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February 3, 2014
MEMORANDUM
SUBJECT: CAS AC Review of Health Risk and Exposure Assessment for Ozone, Second
External Review Draft and Welfare Risk and Exposure Assessment for Ozone,
Second External Review Draft
The draft documents, Health Risk and Exposure Assessment for Ozone: Second External Review
Draft and Welfare Risk and Exposure Assessment for Ozone: Second External Review Draft,
prepared by the Environmental Protection Agency's (EPA) Office of Air Quality Planning and
Standards (OAQPS) staff as part of EPA's ongoing review of the national ambient air quality
standards (NAAQS) for ozone (O3), are being made available on EPA's website for review by
the Clean Air Scientific Advisory Committee (CASAC) Ozone Review Panel (the Panel) at a
public meeting to be held in Chapel Hill, NC on March 25-27, 2014. The documents can be
found at http://www.epa.g0v/ttn/naaqs/standards/0z0ne/s o3 index.html. Charge questions for
the Panel to consider in its review of these documents are attached to this memorandum. I am
requesting that you forward this memorandum and the attached charge questions to the Panel
members to prepare for the March meeting.
As part of the review of the current NAAQS for O3, EPA's OAQPS staff has prepared second
draft risk and exposure assessments (REAs) for both health and welfare effects. These draft
REAs evaluate the risks to human populations and to agricultural and forest ecosystems when O3
concentrations just meet the current primary O3 standard and several alternative primary and
secondary standard levels. The REAs are based on applications of results of scientific studies
summarized in the final Integrated Science Assessment of Ozone and Related Photochemical
Oxidants. This document, along with EPA's Integrated Review Plan, can be found at
http://www.epa.g0v/ttn/naaqs/standards/0z0ne/s o3 index.html. The REAs include descriptions
of the scope of the assessments and the methodologies used as well as key results, observations,
and related uncertainties associated with the quantitative analyses conducted.
FROM: Erika Sasser, Acting Director /s/
Health and Environmental Impacts Division (C504-02)
Office of Air Quality Planning and Standards
United States Environmental Protection Agency
TO:
Holly Stallworth
Designated Federal Officer
Clean Air Scientific Advisory Committee
EPA Science Advisory Board Staff Office
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The second draft REAs incorporate a number of changes from the first drafts of these documents.
One important change is that the assessments now provide estimates of the changes in risks
resulting from just meeting alternative standard levels relative to just meeting the existing
standards. Many of the other changes in the assessments are in response to comments offered by
the Panel following their peer review of the first draft documents. The Panel presented its
comments on the first draft assessments in a letter to the Administrator dated November 19,
2012.1 We are appreciative of the Panel's review, which contributed to improvements in the
second draft assessments. Some of the most significant changes made in consideration of
CASAC comments on the first draft REAs are summarized below.
Responses to CASAC comments on the first draft health risk and exposure assessment:
•	We have restructured Chapter 2 to more fully describe the conceptual steps in the
exposure and risk assessment, identifying the important elements and types of methods
and tools that are used. We have included additional conceptual diagrams throughout the
REA connecting each analytical component back to the overall conceptual framework.
•	We have implemented a model-based approach to adjust O3 concentrations to just meet
the existing standard and several alternative standard levels.
•	We have performed model input and output data evaluations including among others
evaluations of historical trends in CHAD activity pattern data and comparison of CHAD
data with recent American Time Use Survey (ATUS) data, comparison of APEX
estimated exposures with personal exposure measurement data, and comparison of APEX
estimated ventilation estimates with independent methods used to estimate ventilation.
•	Consistent with CASAC recommendations, we have implemented the McDonnell,
Stewart, and Smith (2012) lung model of FEV1 decrements, using the threshold model
specification. We have explored the model in detail and provide a number of sensitivity
analyses exploring aspects of the model including the impact of age related factors.
•	We are providing estimates of risks for the entire range of 03 concentrations down to
zero, as well as providing the distributions of risk and risk changes along the full range of
ozone concentrations.
•	We have substantially expanded our discussion of the potential role of exposure
measurement error to include a detailed discussion of the sources of exposure
measurement error and the ways in which exposure measurement error can add
uncertainty to effect estimates.
•	To reduce repetition and consolidate and prioritize results, we have made several changes
to the way we present and summarize risk estimates (both in tabular and graphical form)
and the way in which we discuss the results in the text. Specifically, we have modified
the color scheme on the heat maps to make them easier to interpret and added line charts
which allow readers to evaluate trends in risk reduction for short-term exposure-related
mortality across the standard levels we evaluated. We have also reduced the total number
of tables, focusing on those risk metrics most informative to policy-relevant questions.
1 Frey, C. and Samet, J. (2012). Letter from Clean Air Scientific Advisory Committee to the Honorable Lisa P.
Jackson, Administrator, US EPA. CASAC Review of the EPA's Health Risk and Exposure Assessment for Ozone
(First External Review Draft-Updated August 2012) and Welfare Risk and Exposure Assessment for Ozone (First
External Review Draft-Updated August 2012) November 19, 2012.
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•	We have included risk estimates for long-term exposure-related mortality. We have also
included sensitivity analyses exploring the impact of using regionally differentiated effect
estimates to model this endpoint, instead of a single national-scale effect estimate.
•	We have restructured Chapter 9 (Synthesis) to focus more on comparing and contrasting
exposure and risk results to identify common patterns, or important differences. The
comparisons focus on patterns across urban areas, across years of analysis, and across
alternative standards. Chapter 9 provides an overall integrated characterization of
exposure and risk in the context of key policy-relevant questions introduced in Chapter 2
and assesses the degree to which the integrated results are representative of national
patterns of exposure and risk.
Responses to CASAC comments on the first draft welfare risk and exposure assessment:
•	We have implemented a model-based approach to adjust O3 concentrations to reflect just
meeting the existing standard and alternative W126-based standards. This approach uses
national reductions in NOx to adjust O3 concentrations at monitors throughout a region
such that the highest monitor in the region meets a specified W126 concentration.
Resulting W126 concentrations are interpolated to provide national surfaces of W126
concentrations for use in the risk analyses.
•	We have restructured the chapters to provide a more integrated treatment of ecosystem
functions, e.g. biomass loss and ecosystem services, including the dollar value of changes
in commercial timber and crops.
•	We have added a number of additional analyses of risks of yield loss for agricultural
crops. These include analyses of county level patterns of yield loss for individual species
remaining after just meeting the existing standard and yield gains from meeting
alternative standards.
•	We have added analyses of forest ecosystem impacts based on biomass loss weighted by
species basal area.
•	We have added an analysis of uncertainties associated with use of seedling biomass loss
to represent biomass loss in mature trees.
•	We have restructured Chapter 8 (Synthesis) to focus more on comparing and contrasting
exposure and risk results to identify common patterns, or important differences, focusing
on patterns across different geographic areas of the U.S., across years of analysis, and
across alternative W126 standard levels. Chapter 8 provides an overall integrated
characterization of risk in the context of key policy-relevant questions raised in Chapter 2
and assesses the degree to which the integrated results are representative of national
patterns of risk.
The CASAC and public comments on the draft REAs will be taken into consideration in making
revisions to the draft document. Final REAs will be released in Summer 2014. Draft documents
are being made available to the Panel in the form of electronic files, available from the EPA
website at http://www.epa.g0v/ttn/naaqs/standards/0z0ne/s o3 2008 rea.html.
A set of charge questions related to the draft REAs are attached. These charge questions focus
on the overall design of the analyses and the methods, results, and interpretations of the different
analytical elements of the assessments.
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We look forward to discussing the second draft health and welfare risk and exposure assessments
with the Panel at our upcoming meeting. Should you have any questions regarding the REAs,
please contact me (919-541-3889; email sasser.erika@epa.gov) or Dr. Bryan Hubbell (919-541-
0621; email hubbell.bryan@epa.gov).
cc: Chris Zarba, SAB, OA
Holly Stallworth, SAB, OA
John Vandenberg, ORD/NCEA-RTP
Steve Dutton, ORD/NCEA-RTP
James Brown, ORD/NCEA-RTP
Bryan Hubbell, OAQPS/HEID
Karen Wesson, OAQPS/ HEID
Susan Anenberg, OAQPS/HEID
Chris Davis, OAQPS/HEID
Stephen Graham, OAQPS/HEID
Scott Jenkins, OAQPS/HEID
Amy Lamson, OAQPS/HEID
Robin Langdon, OAQPS/HEID
John Langstaff, OAQPS/HEID
Deirdre Murphy, OAQPS/HEID
Zachary Pekar, OAQPS/HEID
Travis Smith, OAQPS/HEID
Susan Stone, OAQPS/HEID
Richard Wayland, OAQPS/AQAD
Tyler Fox, OAQPS/AQAD
James Hemby, OAQPS/AQAD
Liz Naess, OAQPS/AQAD
Neil Frank, OAQPS/AQAD
Heather Simon, OAQPS/AQAD
Ben Wells, OAQPS/AQAD
Alison Davis, OAQPS/PACS
Attachments
Charge to the CASAC Ozone Review Panel for Review
Exposure Assessment for Ozone
Charge to the CASAC Ozone Review Panel for Review
Exposure Assessment for Ozone
of the Second Draft Health Risk and
of the Second Draft Welfare Risk and
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Attachment
Charge to the CASAC Ozone Review Panel for Review of the Second Draft Health Risk
and Exposure Assessment for Ozone
The second draft Health Risk and Exposure Assessment (REA) provides estimates of human
exposures and health risks associated with O3 concentrations adjusted to just meet the existing
primary 03 standard and several alternative standard levels. The assessment also provides
descriptions of the data and methods used to develop the estimates. For the Health Risk and
Exposure Assessment, following an introductory chapter (chapter 1), the document provides a
conceptual framework for considering exposures and risks associated with ambient O3 (chapter
2), discusses the scope of the risk assessment (chapter 3), the air quality information used to
inform the exposure and risk assessments (chapter 4), methods used to estimate population
exposure to 03 and results of the exposure analysis (chapter 5), methods used to estimate lung
function risk based on controlled human exposure studies and results of the risk analysis (chapter
6), methods used to estimate risks based on results of epidemiology studies and results of the
urban case study risk analyses (chapter 7), a national-scale assessment of premature mortality
associated with recent 03 levels, an evaluation of the representativeness of the urban study areas
in a national context (chapter 8), and a synthesis of the assessment including key results and
observations (chapter 9). Also included is an Executive Summary for the information presented
in chapters 1-9.
We ask the CASAC Ozone Panel to focus on the charge questions below in their review of the
second draft REA, but we would appreciate comments on any other topics as well.
Chapter 1: Introduction
1.	To what extent does the Panel find the introductory and background material, including that
pertaining to previous reviews of the O3 standards and the current review, to be clearly
communicated and appropriately characterized?
Chapter 2: Conceptual Model
2.	To what extent does the Panel find that the discussions accurately and clearly reflect the air
quality, health effects, exposure and risk considerations relevant for quantitative exposure
and risk assessment, building from information contained in the final ISA? What are the
views of the Panel on the additional flowchart provided for the overall assessment and the
additional information regarding specific elements of the exposure and risk assessments?
Chapter 3: Scope
3.	To what extent does the Panel find the scope of the health risk and exposure assessment is
clearly communicated? To what extent does the panel find the additional flowcharts for each
analytical component to be useful additions?
Health REA Charge Questions—Page 1

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Chapter 4: Air Quality Considerations
4.	What are the views of the Panel on the appropriateness of the methods used to characterize
03 air quality for the exposure and risk assessment? What are the views of the Panel on the
HDDM-based adjustment methodology used to adjust O3 concentrations to just meet the
existing 03 standard and alternative standards?
5.	To what extent does the Panel find that the discussion of uncertainty related to the air quality
inputs to the exposure and risk assessment appropriately covers important sources of
uncertainty?
Chapter 5: Characterization of Human Exposure to Ozone
6.	To what extent does the Panel find the assessment, interpretation, and presentation of the
methods and results of the updated and expanded population-based exposure analysis to be
technically sound, appropriately balanced, and clearly communicated?
7.	Chapter 5 includes several evaluations of key APEX inputs and model outputs, including for
example analysis of time-activity data and comparison of actual personal exposures with
modeled exposures. What are the views of the Panel on the appropriateness and usefulness
of these evaluations and the conclusions drawn from these evaluations?
8.	Chapter 5 includes several scenario-based exposure simulations that focus on specific
populations or behaviors. What are the views of the Panel on the design, results, and
interpretation of these additional scenario-based exposure simulations?
9.	To what extent does the Panel find that the discussion of uncertainty and variability have
covered important sources of uncertainty and variability and appropriately characterized their
relationship to the exposure estimates?
Chapter 6: Characterization of Health Risk Based on Controlled Human Exposure Studies
10.	To what extent does the Panel find the assessment, interpretation, and presentation of the
methods and results of the updated and expanded lung function risk analysis to be technically
sound, appropriately balanced, and clearly communicated?
11.	What are the views of the Panel on the implementation of the McDonnell-Stewart-Smith
model to specify the exposure-response function linking the change in FEV1 to O3 exposure?
12.	To what extent does the Panel find that the discussion of uncertainty and variability have
covered important sources of uncertainty and variability and appropriately characterized their
relationship to the risk estimates?
Health REA Charge Questions—Page 2

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Chapter 7: Characterization of Health Risk Based on Epidemiological Studies
13.	To what extent does the Panel find the assessment, interpretation, and presentation of the
methods and results of the updated epidemiology-based risk assessment to be technically
sound, appropriately balanced, and clearly communicated?
14.	To what extent does the Panel find that the discussion of uncertainty and variability have
covered important sources and appropriately characterized the relationship of those sources
of uncertainty and variability to the risk estimates?
15.	Adjusting the distributions of O3 concentrations based on decreasing NOx emissions to just
meet the existing and alternative 03 primary standards resulted, in some cases, in substantial
shifts in the spatial and temporal patterns of O3 across case study urban areas relative to
patterns of 03 that existed for recent air quality, and presumably relative to the patterns
present in the study locations of the epidemiology studies from which the concentration-
response functions were drawn (see section 7.1.1 of the TSD, USEPA, 2012). What are the
views of the Panel on the characterization of the degree to which these changes in spatial
patterns of 03 introduce uncertainty in risk estimates when effect estimates based on one
spatial/temporal pattern of O3 (the pattern in the epidemiology study) are applied to a
substantially different spatial/temporal pattern of 03 concentrations?
16.	In particular, what are the views on the Panel on the characterization of the level of
uncertainty associated with estimates of risk associated with days with relatively lower
composite (area-wide average) 03 concentrations and those with relatively higher composite
O3 concentrations?
Chapter 8: National Scale Mortality Risk Burden Based on Application of Results from
Epidemiological Studies
17.	To what extent does the Panel find the assessment, interpretation, and presentation of the
methods and results of the updated national-scale risk analysis to be technically sound,
appropriately balanced, and clearly communicated?
18.	To what extent does the Panel find the risk and air quality representativeness analyses to be
technically sound and clearly communicated?
Chapter 9: Synthesis
19.	To what extent does the Panel find the synthesis to be a useful integration and summarization
of key results and insights regarding the overall health exposure and risk assessment?
20.	To what extent does the Panel find that the discussion of overall uncertainty provides an
appropriate context for interpretation of the exposure and risk results?
Health REA Charge Questions—Page 3

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Executive Summary
21. To what extent does the Panel find the Executive Summary to be a useful summary of the
data and methods used to estimate human exposures and heath risks and the key results of the
assessment?
Health REA Charge Questions—Page 4

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Attachment
Charge to the CASAC Ozone Review Panel for Review of the Second Draft Welfare Risk
and Exposure Assessment for Ozone
The second draft Welfare Risk and Exposure Assessment (WREA) includes descriptions of the
data and methods used to estimate exposures and risks to ecosystems associated with recent O3
levels and with O3 levels adjusted to just meet the current secondary O3 standard of 75 ppb and
alternative W126 standard levels of 15, 11, and 7 ppm-hrs. For the WREA, following an
introductory chapter (chapter 1), the document provides a conceptual framework for considering
exposures and risks to ecosystems associated with ambient O3 (chapter 2), discusses the scope of
the risk assessment (chapter 3), the air quality information used to inform the risk assessment
(chapter 4), introduces the ecosystem services framework to help define how the damage to
ecosystems informs determinations of the adversity to public welfare associated with changes in
ecosystem functions (chapter 5), presents analyses that characterize ambient O3 exposures on
two important ecological effects - biomass loss and foliar injury - and estimate impacts to the
following ecosystem services: supporting, regulating, provisioning, and cultural services
(chapters 6 and 7), and provides a synthesis of the assessment including key results and
observations (chapter 8). Also included is an Executive Summary for the information presented
in chapters 1-8.
We ask the CASAC Ozone Panel to focus on the charge questions below in their review of the
second draft WREA, but we would appreciate comments on any other topics as well.
Chapter 1: Introduction
1.	To what extent does the Panel find the introductory and background material, including that
pertaining to previous reviews of the O3 standards and the current review, to be clearly
communicated and appropriately characterized?
Chapter 2: Conceptual Model
2.	To what extent does the Panel find that the discussions accurately and clearly reflect the air
quality, ecosystem effects evidence, ecosystem services, and exposure and risk
considerations relevant for quantitative assessment, building from information contained in
the final ISA?
Chapter 3: Scope
3. To what extent does the Panel find the scope of the welfare risk and exposure assessment is
clearly communicated?
Welfare REA Charge Questions—Page 1

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Chapter 4: Air Quality Considerations
4.	What are the views of the Panel on the appropriateness of the methods used to characterize
03 air quality for the exposure and risk assessment? What are the views of the Panel on the
HDDM-based adjustment methodology used to adjust O3 concentrations to just meet the
existing 03 standard and levels for average W126 scenarios, coupled with the interpolation
method used to create a national surface of W126 concentrations for all scenarios?
5.	To what extent does the Panel find that the discussion of uncertainty related to the air quality
inputs to the exposure and risk assessment appropriately includes important sources of
uncertainty?
Chapter 5: O3 Risk to Ecosystem Services
6.	To what extent does the Panel find the assessment, interpretation, and presentation of the
methods and results of the updated ecosystem services assessment to be technically sound,
appropriately balanced, and clearly communicated?
7.	To what extent does the Panel support the revised structure of the ecosystem services
discussions, including integrating ecological effects analyses directly with the ecosystem
services assessments?
8.	To what extent is the combination of 03 exposure data with other data sources (e.g. fire data,
bark beetle maps, trail maps) to link areas of concern/interest with areas of higher vegetation
risk due to 03 technically sound?
9.	To what extent does the Panel find that the discussion of uncertainty and variability has
included all important sources of uncertainty and variability and appropriately characterized
their relationship to the ecosystem services estimates?
Chapter 6: Biomass Loss
10.	To what extent does the Panel find the assessment, interpretation, and presentation of the
methods and results of the biomass loss risk assessment to be technically sound,
appropriately balanced, and clearly communicated?
11.	To what extent does the Panel find the carbon sequestration estimates from the Forest and
Agricultural Sector Optimization Model Greenhouse Gas version (FASOMGHG) (Section
6.6.1) to be technically sound and appropriately characterized?
12.	To what extent does the Panel find the weighted biomass loss analysis in Section 6.8 to be a
technically sound approach to assess potential ecosystem-level effects nationwide and in
Class I areas?
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13.	To what extent does the Panel find that the discussion of uncertainty and variability has
included all important sources of uncertainty and variability and appropriately characterized
their relationship to biomass loss estimates?
Chapter 7: Foliar Injury
14.	To what extent does the Panel find the assessment, interpretation, and presentation of the
methods and results of the foliar injury risk assessment to be technically sound, appropriately
balanced, and clearly communicated?
15.	What are the views of the Panel on the analysis of the Forest Health Monitoring data in
Section 7.2, including the finding of the lack of a statistical relationship between the severity
of foliar injury and W126 index values or soil moisture levels?
16.	What are the views of the panel on the appropriateness of the characterization of vegetation
strata (i.e., herb, shrub, tree) for the analyses of sensitive species cover in the three national
park case studies (Section 7.4)?
17.	What are the views of the Panel on the usefulness of the screening-level assessment of visible
foliar injury in national parks in Section 7.3? Specifically, what are the views of the Panel
regarding conclusions appropriate to draw from applying the W126 benchmark scenarios
derived from the national-scale Forest Health Monitoring data analysis in the screening-level
assessment?
18.	To what extent does the Panel find that the discussion of uncertainty and variability have
covered important sources of uncertainty and variability and appropriately characterized their
relationship to foliar injury risks?
Chapter 8: Synthesis
19.	To what extent does the Panel find the synthesis to be a useful integration and summarization
of key results and insights regarding the overall welfare exposure and risk analyses?
Executive Summary
20.	To what extent does the Panel find the Executive Summary to be a useful summary of the
data and methods used to estimate exposures and risks to ecosystems and the key results of
the assessment?
Welfare REA Charge Questions—Page 3

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