osr UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
-^ % WASHINGTON D.C. 20460
OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD
November 14, 2007
EPA-CASAC-08-001
Honorable Stephen L. Johnson
Administrator
U.S. Environmental Protection Agency
1200 Pennsylvania Avenue, NW
Washington, DC 20460
Subject: Clean Air Scientific Advisory Committee's (CASAC) Consultation on
EPA's Nitrogen Dioxide Health Assessment Plan: Scope and Methods
for Exposure and Risk Assessment (September 2007 Draft)
Dear Administrator Johnson:
The Clean Air Scientific Advisory Committee (CASAC), augmented by subject-matter-
experts to form the CASAC Oxides of Nitrogen Primary NAAQS Review Panel, met on
October 24-25, 2007 and has completed its consultative review of EPA's Nitrogen Dioxide
Health Assessment Plan: Scope and Methods for Exposure and Risk Assessment ('September
2007 Draft). The CASAC uses a consultation as a mechanism for individual technical experts
to provide comments to guide the Agency on technical issues early in the development of a
document, before the first draft is ready for peer review. Panel members offered oral comments
at the meeting and their comments are reflected in the official minutes of the meeting. Written
comments provided are attached to this letter. A consultation is conducted under the normal
requirements of the Federal Advisory Committee Act, which include advance notice of the
public meeting in the Federal Register.
There will be no formal report from the CASAC as a result of this consultation, nor do
we expect any formal response from the Agency. We look forward to conducting a peer review
of the first draft for the Exposure and Risk Assessment document as part of the primary oxides
of nitrogen National Ambient Air Quality Standard review.
Sincerely,
/Signed/
Dr. Rogene Henderson, Chair
Clean Air Scientific Advisory Committee
Attachments
Attachment A: Roster of CASAC Oxides of Nitrogen Primary NAAQS Review Panel
Attachment B: Compilation of Individual Panel Member Comments on EPA's Integrated Science
Assessment (ISA) for Oxides of Nitrogen - Health Criteria (First External Review Draft, August 2007,
EPA/600/R-07/093)
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Attachment A: Roster of CAS AC Oxides of Nitrogen Primary NAAQS Review Panel
U.S. Environmental Protection Agency
Clean Air Scientific Advisory Committee
Oxides of Nitrogen Primary NAAQS Review Panel
CHAIR
Dr. Rogene Henderson, Scientist Emeritus, Lovelace Respiratory Research Institute,
Albuquerque, NM
CASAC MEMBERS
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 Crapo, Professor of Medicine, Department of Medicine, National Jewish
Medical and Research Center, Denver, CO
Dr. Douglas Crawford-Brown, Professor and Director, Department of Environmental
Sciences and Engineering, Carolina Environmental Program, University of North
Carolina at Chapel Hill, Chapel Hill, NC
Dr. Donna Kenski, Data Analyst, Lake Michigan Air Directors Consortium, Des
Plaines, IL
Dr. Armistead (Ted) Russell, Professor, Department of Civil and Environmental
Engineering , Georgia Institute of Technology, Atlanta, GA
Dr. Jonathan M. Samet, Professor and Chair of the Department of Epidemiology,
Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD
PANEL MEMBERS
Mr. Ed Avol, Professor, Preventive Medicine, Keck School of Medicine, University of
Southern California, Los Angeles, CA
Dr. John R. Balmes, Professor, Department of Medicine, Division of Occupational and
Environmental Medicine, University of California, San Francisco, CA
Dr. Terry Gordon, Professor, Environmental Medicine, NYU School of Medicine,
Tuxedo, NY
Dr. Dale Hattis, Research Professor, Center for Technology, Environment, and
Development, George Perkins Marsh Institute, Clark University, Worcester, MA
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 Chief, Laboratory of Respiratory Biology,
National Institute of Environmental Health Sciences, National Institutes of Health,
Research Triangle Park, NC
Dr. Timothy V. Larson, Professor, Department of Civil and Environmental Engineering,
University of Washington, Seattle, WA, USA
Dr. Kent Pinkerton, Professor, Regents of the University of California, Center for
Health and the Environment, University of California, Davis, CA
*Unable to participate in the October 25, 2007 Consultation
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Dr. Edward Postlethwait, Professor and Chair, Department of Environmental Health
Sciences, School of Public Health, University of Alabama at Birmingham, Birmingham,
AL
Dr. Richard Schlesinger,* Associate Dean, Department of Biology, Dyson College,
Pace University, New York, NY
Dr. Christian Seigneur, Vice President, Atmospheric & Environmental Research, Inc.,
San Ramon, CA
Dr. Elizabeth A. (Lianne) Sheppard, Research Professor, Biostatistics and
Environmental & Occupational Health Sciences, Public Health and Community
Medicine, University of Washington, Seattle, WA
Dr. Frank Speizer, Edward Kass Professor of Medicine, Channing Laboratory, Harvard
Medical School, Boston, MA
Dr. George Thurston, Professor, Environmental Medicine, 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 Officer, 1200 Pennsylvania Avenue, NW
1400F, Washington, DC, Phone: 202-343-9981, Fax: 202-233-0643,
(nugent.angela@epa.gov)
*Unable to participate in the October 25, 2007 Consultation
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Attachment B: Compilation of Individual Panel Member Comments on EPA's
Integrated Science Assessment (ISA) for Oxides of Nitrogen-Health Criteria (First
External Review Draft, August 2007, EPA/600/R-07/093)
Comments from CAS AC Oxides of Nitrogen Primary NAAQS Review Panel on EPA's
Draft Nitrogen Dioxide Health Assessment Plan: Scope and Methods for Exposure and
Risk Assessment (September 2007 Draft)
Comments from Mr. Ed Avol 5
Comments from Dr. JohnBalmes 9
Comments from Dr. Ellis Cowling 10
Comments from Dr. James Crapo 13
Comments from Dr. Douglas Crawford Brown 14
Comments from Dr. Terry Gordon 17
Comments from Dr. Dale Hattis 18
Comments from Dr. Donna Kenski 20
Comments from Dr. Timothy Larson 21
Comments from Dr. Kent Pinkerton 22
Comments from Dr. Edward Postlethwait 24
Comments from Dr. Armi stead Russell 26
Comments from Dr. Jonathan Samet 30
Comments from Dr. Christian Seigneur 31
Comments from Dr. 'Lianne' Elizabeth Sheppard 33
Comments from Dr. Frank Speizer 40
Comments from Dr. George Thurston 43
Comments from Dr. Ronald Wyzga 45
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Comments from Mr. Ed Avol
Nitrogen Dioxide Health Assessment Plan: Scope and Methods for Exposure and Risk
Assessment (Draft September 2007)
General Comments:
The document provides a useful road map for how the Agency will proceed on the Risk
Assessment. If the plan is to only provide a Tier I assessment (air quality
characterization) and attempt to argue that insufficient information exists to assess
exposure, I believe the Agency will find its own credibility and level of commitment
questioned. The annexes provide a wealth of information about the current state of
knowledge regarding NO2, and most reasonable and objective reviewers will conclude, I
believe, that sufficient information exists to perform the Tier II assessment, and to
seriously consider the Tier III assessment. The modeling approaches can provide us with
guidance if they are applied appropriately, and we should move forward. Continuing to
vacillate and wait for complete and perfect information before deciding that there is
sufficient data to proceed (which will ultimately end with an estimate and range, anyway)
does not serve the public health or the public's interest.
It would be helpful to have a listing of Abbreviations and Acronyms in this document, to
which the reader could refer for clarification.
Specific Comments:
P6, Sec 3.1, para2, line 1 - "Several tools would..." should be "Several tools will..."
P6, Sec 3.1, last paragraph discussing evaluation of uncertainties: This discussion is
well-intentioned but not well-constructed. What are the objective criteria by which the
exposure assessment will be determined to be worthy of a qualitative or quantitative
assessment? How will the magnitude of uncertainty (minimal/moderate/maximal) be
assigned? Does a rating of "minimal" (which I would think would be the starting point
for every evaluation) lead to qualitative or quantitative determinations? How about two
"minimals" and one "moderate" in the matrix of uncertainties, or other possible
combinations? And what about over and under-estimates - are over-estimates going to be
viewed as more conservative and therefore less uncertain, or vice versa? It is difficult to
see how this proposed process will lead to a logical, credible determination, based on
what is provided here. Staff may well have a clear understanding and process in mind,
but that procedural clarity has not been effectively communicated in writing in the
document.
P7, Sec 3.2, para2, last sentence - How will ".. .those commuting on roadways and
persons who reside near major roadways..." be incorporated into the modeled
population?
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P8, Sec3.3, para 1, first sentence - "All available ambient monitoring data collected
since... 1995.. .will be used as is." Presumably what is meant is that all quality-assured
ambient air monitoring data collected since 1995 will be used?
P8, Sec 3.3.1, paral (regarding the selection of CMS As for evaluation) - Presumably
some tabular summary will validate this selection of cities, but why Atlanta, Philadelphia,
and Chicago over New York, Phoenix, and Denver? Some additional and transparent
justification for CMSA selection should be provided.
P13, Sec 3.3.1.3, para 1, last sentence- This summary claim of "...insignificant to
limited contribution..." of biomass combustion and ETS toNO2 personal exposure is an
over-simplification and over-interpretation of what is presented in the referenced Chapter
of the ISA. Please review the referenced chapter and re-evaluate the accuracy of this
summation.
P. 15, Sec 3.3.3, para 1 (Ambient NO2 measurement), last sentence - In areas like Los
Angeles, where significant reductions in NO2 in the past decade have only recently
resulted in achievement of NAAQS compliance, the assumption that sources present in
the past are the sources present now is almost certainly a poor one; some sources are no
longer present, and engine/boiler/source emission reduction controls have changed
substantially to achieve emission reductions. How will this be addressed or handled?
P15, Sec 3.3.3, para 3 (Spatial Representativeness), line 6 -Low spatial correlations
could be the result of several circumstances other than the presence of local sources (for
example, topographical intrusions such as canyons, hills, or slopes between sampling
locations leading to local variations in wind direction or wind speed).
P16, Sec 3.3.3, para 1 (Roadway to Ambient Monitor Relationship), lines 14-19 - Is the
implication here that NO2 is a "... reactive pollutant..." and will tend to have a lower I/O
ratio? This assertion should be compared to more recent information about in-vehicle
measurements. It is my understanding that based on the available information, NO is
higher in the passenger compartment (due to the fresh emissions from combustion
exhaust being drawn into the vehicle compartment), and that NO2 is somewhat elevated
over ambient (reflecting on-roadway conditions), but that NO2 is not as high as near off-
roadway (because there has been insufficient time for NO to oxidize to NO2.
P16, Sec 3.3.3, para 1 (Roadway to Ambient Monitor Relationship), last sentence) -
Some qualifier must be missing from this statement, because this seems to directly
contradict the earlier explanation made in the justification of Equation 3.
PI7, Sec3.4 Tier II Screening-Level Exposure..., para 1, bullet 3 - "...factors that
contribute to lessened personal exposures to ambient NO2.. .including time spent indoors
and indoor vehicles..." - Doesn't the recent in-vehicle measurements suggest in-vehicle
NO2 is somewhat elevated?
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P17, Sec3.4 Tier II Screening-Level Exposure..., para 2, lines 6 thru 8 - Is there some
protocol for when to apply one of these approaches or the other? Presumably one or two
hourly gaps could be filled in using interpolation between valid values at the ends of the
missing gap, but this approach would lead to incorrect values if gaps included morning or
afternoon traffic hour peaks (since it would not capture or re-construct the peak
structure).
P17, Sec 3.4.1 Short-Term Exposure Approach, paral, "... TIGER ROAD network..." If
this refers to the road structures based from the highway transportation files, there may be
some issues with road placement accuracy, compared to commercially available Tele-
Atlas road files. In working with the road files in Southern California to locate streets
and residents' homes for Children's Health Study-related research, the transportation files
were demonstrated to be occasionally mis-located by 100 meters or more compared to the
Tele-Atlas files and the actual location of the roadways. This variation can be critical
when considering near-road pollutant exposure (see figure below), given the decay of
pollutants with distance from roadways.
Riverside Surface Street Comparison
Catvans Surface Street*
'TeleAtlas Surface Sheets
R**id*nc«? Locations
4-.
0 200 400 SOO 800 Meters
P31, Sec 4.1 Risk Assessment Scope Overview..., para2, last sentence - Failing to assign
some risk estimate to long-term NO2 exposures runs the risk of not protecting public
health from the more potentially more serious and persistent health effects (from long-
term, low-level exposures). This sounds akin to ignoring the quantification of the impact
because we don't yet fully understand it. At the very least, a statement or discussion
should be included discussing this.
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P33, Sec 4.3 Tier II Risk... - "health responses reported to be related to NO2 include.
lists several health outcomes, but does not include low lung function (from the Children's
Health Study).
P37, Sec 4.4 Criteria for Determining Approach, last bullet- This undertaking is supposed
to lead to the Agency's best efforts to assess the current information regarding NO2
health effects. The suggestion that there might not be enough time (after allowing 14
years to pass since the previous document release) or insufficient resources to accomplish
what the Agency is charged to do is simply not credible; this bullet should either be
revised or removed.
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Comments from Dr. John B alines
In general, I think the approaches described in the document are appropriate to provide
important information that will be useful in the process of review of the NAAQS for
NOx. I urge the agency to try to use emergency department (ED) asthma visit data in the
risk assessment. This is especially important given the strength of the epidemiologic
evidence of an association between NO2 exposure and asthma outcomes. Asthma
hospitalization data only capture the tip of the iceberg of asthma morbidity and the
addition of ED data allow a greater proportion of the burden of asthma to be assessed. I
made this same point during the ozone NAAQS review and was told that for the cities in
which the exposure assessment was done, there were inadequate asthma ED data to use in
in the risk assessment. For this review, more ED data should be available - for example,
California now has ED as well as hospital discharge data available state-wide.
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Comments from Dr. Ellis Cowling
Individual Comments on the Nitrogen Dioxide Health Assessment Plan:
Scope and Methods for Exposure and Risk Assessment
My comments are organized below in response to each of the several Charge Questions
posed in Karen Martin's September 2007 transmittal letter to Angela Nugent.
Air Quality Considerations
1. Do the Panel members generally agree with using historic air quality data (e.g.,
pre2000) in certain analyses as a reasonable approach to simulating air quality
scenarios with higher NCh concentrations, given that current ambient air quality
concentrations are lower than the current standard?
Yes, I agree that historical data is a reasonable approach even though some of the
historical air concentration measurements may be higher than current ambient air
concentrations.
2. Based on the low estimated contribution of policy-relevant background NCh to
overall ambient NCh levels, staff is considering a proportional (i.e., linear) approach
to adjusting air quality to simulate just meeting potential alternative NCh standards
that are lower than current air quality concentrations. Do the Panel members have
comments on adopting a proportional approach to simulate just meeting more
stringent alternative air quality standards?
Although I am surprised that the contribution of policy-relevant background is as low as
it is currently estimated to be, I see no great problem in using a proportional method of
adjustment. I have no additional comments to add.
Exposure Analysis
1. In considering the exposure analysis broadly:
a. Do Panel members have any comments on the general structure and overall
three-tier approach that staff plans to use for the exposure analysis? Are the criteria
that staff plans to use for deciding whether to conduct a Tier II or Tier III analysis
clear and appropriate?
The three tier approach seems reasonable to me and the criteria suggested by staff also
seem reasonable.
b. Have the most important factors influencing exposure to NCh been clearly
accounted for and described?
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My only major concern is to know whether, and if so, how indoor exposures will be
considered and evaluated.
c. The draft plan describes the basis for and selection of population groups of
interest (i.e., children, asthmatics (children and adults), and the elderly) for which
NCh exposure estimates are to be developed. Do Panel members generally agree
with the groups of interest identified in the draft plan?
The suggested population groups seem very reasonable to me.
2. In considering the Tier I exposure assessment:
a. Do Panel members agree that an exponential model is appropriate for estimating
expected exceedances of short-term health effect benchmarks based on long-term
annual average air quality?
I have no experience on which to base an informed judgment in response to this question.
b. Do Panel members agree with the approach to enhance NCh air quality data by
accounting for the influence of roadway emissions?
Yes, this approach seems reasonable to me.
3. In considering a potential Tier II exposure assessment:
a. Do Panel members agree with the combined emissions/dispersion modeling
approach to estimate short-term (hourly) on- and near-roadway NCh
concentrations?
I have no experience on which to base an informed judgment in response to this question.
b. Is the proposed use of time-location-activity diary data reasonable for estimating
short-term exposures for population cohorts?
I have no experience on which to base an informed judgment in response to this question.
c. Do Panel members agree with the use of HAPEM6 to estimate long-term
exposures (annual average) and the approach to account for on- and near-roadway
NCh concentrations?
I have no experience on which to base an informed judgment in response to this question.
4. In considering a potential Tier III exposure assessment:
Do Panel members generally agree that developing individual exposure profiles
through the use of APEX is reasonable and appropriate to estimate both short- and
long-term NCh exposures?
I have no experience on which to base an informed judgment in response to this question.
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5. Do Panel members have any comments or advice regarding the general approach
to addressing uncertainty and variability in each Tier of the exposure assessment as
described in the draft plan?
I have no experience on which to base an informed judgment in response to this question.
Health Risk Assessment
I have no experience on which to base an informed judgment in response to any of these
several Health Risk Assessment questions.
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Comments from Dr. James Crapo
NOx Health Assessment Plan: Scope and Methods for Exposure and Risk Assessment.
The document provides an appropriate plan for carrying out both and Exposure and Risk
assessment for NOx. The tiered approach is appropriate and well laid out in the
document. A substantial number of studies have been published during the past decade
which suggest that NOx exposures are an important contributing factor in creating
adverse health effects from air pollutants at levels of exposure that are substantially
below the current NAAQS. The form of the standard is an important question to include
in the risk assessment. Current data suggest that short term peak exposures may be more
important than long term average exposures as currently regulated in the NAAQS. There
are also unique populations at risk both in terms of disease (eg. Asthma patients) and
proximity to peak NOx exposures (Those living near roadways or traveling on them
frequently).
I feel strongly that both tier I and Tier II of the proposed risk assessment should be done.
As part of these assessments I concur with the proposed focus on short term exposures at
levels of NO2 in the range of 0.2 tp 0.3 ppm. The tier II assessment to provide data on
incidence of expected adverse outcomes will be essential for the subsequent
consideration of a recommended change in the NAAQS. I also concur with the
recommendation that outcomes for both hospitalizations and ER admissions be
considered for asthmatic patients.
Finally it will be important to assess the magnitude of confounding in the risk estimates
for NOx by co-exposures to particulates and ozone. The agency should explore ways to
include this in their models of exposure and risk assessment.
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Comments from Dr. Douglas Crawford Brown
Review of the Draft Nitrogen Dioxide Health Assessment Plan: Scope and Methods
for Exposure and Risk Assessment
Doug Crawford-Brown
This review follows the Charge Questions for the chapter on Exposure. A general
comment is that I approve of the overall methodology to the extent it is specified in the
document. The outline of the methodology comports with past Agency practice and has
the potential to generate the kinds of variability and uncertainty characterizations of risk
needed for a rigorous setting of a NAAQS for NO2. However, the devil is in the details,
and this document does not lay out very clearly how the detailed computational steps will
be performed. It mentions the kinds of models and databases that will be considered, and
I generally agree with these, but the real question is how they will be employed. This is
especially true for the uncertainty analysis, where I think there is a lot of work still
needed (not necessarily in this plan) to determine how the more qualitative and
quantitative uncertainty results will be combined into an overall measure of uncertainty
that can also serve to guide future research. Still, as a plan, this one is reasonable so long
as the Agency can decide how to treat the on-going evolution of sources when depicting
future exposures and risks..
One other general comment is that the Agency should consider how to balance an
assessment based on individual rights, which would focus on setting a NAAQS that
protects some upper percentile of the distribution of risk, with one based on cost-benefit
analysis, which would focus on the entire variability distribution. The former might be
easier to do, and could be a back-stop approach should the complete variability
distribution (Tier III) prove infeasible.
la. Is the three-tier approach appropriate, and are the criteria for deciding whether a given
tier is needed clear and appropriate? Yes, I like the three tiered approach. I would just
caution that Tier I, while providing some useful insights, is unlikely to yield a
scientifically rigorous basis for setting a NAAQS. I would instead view Tier I as
producing only a decision as to whether a new NAAQS is needed at all. If the answer is
yes, then Tiers II or III would be required to actually generate that NAAQS. And I am
confident that the methodologies and databases exist to allow at least Tier II. I did not
find the criteria well specified, and kept wondering throughout how a decision would be
made to move to Tier II or III. After several readings, I am not certain what the Agency
would need to see in Tier I to motivate it to move to Tier II, and from II to III. There are
qualitative criteria given, but I don't know how these would relate to any specific
quantitative results.
Ib. Have the most important factors influencing exposure been accounted for? For the
most part, yes. The largest problem remains in determining how the activity patterns, and
mode choice for travel, will be used to relate ambient air levels to personal exposures.
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These methods have been employed for other pollutants, however, and so I am confident
the Agency staff can obtain at least a first approximation to these issues. On this one
point, it will be important not to get too caught up in trying to characterize intersubject
variability of risk too exactly, because human movement in an exposure field is an
inexact modeling effort at best.
Ic. Is the selection of population groups of interest correct? Yes, with the caveat that
there should be special focus on groups that intersect these criteria.
2a. Is the exponential model in Tier I justified? I think any model here is only a rough
approximation, and the exponential one is as good as any other. As I mentioned
previously, it is important not to get caught up in too much detail here, since individuals
will tend to average out this spatial curve as they move about.
2b. Is the approach to enhance roadside NO2 concentrations appropriate? I don't know
much about this topic, and so cannot comment on it. But it is clear to me that something
does need to be done to produce this enhancement, and also to consider in-vehicle
exposures.
3a. Is the combined emissions/dispersion modeling approach in Tier II justified? As a
general approach, the answer is yes. I am, however, skeptical of the ability to perform
such calculations at a refined spatial scale. This will be especially true in road canyons. It
will be necessary, therefore, to use the modeling results only as averages over significant
geographic areas (not below a census track or block group).
3b. Is the proposed time-location-activity dairy approach correct? This will be a state of
the art approach, although it will be difficult to get the kind of spatially accurate estimates
of ambient air concentration needed to make a refined diary approach really worth the
effort. There will, however, need to be some thought given as to the level of effort put
into the diary approach, and not put in more effort than is justified by the spatial
resolution of the ambient air field.
3c. Is HAPEM6 the correct approach? Yes, this is the model I would have selected. It has
been employed successfully by Agency staff in the past, although the weaknesses noted
during the NATA process should be reviewed.
4. In Tier III, is APEX reasonable? My answer here is the same as in 3c. APEX is a good
approach, and one with which Agency staff have some experience, but just be sure to
match the effort to the level of spatial resolution of the ambient air field.
5. What is our advice on uncertainty and variability in each Tier? Here there is a lot of
work still to be done. I agree with the approach of having both qualitative and
quantitative aspects. I would not try to force everything into a quantitative framework.
The best one can do is a series of conditional uncertainty and variability statements: that
conditional upon a certain set of scenarios, or modeling approaches, or databases, or
corrections to the data, the following quantitative uncertainty and variability distributions
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are obtained. These U and V distributions can be generated for each combination of
scenario, modeling approach, etc, and then an overall judgment of uncertainty and
variability developed from expert judgment based on these quantitative distributions. But
I recommend this for Tiers II and III, not Tier I (where the uncertainty should be more
qualitative and where variability should be treated by examining reasonably maximally
exposed individuals rather than producing an actual variability distribution.
On a related note, the plan does not yet specify very well how model validation will be
preformed. This is an important step required by the uncertainty analysis, and so needs to
be rounded out a bit.
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Comments from Dr. Terry Gordon
The plan is well written and the tiered approach is appropriate for the task. I will
comment only on the health portion of the risk assessment. The conclusion that the
adverse respiratory effects are the strongest health findings appears to be valid and
substantiated by the ISA. The exposure indices for the majority of the adverse functional
and symptomatic effects are, as documented in the ISA, associated with the short term
averaging times. The adverse children's lung growth findings, however, although more
recent, should also be included in the risk assessment and would be associated with
longer term exposure indices.
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Comments from Dr. Dale Hattis
Comments on the Risk Assessment Plan
The overall approach for the risk assessment is described as follows:
"health risk will initially be assessed through the identification of concentration levels
associated with adverse health effects, termed potential health effect benchmarks.
These., will then be used to determine how often air quality concentrations or estimated
exposures exceed concentrations associated with adverse health effects...."
This seems a rather indirect approach that needlessly economizes on helpful theoretical
model-building. I think EPA should essentially discard the evident hope that only a "Tier
1" analysis will be sufficient. What is needed are a set of estimates of the entire
population distribution of likely exposures1 and corresponding distributions of population
sensitivity to various health effects. These two distributional inputs could then be used
to develop estimates of the current burden of adverse health associated with the current
exposure distribution, and the capability to estimate how the burden would change with
hypothetical changes in the exposure distribution or with possible changes in the NAAQS
or other regulatory standards or feasible non-NAAQS technical measures (e.g. standards
for auto emissions). The paragraph goes on to say that "an additional characterization of
risk may involve use of concentration-response functions..." In my view it is not a
question of whether this level of analysis will be needed. It is certainly needed to support
the technical and policy choices that EPA needs to make in seriously considering the
effects of various options to revise and restructure the NOx NAAQs. The EPA authors
need to immediately start their analysis by going about the business of constructing these
exposure/response functions, with due cognizance of the need to quantitatively represent
uncertainties in the functions used to estimate health endpoints of various types from the
various sources of available scientific information.
p. 9, equation 1.
This exponential equation is not discussed in terms of theoretical mechanisms. I am
prepared to believe that distributions of concentrations by exposure time are likely
lognormal, but it is not clear that this is the basis of equation 1 or how equation 1 is in
fact derived from this basis. Equation 1 is simple enough to use, but there should be
some comparative testing with data to show it really works for existing NO2 data in the
sense of being free of systematic distortions in the incidence of exceedances out to levels
that are very far from the mean.
1 This does not necessarily correspond to the distribution of concentrations/"exposures"
at regulatory monitoring sites, as people may live in locations that are differentially
represented by the monitoring sites, in addition to the distortion discussed in the
document between ground level locations of people and the elevated locations of the air
monitors.
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p. 10, Table 2. The occurrence of zero's in this table, rather than fractional values below
1, seems unwise and potentially misleading. (As an asidethe assertion that there are
absolutely zero places in the U.S. that exceed the current standard of 0.53 ppm annual
average also seems dubious.) The equation provided cannot yield true zero incidences.
In general I question the whole "exceedance" basis of the key calculations that seem to be
aimed at. This framework is probably derived from an implicit threshold theory of the
incidence of effects as a function of concentration, and threshold theories seem to have
little support in the existing epidemiological data. Another presumption seem to be that
long term effects, if any, depend on short term episodes of relatively high concentration.
This assumption does not appear to be supported by either empirical observations or
theoretical analysis. Rather, I thank what would be more useful is a distributional
expression of the total fraction of time spent at various levels of exposure for the
population as a whole and for various at groups that are at risk because of either unusual
susceptibility or residence in locations with various levels of annual average
concentrations. Many of the exposure-response observations seem equally well analyzed
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Comments from Dr. Donna Kenski
Comments on Nitrogen Dioxide Health Assessment Plan: Scope and Methods for
Exposure and Risk Assessment
Donna Kenski
October 22, 2007
Air Quality Considerations: Using historic data to simulate scenarios with higher
concentrations seems reasonable, as does the proposed choice of a linear approach to
adjusting data to lower concentrations. The proposed list of CMSAs did not include New
York, which the ISA indicated had the highest mean NO2 concentrations of selected
urban areas with multiple monitors (Table 2.5-1). Presumably it will show up in the
identification of additional locations of interest?
Exposure Analysis: The 3-tier approach is satisfactory. The important factors
influencing exposure have been accounted for. This plan emphasized traffic exposures
far more than they were discussed in the ISA, which I thought somewhat neglected this
source, so that's a definite improvement. The groups of interest are appropriate.
The choice of exponential model is probably okay, although it would be helpful to see
what other approaches were considered and to have some comparative assessmentthe
McCurdy report is not readily available. Was survival regression considered? How does
the change in variance over time (apparent from Fig. 1) affect this model? It is not clear
from the text why the predictive equation for each location is lumping all monitors
together when, in some locations, significant siting differences exist that will impact the
number of exceedances. Why not include a site variable in the model? As above, a
comparison of various models or additional rationale for this particular one would be
helpful.
Health Risk Assessment: The approach outlined here seems fine. In particular the
proposed method of characterizing uncertainty and variability is conceptually appealing.
The actual implementation of the Tier I/Tier II risk assessment may uncover issues not
dealt with in this document, but it seems like a reasonable approach that can be modified
as needed and especially as the data require.
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Comments from Dr. Timothy Larson
Comments on NO2 Health Assessment Plan
I have several general comments on the exposure assessment portion of this plan. The
multi-tiered approach is a reasonable one, moving from more general to more specific in
the exposure assessment. The Tier I approach will provide a reasonable ranking of urban
areas for further consideration. However, I have concerns about the Tier II approach. In
particular, the use of near road gradient algorithms and Gaussian plume models from line
sources will not capture the actual traffic related gradients in many urban areas. The
reason for this is the presence of buildings and associated street canyons. There are many
urban areas where this is an important factor. It would be useful to identify the presence
of canyons as part of this screening procedure prior to using 'flat world' gradients and
models. The Danish AirGIS system has this capability if information is available on
building footprints and approximate building heights. It would also be useful to develop
information on the vertical distribution of personal residences in these same urban areas,
given the importance of this parameter. Inclusion of the above factors in a Tier III
SHEDS type model seems promising, but only if the Tier II screening is done properly.
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Comments from Dr. Kent Pinkerton
Review comments for the Nitrogen Dioxide Health Assessment Plan: Scope and
Methods for Exposure and Risk Assessment
Kent E. Pinkerton, Ph.D.
University of California, Davis
Center for Health and the Environment
To assess risks and exposures using a tiered assessment approach for the level of analysis
required and the anticipated utility of the results is a highly logical process, especially in
the face of possible future limited resources and budget constraints.
Exposure estimates to compare to potential health effect benchmarks to 1) estimate the
number of individuals experiencing exposures of concern and to 2) estimate the range of
exposures above levels of concern are appropriate and laudable. Since epidemiologic
data appears to be the major driver to establish health effects, it is also important to better
define whether uncertainties in the degree of health effects observed are due to NO2 or an
associated co-pollutant.
Since at the present time rare excursions of NO2 above the current NAAQS occur in the
nation, yet numerous health effects due to NO2 exposure have been reported in the
literature, it is highly likely this tiered assessment approach will need to be applied well
beyond Tier I assessment. Tier II is a critical and needed parameter, especially for NO2
exposures to allow for screening-level exposure assessments to establish the relationship
between ambient concentrations, local sources and human exposure.
It is my opinion and recommendation that exposure assessment for NO2 include both
short and long-term measurements of ambient concentrations through routine air quality
monitoring and modeling analysis. The identification of uncertainties in exposure
estimates is also essential to determine.
The populations to be modeled which include children (normal and asthmatic), asthmatic
adults and the elderly are the proper groups. It may become essential in the future to
further determine the influence of gender and genetic predisposition to respiratory disease
as well.
In the Tier I air quality characterization, how were the 5 cities of Los Angeles, Houston,
Atlanta, Philadelphia and Chicago chosen? Some justification for city selection would be
good. Although it is understood motor vehicles, electric utilities and industrial
combustion processes represent the major sources of total NO2 emissions, why totally
exclude rural and areas of high agricultural activity? For example, in figure 2 of the
document what is the contribution of agriculture to off-highway emissions of NO2?
A nice example is provided for Tier I air quality characterization in Table 2. However, it
appears Los Angeles would be the only city to experience exceedances in NO2 levels,
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based on the current standard. Therefore, how useful would this model be for other
portions of the country to explain potential health effects associated with NC>2 exposure?
Perhaps it is important to clarify this model can be adjusted to deal with lower NC>2 levels
should the air quality standard be changed to provide greater health protection.
A clear explanation of both short-term and long-term exposure approaches to be
implemented in Tier I and II exposure assessment is provided in the document. The
Decision Flow diagram for Tier II screening, as well as the basic data required to estimate
the numbers of person occurrences of short-term exposures in Tier II exposure
assessments are provided and extremely helpful.
Again, the explanation provided for Tier III refined exposure assessments is very helpful
to better understand the approach to be used, generated outcomes, as well as variability
and uncertainty factors that may be encountered and handled.
Figure 5 is excellent in providing an overview of the entire tiered assessment process.
Using a tiered approach as outlined seems very reasonable and highly appropriate to
insure the proper assessment of exposure levels to NOx.
Under the overview (4.1) for risk assessment scope and methods, one of the goals of the
NC>2 risk assessment is to estimate the number of people exposed at or above potential
health effect benchmarks associated with NC>2 exposures at levels just meeting the current
standard. This goal could be more specific by estimating subgroups such as children,
those with asthma, the elderly and socioeconomic classes.
It is important to clearly indicate what constitutes sufficient scientific data to develop
population-based health risks for health effect endpoints in at-risk population groups.
Under the overview (4.1) it is not clear why the EPA would not develop risk estimates for
NO2-related effects associated with long-term NC>2 exposures. Although the evidence is
not strong, it has been described as "suggestive" for long-term health effects associated
with NC>2 exposure. Mobile, stationary and indoor sources of exposure can clearly be
long-term.
Under Tier I health effect benchmarks, susceptible populations composed of asthmatics
and allergen-sensitive individuals also factor in children and gender-based differences.
The inclusion of baseline data for emergency department visits and respiratory-related
hospital admissions for candidate US locations in Tier II risk assessment to enhance risk
assessment seems logical and desirable.
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Comments from Dr. Edward Postlethwait
Comments on: Scope and Methods for Exposure and Risk Assessment
1. The draft appears to provide a solid foundation for conducting the planned exposure
and risk assessments. It is clear that thorough and in depth considerations were
incorporated.
2. Although it might have been dealt with elsewhere, it would seem appropriate to have
addressed the issue of the potential for confounding in determining exposure/response
relationships based on the current NOx measurement approaches. The issue of PRB and
long range transport was addressed on page 4, with the available information suggesting
that contributions were negligible. Because NO2 values represent {NOx - NO}, some
effort to speciate the various NOx and how much non-NO2 NOx (e.g. N2Os, ^Os, etc)
might contribute to the overall NO2 values would be beneficial in terms of characterizing
uncertainties. This may be critical when/if clinical and/or indoor studies are compared to
environmental exposures if atmospheric NOx contains appreciable amounts of species
other than NO2.
3. On page 13, indoor source influences suggest that gas cooking etc may contribute to
NO2 exposures but biomass combustion (word stoves, fireplaces) appeared to be
discounted under proper ventilation conditions. Would not ventilation conditions also
affect the other indoor NO2 sources?
4. An uncertainty apparently not addressed was measurement accuracy across
monitoring stations. This becomes critical when attempting to utilize disparate
population-based studies to predict health outcomes based on predicted exposure
concentrations. The current chemiluminescent approach for measuring NO2 can be
affected by numerous factors and thus it would seem important to be able to estimate
measurement error.
5. On page 22 it is stated that "The ME describes the physical location of an individual,
allowing for direct contact with the immediate surrounding air that contains a
homogenous pollutant concentration." It is assumed this statement refers to NO2 per se
rather than the admixture of co-occurring pollutants wherein all pollutants would be
assumed to be present in equivalent concentrations.
6. On page 25, the document refers to ME being calculated using "a mass-balance."
This should be clarified since on a chemical reaction and/or diffusion basis it is unclear
how the use of mass balance is intended.
7. Only very limited attention was paid to issues regarding biological plausibility and
NO2 acting as a surrogate (ie., pg 34). If health predictions are to be constructed, then it
would seem critical that they be placed into an appropriate biological context, especially
since NO2 is generated endogenously via peroxidase activities. Furthermore, it was not
clearly evident how co-pollutants would be dealt with in interpreting especially
epidemiologic studies wherein frequently there is limited consideration of the dose/effect
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relationships unique to individual pollutants. In some studies relative toxicities are
poorly considered. Because ozone, for example, is significantly more toxic than NC>2,
one would anticipate a need to go beyond simple considerations wherein all pollutants are
treated equally relative to exposure concentrations.
8. It is assumed that the impact of uncertainties will be quantified via model output
confidence intervals although it was not made specifically clear. Clarifying this issue and
discussing the potential magnitude of uncertainty impacts would strengthen the
document.
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Comments from Dr. Armi stead Russell
Review of EPA NO2 Scope and Methods
I am generally pleased with the scope and methods as laid out. It appears, and I hope this
to be the case, that it is building upon and building further, EPA's other exposure and risk
assessments for reviewing the NAAQS. At the end of one or two more pollutant reviews,
it should be almost a well oiled machine (though one that continually improves and
considers the unique aspects of the pollutant under consideration).
In regards to its application to nitrogen dioxide, one of the first question that arises is that
the ISA considers more than just NO2, but nitrogen oxides in the broad sense (not just
NO and NO2). Does the Scope and Methods also have to consider such (e.g., at least
consider what the response might be if the determination is that one should look at other
components or a sum of components)?
While I generally find that their approaches for assessing the distributions of NO2
exposures are viable and at the level that is appropriate. One could always do a better
job, but it is not apparent that for the task at hand it is necessary, with one exception at
present. They use an exponential decrease in NO2 going away from a road. They should
use the exponential decrease in NOx going away from the road, and then use an
appropriate method to split NOx between NO and NO2. In an oxidant limited situation,
this could be significant. Also, this will allow them to more explicitly account for
changing NO2:NO ratios in the emissions, and assess the overall sensitivity to that split.
Another comment is to try to identify up front the broad levels at which the standard
might be set and do some exploratory analyses to show how EOC will very, and the
primary sensitivities. While, in the end, the panel will be interested in uncertainties and
variabilities, some assessment early on about the sensitivities will be quite useful.
Some other specifics:
In eq (3), the m should be found using linear regression, not as a ratio.
k in eq (2) is not a rate constant. One could call it a dispersion constant, or the like.
Carrying on my comments from the ISA: The monitor uncertainty is overemphasized,
and I do believe, mischaracterized. Further, if one is using epidemiologic study results,
that bias is built in.
Fairly early on in the process, the results from the exposures and risks in the five cities
should be put in perspective of the broader population.
In replying to the given questions:
1. Do the Panel members generally agree with using historic air quality data (e.g.,
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pre2000) in certain analyses as a reasonable approach to simulating air quality
scenarios with higher NCh concentrations, given that current ambient air quality
concentrations are lower than the current standard?
a. Answer: It is necessary to know exactly when and how this would be
used, but is probably fine. A specific concern is that the older data may
have a different NO:NO2 split due to different ozone levels and a different
NO:NO2 split in the emissions. The data should be corrected for this if
older data is used, and should also be corrected for this when considering
future scenarios (this may be a small difference, and if they can show this,
great, and then move on).
2. Based on the low estimated contribution of policy-relevant background NCh to
overall ambient NCh levels, staff is considering a proportional (i.e., linear)
approach to adjusting air quality to simulate just meeting potential alternative
NCh standards that are lower than current air quality concentrations. Do the Panel
members have comments on adopting a proportional approach to simulate just
meeting more stringent alternative air quality standards?
a. Answer: Do you mean proportional or linear? I would prefer linear,
though it is recognized there is little difference in this case.
Exposure Analysis:
1. In considering the exposure analysis broadly:
a. Do Panel members have any comments on the general structure and
overall three-tier approach that staff plans to use for the exposure analysis? Are the
criteria that staff plans to use for deciding whether to conduct a Tier II or Tier III analysis
clear and appropriate?
Answer: Yes. (The approach is fine.) EPA should compare and contrast their
approach to that used for other pollutants, and document why different methods are used.
Again, use each review to make the exposure and risk assessment a more systematic,
documented and turn-key. One could see that in about three years (a couple more
pollutants) that a system much like that used for air quality modeling is used such that
with relatively little effort exposures, risks, variabilities, sensitivities and uncertainties
can be calculated, and the system as a whole has been intensely reviewed such that staff
need not spend such effort, and the community is more comfortable with the results.
b. Have the most important factors influencing exposure to NCh been clearly
accounted for and described?
Answer: Not totally... The large role of indoor sources on NOx, and how that gets
converted to NO2, needs a bit more work. This issue probably should be picked up more
in the ISA as well. Also, the role of NOx in forming and destroying ozone feeds back in
to converting NOx to NO2. Further, the discussion here should also deal with the co-
occurrence of other pollutants of concern.
c. The draft plan describes the basis for and selection of population groups of
interest (i.e., children, asthmatics (children and adults), and the elderly) for which NO2
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exposure estimates are to be developed. Do Panel members generally agree with the
groups of interest identified in the draft plan?
Answer: Yes.
2. In considering the Tier I exposure assessment:
a. Do Panel members agree that an exponential model is appropriate for
estimating expected exceedances of short-term health effect benchmarks based on long-
term annual average air quality?
Answer: This is fine as long as the model is tested and the appropriate measures of
performance are given.
b. Do Panel members agree with the approach to enhance NCh air quality
data by accounting for the influence of roadway emissions?
Answer: See discussion above.
3. In considering a potential Tier II exposure assessment:
a. Do Panel members agree with the combined emissions/dispersion
modeling approach to estimate short-term (hourly) on- and near-roadway NCh
concentrations?
Answer: Yes, as long as the model is evaluated and performance documented.
b. Is the proposed use of time-location-activity diary data reasonable for
estimating short-term exposures for population cohorts?
Answer: Yes, as long as the model is evaluated and performance documented.
c. Do Panel members agree with the use of HAPEM6 to estimate long-term
exposures (annual average) and the approach to account for on- and near-roadway NCh
concentrations?
Answer: See discussion above (in regards to NO:NO2 splits).
4. In considering a potential Tier III exposure assessment:
a. Do Panel members generally agree that developing individual exposure
profiles through the use of APEX is reasonable and appropriate to estimate
both short- and long-term NCh exposures?
Answer: Yes, as long as the model is evaluated and performance documented.
5. Do Panel members have any comments or advice regarding the general approach
to addressing uncertainty and variability in each Tier of the exposure assessment
as described in the draft plan?
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Answer: Provide, early on, results of some sensitivity analyses. Do not overestimate
uncertainties going in.
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Comments from Dr. Jonathan Satnet
I write to provide brief comments on the draft version of this document dated September
2007. As indicated in my verbal comments during the October 24-25 CASAC meeting, I
found the plan to generally be acceptable in its present form, given the status of the ISA.
The document covers the approach that will be used in the three tiers for exposure
assessment and for health effects estimation. I have two comments:
With regard to exposure to NC>2, indoor sources remain substantial contributors.
The document is rather general in its approach to describing how
microenvironmental concentrations will be estimated. There is a substantial
literature on indoor NC>2 concentrations in the presence of various sources that
needs to be covered.
The plan lists the health outcomes that may be considered in the risk assessment,
based on the first draft ISA. As indicated in my comments with regard to the ISA,
the criteria for finding associations to be causal are not yet sufficiently developed.
In general, the health outcomes considered in the risk assessment should be those
considered as causal in the ISA. A specific statement to that effect is needed, on
the assumption that the plan's authors are in agreement. The current draft plan
does not specifically reflect this criterion.
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Comments from Dr. Christian Seigneur
Comments on the Nitrogen Dioxide Health Assessment Plan: Scope and Methods for
Exposure and Risk Assessment- Draft - September 2007.
Christian Seigneur
Atmospheric & Environmental Research, Inc.
San Ramon, CA
The three-tier approach for exposure assessment and the two-tier approach for risk
assessment appear to be logical ways to proceed. The various steps of each approach are
described with sufficient detail for the reader to understand the technical approach and
the sources of the data to be used.
QA/QC: One aspect which is not articulated in the document is the Quality Assurance/
Quality Control (QA/QC) procedures that will be followed by EPA. As the assessments
proceed to the higher tiers, there will be some very large amounts of data being treated
and one must ensure that the proper QA/QC procedures are in place to avoid input or
calculation errors.
NOi/NO speciation - Equations 2 and 3 on pp. 11 and 12: The use of particulate
emission control devices on diesel vehicles typically leads to a greater fraction of NO2 in
the NOX emissions. Such a change in the NOX speciation for mobile sources could lead to
stronger NC>2 spatial gradients near roadways as the NO2/NOX ratio will increase at the
roadway but the NO2/NOX ratio at background sites, which is driven mostly by
atmospheric chemistry, may not change. The implication is that the spatial gradient
obtained from historical data may not apply (see Equation 2 on p. 11 and associated text).
How will EPA address this possible change in the relationship as the vehicle fleet evolves
over time?
Estimates of NOi concentrations, p. 18: EPA proposes to use the steady-state Gaussian
dispersion model AERMOD to calculate the NC>2 concentrations near roadways.
AERMOD is a dispersion model that was designed for point sources (Cimorelli et al.,
"AERMOD: An dispersion model for industrial source applications - Part 1", J. Appl.
MeteoroL, 44, 682-693, 2005) and which has been evaluated with data from point sources
(Perry et al., "AERMOD: An dispersion model for industrial source applications - Part
2", J. Appl. Meteorol., 44, 694-708, 2005). Emissions from roadways differ from those
from point sources as vehicle traffic induces some additional turbulence. The use of a
simple chemical scheme to account for the rapid titration of NO by ozone to form NO2
appears appropriate here (although it is not clear what is meant in footnote 8 on p. 18 by
"simple reaction rate constant"). However, it is unclear why EPA would want to use a
point source dispersion model that is not designed for roadway emissions when roadway
dispersion models (such as CALINE4) are available. CALINE4 has been subjected to
performance evaluation with measurements made near roadways (Benson, "A review of
the development and application of the CALINE3 and CALINE4 models", Atmos.
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Environ., 26B, 379-390, 1992) and would seem more appropriate for use here,
particularly if AERMOD has not been evaluated for near-roadway estimates.
Example calculation of Table 4: It is not clear how the in-vehicle concentrations are
calculated. One person appears to be in a vehicle at more than 75 m from the road but the
concentration within the vehicle does not appear to be a function of the distance from the
road. Is the NC>2 concentration within the vehicle assumed to be constant regardless of
the location of the vehicle?
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Comments from Dr. 'Lianne' Elizabeth Sheppard
Comments on the Scope and Methods Plan for the Exposure and Risk Assessment
Summary comments:
Overall this is a very thoughtful and structured approach that should help inform
policy. The tiered approach to exposure and risk assessment seems to be
generally reasonable. However, modifications to the risk assessment tier structure
and additional process and detail are necessary.
To the extent feasible, all criteria should be specifically stated in advance. This
should reduce the workload by defining a clear path. It will also make the
decisions in the process more transparent.
Clarify whether the tiers of each assessment are purely conditional on the results
of the previous tier or whether they use different information to address details
that overlap. If tiers are modified to be a pure progression (i.e. conditional on the
results of the previous tier), this may reduce effort.
Throughout the document the word "would" is used when "will" is more correct.
This is after all a plan, not a hypothetical plan.
In order to help assure the process is open and transparent, all tiers of the
exposure and risk assessment need to be covered in the risk and exposure
assessment document. In order to make the document as transparent as possible,
this policy should be followed even if the final judgment is that the data are
insufficient to conduct a specific tier of the assessment. This policy should be
stated in the introduction.
Section 2: Shouldn't this section be folded into Section 3? It seems premature to be
discussing simulated air quality data when the purpose of the simulation hasn't been
stated.
Section 3: My suggested general improvements for this section are to clearly state
criteria and to make equations more explicit by adding indices.
Section 3.1: Clearly define each tier in the overview section. Add the tier numbers to
Table 1. Clarify whether the information used in each tier is conditional on the data,
information, or choices made in the previous tier.
Section 3.2: Why are no population groups defined based on exposure? I suggest adding
people living or working near roads.
Section 3.3:
Clearly state the intended use of the air quality characterization. Different
simplifying assumptions will be realistic for different purposes (e.g. prediction of
long-term averages vs. traffic-dependent hourly-resolved exposure). Without the
intended use stated, it is difficult to evaluate the objectives of the analysis
(paragraph 2). For instance, why would the analysis be limited to areas of
potential concern, and what are the criteria for "potential concern". As another
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example, with regard to a statistical model (objective 3), clarifying all purposes of
the analysis can be followed by identification of reasonable simplifying
assumptions, thus reducing the modeling effort.
It is also necessary to distinguish long-term from short-term metric objectives.
This distinction needs to be revisited throughout the section.
Section 3.3.1:
The first sentence is good, but now this summary statement needs to be made
clear.
The second sentence appears to be missing a word at the end.
As an example of clarifying "aggregating data", it should be stated that the
objective is to create a single daily (hourly?) time series over space of monitors
that are similar. Note that criteria are needed for "similar".
The criteria for the selected cities are generally listed, but the reader is not
informed why those cities were selected.
Shouldn't site characteristics be included in the list of criteria used to identify
additional locations? This is alluded to with the motor vehicle traffic density
criterion, although the reference to "by location, not monitor" is cryptic.
State how the aggregation will be done and what are the criteria for including
monitors in the aggregation. Make it clear whether this is temporal or spatial
aggregation, or both. I don't understand the purpose of all the statistical tests that
are planned and what criteria will be used to determine if additional aggregation is
appropriate, (p 8-9).
p 9: The first full paragraph confuses me. What are the purpose and the outcome
of the comparisons within and between locations? What data are to be used?
p 9: Please add indices to all variables in all equations and define these indices!!
Are these data indexed in time by year, day, or hour? What are the spatial indices
- site within location?
p 10: This document is very short on specifics. For instance, how will
"regression models, parameters, and respective concentration exceedance
estimates" be compared?
p 10: I don't understand how the two parts of the sentence fit together: "The
regression model is highly dependent on the prevalence of concentration
exceedances, justifying the aggregation of particular (and similar) locations."
Footnote 4 suggests a valid year could have an entire season missing.
Section 3.3.1.1:
Equation (2) is a general equation. None of the parameters have values. Will
they be estimated from data? What time scale is being considered? Add indices.
Are Cv and Cb data or predictions? How are they obtained?
How will the equation (2) result be used to derive (3)? Add indices.
The entire plan for this section is wide open and subject to many interpretations.
Why is the goal to obtain on-road estimates of NC>2 instead of characterizing NC>2
as a function of distance from road?
Note that "on-road NO2 concentrations" are predictions., not data.
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Section 3.2: Descriptive statistics should include measures of spread as well as central
tendency.
Section 3.3:
Paragraph 2: Restate sentence to say the tiered approach uncertainty assessment
is done with the goal of identifying the best supported quantitative analysis.
Paragraph 2: Presumably the "identified components are, in a broad sense, also
relevant to subsequent exposure analyses" because this tier I analysis is the input
to the tier II analysis. Correct? Please state clearly.
Add "Choice of NC>2 as the index compound" as one of the components of
uncertainty.
Temporal representativeness: State what the "temporal profiles" are. Are these
estimated hourly average air quality over a multi-year period for a given spatially
aggregated location with specific spatial features?
Spatial representativeness: The purpose of the predictions really matters when
deciding how to proceed with limited spatial data. State the purpose. What
prediction equations are being referred to? What kind of correlations will be
evaluated?
Monitor to exposure representativeness: Why is personal exposure even being
mentioned in the Tier I estimates? Isn't it more important that the AQ
characterization is done in locations that are representative of population exposure
to ambient concentration?
Section 3.4:
p 17 line 2 - add "ambient-source" to describe the possible lower bound estimate.
Gas stoves are an important factor in greater personal exposure and should be
listed in the example to indicate home characteristics will also be considered.
In doing spatial interpolation of exposure, it will be important to only include
monitors that are representative of usual population ambient source exposure (as
opposed to those highly influenced by local sources that won't apply to the entire
census tract or adjacent tracts). I am concerned that some factors could be
counted twice if the local source monitors aren't removed first, since local sources
will be added in with the planned adjustment.
Following the previous comment, I suggest discussing locations represented by
ambient monitors as a function of monitor siting criteria and/or GIS covariates.
Insert the word "predicted" to clarify the complete set of concentrations won't
necessarily be data.
Section 3.4.1:
Organizationally, why not define the on-road concentrations as the 0 m road
proximity class?
Why do indoor sources need to be identified as important contributors to ambient
air concentrations to be considered?
Figure 4: Why can there be significant on-road concentration but little elevated
concentration at <75m? (see the first site)
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Table 4: While it is clear that the total column is a weighted average, it is completely
unclear what the average concentration total row means (particularly given the numbers
provided).
Section 3.4.1.2:
There is an assumption that the spatial and temporal contributions to NC>2 are
relatively simply related, i.e. temporal estimates from one location can be linearly
transformed to get estimates at a new spatial location. Ideally this assumption
should be checked. At least it should be discussed.
I think uncertainty in model structure can be evaluated with sensitivity analyses.
Section 3.4.2:
Does the term "long-term exposure" mean "annual average exposure"?
Add an introductory paragraph and start a new section subheading for the material
already at the beginning of this section.
Equation (4) needs indices for time, space, and microenvironment type. Clarify
the range and units of the indices.
Note a different approach to roadway contribution is being used here.
Section 3.4.2.1:
Give an equation to show the relationship described in the first sentence.
On what time scale will the additional exposure metric be calculated? (p 24 top)
Section 3.5.1:
p 26 first sentence first full paragraph: The approach to predicting hourly NC>2
from monitoring data and dispersion models is a major research topic in itself.
The approach taken here is relatively simple, and thus it should be mentioned as a
limitation and source of uncertainty.
Should in-vehicle estimates be separated by road type?
Section 3.5.3: Instead of relying solely on informed judgment, why not compare
estimates from plausible models formulated differently?
Section 3:6: Define number of peak concentrations. Discuss Figure 5 in more detail, and
possibly move it to the beginning of Section 3.
Section 4:
I think the risk assessment needs to be reorganized to have 3 tiers. The first tier
should be a qualitative assessment of the health evidence. This will list and
consider all important health effects based on human and animal studies. Not all
of these can be used for benchmark calculations or quantitative risk assessment,
but it will be important to review them all first and get a sense of the scope of the
risk qualitatively. Then a narrower list will be used for the second and third tier
assessments. Not only does this proposed new tier structure allow for better
progression in the treatment of the health results, but it also elevates the
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importance of the qualitative risk assessment in the document and protects against
it being treated as an afterthought.
Criteria for acceptable outcomes to use in the risk assessment (as well as other
aspects of the RA such as choice of city for the analysis) needs to be specified in
advance for each tier.
Criteria for even conducting a quantitative risk assessment (the proposed second
tier) need to be specified in this document in advance of the risk assessment.
The quantitative risk assessment should move towards incorporating an integrated
uncertainty assessment as an integral part of the process. This would extend
uncertainties in underlying assumptions into the estimated risks by incorporating a
probabilistically weighted range of assumptions into the risk estimates and
uncertainties estimated. This will be most appropriate for the highest tier of
quantitative assessment.
Section 4.2: State the criteria for selecting health effects to be used for the benchmark
analysis.
Section 4.2.1: State the planned health effect benchmark levels or criteria for selecting
these levels.
Section 4.2.3: Third paragraph: In addition, a distribution of benchmarks could be
applied rather than sensitivity analyses of a set of single values. I'm confused by the end
of this paragraph (starting "From a directional perspective..."). My understanding
suggests either the wording is backwards or I am confused. Perhaps an example will help
the reader's comprehension.
Section 4.3: The criteria for what is sufficient information to develop credible exposure-
response relationships must be stated. I note there is information about such criteria in
later subsections. Restating the criteria in another form, such as a list, may be helpful.
Section 4.3.1.1 (and 4.4): I believe that the last two additional factors (2: availability if
sufficient C-R data in locations relevant to the US and 3: availability of baseline
incidence data) should be given less weight in the decision to proceed. Both can be
evaluated with sensitivity analyses.
Section 4.3.3. The analysis should move towards an integrated representation of all the
most important uncertainties. Sensitivity analyses are typically done by altering one
assumption at a time. This approach can be useful for identifying the most influential of
the uncertainties. It is possible statistical uncertainty (e.g. estimated variance of a
parameter) will be the least influential; rather the more influential uncertainties may be
due to the form and structure of the risk assessment such as the choice of model, rollback
assumptions, etc. The integrated analysis would extend the Monte Carlo analysis to
jointly assess a range of model assumptions by putting probabilities on different
assumptions, such as several choices of the concentration-response model coefficient
and/or its functional form. The difficulty with the integrated approach is there is another
layer of assumptions and reasonable ranges that need to be elicited and incorporated into
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the analysis. The advantage is the quantitative risk estimates will have additional sources
of uncertainty incorporated directly into the result. Moving towards an integrated
analysis of these uncertainties will give a fresh perspective of the range of possible
effects and the probability of effects at different levels.
Section 4.5: Restating an earlier comment: Summary of the health effect data should
precede the quantitative risk assessment as the first tier risk assessment. The qualitative
risk assessment should do more than just provide the "broad context for the quantitative
risk estimates". It should be the foundation.
Response to charge questions: Exposure assessment
1. Broad exposure analysis evaluation: a. The 3-tier structure is fine. In the final
document all tiers should be covered, even if the only text is justification for why
the tier was not conducted, b. See comments regarding Charge questions 1-3 of
the ISA. c. Add populations at higher risk due to high exposure.
2. Tier I assessment: a. Without seeing an analysis of the data, I can't comment. I
suspect sites that differ by important NOx sources (e.g. distance to road) may fit
this model more or less well. b. The roadway emissions approach seems to be
overly simplistic, but may be the most reasonable approach given this is a lower
tier assessment.
3. Tier II assessment: a. Again, I would like to see an analysis of the data before I
can form an opinion. I am concerned that near road monitors should not be used
for the spatial interpolation model. Regardless, there may be too few monitors
over space to do a reasonable spatial interpolation. It is not clear why the
outcome generated should be a measure of exceedance, or how the criteria for
exceedances will be chosen, b. This appears reasonable, although it treats people-
hours as exchangeable. For this purpose that appears to be acceptable, c. No
comment without further data analysis.
4. Tier III assessment: APEX is a reasonable approach. Presumably the ambient
monitoring predictions are conditional on the Tier II exposure assessment. In
fact, coming up with the "modified and interpolated hourly NO2 concentration
measurements" is a major research topic in itself. The approach taken is
relatively simple and thus needs to be recognized as a source of uncertainty.
5. Advice on general approach to addressing uncertainty and variability: Our best
collective scientific understanding should help us prioritize sources of uncertainty
and variability and focus on the most important ones. For those, I suggest
comparing estimates for plausible models formulated under different assumptions
(sensitivity analyses) and working towards extending the uncertainty analysis to
jointly assess multiple different sources of uncertainty simultaneously (integrated
uncertainty analysis).
Response to charge questions: Risk assessment
1. Overall structure and two-tier risk assessment approach: I think there should be
3 tiers for the risk assessment with the first tier being a qualitative risk
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assessment. The criteria for selecting the endpoints should flow from the ISA,
particularly the Chapter 5 summary rewritten to use open and transparent criteria.
I think the Pilotto et al (2004) study estimates are based on a strong enough study
design that even though they haven't been directly replicated, they should be
considered for the risk assessment. I don't consider the same location or no
outside US location criteria to have sufficient weight to limit a Tier II risk
assessment.
2. Tier I risk assessment: a. Criteria for identifying benchmarks must be clearly
stated in advance, b. I think the lung growth effects are also important to
evaluate, c. While the Pilotto et al (2004) study is not a controlled study, it is an
intervention study and a much stronger design than a pure observational study.
3. Tier IIassessment: a&b. See section 4.3 comments.
4. Addressing uncertainty and variability: An integrated uncertainty assessment
should be considered. See section 4.3.3. comments.
Reference: Additional thoughts on how to proceed with the integrated uncertainty
analysis may be found in this report:
Committee on Estimating the Health-Risk-Reduction Benefits of Proposed Air Pollution
Regulations, National Research Council. Estimating the Public Health Benefits of
Proposed Air Pollution Regulations. NRC 2002 (see Chapter 5)
id=10511
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Comments from Dr. Frank Speizer
Nitrogen Dioxide Health Assessment Plan: Scope and Methods for Exposure and
Risk Assessment (September 2007 draft)
Answers to Charge Questions (paraphrased)
Submitted by Frank E. Speizer
Date: October 17, 2007
Air Quality Considerations
1. Use of historic air quality data pre 2000.
This is not an unreasonable use of historical data. Figure 1 on page 5 suggest a
marginally significant decline in the annual average NO2, but the variation seems to have
changed substantially with a marked drop in the 90%tile level starting around 1997. In
table 2.5-1 in ISA on page 2-52 spatial variations are wide in some cities. Thus, for the
last 10 years may want to inflate the variance to better take into account the individual
city variation.
2. Use of a proportional approach to modeling alternative air quality standards.
I think the same observation made above applies to the use of proportional
adjustments. Somehow the drop in the 90%tile values along with the variation across
regions (cities) needs to be dealt with. If proportional models works that is fine.
Exposure Analysis
1. Broad considerations.
General Structure. This seems reasonable but I would be disappointed if Staff
concluded that they could not get past Tier I. For factors influencing exposure perhaps
there needs to be some discussion on how the interaction with Ozone will be handled. In
some of the regions there are likely to be competing interaction, with quenching affecting
what is being measured and difficulties attributing risk. (This may all come up later). In
addition, it might be indicated as to how, at least in a general sense indoor exposure, will
be considered. Population groups of interest. If possible I think it would be useful to
consider children broken down somewhat differently. The text in section 3.2, page 7,
suggests birth to age 18.1 think it would be better to consider birth- preschool (near
home); 4 or 5 to 9 (local community); and 10-18 (active outdoor physical activity). I
recognize that the data may not exist but at least the breakdowns for exposure might be
considered. The other grouping seem appropriate, except might want to consider those
adults carrying a cardiovascular disease diagnosis as a separate (potentially more
susceptible) group.
2. Tier I exposure assessment
For exponential model and accounting for emissions this seems to be appropriate,
however, what will need to be discussed later is how this model deals with the time-
varying patterns of exposure that might occur as people "move through" their
approximate exposures. This forms the basis of the discussion of uncertainties in section
3.3.3. Although the potential issues that might vary exposure and uncertainties are well
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described, it is not made clear just how these will be handled. (Perhaps there will not be
a variable added to Equation 3 and residential time within x number of meters of a
roadway value will only be discussed qualitatively at this level of analysis but such
should be stated. Alternatively, if there would be a way to incorporate residential time
(or other modifiers of exposure) in the equations that would be useful.
3. Tier II. This is a exceeding well written description of what needs to be done, and if
accomplished should satisfy the numbers needed for any risk assessment. As I read
through this I am wondering if all the comments above on Tier I are irrelevant as many of
the comments above are answered in this section. Therefore should consideration be
given to combining the two Tiers into a more expanded discussion, since much of the
uncertainty in Tier I and specified again on page 17 are dealt with here . (Leaving it own
uncertainties.) In picking the distance to roadways (<75 m, 75-200 m, >200 m) some
justification needs to be added on page 18. Particularly since on page 11 the spatial drop
off exposure levels gives a range of 200-500m to get to ambient. Note also the footnote
on page 18 on age distributions is more in line with my comments above on age groups.
What is not clear in the discussion of uncertainty is the how the nature of the monitoring
station (residential, commercial, industrial) as well as nature of residence near roadway
(single family houses, large apartment blocks) get taken into account, for example in
table 4. Will sites that are used for regulatory control at the edge of a factory be
excluded? What if all the people in the tract live more than 200m from the monitor? In
addition I assume that "fraction of the population in each location" somehow gets
factored in when census tract is used (as total population, and age distribution within in
each census tract, are not all the same). Again, many of these issues are discussed in the
Tier III section, and again it makes me question whether the separation into separate
Tiers in imposing more criticism than is necessary. Figure 3 on page 29 outlines the
criteria needed, it seems likely that sufficient data are available to proceed, so no more
than a descriptive discussion of how staff gets to Tier 3 is needed and they should get on
with doing the assessment as proposed.
Risk Assessment Scope and Methods
On page 33 section 4.3 I would recommend to staff that they reverse the order of
discussion on the credible exposure response relationships for controlled human exposure
studies and the epidemiological studies, particularly sine the section title is Risk Based on
Epidemiological Studies. Clear most if not all of the controlled studies have been carried
out in normal healthy volunteers; whereas the epidemiological studies are in general
observations on free-living population groups that obviously contain people with vary
levels of risk. Judgment on risk assessment should be made on the latter group with the
controlled human exposures experiments mostly designed to assess and understand
potential mechanisms for the risk observed in free-living populations.
The plan as outlined a two Tier effort, like for the exposure assessment seems
somewhat arbitrary as to whether it is called a two tier effort or a logical progression in
gathering the data necessary (and I believe from the draft ISA) available to do all that is
proposed. The short term exposure assessment is well documented to move forward,
particularly for the respiratory outcomes described. With regard to the long term
assessment particularly for hospitalizations and mortality by sub-regions, this may have
to await the assessment of the draft ISA.
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With regard to the criteria for determining the approach to tier ii on page 37,1
accept that the thinking of these steps are necessary to get to the data but as indicated
above I believe there are sufficient evidence, particularly for the short term effects, that
doing the risk assessment for respiratory outcomes should be straight forward. However,
I totally reject the placement of the last bullet on page 37, in section 4.4 as a criteria for
doing what is needed. There should be sufficient resources to complete the task in the
next 15 months. It is a priority for the task to be done in the next 15 months and if
resources must be borrowed from other activities to get it done, that should be the
decision.
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Comments from Dr. George Thurston
COMMENTS FROM GEORGE D. THURSTON
Comments on Nitrogen Dioxide Health Exposure and Risk Assessment (September 2007)
General Comments
This plan successfully outlines the scope and approaches for, and highlights key issues in,
the estimation of population exposures and health risks posed by NOx under: 1) existing air
quality levels; 2) upon just meeting the current NO2 primary NAAQS, and; 3) upon just meeting
potential alternative standards under consideration by the Administration.
The main concern I have is in the selection of the key CMSA's for evaluation. More
justification for these choices needs to be presented. In particular, it is surprising to me that New
York City, which has a high concentration of those whom the ISA is pointing to as most affected
(e.g., poor children with asthma living near roadways). I think consideration of both LA and
NYC would give balance to the document, as LA has a high concentration of NOX exposures,
while NYC includes a high concentration of especially affected individuals. The other three
cities selected should provide more "typical" U.S. urban exposures/populations.
I also feel that the U.S. EPA should consider emergency department (ED) visits to the
extent possible. These data are becoming more widely available on a routine basis throughout
the U.S., and may more accurately reflect the extent of effects, given recent cost-saving efforts to
treat problems like asthma in the ED, rather than as a hospital admission.
Specific Comments
P8, Sec 3.3.1, par. 1 (regarding the selection of CMS As for evaluation) - Why Atlanta,
Philadelphia, and Chicago over New York, Phoenix, and Denver? More justification for CMSA
selection should be provided.
P8, Sec. 3.3.1, par. 2. I feel this list of criteria should include some involving exposed
populations in each CMSA in addition to the exposure concentration profiles discussed here
(perhaps %poor, ssthma prevalence, % living within 200 yards of a highway, % minority, or the
like),
P35, Sec 4.3.1.2, par. 3. I agree with the balanced discussion of the multi-pollutant issue
presented here. My only addition is that, when possible, the models considered should consider
no more than two pollutants at a time to help clarify the role of each pollutant relative to each of
the others. When more than that are included, it becomes much harder to sort out real effects
from multi-collinearity effects.
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Comments from Dr. George Thurston
General Comments
This plan successfully outlines the scope and approaches for, and highlights key issues in,
the estimation of population exposures and health risks posed by NOx under: 1) existing air
quality levels; 2) upon just meeting the current NCh primary NAAQS, and; 3) upon just meeting
potential alternative standards under consideration by the Administration.
The main concern I have is in the selection of the key CMSA's for evaluation. More
justification for these choices needs to be presented. In particular, it is surprising to me that New
York City, which has a high concentration of those whom the ISA is pointing to as most affected
(e.g., poor children with asthma living near roadways). I think consideration of both LA and
NYC would give balance to the document, as LA has a high concentration of NOX exposures,
while NYC includes a high concentration of especially affected individuals. The other three
cities selected should provide more "typical" U.S. urban exposures/populations.
I also feel that the U.S. EPA should consider emergency department (ED) visits to the
extent possible. These data are becoming more widely available on a routine basis throughout
the U.S., and may more accurately reflect the extent of effects, given recent cost-saving efforts to
treat problems like asthma in the ED, rather than as a hospital admission.
Specific Comments
P8, Sec 3.3.1, par. 1 (regarding the selection of CMS As for evaluation) - Why Atlanta,
Philadelphia, and Chicago over New York, Phoenix, and Denver? More justification for CMSA
selection should be provided.
P8, Sec. 3.3.1, par. 2. I feel this list of criteria should include some involving exposed
populations in each CMSA in addition to the exposure concentration profiles discussed here
(perhaps %poor, ssthma prevalence, % living within 200 yards of a highway, % minority, or the
like),
P35, Sec 4.3.1.2, par. 3. I agree with the balanced discussion of the multi-pollutant issue
presented here. My only addition is that, when possible, the models considered should consider
no more than two pollutants at a time to help clarify the role of each pollutant relative to each of
the others. When more than that are included, it becomes much harder to sort out real effects
from multi-collinearity effects.
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Comments from Dr. Ronald Wyzga
In general the approach appears to be reasonable, but ambitious. The challenge will be to
implement this plan with available resources in a way that is scientifically credible and in a way
that illuminates the available information to inform further discussions about the NO2 primary
NAAQS.
Within this approach there are two points that I want to raise:
The input data for the assessment are subject to uncertainties (multiple studies with different
results, missing information, etc.). I would urge the investigators to consider ways to internalize
the uncertainties within the analyses rather than to undertake base analyses accompanied by
sensitivity analyses. The outputs of such analyses are likely to ranges or distributions of
estimates rather than point estimates, but such ranges more accurately portray reality than do
point estimates.
Secondly I am disturbed by the approach taken in evaluating the risks and exposures associated
with ambient levels of NO2 associated with just meeting the current standard. Since the entire
US is currently within compliance, the entire country has NO2 levels below the current standard.
To assume under this scenario that the entire country has NO2 levels at the standard will clearly
lead to overestimates of risk and exposure, and there is concern that the resulting estimates will
be accepted at face value and misinterpreted. I urge the staff to consider ways to confront this
issue in a way that more realistically portrays the exposures/risks associated with current and
alternative standards.
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