Review of the National Ambient Air Quality Standards for Ozone

609 Pages·2007·9.38 MB·English

Review of the National Ambient Air Quality
Standards for Ozone:

Policy Assessment of Scientific
and Technical Information

OAQPS Staff Paper
EPA-452/R-07-007
July 2007

REVIEW OF THE NATIONAL AMBIENT AIR QUALITY
STANDARDS FOR OZONE:

POLICY ASSESSMENT OF SCIENTIFIC AND
TECHNICAL INFORMATION

OAQPS STAFF PAPER

U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina
DISCLAIMER

This document has been reviewed by the Office of Air Quality Planning and Standards
(OAQPS), U.S. Environmental Protection Agency (EPA), and approved for publication. This
final OAQPS Staff Paper contains the conclusions and recommendations of staff of OAQPS and
does not necessarily represent those of the EPA. Mention of trade names or commercial
products is not intended to constitute endorsement or recommendation for use.
PREFACE TO JULY 2007 EDITION

The purpose of this July 2007 edition is to include the March 26, 2007 letter from
the Clean Air Scientific Advisory Committee (CASAC) to the Administrator providing
its final comments and advice on the January 2007 edition of the OAQPS Staff Paper.
The CASAC letter has been included as an Attachment to this edition (Attachment B). In
addition, this edition of the Staff Paper includes technical corrections to the exposure
model resulting in revised exposure estimates and revised lung function risk estimates.
As noted in chapters 4 and 5 of this edition of the Staff Paper, a small error was detected
in the exposure model in January 2007 that resulted in small increases in the exposure
estimates. This error has been corrected and the model runs have been redone, generally
resulting in small increases in the exposure estimates. The corrected results are presented
in this edition of the Staff Paper and in the revised Exposure Analysis technical support
document. The lung function risk estimates also have been redone based on the corrected
exposure estimates and are generally slightly higher than the original estimates presented
in the January 2007 edition of the Staff Paper. The corrected lung function risk estimates
are presented in this edition of the Staff Paper and in the revised Risk Assessment
technical support document. Also, Figure 3-4 on page 3-56 has been modified to include
a legend of the studies used to create the figure. Additional minor edits to Chapters 4 and
5 are listed in the errata.
ACKNOWLEDGMENTS

This Staff Paper is the product of the Office of Air Quality Planning and Standards
(OAQPS). For the chapters on ozone-related health effects, exposure, risk, and primary
standards, the principal authors include Karen Martin, David McKee, Harvey Richmond, Susan
Lyon Stone, and John Langstaff. For the chapters on ozone-related welfare effects and
secondary standards, the principal authors include Vicki Sandiford and Jeffrey Herrick. The
principal authors of the chapter on air quality characterization include Lance McCluney and
Michael Rizzo. Staff from other EPA offices, including the Office of Research and
Development, the Office of General Counsel, and the Office of Transportation and Air Quality,
also provided valuable comments.
Earlier drafts of this document were formally reviewed by the Clean Air Scientific
Advisory Committee (CASAC) and made available for public comment. This document has
been informed by the expert advice and comments received from CASAC, as well as by public
comments submitted by a number of independent scientists, officials from State and local air
pollution organizations, environmental groups, and industrial groups and companies.
Table of Contents

List of Tables.................................................................................................................................ix
List of Figures...............................................................................................................................xii

1. INTRODUCTION..........................................................................................................1-1
1.1 PURPOSE..................................................................................................................1-1
1.2 BACKGROUND.......................................................................................................1-2
1.2.1 Legislative Requirements.................................................................................1-2
1.2.2 History of Ozone NAAQS Reviews................................................................1-3
1.2.3 Litigation Related to the 1997 Ozone Standards.............................................1-4
1.2.4 Current Ozone NAAQS Review......................................................................1-5
1.3 GENERAL APPROACH AND ORGANIZATION OF THE DOCUMENT...........1-7
REFERENCES......................................................................................................................1-9

2. AIR QUALITY CHARACTERIZATION..................................................................2-1
2.1 INTRODUCTION.....................................................................................................2-1
2.2 CHEMICAL AND PHYSICAL PROPERTIES, FORMATION, AND
TRANSPORT............................................................................................................2-1
2.2.1 Properties and Formation.................................................................................2-1
2.2.2 Relationship of Ozone to Photochemical Oxidants.........................................2-7
2.2.3 Transport..........................................................................................................2-7
2.3 DATA SOURCES.....................................................................................................2-9
2.3.1 Air Quality System (AQS)...............................................................................2-9
2.3.2 CASTNET......................................................................................................2-10
2.4 OZONE MONITORING METHODS AND DATA QUALITY............................2-12
2.4.1 Effect of Measurement Precision on 8 hour Ozone Averages.......................2-12
2.5 CHARACTERIZATION OF GROUND-LEVEL OZONE
CONCENTRATIONS.............................................................................................2-13
2.5.1 Metrics...........................................................................................................2-13
2.5.2 Spatial Variability..........................................................................................2-15
2.5.2.1 Distributions of 1-hr, 8-hr, and 24-hr Ozone Metrics...............................2-15
2.5.2.2 8-Hour and 1-Hour Statistics....................................................................2-19
2.5.2.3 Cumulative Concentration-Weighted Statistics........................................2-19
2.5.3 Temporal Variability......................................................................................2-30
2.5.3.1 Long Term Variability – Trends...............................................................2-30
2.5.3.2 Short Term Variability – Annual..............................................................2-35
2.5.3.3 Seasonal Variability..................................................................................2-35
2.5.3.4 Short Term Variability – Diurnal..............................................................2-35
i
2.6 CHARACTERIZATION OF OZONE EPISODES.................................................2-39
2.7 POLICY RELEVANT BACKGROUND LEVELS................................................2-48
REFERENCES....................................................................................................................2-56

3. POLICY-RELEVANT ASSESSMENT OF HEALTH EFFECTS
EVIDENCE....................................................................................................................3-1
3.1 INTRODUCTION.....................................................................................................3-1
3.2 MECHANISMS OF TOXICITY...............................................................................3-3
3.3 NATURE OF EFFECTS............................................................................................3-3
3.3.1 Morbidity.........................................................................................................3-4
3.3.1.1 Effects on the Respiratory System from Short-term Exposures.................3-4
3.3.1.2 Effects on the Respiratory System from Long-term Exposures...............3-20
3.3.1.3 Effects on the Cardiovascular System......................................................3-26
3.3.2 Premature Mortality.......................................................................................3-27
3.3.2.1 Mortality and Short-term O Exposure.....................................................3-27
3
3.3.2.2 Mortality and Long-term O Exposure.....................................................3-34
3
3.3.3 Ozone Effects on UV-B Flux.........................................................................3-36
3.3.4 Summary........................................................................................................3-36
3.4 ASSESSMENT OF EVIDENCE FROM EPIDEMIOLOGICAL STUDIES.........3-37
3.4.1 Strength of Associations................................................................................3-38
3.4.2 Robustness of Associations............................................................................3-39
3.4.2.1 Exposure Error..........................................................................................3-39
3.4.2.2 Confounding by Copollutants...................................................................3-42
3.4.2.3 Model Specification..................................................................................3-44
3.4.3 Consistency....................................................................................................3-45
3.4.4 Lag Structure in Short-term Exposure Studies..............................................3-45
3.4.5 Concentration-Response Relationships and Potential Thresholds.................3-46
3.4.6 Health Effects of Pollutant Mixtures Containing O .....................................3-48
3
3.5 BIOLOGICAL PLAUSIBILITY AND COHERENCE OF EVIDENCE...............3-50
3.5.1 Animal-to-Human Extrapolation Issues........................................................3-51
3.5.2 Coherence and Plausibility of Short-term Effects on the Respiratory
System...........................................................................................................3-55
3.5.3 Coherence and Plausibility of Effects on the Cardiovascular System...........3-58
3.5.4 Coherence and Plausibility of Effects Related to Long-Term O
3
Exposure........................................................................................................3-60
3.5.5 Coherence and Plausibility of Short-Term Mortality-Related Health
Endpoints......................................................................................................3-61
3.6 OZONE-RELATED IMPACTS ON PUBLIC HEALTH.......................................3-62
3.6.1 Factors that Modify Responsiveness to Ozone..............................................3-63
3.6.2 Susceptible Population Groups......................................................................3-64
3.6.2.1 Active People............................................................................................3-64
3.6.2.2 People with Lung Disease.........................................................................3-66
3.6.2.3 Children and Older Adults........................................................................3-69
ii
3.6.2.4 People with Increased Responsiveness to Ozone.....................................3-70
3.6.2.5 Other Population Groups..........................................................................3-71
3.6.3 What Constitutes an Adverse Health Impact from Ozone Exposure?...........3-72
3.6.4 Estimation of Potential Numbers of People in At-Risk Susceptible
Population Groups in the United States........................................................3-78
3.7 SUMMARY AND CONCLUSIONS FOR OZONE HEALTH EFFECTS............3-79
3.7.1 Respiratory Morbidity Effects of Short-term Exposures to Ozone...............3-80
3.7.2 Cardiovascular Morbidity Effects of Short-term Exposures to Ozone..........3-83
3.7.3 Mortality-Related Effects of Short-term Exposures to Ozone.......................3-84
3.7.4 Health Effects of Repeated Short-term Exposures to Ozone.........................3-85
3.7.5 Confidence in Various Health Outcomes Associated with Short-term
Exposures to Ozone......................................................................................3-86
3.7.6 Health Effects of Long-term Exposures to Ozone.........................................3-87
3.7.7 Health Effects of Pollutant Mixtures Containing Ozone...............................3-89
3.7.8 Populations at Risk/Susceptibility Factors Associated with Ozone
Exposure........................................................................................................3-90
REFERENCES....................................................................................................................3-91

4. CHARACTERIZATION OF HUMAN EXPOSURE TO OZONE..........................4-1
4.1 INTRODUCTION.....................................................................................................4-1
4.2 OZONE EXPOSURE STUDIES...............................................................................4-2
4.2.1 Exposure Concepts and Definitions.................................................................4-2
4.2.2 Monitoring Equipment Considerations............................................................4-4
4.2.3 Personal Ozone Exposure Assessment Studies................................................4-5
4.2.4 Microenvironmental Studies............................................................................4-5
4.3 EXPOSURE MODELING.........................................................................................4-6
4.3.1 The APEX Model............................................................................................4-6
4.3.2 Key Algorithms..............................................................................................4-11
4.3.3 Model Output.................................................................................................4-12
4.3.4 Strengths and Limitations of the Model.........................................................4-13
4.3.4.1 Estimation of Ambient Air Quality...........................................................4-14
4.3.4.2 Estimation of Concentrations in Indoor Microenvironments...................4-15
4.3.4.3 Characterization of Population Demographics and Activity Patterns......4-16
4.3.4.4 Modeling Physiological Processes............................................................4-17
4.4 SCOPE OF EXPOSURE ASSESSMENT...............................................................4-18
4.4.1 Selection of Urban Areas to be Modeled.......................................................4-18
4.4.2 Time Periods Modeled...................................................................................4-18
4.4.3 Populations Modeled.....................................................................................4-18
4.5 INPUTS TO THE EXPOSURE MODEL................................................................4-20
4.5.1 Population Demographics..............................................................................4-20
4.5.2 Population Commuting Patterns....................................................................4-21
4.5.3 Human Activity Data.....................................................................................4-22
4.5.4 Physiological Data.........................................................................................4-24
iii
4.5.5 Microenvironments Modeled.........................................................................4-24
4.5.5.1 Air Exchange Rates for Indoor Residential Environments.......................4-24
4.5.5.2 AER Distributions for Other Indoor Environments..................................4-26
4.5.5.3 Proximity and Penetration Factors for Outdoors and In-vehicle..............4-27
4.5.5.4 Ozone Decay and Deposition Rates..........................................................4-27
4.5.6 Meteorological Data.......................................................................................4-27
4.5.7 Ambient Ozone Concentrations.....................................................................4-28
4.5.8 Modeling Alternative Standards....................................................................4-28
4.6 MODEL EVALUATION, SENSITIVITY, & UNCERTAINTY ANALYSES.....4-30
4.6.1 Comparison with Exposure Estimates from the Prior Review......................4-30
4.6.2 Comparison of Model Estimates with Measured Personal Exposures..........4-31
4.6.3 Sensitivity Analyses.......................................................................................4-33
4.6.3.1 Near-Road Residential Exposures............................................................4-33
4.6.3.2 Air Exchange Rates and Prevalence of Residential Air Conditioning.....4-33
4.6.3.3 Activity Patterns: Representativeness of CHAD......................................4-34
4.6.3.4 Activity Patterns: Underestimation of Repeated Exposures.....................4-34
4.6.4 Uncertainty Analysis......................................................................................4-37
4.6.5 Key Findings..................................................................................................4-41
4.7 EXPOSURE ASSESSMENT RESULTS................................................................4-43
4.7.1 APEX Modeling Results................................................................................4-43
4.7.2 Estimated Exposures above Selected Benchmark Levels..............................4-43
4.7.3 Estimates of Repeated Exposures..................................................................4-64
REFERENCES....................................................................................................................4-68

5. CHARACTERIZATION OF HEALTH RISKS.........................................................5-1
5.1 INTRODUCTION.....................................................................................................5-1
5.1.1 Overview of Risk Assessment From Last Review......................................5-2
5.1.2 Development of Approach for Current Risk Assessment............................5-2
5.2 SCOPE OF OZONE HEALTH RISK ASSESSMENT.............................................5-5
5.2.1 Selection of Health Endpoint Categories.....................................................5-6
5.2.2 Selection of Study Areas..............................................................................5-9
5.2.3 Air Quality Considerations........................................................................5-11
5.3 COMPONENTS OF THE RISK MODEL..............................................................5-14
5.3.1 Assessment of Risk Based on Controlled Human Exposure Studies........5-14
5.3.1.1 General Approach.....................................................................................5-14
5.3.1.2 Exposure Estimates...................................................................................5-18
5.3.1.3 Exposure-Response Functions..................................................................5-18
5.3.1.4 Characterizing Uncertainty and Variability..............................................5-22
5.3.2 Assessment of Risk Based on Epidemiological Studies............................5-29
5.3.2.1 General Approach.....................................................................................5-29
5.3.2.2 Air Quality Considerations.......................................................................5-32
5.3.2.3 Concentration-Response Functions..........................................................5-34
5.3.2.4 Baseline Health Effects Incidence and Population Estimates...................5-37
iv
5.3.2.5 Characterizing Uncertainty and Variability..............................................5-40
5.4 OZONE RISK ESTIMATES...................................................................................5-46
5.4.1 Recent Air Quality.....................................................................................5-47
5.4.2 Just Meeting Current and Alternative Ozone Standards............................5-63
5.4.3 Sensitivity Analyses...................................................................................5-81
5.4.3.1 Impact of Alternative Assumptions About Background...........................5-80
5.4.3.2 Impact of Alternative Assumptions About the Shape of Exposure-
Response Relationships for Lung Function Decrements.........................5-82
5.4.4 Comparison with Risk Estimates from Prior Review................................5-87
5.4.5 Key Observations.......................................................................................5-92
REFERENCES..................................................................................................................5-100

6. STAFF CONCLUSIONS AND RECOMMENDATIONS ON THE
PRIMARY O NAAQS..................................................................................................6-1
3
6.1 INTRODUCTION.....................................................................................................6-1
6.2 APPROACH..............................................................................................................6-1
6.3 PRIMARY O STANDARD.....................................................................................6-4
3
6.3.1 Adequacy of Current O Standard...................................................................6-5
3
6.3.1.1 Evidence-based Considerations..................................................................6-8
6.3.1.2 Exposure- and Risk-based Considerations................................................6-17
6.3.1.3 CASAC and Public Commenters’ Views on the Adequacy of the
Current Standard......................................................................................6-42
6.3.1.4 Staff Conclusions on the Adequacy of the Current Standard...................6-46
6.3.2 Indicator.........................................................................................................6-53
6.3.3 Averaging Time.............................................................................................6-53
6.3.3.1 Short-Term and Prolonged (1 to 8 Hours)................................................6-53
6.3.3.2 Long-Term................................................................................................6-56
6.3.4 Level..............................................................................................................6-57
6.3.4.1 Evidence-based Considerations................................................................6-58
6.3.4.2 Exposure/Risk-based Considerations........................................................6-61
6.3.4.3 CASAC and Public Commenters’ Views on the Level of the
Standard....................................................................................................6-76
6.3.4.4 Staff Conclusions on the Level of the Standard........................................6-77
6.3.5 Form...............................................................................................................6-82
6.3.6 Summary of Staff Conclusions and Recommendations on the Primary
O NAAQS....................................................................................................6-85
3
6.4 SUMMARY OF KEY UNCERTAINTIES AND RESEARCH
RECOMMENDATIONS RELATED TO SETTING A PRIMARY O
3
STANDARD............................................................................................................6-87
REFERENCES....................................................................................................................6-92

v