co-pollutants on the sensitivity of individuals to CO?

The document doesn’t give much of a hint as to how this issue will be treated. There is a sense at

several points in the document that clinical, controlled studies might form the basis for any 

effects measures, which could avoid this issue, but this sense is never made fully concrete. There 

also is a hint that the assessment might stop at exposure or at blood levels, which again would 

avoid this issue (much as in the case of the early Pb standards). It would be good if some clarity 

on this issue could be provided. 

On Page 3-2, the authors ask whether new data might indicate that effects occur at exposures 

lower than those previously found to induce effects. This question is too one-sided. It presumes 

that the only thing new data can do is push the assumed threshold for effects to lower values. 

New data might suggest that previous data suggesting a lower threshold were incorrect, and that 

the threshold is in fact higher than thought. 

On Page 4-1, the authors mention a formal framework for integrating health effects, found in the 

second draft of the NOx document. The reader should not need to go to that document to at least 

find a summary of this framework, and in any event that document provides no such summary 

framework and so readers will come away from it with different conceptions of what the 

framework might be when applied to CO. More clarity is needed on precisely what this 

framework consists of. 

13
On Page 4-2, the authors state that welfare effects will be noted if any are found during the 

search. However, the literature that is mentioned as forming the basis for the search, rooted only 

in human health sciences, is not the appropriate set of disciplines to locate papers on welfare 

effects. So I cannot see how the literature review will constitute a “hard look” at the relevant 

science on welfare effects. 

Around Pages 4-7 and 4-8, the authors discuss the need to perform analyses of spatial and 

temporal variability. There is no description, however, of the role of these analyses in any 

specific decision on exposure, exposure-response, risk, etc. I certainly agree that analysis of 

variability is needed, but without a clear statement as to the purpose of the analyses, and the 

questions they are intended to support, it will not be possible to determine whether appropriate 

statistical methods and databases are being used. 

The same problem arises on Page 4-8 when the authors discuss uncertainty analyses. They 

mention, for example, uncertainty in extrapolating between area monitors and personal 

exposures. However, no insight is provided as to why this uncertainty would be important for 

specific questions to be addressed (I agree it IS important, but the document doesn’t give a hint 

as to why). 

On Page 4-9, at the bottom, the authors list a series of effects that will be considered. While I 

agree with this list, no hint is given as to how it was compiled based on past studies. Clarity is 

needed here.

On Page 4-12, developmental and birth outcomes are mentioned as chronic effects. Why are they 

only considered chronic effects? Surely such effects might occur with shorter-term exposures 

during critical developmental periods. 

On Page 4-12, the authors raise the issue as to whether CO might stand as a surrogate for 

exposure to the mixture of pollutants from vehicles. I could not find any explanation as to why 

they might want to know this. The CO NAAQS doesn’t stand as a surrogate for control on 

exposures to these other pollutants. 

On that same page, the authors mention the exposure-response curve for CO. They formulate the 

question as one of determining the shape of that curve. But they don’t formulate it as an issue of 

uncertainty ABOUT the shape of that curve, or how different curves would produce different 

NAAQS results. That bullet needs to be rethought. 

At the bottom of Page 4-14, the authors ask for any medical conditions or medications that make 

an individual susceptible. I suspect that there might also be activities (e.g. running near 

roadways) that make them susceptible. 

On Page 4-15, the authors ask about the extent to which the elderly and fetuses are more 

susceptible. This seems to me to beg the question, which should be about the extent to which 

they DIFFER in susceptibility one way or the other. If the authors want to restrict the question to 

increased susceptibility, they need to include a justification for this (perhaps in past literature 

suggesting increased susceptibility in these groups). 

14
On Page 5-3, the authors first introduce the idea of using 2.1 % COHb as an effects threshold. 

But no justification is given for this. I realize it is analogous to the approach in Pb exposures, and 

that the figure of 2.1 % is based on past decisions at the EPA, but this needs to be explained so 

the reader has some context for the decision here. 

On Page 5-4, it would be good to know why the CO NAAQS review in 1999 was put on hold 

and never completed. 

Some material is missing in the incomplete bullet at the top of Page 5-6. 

The final bullet on that page considers the relationship between the 1 and 8 hour exposures. But 

no explanation is given as to why this is of interest (I agree it is, but the document should state 

the reason).

On Page 5-8, it is not clear whether temporal variability will be used to estimate a rolling average 

for exposures, or whether the timeline will be discretized and averages calculated only in the 

discrete intervals. These generally give slightly different results with differing degrees of 

variability. 

On the bottom of Page 5-10, the authors ask whether a given factor contributes to uncertainty in 

a way that over-or-under-states the risk/exposure. But a given factor could be neutral on average, 

neither systematically under-or-over-stating the risk/exposure. 

On Page 5-11, the authors state that the ideal way to assess uncertainty due to model formulation 

is to compare model results against data. No further clarification of this comment is given. I note 

first that such an approach requires assumptions as to the validity of the data, especially in 

geographic areas with high degrees of spatial variability. And I can see how this can be used to 

assess the quality of one model, but don’t see how it is to be used to compare the degrees of 

belief in competing models in characterizing uncertainty due to model formulation. 

In that same paragraph, the authors speak of partitioning uncertainty into model components. Is 

some form of contribution to variance intended here? I assume it is, but this is not stated. 

Section 6 is too generic to justify any further statements here. It would be of interest only if the 

reader were provided a succinct statement of the policy questions to be addressed and how these 

are related to the answers to specific questions asked in the previous sections. 

The Morgan and Henrion 1990 reference appears to be missing from the References section even 

though it is called out in the text. 

15
Dr. Thomas Dahms 

Two of the main areas of evidence of health effects of Carbon Monoxide seem to be 1) on the 

cardiovascular system in susceptible adults based both on acute controlled effects (time to onset 

of angina/ischemia) and on population studies of infarction rates, arrhythmias etc. and 2) on the 

respiratory system as shown by effects in fetuses/infants based on population studies. It is not 

clear whether the fetus/infant is susceptible to cardiovascular effects of Carbon Monoxide. If this 

effect requires underlying cardiovascular disease, then the lack of a cardiovascular effect in 

infants would be understandable. This issue should be raised somehow as part of page 4-11 lines 

17-20. 

The respiratory health effects of CO need to be raised based on recent evidence rather than the 

concern identified on page 4-11 lines 7-9. 

The absence of any acute effect of CO on the respiratory system in adult humans and animals 

was a conclusion of the data in the 1990 AQC document which was supported by the 2000 AQC 

document. The question then becomes: what conditions make the fetal/infant lung more 

susceptible to carbon monoxide? (This is obviously the case given the relationship between 

atmospheric CO and respiratory deaths). Understanding the potential predisposing factors in fetal 

death due to respiratory problems would be essential in determining risk. 

Since many of the other regulated air pollutants have measurable effects directly on the lungs, 

the distinct effects of CO alone need to be carefully assessed. This is especially the case with 

populations living and working next to highly traveled roadways where CO is part of the multipollutant mixture. 

In addition, one of the consistent findings relates to the anti-inflammatory effects of both 

exogenous and endogenous effects of CO. However, many of the identified respiratory causes of 

infant death appear to involve inflammation. It is not clear how to ensure that this issue is part of 

the item identified on page 4-11, line 25-28. 

Section 3 

What is not clear to me from an organizational standpoint is how the issues identified in Section 

3 relate to the more specific issues in the following sections. First, are they supposed be overarching issues, i.e., less specific? Also, it appears as though some of these identified issues in the 

Draft Plan are asking questions that would require new research and that the requested endpoints 

are not clearly linked to the identified issues. I have commented on these issues. Following past 

reviews, summary sessions were held where such issues were identified as needs for addressing 

areas of uncertainty. 

It is not clear how the writers of the ISA and those of us on the panel are to deal with multipollutant data. Some direction as to its relative importance should be clearly spelled out in the

16
Plan as some attention to this issue may provide insight into future use of such data even though 

it may not be possible to use this information for this review. 

Page 3-1, lines 22-23: The words short- and long-term probably refer to 1-hr and 8-hr exposures 

(primary standard). However given the newer population exposure data in fetuses/infants, these 

terms need to be more narrowly defined. 

Page 3-2, lines 10-12: This issue of alternate dose indicators other than carboxyhemoglobin 

(COHb) levels probably requires future research and therefore should be eliminated from this 

section. As pointed out by Dr. Hazucha, this is not an easy task because the current pulse 

oximeters would provide erroneous data as they can not account for COHb or metHb by design. 

That is the easily obtained non-invasive data would be incorrect. 

Page 3-2, lines 13-14: How is this issue different from the one presented on page 3-1, lines 22-

23? If the issue is different, the question needs to be restated.

If there is felt to be any evidence that would support a secondary standard, should this issue be 

raised directly in section 3? I assume that this would include effects of exposures beyond 24 hrs 

and have public health consequences as is indicated in Section 4 under long-term exposures. 

Section 4

Page 4-1, lines 29-30: “Emphasis will be placed on studies conducted at or near CO 

concentrations found in ambient air.” Given the uncertainty in CO dosimetry and the falling 

atmospheric levels of CO, should this statement provide better guidance?

Page 4-2, line 1: Multiple studies have been carried out in the most sensitive population for CO. 

This language does not provide the ISA authors’ clear direction. 

Literature Search: Will only peer reviewed material be included in the database? The previous 

AQC documents in this field have unreferenced material in them. It is not clear how this 

material should be used by the authors of the ISA. 

It is not clear how this data base will be made available to the authors of the ISA. Will articles 

not referred to by the authors be in this literature data base? This is implied by the way it is 

written. 

Page 4-5, line 1: This statement implies that if the data is unique that the paper(s) should be 

included even though they do meet the other stringent criteria? It also implies that confirmatory 

data is of less importance which is clearly not the case. 

Page 4-6, lines 4-10: The toxicology experiments and the health effects experiments often used 

exposures that result in relatively rapid increases in concentrations of COHb. Hardly any of these 

experimental exposures would meet the guidelines as written in the draft. Alternate guidance 

should be provided. 

17
Page 4-7, line 21: What do current atmospheric levels of CO have to do with setting levels of 

acceptable human exposure? It should not matter if atmospheric levels have decreased, there 

should remain a level(s) that should not be exceeded. If atmospheric levels are decreasing, the 

issue becomes one of how to alter enforcement not alter criteria setting. Perhaps I have read too 

much into this language 

Page 4-8, lines 15-19: Given the concern about near roadway exposure, the following questions 

should be considered for inclusion. What are the uncertainties when extrapolating between 

stationary CO monitoring instruments and concentrations near roadways? What is the spatial 

effect of roadway traffic on stationary CO monitoring?

 

Page 4-9, line 14: The original CFK model includes endogenously produced CO in the factors 

considered for predicting increments in COHb. 

Page 4-10, line 26-31: Angina does not occur in healthy individuals even at maximal exercise. 

Therefore this question needs to be restated. 

Page 4-11, lines 1-6: Delete since it is a repeat of previous question on page 4-10, lines 26-31. 

Page 4-11, lines 7-9: This issue probably requires future research and therefore should be 

eliminated from this section. Lung diffusion capacity is routinely measured using CO. This is 

potentially an important issue because if it were true, it would cause a re-evaluation of basic 

assumptions regarding oxygen transfer in the lung. However there does not seem to be any 

support for this issue in the literature, prior to 2000 nor since that review. 

Page 4-11, lines 23-24: Since there is no guidance for consideration of multi-pollutant air quality 

standards, how should this information be dealt with in the ISA and how are we to consider such 

data? It is not clear that the population is ever exposed to CO alone in the environment. The 

only data possible seems to be from multi-variant statistics. 

Page 4-14, lines 5-6: I believe that this question is based upon the presumed mechanism by 

which CO has its primary effect: through a relative hypoxemia. This is demonstrated in patients 

who have coronary artery disease and have lost the ability to dilate their coronary arteries to meet 

increased oxygen demands of the heart that occur during progressive exercise. However, the 

decrease in time to onset of angina or time to ischemic changes in the ECG appears to occur 

when estimates of oxygen delivery to the heart predict an adequate supply of oxygen in the 

arterial blood. Therefore the mechanism of action of CO in this susceptible population remains 

unidentified as does a marker of its action. So to raise the issue that oxygen saturation which can 

be estimated non-invasively might be a surrogate for COHb is based on a false assumption. 

Page 4-14, lines 25-29 through page 4-15, lines 1-3: An important part of this question should 

be how does the pathophysiologic changes in this population alter the normal compensatory 

responses to low levels of CO observed in healthy individuals?

18
Dr. Russell R. Dickerson 

Comments EPA’s Draft Plan for Review of the Primary National Ambient Air Quality Standard 

for Carbon Monoxide for the teleconference on April 8, 2008.

Three noteworthy topics: The current monitoring program is inadequate but could easily be 

improved; CO plays an major role in the budgets of other criteria pollutants and other 

environmental problems and thus a secondary standard warrants serious consideration; the 

process by which the scientific judgment of the CASAC and its focus groups is used in forming 

policy needs careful consideration - especially in light of the recent problems with PM2.5 and 

ozone standards. 

On page 4-7, we may be asking the wrong questions. It might be better to ask “how can current 

monitoring methods for CO be modified to provide information adequate to determine CO 

exposure, statistics of ambient concentrations, to evaluate models, etc?” CO, even at 

concentrations well below the NAAQS, is responsible for a large fraction of the OH reactivity 

and thus production of HO2, H2O2, and O3 over the US, but emissions inventories and monitoring 

methods are inadequate. Direct investigation of HOx chemistry has quantified the role of CO as 

responsible for 10’s of percents of the total OH reactivity (e.g., Ren et al., 2005; Ren et al., 

2008). The ratio of emissions of CO/NOx (based on road-side research grade measurements) has 

decreased dramatically, but MOBILE6 CO/NOx emission ratios have not followed this trend - 

they are too high now. MOBILE6 indicates a ratio of 15:1 while current measurements show 5-8

(Bishop and Stedman, 2008; Parrish, 2006). In other words, current CO monitors as employed 

can not determine the concentration of CO much of the time, but with relatively minor 

modifications, these monitors can be improved such that the detections limits are essentially 

always sufficient for ambient CO mixing ratios [Dickerson and Delany, 1988; Parrish et al. 

2000). The Maryland Dept. of the Environment operates one at Piney Run, MD. The 

manufactures of CO analyzers have indicated a willingness to improve the instruments for 

commercial sales. 

The atmospheric chemistry and physics of CO are relatively simple and well understood, making 

it enormously useful as a tracer. Improved monitors would provide data useful to 

• evaluate emissions inventories 

• investigate the epidemiology of CO 

• evaluate chemical transport models (such as CMAQ) for ozone and PM2.5 

• determine the impact of CO emissions on the large scale composition of the atmosphere 

and climate.

Although the EPA did not complete the review which started in 1997, a revised CD was prepared 

and reviewed. That CO CD recommended changes in monitoring technique to provide data 

19
useful to models. Ambient concentrations are typically below 300 ppb and commercial CO 

analyzers can be easily modified to improve the resolution from 200 to 20 ppb. While current 

monitors are adequate to demonstrate compliance with the NAAQS, ambient concentrations are 

frequently below detection limits. 

Global atmospheric composition, the oxidizing capacity of the troposphere, and climate forcing 

should be considered in formulating a secondary standard for CO to protect public welfare. In 

addition to its direct health effects, the environmental effects of CO include: 

• A core precursor to ozone. 

• As a precursor to the oxidants that form PM2.5. 

• An impact on the large-scale composition, and oxidizing capacity of the atmosphere. 

• A role in global radiative balance and climate. 

I am not clear on the new review procedures, but the comment by Dr. Henderson “The CASAC 

is a science advisory body and we cannot give the EPA our advice if the scientific analyses of the 

EPA staff are obscured from us,” needs substantial discussion.

References

Bishop, G. A., and D. H. Stedman, A Decade of On-road Emissions Measurements, Environ Sci. 

Technol., 2008. 

Dickerson, R. R., and A. C. Delany (1988), Modification of a commercial gas filter correlation 

CO detector for enhanced sensitivity, J. Atmos. Ocean Technol., 5, 424-431. 

Parrish, D.D., Critical evaluation of US on-road vehicle emission inventories, Atmospheric 

Environment, 40, 2288-2300, 2006. 

Parrish, D.D., and F. C. Fehsenfeld, Methods for gas-phase measurements of ozone, ozone 

precursors, and aerosol precursors, Atmospheric Environment, 34, 1921-1957, 2000.

Ren, X.R., et al., Hydroxyl and Peroxy Radical Chemistry in a Rural Area of Central 

Pennsylvania: Observations and Model Comparisons, J. Atmos. Chem., 2005. 

Ren, X.R., et al., HOx chemistry during INTEX-A 2004: Observation, model calculation, and 

comparison with previous studies, J. Geophys. Res., 2008. 

20
Dr. Milan Hazucha

The Plan for Review (Plan) is structured around a series of critical activities/tasks clustered into 

four key components that have to be accomplished in developing the ISA and Annexes for CO. 

Generally, the ISA and supporting Annex documents approach has been successfully used in the 

development of recent NAAQS documents. The Plan review schedule as proposed is reasonable. 

One of the changes from the previous approaches to NAAQS reviews is the proposed elimination 

of a staff paper. The staff paper served as a compendium, identifying supporting evidence and 

providing rationale for decision making. It was an extended summary of the ISA, generally 

incorporating answers to questions raised in a review plan. In the absence of staff paper the ISA 

should include a Chapter where each of the questions raised in the Plan will be briefly, in a 

couple of sentences or a short paragraph, answered. This will help to quickly identify the areas 

which may have not been addressed or overlooked as well as identify the gaps in the current 

scientific knowledge and database(s). 

Apart from eliminating the staff paper, I think that only minor adjustments, most likely specific 

in nature, will be required to the proposed Plan. My suggestions for changes/modifications in 

Chapters 3 and 4 are listed below. 

Page 3-2: One of the issues that should be considered in this section is the interaction between 

high altitude and CO. Both result in hypoxia, however, CO at altitude may have additional 

detrimental effects. Moreover, idle emissions are supposedly much higher at altitude which may 

increase exposure load. Consequently, health risk may be greater. 

Page 3-2, line 1-2: After “near-roadway” insert the words “and hot-spots such as bus stops, cityintersections, etc,”. These are the places where ambient CO concentration may transiently reach 

high levels exposing substantial population including individuals with compromised health. 

Page 3-2, line 10-12: Percent of oxygen saturation as typically measured would be a misleading 

indicator of CO exposure. Great majority of O2 saturation measurements are done by pulse 

oximeters that are known to be unreliable for COHb estimation. Only when O2 saturation is 

determined by specialized blood gas instruments the COHb level can be reasonably 

approximated. But, in such setting, one may as well measure COHb level directly by COoximeter. 

Page 4-4, line 5: Include ISI Web of Knowledge database in the search list. Of all mentioned 

databases, ISI is the most comprehensive database and includes publications not found in other 

databases. 

Page 4-4, line 19: Delete “pertinent”. We do not know yet how pertinent those studies are. All 

potentially pertinent studies will have to be assessed first using study selection criteria listed in 

subsequent section. 

21
Page 4-4: Will EPA consider potentially pertinent studies published in a foreign language? Will 

they be translated by EPA if they satisfy selection criteria? 

Page 4-5 line 4: List of conditions should be expanded to add “Sufficient statistical power”. 

Surprisingly high number of studies is statistically deficient. Particularly the lack of statistical 

power is a frequent deficiency of published studies. This criterion should be specifically stated 

in the criteria list. 

Page 4-5, line 9: The cons and pros of potentially pertinent studies, i.e. design strength or 

deficiencies, poor statistics, etc., should be discussed in respective Annexes. Studies that did not 

pass the muster should still be discussed. Insert after the word “issues“ following the text “fully 

discussed in Annexes”. 

Page 4-5. Change the subtitle to read “Criteria for Selecting Field and Epidemiological Studies.” 

The design of field studies is different and some selection criteria may differ as well. 

Page 4-5, line 24-27: The argument for more detailed discussion of US and Canadian studies is a 

concern “the potential impact of differing health care systems” or other geographic regions may 

have on the assessment. Well, Canada has substantially different health care system. Suggest 

changing the sentence to read: ”Certain findings of the studies conducted in the U.S. may 

generally be discussed .......”. 

Page 4-6, line 4: Change subtitle to “Criteria for Selecting Human Laboratory, Clinical and 

Animal Toxicological Studies.” Each type of studies should have its own criteria, particularly 

animal toxicological studies. 

Page 4-6, 2nd para: There is no discussion about the selection criteria for animal studies. Many 

animal toxicological studies may not be relevant because of very high CO concentration used, 

exposure duration, extrapolation difficulties, or other experimental conditions. 

Page 4-6, line 8-10: It is highly unlikely that any of the mechanisms can be elucidated under 

atmospherically relevant conditions, which should be defined. Studies of mechanisms require 

more severe exposure conditions so that the mechanisms are easier to identify and study. The 

sentence should be reworded. 

Page 4-7, l. 24: Insert “and temporal “ between the words spatial and variability. Both temporal 

and spatial variability will influence averaging time. 

Page 4-8: One of the questions that should be included in this section is: “What is the effect of 

averaging time and methodology on health risk assessment?” Peak ambient CO concentrations 

in hot-spot areas are blunted by the current averaging method. But it is the peak CO 

concentrations that will increase the health risk to individuals. It would be desirable to weigh the 

peak or hourly peak concentrations when calculating averages. 

Page 4-9, line14-15: The models estimating COHb should be capable of including endogenously 

produced CO as a variable endpoint and not a constant. Several diseases, such as asthma or 

22
COPD, or transient airway inflammation are known to increase production of endogenous CO to 

the level that may exceed ambient concentration of CO. 

Page 4-10, line 28: Reword. The time to onset of angina is not an endpoint for healthy 

individuals. 

Page 4-11, lines 1-6: This aim is identical to the preceding one on p.10, line26-31. Delete. 

Page 4-11, line 7-9: The effects of CO on respiratory gas exchange have been studied 

extensively in the past. At ambient CO concentrations these effects are of no clinical relevance 

even in at-risk population. A simple statement to this fact should be sufficient. 

Page 4-13, line 10: Change to read “... human laboratory, clinical and toxicological...” The 

evaluation should include human laboratory and relevant clinical studies as well. 

Page 4-15, line 28-29: The first goal should be “to comprehensively and critically review the 

literature and subsequently identify.......” as stated on p.1-2, line 11-13. I also suggest adding a 

Chapter at the end of the ISA discussing commonalities and differences, if any, of key factors 

and studies that have led to and determined the current WHO, EU and the NAAQS for CO. 

23
Dr. Rogene Henderson 

Comments on Section 6. Policy Assessment/Rulemaking of the US EPA Draft Plan for Review 

of the Primary NAAQS for Carbon Monoxide. 

In a letter to the Administrator dated January 23, 2008, the CASAC expressed their 

opposition to the use of an ANPR as a Policy Assessment document at the end of the NAAQS 

review process and that opposition still exists. As pointed out in that letter, the ANPR is a 

document that belongs at the beginning of the review process, not at the end, because the ANPR 

(Advance Notice of Proposed Rulemaking) is meant to describe every possible choice that might 

be considered. 

 

In a memo from Assistant Administrator Marcus Peacock of December 7, 2006, the 

ANPR/Policy Assessment Document was described as containing essentially the analyses that 

had been in the former staff paper plus modifications related to EPA management concerns. The 

ANPR that was presented to CASAC at the end of the lead review process was NOT such a 

document, but was the standard ANPR with all options described but with no scientific 

justification for the options. It is not acceptable to CASAC to remove from the review process 

the scientific analyses of the data that was formerly provided in the Staff Paper and substitute an 

ANPR that provides little or no scientific justifications. 

The CASAC is a science advisory body and we cannot give the EPA our advice if the 

scientific analyses of the EPA staff is obscured from us. 

24
Dr. Donna Kenski

This draft plan puts forward a logical framework for the coming review of the CO NAAQS. It is 

very similar to the plans for NOx and SOx and, because the work hasn’t been done yet, it’s hard 

to find any serious flaws. I have two general comments. First, a potentially significant problem

with respect to ambient CO data in both the ISA and subsequent risk assessment. Past efforts to 

control CO have been remarkably successful and thus ambient concentrations are very low -- as 

with NOx and SOx, well below the NAAQS almost everywhere. Consequently many monitors 

have been removed from state networks, since there is little incentive for states to bear the cost of 

running monitors in areas where there is no reasonable expectation of nonattainment. Where 

monitors remain, concentrations are frequently at or below the detection limit. With few 

monitors and a significant fraction of data below the detection limit, the adequacy of the ambient 

data for assessing population exposure and risk is severely limited. It would be helpful to have 

EPA discuss these limitations and their expected impact on the exposure and risk assessment in 

particular. 

Second, as we discovered in the review of the lead NAAQS, the use of the ANPR as a tool to 

present EPA’s policy assessment was not successful in communicating EPA’s views on NAAQS 

revision. I saw no indication in this document that the process had been changed to incorporate 

CASAC’s concerns. Perhaps it is too early and EPA is still contemplating how to use the ANPR 

more appropriately as a policy assessment vehicle? In any case, I look forward to an ANPR that 

makes genuine assessments of the science and presents rational policy options for consideration. 

p. 5-6 is missing text at the top. 

25
Dr. Michael T. Kleinman 

Section 3 

A policy relevant issue that is not explicitly addressed is the non-uniformity of CO exposures in 

various environments. This has a profound effect on the adequacy of our ability to judge health 

effects as a function of high local exposures, i.e. near heavily trafficked roads. Monitoring plans 

for CO should take this into account. Perhaps this could be folded into the question: “What do 

recent studies focused on the near-roadway environment tell us about high-exposure subpopulations 

and the health effects of CO?”

Alternatively, it might be advisable to raise the issue of whether the current network of air sampling 

monitors adequately represents population exposures to CO as an explicit charge question. 

Section 4

4.1 SCOPE AND ORGANIZATION

Vis-à-vis the issue stated above, if ”emphasis will be placed on studies conducted at or near CO 

concentrations found in ambient air.” Some guidance should be provided with respect to ranges of 

exposures measured near areas of unusually high concentration that are not always represented by the 

placement of monitors for other criteria pollutants. 

4.2 ASSESSMENT APPROACH

Literature Search

The suggested search terms are rather limited. An important aspect of the current literature 

relates to long-term sequelae which include neurological as well as cardiovascular endpoints. 

While this may be subsumed in the guidance to look at specific health outcomes, it might be 

useful to state this explicitly. It might be useful to specifically include terms related to the 

possible effects of co-pollutants both from the effects standpoint and from the mechanistic area 

(i.e. pollutants that induce inflammatory effects could up regulate HO-1 activity which would 

increase endogenous CO production). 

General Criteria for Study Selection

The criteria are well thought out. In keeping with my previous comments I suggest that we 

discuss the following criterion: “To what extent are the aerometric data, exposure, or dose 

metrics of adequate quality and sufficiently representative to serve as indicators of exposure to 

ambient CO?” 

This should be placed into a context of the exposure range for populations with exceptional 

exposures since this criteria might be interpreted to exclude some studies near CO sources that 

use measured values that are in excess of those seen at central site monitoring stations. 

26
Criteria for Selecting Animal and Human Toxicological Studies

“Criteria for the selection of research evaluating animal toxicological or controlled

exposure studies will focus primarily on those studies conducted within about an order of 

magnitude of ambient CO concentrations and those studies that approximate expected human 

exposure conditions in terms of concentration and duration.”

There are seasonal and site-specific factors that contribute to the non-homogeneity of CO 

exposures. The order of magnitude requirement may be too restrictive. 

Many toxicological studies are limited with respect to exposure durations and amounts of time 

subjects can be kept in the experimental setting. Perhaps criteria should assess whether the study 

was performed to assess subjects with reasonable levels of some biomarker even when the 

exposure concentrations are greater than ambient rather than putting too tight limitations on the 

acceptable concentration ranges. 

One important factor that should be considered for assessing the acceptability of human

toxicological studies is whether the study was appropriately blinded. 

Section 5

Page 5-5, line29: incomplete sentence 

Page 5-6, line17: This area should be expanded to include issues related to inhomogeneity of 

exposures. A key question is “What is the relationship between peak 1 and 8 hr levels near roads 

and other hotspots vs. levels measured near central sites?” 

Page 5-7, line19: The manner in which the health, risk and exposure assessments will deal with 

the issue of non-homogeneous concentrations should be more clearly described and considered. 

This is a cross-cutting problem that brings into play considerations of environmental justice as 

well as the critical distinction between “compliance” monitoring and monitoring for the purpose 

of providing the information needed to assess the adequacy of health protection afforded by the 

NAAQS. 

27
Dr. Arthur Penn 

Page 1-3, lines 7-8: Why was the staff paper omitted? By putting the information into the 

Federal Register notice (not the most “reader friendly” of document formats) rather than 

providing the historical perspective within the IP could essentially make it more difficult, 

especially for members of the general public, to find important, clearly presented information?

Page 3-1, line 29: Are there sufficient data available from fetal monitoring to allow assessment 

of fetal sensitivity?

Page 4-2, line 14: Please define “welfare effects”. What else does this describe besides 

“ecosystem effects”? 

Page 4-4, line 27: “sufficiently representative”--of CO levels? 

Page 4-4, line 30: “meaningful and reliable”. “Meaningful” is vague. Is this independent of 

“statistically significant”? What are the specific criteria that determine “reliability”?

Page 4-6, lines 8-10: Should studies that elucidate mechanisms be a major part of the data to be 

analyzed? This seems like a major goal of a possibly related, but distinct set of analyses. 

Page 4-8, lines 12-13 (also see Page 4-13, lines 12-14): Interactions between CO and these other 

factors will likely be very important. A large amount of data from diverse sources will have to be 

examined and analyzed. Who will do this? 

Page 4-11, line 18: “Other systems”--genito-urinary? digestive? endocrine? By what criteria 

would any of these, or other systems, be selected? 

Page 4-15, lines 5-6: “Older adults and fetuses”. No neonates? How are effects on fetuses 

assessed?

Page 5-2, line 6: “Four scenarios”-Is there a summary of these scenarios available so that 

people, especially members of the public, do not have to find and wade through the 1992 

document?

Page 5-2, line 6: Why was the CO NAAQS review put on hold? Why, 9 years later, has the 

exposure analysis not been completed? Has there been a public inquiry about this and a formal 

response?

Page 5-6, lines 1-4: Is there a missing paragraph, or is this just a spacing error?

28
Page 5-11, lines 3-17: During the teleconference, a couple of the discussants noted that the 

distribution of CO monitors was uneven and that the monitors might be completely absent from

certain communities within a large monitoring zone. It was also noted that “the emissions history

was a disaster” and that in general, ambient CO measurements were inadequate. Other 

committee members supported these comments. Given these concerns, how reliable are the 

primary sources of the data (see lines 4-5) that will be included in the APEX model inputs? 

Page 5-11, line 14: The specific reference to Morgan &Henrion, 1990, was not included in 

pages 7-1 or 7-2 in the draft plan. There are multiple publications listed for them in 1990. 

29
Dr. Beate Ritz

Chapter 4: 

page 4-4 "Emphasis in the text will be placed on discussion of (1) new, multi-city studies that 

employ standardized methodological analyses for evaluating CO effects and that provide overall 

estimates for effects based on combined analyses of information pooled across multiple cities; " 

The emphasis on pooled results from multi-city studies that use standardized methods might be 

misplaced i.e. it is not clear that such approaches will be informative. The problem with CO is its 

intra-community heterogeneity due to local sources, heterogeneity may not be reflected in 

ambient monitoring station measurement data. Depending on how ambient monitoring is used to 

derive exposure estimates in different communities, this could lead to differences in 

measurement errors depending on how dense the network is. Concerning standardized exposure 

modeling approaches, if different sources contribute to high CO in different cities, a 

'standardized model' for different cities might not work or be appropriate e.g. in some cities CO 

may depend more on vehicular traffic and in others on power plant emissions etc. 

 

Similarly questionable is the emphasis on "studies that consider CO as a component of a 

complex mixture of air pollutants." It is unclear whether this means only multi-pollutant models 

will be taken into consideration and how the expected (and possibly strong) correlational pattern 

with particles and NO2 will be dealt with in such models. It might be impossible to adjust for 

(highly) correlated pollutants in the model, and it is not clear how this may be addressed and/or 

evaluated in the report. 

Furthermore, it is unclear what the emphasis on "new studies that provide quantitative effect 

estimates for populations of interest" means. For pregnancy outcomes, the issue of scaling 

according to a (susceptible) time period is essential and it is not clear that 1ppm exposure on 

average during a trimester is comparable to a 1ppm average exposure during a month or week of 

pregnancy. 

Chapter 5, page 5-4 

 "For this current review, EPA staff will build upon the 1999 work and subsequent improvements 

to the exposure model (now called APEX) in developing its plan for CO exposure assessment. " 

It is unclear what this work will be i.e. what kind of data will be used to develop these models 

and whether the data already exist and/or will be retrieved from existing research (e.g. the LA 

RIOPA study that monitored CO). 

Given that the highest CO exposures might occur inside cars during commute, it is unclear how 

this will be integrated into the stated goals for CO exposure assessment (page 5-5), even though 

the Apex model uses in-vehicle microenvironments and this is also mentioned on page 5-10.

30
Dr. Paul T. Roberts 

Note that this document outlines a plan for the several year review process for the CO NAAQS 

and thus includes little or no technical detail. In general, this plan is well-written, is adequate to 

meet its objectives, and (presumably) matches the review process currently ongoing for sulfur 

dioxide and nitrogen oxides, which are both further along than the process for CO. Overall, I am

concerned about the elimination of the EPA staff paper from the process, since I am not sure how 

the summary and integrative aspects of the staff paper will be handled in the new process (within 

the ISA and the Scope and Methods Plan). Maybe this should be addressed directly in the 

“Plan”. 

In Section 1.3, I think that there should be some discussion of why the previous 1997-2000 CO 

NAAQS review process was not completed (see page 1-6, lines 23-24). 

Table 2-1 seems to have a duplicate listing for the first draft of the risk and/or exposure 

assessments in January 2010 (see 3rd and last entry under Risk/Exposure Assessment in the 

table). 

Specific comments on Sections 4 and 5: 

• The introduction to Section 4 mentions that a formal framework for the integration of 

health effects evidence was developed in the NOx ISA (see page 4-1, lines 13-16); I think 

this should be summarized here in the draft plan. 

• As far as I can tell, the WHO guidelines referenced on page 5-5, lines 3-4 do not include 

CO; information on CO was not updated from the earlier WHO Air Quality Guidelines 

for Europe, 2nd edition published 2000. 

• I do think that a comparison and explanation of the different standards (and studies 

supporting them) published by WHO and others for CO should be discussed in summary 

form in this plan and in more detail in the ISA and/or the Scope and Methods Plan. This 

specifically could help on the short-term issues discussed on pages 4-10 to 4-12 etc., 

since short-term standards is one major area of difference. 

• Text is missing from the bullet that begins on page 5-5 and continues onto the top of page 

5-6. 

• There are several potential CO ambient exposure environments which are not mentioned 

in this document, but should be mentioned here and information for them explored during 

the development of the ISA and the Scope and Methods Plan. Existing study data may be 

useful for determining levels and averaging times, as well as relevant to future exposure 

environments. These ambient exposure environments include other near-source 

environments such as near ship loading and unloading ports (potential exposure from

trucks and other vehicles plus potential exposure from the ships themselves) and 

exposures near recreational boats. Both of these environments cover locations where 

people live, work, and play. Recreational boat engines, including both 2-stroke and 4-

stroke engines, do not have exhaust controls and several potential environments can 

result in very high CO concentrations in the near-source environment. Even with coming 

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emissions controls on new boats, fleet turnover is extremely slow and such exposures will 

likely persist for 10-20 years. Places in the draft plan where these additional 

environments might be mentioned include: page 3-2, lines 1-2; page 4-8, lines 3 and 28-

29; page 4-10 subsection on short-term exposure; and page 5-3, lines 23-26. 

• There should be some discussion of the types of CO monitoring sites and how data from 

all types of sites will be used to characterize CO air quality and exposures (specifically 

mentioned in Section 5.3, pages 5-5 to 5-7). In particular, there are official CO 

monitoring sites, “hot-spot” sites, and data from special purpose monitoring sites which 

all might inform the analysis being undertaken. This section of the plan should discuss 

these additional data sets and how they might be used to further the objectives of the 

exposure assessment (note that this is also of importance for the discussions on pages 4-7 

and 4-8 regarding spatial and temporal analyses). In addition, the appropriateness of 

current monitoring sites, relative to their purposes, should be discussed in the ISA and/or 

the Scope and Methods Plan. Also, existing sites should be evaluated in some consistent 

manner in order to ensure that the CO data being collected is appropriate for the stated

purposes, both for the current review and for future uses relative to the NAAQS. 

• Based on discussions I heard on the April 8th call, I was wondering how the binding time

of COHb might be related to potential averaging time of the CO data? In particular, 

might the COHb binding time lead to a short-term standard that has otherwise been 

ignored?

• In addition to these comments, I support the following comments by others on the Panel: 

- Interest in having a short discussion of why the secondary CO standard was 

revoked in 1985. 

- The need for the Draft Plan to specifically address the issue whether the existing 

monitoring methods and network are adequate to address the questions outlined in 

Section 3. 

- Potential upgrading of present CO monitors to high-sensitivity monitors, which 

have been tested and evaluated by OAQPS staff in the recent past. 

- The notion that CO characteristics might be different in different cities, especially 

as it relates to ‘hot spots’, thus requiring different types of data analysis 

approaches and methods. 

- The concern that co-pollutants might also have an affect on the impact of CO 

concentrations on health. 

- How will the CO ANPR show the results of the assessment of the full range of

potential science and policy questions which will have been address by that time?

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Dr. Armistead Russell 

Similar to past draft plans provided to CASAC, this draft plan lays out a well thought out 

approach to reviewing the CO NAAQS. I was pleased to see that they plan to organize the CO 

ISA similar to that for the NOx and SOx primary NAAQS, which I found to be a very good 

approach. In particular, what I liked about the NOx and SOx primary NAAQS ISA’s was having 

an initial chapter going from source to dose, then the future chapters dealing with health 

endpoints, with a conclusion/summary chapter at the end. (However, the bullet points do not 

follow this order.) This worked well, and communicated the needed information in a more 

integrated and briefer fashion. In so doing, however, EPA staff should continue to provide the 

information necessary to review the science that is most pertinent to reviewing the various 

aspects of the NAAQS. 

In regards to the atmospheric dynamics of CO, and the distribution of the primary sources 

(automobile exhaust), CO is somewhat unique compared to the other criteria pollutants. It is 

chemically reactive, both being destroyed and formed in the atmosphere. CO exposures of most 

concern are from primary emission, with the highest levels being near the source, and dropping 

off rapidly as one moves away, though policy relevant background (PRB) levels are from

secondary formation. Thus, the type of model used to estimate PRB CO levels is very different 

from the type that would be used to estimate exposures. Indeed, as suggested in the Draft Plan, 

PRB levels will appropriately be estimated using chemical transport models. On the other hand, 

the model(s) used to help estimate exposures may be quite different, e.g., dispersion models. 

This is not well spelled out in the Draft Plan. What type of dispersion models, or chemical 

transport models, should be more thoroughly discussed and assessed. Indeed, one of the driving 

questions down the road as to the exposure assessment may be the modeling approach. A further 

question will be how to evaluate the model, particularly if a case study (or studies) is used for 

which such an evaluation is not done. This is going to be particularly important as one of the 

possible susceptible populations is rather unique in regards to how air quality models have been 

employed when estimating exposures, as discussed below. The Draft Plan refers to 

consideration being made for confounding. The Source-to-Dose chapter (and associated Annex) 

will need to address this is detail. It will be critical. 

The Draft Plan identifies APEX as the likely model to be used for conducting the exposure 

modeling. This is a reasonable choice. It should be noted, again, that the continued use of 

APEX in NAAQS assessments should continue to motivate EPA to further enhance and evaluate 

APEX, and that evaluation should consider subpopulations of interest. In this case, what I think 

is a rather new and unique subpopulation is the target, that being pregnant women. What 

population specific information exists for APEX to use for this target, and when insufficient 

information is not available, how is EPA going to modify APEX for this group? Further, how 

are they going to integrate results from the air quality modeling for use in APEX? On page 5-6, 

it notes that they will include various types of exposures... how, in a probabilistic framework, 

will you consider pregnancy in the matrix. 

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I would have liked to see more information on the planned use of case studies. This has been a 

critical issue in past reviews. This Draft discussed the Denver case study, and mentions a Los 

Angeles study. Both would be of interest, still, along with, possibly, an Alaskan city (Fairbanks 

or Anchorage). Los Angeles would provide an interesting contrast to Denver due to the different 

magnitude in the variation between seasons and temporal distributions, and, possibly, the 

population distributions. This might be of particular interest if the exposure period of interest is 

long... multi-day/week/month (e.g., for fetal exposures). Alaskan cities might be extreme in the 

other direction, and also may have the most extreme short term exposures. Perhaps the analyses 

discussed on pages 5-5 to 5-6 (that is missing on mine) covers this. 

Other minor issues: 

Pages 4-7 to 4-8 There seems to be an over-reliance on chemical transport models verses 

dispersion models or other micro-scale modeling approaches. There should be a fairly major 

section on various modeling approaches for estimating CO concentrations and how they can be 

used to assess exposure and dose. 

Page 4-8, line 23: Pet peeve (though I make this mistake as well): “particle” is not a phase, 

“condensed” can be used. 

Page 4-9, line 7: This bullet asks a simple question, though the real question is how does one 

evaluate the models being employed, and how does one interpret those results. 

Page 4-9: A similar bullet point for exposure models as above. 

Page 5-6: You may want to consider what other procedures one might use to rollback levels as 

part of an uncertainty assessment. Further, you note on page 5-6 about assessing exposures for 

levels just meeting the standard... that means you also have to rollup levels, too. The methods 

should be consistent. Also, given that the methods likely used to reduce CO emissions may rely 

on automotive standards, consideration as to how exposure reductions are linked between cities 

may be appropriate. 

Page 5-6: You note that you will evaluate the relationships between 1- and 8-hour peaks... you 

should look to other averaging times. 

Pages 5-5 to 5-7: Something is missing. (Maybe this is where other case studies are identified.) 

Summary: The Draft Plan provides a suitable map for going forward, though given the 

introduction of a rather unique susceptible population not treated previously (fetus’s) and 

exposure route (pregnant women) how exposure and dose will be linked to ambient 

concentrations and forms of the standard requires greater discussion and detail as to how this will 

be accomplished. 

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Dr. Jonathan M. Samet 

General Comments:

• This Draft Plan follows the model that is now coming into place for developing a 

primary National Ambient Air Quality Standard (NAAQS). As such, the plan draws on 

approaches taken already over the last several years. The overall plan and approach is 

appropriate. 

• However, the new plan appears to draw little on “lessons learned” to date from dealing 

with nitrogen oxides and sulfur oxides. The plan suffers from an overall lack of 

specificity and vagueness of wording that will undoubtedly become a limitation during its 

implementation. Additionally, there has been little advance in the EPA’s formulation of 

such critical concepts as causality, confounding, effect modification, and susceptibility. 

On reading over the questions that will guide the review, problems arising from this 

vagueness are abundant. I highlight a number of examples in my specific comments.

Specific Comments:

Page # Line # Comment 

4-4 27 “...sufficiently representative” Of what? Representative in what regard?

4-4 29 Not clear at all 

4-4 30 “meaningful” From what perspective? Reliable means repeatable. Is the 

concern about misclassification?

4-5 5 “potential confounders...” Specify criteria for these 

4-8 20 This needs greater specificity 

4-8 24 Temporal and spatial?

4-9 19 What does variability mean here?

4-10 7-10 Lines 7-10 are sweeping. What is this saying?

4-11 18 All other systems?

4-11 23 “...nature of health effects...” Effect modification?

4-12 

4-13 

20-22 

1-2 

What is meant by evidence against a causal association? Could more be said 

about EPA’s approach to causal inference?

4-13 9 “evaluate uncertainty...” Any attempt to quantify?

4-13 17-19 What does this mean? Is this in reference to potential effect modification?

4-15 6 Reference to fetuses not clear. 

4-15 10 What results?

4-15 19-21 Not clear in the formulation of attributable risk 

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Dr. Stephen R. Thom 

Approach & format for the integrated science assessment section are well organized and 

logical. 

Specific comments I suggest be included in the EPA document are: 

A. Human exposure studies: Environmental pollution causes a variety of disorders, although 

not all studies have documented CO per se as the etiologic agent. 

1. Neonates/infants: 

a) Preterm labor/delivery - association with environmental CO and also particulates (PM) 

(as separate risk factors & also in combination) 

b) Infant mortality - association with CO plus PM 

c) Neonate hospitalizations for respiratory diseases - association with CO 

d) Intra-uterine growth retardation/low birth weight (risks with CO, PM and NO2) 

e) No relation between SIDS and CO, but a link has been established with NO2 and SO2 

2. Children 

a) Childhood respiratory symptoms (wheezing) - association with CO and also PM. 

3. Adults 

a) Correlations between ambient CO and ischemic heart disease ED visits (CO and also NO2) 

b) Cardiovascular mortality (esp. elderly) - associations with CO and CO/PM & O3

c) Respiratory-related ED visits - association with CO and CO+O3

d) Depression-related ED visits 

e) Pneumonia hospitalizations (CO + O3) 

f) No link between CO and tachyarrhythmias (but + link with ultra-fine particulates) 

g) Risk of CVA elevated with CO, PM, NOx

h) Cardiac irregularity (HR variability) and CO (+ link in some but not all trials) 

i) Plasma markers of inflammation - atmospheric CO contamination only linked with altered 

albumin. PM and O3 showed additional changes in plasma levels of vWF, Factor VIII, 

fibrinogen. Higher CO concentrations (& shorter exposure times) linked to elevated plasma

myeloperoxidase. 

B. Issues of CO dose-response, as well as time-course of responses, are not clear. The weight 

of the scientific findings probably does not warrant an alteration in EPA CO guidelines (1 hr 35 

ppm; 8 hr 9 ppm). Also, the variability among findings in some trials indicates that combinations 

of CO with co-pollutants can yield disparate results, leaving the issue of pathophysiological 

mechanisms unclear. 

C. Dosimetry questions persist, and there needs to be some focus on mechanisms unrelated to 

CO-O2 competition for hemoproteins (e.g. the CFK equation alone is not adequate to ‘predict’ 

biological stresses). These include pro-inflammatory processes such as intravascular platelet36
neutrophil interactions, and a growing body of information on oxidative stress/free radical 

mediated mechanisms (some linked to ‘therapeutic’ pathways such as activation of MAPKs, 

NFκB inactivation, caspase 8 inactivation). Endogenous CO production impacts mitochondrial 

respiration but whether environmental CO will compound this effect is unknown (current kinetic 

modeling suggests this is unlikely). 

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