&EPA
United Staies
Environmental Protection
Agency
Office of Air
Planning and Standards
Research Triangle Park NC 27711
EPA-4SO/2-92-001
JUNE 1989
Air
REVIEW OF THE NATIONAL AMBIENT AIR QUALITY STANDARDS
FOR OZONE
ASSESSMENT OF SCIENTIFIC AND TECHNICAL INFORMATION
OAQPS STAFF PAPER
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The cover illustration is an air quality map of the U.S. which
displays the highest second daily maximum 1-hour average ozone
concentration by metropolitan statistical area (MSA) for 1988.
(National Air Quality and Emission Trends Report, 1988,
EPA-450/4-001)
This report has been reviewed by the Office of Air Quality
Planning and Standards, EPA, and approved for publication.
Mention of trade names or commercial products is not intended to
constitute endorsement or recommendation for use.
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Preface
This document was finalized in June 1989 and reviews
information from relevant studies of O3 health and welfare
effects and of exposure and risk analysis through early 1989.
The assessment contained in this staff paper reflects information
in the documents "Air Quality Criteria for Ozone and Other
Photochemical Oxidants" (EPA-600/8-84-020F) and "Summary of
Selected New Information on Effects of Ozone on Health and
Vegetation: Supplement to Air Quality Criteria for Ozone and
Other Photochemical Oxidants" (EPA-600/8-88/l-5a).
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Acknowledgements
This staff paper is the product of the Office of Air Quality
Planning and Standards (OAQPS). Tables and Figures not otherwise
cited are original to this report. The principal authors include
Dr. David J. McKee, Ms. Pamela M. Johnson, Mr. Thomas R. McCurdy,
and Mr. Harvey M. Richmond. This report has been improved by
comments from other staff within OAQPS, the Office of Research
and Development, the Office of Policy and Program Evaluation, and
the Office of General Counsel within EPA. Three drafts were
formally reviewed by the Clean Air Scientific Advisory Committee
and comments incorporated. Particularly important in the final
review of this staff paper was the technical and editorial
support provided by Ms. Victoria Atwell and the clerical and
editorial support of Mrs. Patricia R. Crabtree and Mrs. Barbara
*t
Miles.
Helpful comments and suggestions were also submitted by a
number of independent scientists, by officials from the State
environmental agencies of Illinois, Minnesota, California and
Texas, by the Department of the Navy, and the Department of
Energy, and by environmental and industrial groups including the
Natural Resources Defense Council, the American Lung Association,
the Chemical Manufacturers Association, the American Petroleum
Institute, and the Motor Vehicle Manufacturers Association.
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11
Project Team For
Review of the National Ambient Air Quality Standards for Ozone
Dr. David J. McKee, Project Manager and Author of Chapters I
through III and VI through VIII
Ambient Standards Branch, Air Quality Management Division
Office of Air Quality Planning and Standards (MD-12)
U.S. Environmental Protection Agency
Research Triangle Park, N.c. 27711
Ms. Pamela M. Johnson, Author of Chapters IX through XI
Ambient Standards Branch, Air Quality Management Division
Office of Air Quality Planning and Standards (MD-12)
U.S. Environmental Protection Agency
Research Triangle Park, N.c. 27711
Mr. Thomas R. McCurdy, Author of Chapters IV and V and Appendix A
Ambient Standards Branch, Air Quality Management Division
Office of Air Quality Planning and Standards (MD-12)
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
Mr. Harvey M. Richmond, Author of Section VII.B.
Ambient Standards Branch, Air Quality Management Division
Office of Air Quality Planning and Standards (MD-12)
U.S. Environmental Protection Agency
Research Triangle Park, N.C. 27711
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Ill
U.S. Environmental Protection Agency
Science Advisory Board
Clean Air Scientific Advisory Committee
Subcommittee on Ozone
Chairman
Dr. Roger O. McClellan
CUT
Post Office Box 12137
Research Triangle Park, NC 27709
Members
Dr. Eileen G. Brennan
Department of Plant Pathology
Martin Hall, Room 213
Lipman Drive
Cook College-NJAES, Rutgers Univ.
P.O. Box 231
New Brunswick, New Jersey 08903
Dr. Edward D. Crandall
Division of Pulmonary Medicine
Starr Pavilion 505
Cornell Medical College
1300 York Avenue
New York, New York 10021
Dr. James D. Crapo
Box 3177
Duke University Medical Center
Durham, North Carolina 27711
Dr. Robert Frank
Professor of Environmental Health
Sciences
Johns Hopkins School of Hygiene and
Public Health
615 N. Wolfe Street
Baltimore, Maryland 21205
Prof. A. Myrick Freeman, III
Department of Economics
Bowdoin College
Brunswick, Maine 04011
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IV
Dr. Jay S. Jacobson
Plant Physiologist
Boyce Thompson Institute
Tower Road
Ithaca, New York 14853
Dr. Jane Q. Koenig
Research Associate Professor
Department of Environmental
Health SC-34
University of Washington
Seattle, Washington 98195
Dr. Timothy Larson
Environmental Engineering and
Science Program
Department of Civil Engineering
FX-10
University of Washington
Seattle, Washington 98195
Dr. Morton Lippmann, Professor
Institute of Environmental Medicine
NYU Medical Center
Tuxedo, New York 10987
Prof. M. Granger Morgan
Head, Department of Engineering
and Public Policy
Carnegie-Mellon University
Pittsburgh, Pennsylvania 15253
Dr. D. Warner North, Principal
Decision Focus, Inc.
Los Altos Office Center
Suite 200
4984 El Camino Real
Los Altos, California 94022
Dr. Gilbert S. Omenn,
Professor and Dean
School of Public Health and
Community Medicine SC-30
University of Washington
Seattle, Washington 98195
Dr. Robert D. Rowe
Energy and Resource Consultants
P.O. Drawer 0
Boulder, Colorado 80306
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Dr. Marc B. Schenker, Director
Occupational and Environmental
Health Unit
University of California
Davis, California 95616
Mr. Stephen Smallwood
Air Pollution Control Program
Manager
Bureau of Air Quality Management
Florida Department of Environmental
Regulation
Twin Towers Office Bldg.
2600 Blair Stone Road
Tallahassee, Florida 32301
Dr. George Taylor
Environmental Sciences Division
P.O. Box X
Oak Ridge National Laboratory
Oak Ridge, Tennessee 37831
Dr. Mark J. Utell
Pulmonary Unit - Box 692
Strong Memorial Hospital
Rochester, New York 14642
Dr. Jerry Wesolowski
1176 Shattuck Avenue
Berkeley, California 94704
Dr. George T. Wolff
Senior Staff Research Scientist
General Motors Research Labs
Environmental Science Department
Warren, Michigan 48090
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VI
EPA Reviewers
Mr. Allen C. Basala (MD-12)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTP, NC 27711
Mr. Frank L. Bunyard (MD-12)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTP, NC 27711
Dr. Thomas C. Curran (MD-14)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTP, NC 27711
Mr. Robert Fegley (PM-221)
Office of Policy Analysis, OPPE
U.S. EPA
Waterside Mall
401 M Street, SW
Washington, DC 20460
Mr. Lewis Felleisen
Air Programs & Engineering Branch
U.S. EPA, Region III
Curtis Building
6th & Walnut Streets
Philadelphia, PA 19106
Mr. Robert A. Flaak (A-107F)
Science Advisory Board, OA
U.S. EPA
Waterside Mall
401 M Street, SW
Washington, DC 20460
Dr. J.H.B. Garner (MD-52)
Environmental Criteria and Assessment Office, ORD
U.S. EPA
RTP, NC 27711
Mr. Gerald K. Gleason (LE-132A)
Office of General Counsel
U.S. EPA
Waterside Mall
401 M Street, SW
Washington, DC 20460
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Vll
Dr. Judith A. Graham (MD-52)
Environmental Criteria and Assessment Office, ORD
U.S. EPA
RTF, NC 27711
Dr. Lester D. Grant (MD-52)
Environmental Criteria and Assessment Office, ORD
U.S. EPA
RTF, NC 27711
Dr. Carl G. Hayes (MD-55)
Health Effects Research Laboratory, ORD
U.S. EPA
RTF, NC 27711
Dr. Donald H. Horstman (MD-58)
Health Effects Research Laboratory, ORD
U.S. EPA
RTP,-NC 27711
Mr. William F. Hunt (MD-14)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTF, NC 27711
Mr. Michael H. Jones (MD-12)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTF, NC 27711
Mr. Bruce C. Jordan (MD-12)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTF, NC 27711
Mr. Bruce Madariaga (MD-12)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTF, NC 27711
Dr. William F. McDonnell (MD-58)
Health Effects Research Laboratory, ORD
U.S. EPA
RTF, NC 27711
Mr. Thomas B. McMullen (MD-52)
Environmental Criteria and Assessment Office, ORD
U.S. EPA
RTF, NC 27711
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Vlll
Dr. Edwin L. Meyer (MD-14)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTF, NC 27711
Dr. John J. O'Neil (MD-58)
Health Effects Research Laboratory, ORD
U.S. EPA
RTP, NC 27711
Mr. Norman C. Possiel (MD-14)
Office of Air Quality Planning and Standards, OAR
U.S. EPA
RTP, NC 27711
Mr. James A. Raub (MD-52)
Environmental Criteria and Assessment Office, ORD
U.S. EPA
RTP, NC 27711
Mr. Robert Rose (ANR-443)
Office of Policy, Planning, and Evaluation
U.S. EPA
Waterside Mall
401 M Street, SW
Washington, DC 20460
Mr. Joel Scheraga (PM-221)
Office of Policy Analysis, OPPE
U.S. EPA
Waterside Mall
401 M Street, SW
Washington, DC 20460
Mr. William P. Smith (PM-223)
Office of Stds. & Regulations, OPPE
U.S. EPA
Waterside Mall
401 M Street, SW
Washington, DC 20460
Dr. Joseph Sommers
Emission Control Technology Division
Office of Mobile Sources, OAR
Ann Arbor, MI 48105
Ms. Beverly E. Tilton (MD-52)
Environmental Criteria and Assessment Office, ORD
U.S. EPA
RTP, NC 27711
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Dr. Dave T. Tingey
Environmental Research
Laboratory--Corvallis/ORD
200 S.W. 35th Street
Corvallis, OR 97333
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X
Table of Contents
Page
Acknowledgements i
Project Team for Review of the National Ambient Air
Quality Standards for Ozone ii
Clean Air Scientific Advisory Committee Subcommittee
on Ozone m
EPA Reviewers vi
Table of Contents x
List of Figures xv
List of Tables xviii
Executive Summary .' xxi
I. Purpose 1-1
II. Background II-l
III. Approach III-l
IV. Ambient Ozone Concentrations in Urban and Rural Areasi IV-1
A. Urban Areas IV-1
B. Non-MSA Areas IV-2
C. Natural Ozone Background IV-3
V. Ozone Exposure Analysis V-l
A. Overview of the Ozone NAAQS Exposure Model V-l
B. Air Quality Concentrations in Microenvironments... V-2
C. Simulation of Population Movement -. V-4
D. Study Areas Modeled in Ozone NAAQS Exposure
Model V-4
E. Exercise Modeling in Ozone NAAQS
Exposure Model V-7
F. Eight-Area Aggregated Estimates of Population
Exposure to Alternative Ozone Standards V-8
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XI
Page
G. Caveats and Limitations V-13
VI. Factors Relevant to Review of the Primary Standard(s)
for Ozone VI-1
A. Ozone Absorption and Mechanisms of Effects VI-1
B. Factors Affecting Susceptibility to Ozone VI-3
1. Age VI-4
2. Sex VI-5
3 . Smoking Status VI-6
4 . Nutritional Status VI-7
5 . Environmental Stresses VI-8
6. Exercise VI-8
C. Potentially Susceptible Groups VI-9
1. Individuals Having Preexisting Disease VI-9
2 . Exercising Individuals VI-13
n
VII. Assessment of Health Effects and Related Health Issues
Considered in Selecting Primary Standard(s) for
Ozone VII-1
A. Health Effects of Concern VII-1
1. Alterations in Pulmonary Function VII-2
2 . Symptomatic Effects VII-15
3 . Exercise Performance VII-2 0
4. Bronchial Reactivity and Inflammation Vll-22
5. Aggravation of Existing Respiratory Disease VII-24
6. Morphological Effects VII-28
7. Effects of Ozone on Host Defense Mechanisms
in Experimental Animals VII-32
8. Extrapulmonary Effects VII-35
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Xll
Page
B. Pulmonary Function and Symptom Health Risk
Assessment VII-37
I. Overview of Lung Function and Symptom
Risk Assessment VII-37
2 . Benchmark Risk Results VII-40
3 . Headcount Risk Results VII-45
4. Caveats and Limitations VII-50
C. Related Health Effects Issues VII-52
1. Adverse Respiratory Health Effects of
Acute Ozone Exposure VII-53
2. Attenuation of Acute Pulmonary Effects VII-56
3. Relationship Between Acute and Chronic
Effects VII-58
4. Effects of Other Photochemical Oxidants VII-62
•
5. Interactions with Other Pollutants VI-I-63
VIII. Staff Conclusions and Recommendations for Ozone
Primary Standard(s) VIII-1
A. Pollutant Indicator VIII-1
B. Form of the Standard VIII-4
C. Averaging Time(s) VIII-5
D. Level of the Primary Standard (s) VIII-9
E. Summary of Staff Recommendations VIII-20
IX. Factors Relevant to the Review of the Secondary
Standard for Ozone IX-1
A. Mechanisms of Action for Vegetation IX-1
1. Biochemical Response IX-2
2 . Physiological Response IX-3
B. Factors Affecting Plant Response IX-5
1. Biological Factors IX-6
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Kill
Page
a. Plant Genetics IX-6
b. Developmental Factors IX-7
c. Pathogen and Pest Interactions
with Ozone IX-7
2 . Physical Factors ix-8
3 . Chemical Factors IX-9
a. Multiple Pollutants IX-9
b. Chemical Sprays IX-ll
c. Heavy Metals IX-ll
X. Assessment of Welfare Effects and Related Welfare
Issues Considered in Selecting Secondary Standard(s)
for Ozone X-l
A. Vegetation Effects X-2
1. Types of Exposure Effects. , X-2
a. Visible Foliar Injury Effects X-3
b. Growth and Yield Effects X-6
1. Open Top Chamber Studies X-7
2. Greenhouse and Controlled
Environment Studies X-13
3. Ambient Air Exposure Studies X-14
2 . Related Vegetation Issues X-20
a. Empirical Models Used to Develop
Exposure Response Relationships X-20
b. Statistics Used to Characterize
Ozone Exposures X-21
c. Exposure and Response to
Peroxyacetyl Nitrate X-23
d. Economic Assessments of Agriculture.... X-24
B. Natural Ecosystem Effects X-26
1. Forest Ecosystems X-27
a. Effects on Plant Processes X-29
b. Effects on Growth . X-31
c. Ecosystem Responses: The San
Bernardino Study X-38
2. Interrelated Ecosystems X-40
a. Aquatic Ecosystems X-40
b. Agricultural Ecosystems X-40
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XIV
Page
C. Materials Damage X-41
1. Elastomers X-42
2. Textile Fibers and Dyes X-43
3 . Paints X-4 5
4 . Conclusion X-45
D. Effects on Personal Comfort and Well Being X-45
E. Related Welfare Effects Information and Issues... X-46
1. Air Quality Analyses X-49
2. Crop Loss Estimates X-50
3 . Averaging Times X-54
a. NCLAN/CERL Reanalysis X-54
b. New Studies X-62
4 . Forest Risk Assessment X-66
XI. Staff Conclusions and Recommendations Regarding the
Secondary Standard(s) XI-1
m
y
A. Pollutant Indicator XI-1
B. Form of the Standard and Averaging Time(s) XI-3
C. Level of Standard XI-10
D. Summary of Conclusions XI-16
Appendix A. Air Quality A-l
Appendix B. Glossary of Pulmonary Terms and Symbols B-l
Appendix C. CASAC Closure Letter C-l
References
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XV
List of Figures
VII-1 Group Mean Decrements in 1-sec Forced Expiratory
Volume During 2-hour Ozone Exposures with Different
Levels of Intermittent Exercise VII-4
Vll-2 Fraction of Heavily Exercising Population
Experiencing > 10% and > 20% Change in 1-sec
Forced Expiratory Volume Due to Various Ozone
Levels VII-ll
Vll-3 Fraction of Heavily Exercising Population
Experiencing Mild and Moderate Symptoms
Due to Various Ozone Levels VII-17
Vll-4 Fraction of Heavily Exercising Population Ex-
periencing Lower Respiratory Symptoms Due to Various
Ozone Levels VII-18
VII-5 Benchmark Risk in St. Louis for 1-sec Forced
Expiratory Volume Decrements of > 10% and
> 20%, Under Heavy Exercise, for Three
Exposure-Response Data Sets (Avol, Kulle, and
McDonnell) VII-43
VII-6 Benchmark Risk in St. Louis for Chest Discomfort
Symptoms (any and moderate/severe), under Heavy
Exercise, for Three Exposure-Response Data Sets
(Avol, Kulle, and McDonnell) VII-44
VII-7 Expected Headcount (pulmonary function)
Aggregated for Eight U.S. Urban Areas With a
Total Population of 9.3 Million (number
of heavily exercising people responding during
the ozone season) VII-47
VII-8 Expected Headcount (chest discomfort) Aggregated
for Eight U.S. Urban Areas With a Total Popula-
tion of 9.3 Million (number of heavily
exercising people responding during the ozone
season) VII-48
X-l Examples of the Effects of Ozone on the Yield of
Soybean and Wheat Cultivars X-9
X-2 Examples of the Effects of Ozone on the Yield of
Cotton, Tomato, and Turnip X-10
X-3 Eastern White Pine - Comparisons Across Expert
Judgments X-7 3
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XVI
A-l Correlations Among Short- and Long-Term Air Quality
Indicators in MSAs (Using 2nd High) A-10
A-2 Correlations Among Short- and Long-Term Air Quality
Indicators in MSAs (Using ExEx) A-12
A-3 Proportion (In Percent) of Urban Sites Exceeding
Expected Number of days with an 8-Hour Daily Maximum
Average > .08 ppm for Five 1-Hour Daily Maximum
Standards A-13
A-4 Proportion (In Percent) of Urban Sites Exceeding
Expected Number of Days with an 8-Hour Daily
Maximum Average > .06 ppm for Four 1-Hour Daily
Maximum Standards A-14
A-5 Proportion (In Percent) of Urban Areas Exceeding
Expected Number of Days with an 8-Hour Daily
Maximum Average > .10 ppm for Three 1-Hour
Daily Maximum Standards A-15
A-6 Generalized Relationships of the Current Ozone
NAAQS and Three Alternative 8-Hour Averages A-19
A-7 Cumulative Frequency Distribution of Three Peak
Air Quality Indicators A-28
A-8 Correlations Among Short-Term, Multiple-Peak,
and Longer-Term Air Quality Indicators in Non-
Urban Areas A-3 0
A-9 Proportion (In Percent) of Rural/Remote Sites
Exceeding Specified Expected Number of 8-Hour
Daily Maximum Averages > .08 ppm for Three 1-Hour
Daily Maximum Standards A-31
A-10 Proportion (In Percent) of Rural/Remote Sites
Exceeding Specified Maximum Monthly 1-Hour Daily
Maximum Values for Three 1-Hour Daily Maximum
NAAQS A-32
A-ll Proportion (In Percent) of Rural/Remote Sites
Exceeding Specified Three Month 8-Hour Averages
Daily Maximum Three Month 8-Hour Averages For
Three 1-Hour Daily Maximum NAAQS A-3 3
A-12 Proportion (In Percent) of Rural/Remote Sites
Exceeding Specified Second High 1-Hour Daily
Maximum Values for Three 8-Hour Daily Maximum
Averages > . 08 ppm Standards A-34
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XV11
Page
A-13 Proportion (In Percent) of Rural/Remote Sites
Exceeding Specified Number of Second High 1-Hour
Daily Maximum Values for Three Maximum Monthly Mean
1-Hour Daily Maximum Standards A-35
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XVI11
List of Tables
Table Title Page
V-l Study Areas Modeled in Ozone-National Exposure
Model V-5
V-2 Estimate of the Cumulative Number of Heavy
Exercisers in the 8-Area Aggregation Population
Exposed to One-Hour Average Ozone Concentration
During the Ozone Season at Heavy Exercise Under
Alternative Air Quality Scenarios V-12
V-3 Estimate of the Cumulative Number of Person-
Occurrences of Heavy Exercise in the 8-Area
Aggregation Population Exposed to One-Hour Average
Ozone During the Ozone Season at Very Heavy
Exercise Under Alternative Air Quality
Scenarios ., V-14
VI-1 Estimated Values of Oxygen Consumption and
Minute Ventilation Associated with Representative
Types of Exercise VI-10
VI-2 Prevalence of Chronic Respiratory Conditions by
Sex and Age for 1979 VI-12
VII-1 Key Human Studies Near the Current 1-Hour National
Ambient Air Quality Standard for Ozone VII-7
VII-2 Morphological Effects of Ozone in Experimental
Animals VII-29
VII-3 Effects of Ozone on Host Defense Mechanisms
in Experimental Animals VII-34
VII-4 Percent of Heavy Exercisers Responding Under
Alternative Air Quality Scenarios VII-49
VII-5 Gradation of Response for Healthy Individuals
Acutely Exposed to Ozone VII-55
IX-1 Effect of Ozone on Photosynthesis IX-4
X-l Ozone Concentrations for Short-term Exposure that
Produce 5 or 20 Percent Injury to Vegetation
Growth Under Sensitive Conditions X-4
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XIX
LIST OF TABLES (continued)
Table Title . Page
X-2 Summary of Ozone Concentrations Predicted to
Cause 10 Percent and 30 Percent Yield Losses
and Summary of Yield Losses Predicted to Occur
at 7-hour Seasonal Mean Ozone Concentrations of
0.04 and 0.06 ppm X-ll
X-3 Ozone Concentrations at Which Significant Yield
Losses Have Been Noted for a Variety of Plant
Species Exposed Under Various Experimental
Conditions X-15
X-4 Effects of Ambient Air in Open-Top Chambers,
Outdoor CSTR Chambers, or Growth and Yield of
Selected Crops X-17
X-5 Effects of Ozone on Crop Yield as Determined
by the Use of Chemical Protectants X-19
<
X-6 Continuum of Characteristic Ecosystem
Responses to Pollutant Stress X-28
X-7 Effects of Ozone Added to Filtered Air on the
Yield of Selected Tree Crops X-34
X-8 Potential Ambient Ozone Standards that would
Limit Soybean Crop Reduction to 5, 10, 15, or
20 Percent X-52
•X-9 Percentiles and Mean Predicted Relative Yield
Losses Associated with Various Levels of the Four
Exposure Indices, HDM2, M7, SUM06, and SUM07, for
the 16 NCLAN Cases X-59
X-10 Exposure Levels Associated with Predicted
Relative Yield Losses of 5 to 30% for the Four
Exposure Indices, HDM2, M7, SUM06, and SUM07,
for the 16 NCLAN Studies X-60
X-ll Forest Response Experts X-71
XI-1 U.S. Agricultural Welfare Benefits from Reducing
Rural Ambient Ozone (7-hr seasonal means) to 60,
45, and 30 ppb for Three Alternative Benefit
Measures XI-14
A-l Cumulative Frequency Descriptive Statistics
Associated with Peak and Multiple-Hour Ozone
Air Quality Indicators in Urban Areas A-5
A-2 Cumulative Frequency Descriptive Statistics
Associated with Various 8-Hour Ozone
Air Quality Indicators in Urban Areas A-7
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XX
LIST OF TABLES (continued)
Table Title Page
A-3 Cumulative Frequency Descriptive Statistics
Associated with Longer-Term Ozone Air Quality
Indicators in Urban Areas A-9
A-4 Percent of Days Exceeding the .Current Ozone NAAQS
and 3 Alternative 8-Hour Average Daily Maximum
"CutPoints" A-21
A-5 Estimated Frequency of Daily Ozone Episodes by
Length of the Episodes A-22
A-6 Descriptive Cumulative Frequency Statistics
Associated with Peak Ozone Air Quality
Indicators A-25
A-7 Descriptive Cumulative Frequency Statistics
Associated with Longer-Term Air Quality Indicators
(in ppm) A-27
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XXI
Executive Summary
This revised staff paper evaluates and interprets the
available scientific and technical information that the EPA staff
believe is most relevant to the review of primary (health) and
secondary (welfare) national ambient air quality standards
(NAAQS) for ozone (03) and presents staff recommendations on
alternative approaches to revising the standards. Periodic
review of the NAAQS is a process instituted to ensure the
scientific adequacy of air quality standards and is required by
4
section 109 of the 1977 Clean Air Act Amendments. The assessment
in this staff paper is intended to help build a bridge between
the scientific review contained in the EPA O3 criteria document
(hereafter referred to as CD) (U.S. EPA, 1986), and the CD
Supplement (hereafter referred to als CDS) (U.S. EPA, 1988)
prepared by the Environmental Criteria and Assessment Office
(ECAO) and the judgments required of the Administrator in setting
ambient standards for O3. Therefore, the staff paper is an
important element in the standards review process and provides an
opportunity for review by the Clean Air Scientific Advisory
Committee (CASAC) and the general public on proposed staff
recommendations before they are presented to the Administrator.
This staff paper has been revised based upon comments received
from CASAC and the public and upon staff analyses which are
available for public review.
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XXI1
Ozone is a trace constituent formed in the atmosphere as a
result of a series of complex chemical reactions involving both
anthropogenic and natural hydrocarbons and nitrogen oxides,
oxygen and sunlight. At ambient concentrations often measured
during warmer months, O3 can adversely affect human health,
agricultural crops, forests, ecosystems, and materials.
Interactions of O3 with nitrogen oxides and sulfur oxides may
also contribute to the formation of acidic vapors and aerosols
which might have direct effects on human health and welfare, as
well as indirect effects following their deposition on surfaces.
<
It should be noted that new evidence indicates that co-exposure
to acidic aerosols can potentiate response to O3.
Annual average background surface O3 concentrations in the
northern hemisphere generally range between 0.03 and 0.05 ppm but
are as low as 0.015 to O.o2o ppm in the tropics (U.S. EPA, 1986$
p. 3-80). Stratospheric intrusion is recognized as causing
locally high O3 levels for periods lasting from minutes to hours,
but these intrusions are usually worse in spring, fall, and
winter. In contrast, during the photochemically active summer
months intrusion is less common and less severe. Summertime
hourly O3 levels have recently been reported to be as high as
0.35 ppm in one of the nation's most heavily populated
metropolitan areas. Daily daylight seasonal averages of O3 in
some rural areas have been reported to be 0.06 ppm and higher.
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XXI11
Primary Standard
The staff reviewed scientific and technical information on
the known and potential health effects of 03 cited in the CD and
the CDS. The information includes studies of respiratory tract
absorption and deposition of O3, studies of mechanisms of O3
toxicity, and controlled human exposure, field, epidemiological
and animal toxicology studies of effects of exposure to O3 as
well as air quality information. On the basis of this review,
the staff derives the following conclusions.
1) Inhaled O3 may pose health risks as a result of (a)
penetration of 03 into various regions of the
respiratory tract and absorption of O3 in this tract
(b) provocation of pulmonary response resulting from
chemical interactions of O3 along the respiratory
tract, and (c) extrapulmonary effects caused indirectly
by reaction of O3 in the lungs.
2} The risks of adverse effects associated with absorption
of 03 in the tracheobronchial and alveolar regions of
the respiratory tract are much greater than for
absorption in the extrathoracic region (head).
Increased exercise levels are generally associated with
higher ventilation rates and increased oronasal or oral
(mouth) breathing. Greater 03 penetration and exposure
of sensitive lung tissue occurs when individuals are
heavily exercising.
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XXIV
3) Factors which have been demonstrated to affect
susceptibility to O3 exposure are activity level and
environmental stress (e.g., humidity, high
temperature). Those factors which either have not been
adequately tested or remain uncertain include age, sex,
preexisting disease, nutrition, and smoking status.
4) Major subgroups of the population that may be at
greater risk to the effects of O3 include: (a) any
individual exercising heavily during exposure to O3,
particularly those who are otherwise healthy
individuals who may experience significantly greater
than group mean lung function response to O3 exposure,
and (b) individuals with preexisting respiratory
disease (e.g., asthmatics and persons with allergies).
The data base identifying exercising individuals as
being at greater risk to O3 exposure is much stronger
and more quantitative than that for individuals with
preexisting respiratory disease. This is due to the
large number of clinical studies investigating effects
of 03 on exercising persons.
5) The major effects categories of concern associated with
exposures to O3 include:
(a) alterations in pulmonary function
(b) symptomatic effects (e.g., cough, throat
irritation)
(c) effects on work or athletic performance
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(d) aggravation of preexisting respiratory disease
(e) morphological effects (lung structure damage)
(f) altered host defense systems (e.g., increased
susceptibility to respiratory infection)
(g) extrapulmonary effects (e.g., effects on blood
enzymes, central nervous system, liver, endocrine
system).
6) An important source of applicable exposure-response
information for a short-term standard is controlled
human exposure and field studies, which provide
concentration-response relationships between
alterations in pulmonary function and O3 exposure
concentrations. Other important sources of information
for standard setting are epidemiological and
toxicological studies. Epidemiology has provided
associations between ambient 03 exposures and lung
function decrements and aggravation of existing
respiratory disease, but with greater uncertainties
about the exposures involved than with controlled human
exposure and field studies. Animal toxicology data
provide acute and chronic exposure effects information
on increased susceptibility to respiratory infection,
lung structure damage, and extrapulmonary effects.
Although human exposure, epidemiology, and animal
toxicology studies all have limitations in assessing
adverse effects and risk, it is the weight of evidence
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and integration of findings from all three disciplines which
should be used in assessing health effects associated with
exposure to O3.
Based on scientific and technical reviews, CASAC comments,
and policy considerations, the staff makes the following
recommendations with respect to primary O3 standards:
1) Ozone should remain as the surrogate for controlling
ambient concentrations of photochemical oxidants.
2) The existing form of the standard should be retained
(i.e., that the NAAQS is attained when the expected
number of days per calendar year with maximum 1-hour
average concentrations above the level of the standard
is equal to or less than one).
3) The 1-hr averaging time of the standard should be
retained. t
4) The range of 1-hour average O3 levels of concern for
standard-setting purposes is 0.08 to 0.12 ppm in
concordance with CASAC comments (CASAC, 1986, 1987,
1988) comments. This range is based solely on 1-2 hour
exposure data.
5) Because, there is a good health effects data base
available on 1-2 hour exposures, the staff concurs with
the CASAC conclusion (McClellan, 1989) that review of
the scientific basis for the 1-hr 03 primary standard
be closed out. With this portion of the review
complete, and after considering CASAC's views on all
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issues, the Administrator will be in a position to make
a regulatory decision on how and when to best act on
the 1-hour standard.
6) In response to suggestions made by CASAC (1986, 1987,
1988), staff investigated the potential need and basis
for a longer-term (6-8 hour) primary standard.
Although an emerging data base reporting significant
lung function decrements and symptoms in subjects
exposed to O3 for 6 to 8 hours has provided some
evidence of effects below 0.12 ppm O3, staff concurs
with CASAC's conclusion that ". . . such information
can better be considered in the next review of the
ozone standards." (McClellan, 1989). It is recommended
that EPA continue review of scientific information on
health effects of prolonged exposure to O3. Once these
studies have been moire completely evaluated during the
next CD review, the Administrator will be able to
assess the need for development of a longer-term O3
primary standard.
7) Further review and analysis also will be necessary
before fully assessing the need for a separate standard
to protect against chronic effects of O3. Data on
nasopharyngeal removal, dosimetry modeling and health
effects based on and chronic exposure of animals will
be used for future animal extrapolation and risk
assessment of chronic O3 exposures.
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Secondary Standard
The staff has reviewed the scientific and technical
information on the known and potential welfare effects of O3
cited in the CD and the CDS. This information includes impacts
on vegetation, natural ecosystems, materials, and symptomatic
effects on humans. Based on this review, the staff derives the
following conclusions:
1) The mechanisms by which O3 may injure plants and plant
communities include (a) absorption of O3 into leaf
through stomata, followed by diffusion through the cell
wall and membrane, (b) alteration of cell structure and
function as well as critical plant processes, resulting
from the chemical interaction of O3 with cellular
components, and (c) occurrence of secondary effects
including reduced photosynthesis and growth and yield
and altered carbon allocation.
2) The magnitude of the O3-induced effects depends upon
the physical and chemical environment of the plant, as
well as on various biological factors (including
genetic potential, developmental age of plant, and
interaction with plant pests).
3) The weight of the recent evidence seems to suggest that
long-term averages, such as the 7-hour seasonal mean,
may not be adequate indicators for relating 03 exposure
and plant response.
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4) Repeated peak concentrations are the most critical
element in determining plant response. Exposure
indicators which emphasize peak concentrations and
accumulate concentrations over time probably provide
the best biological basis for standard setting (See
staff paper, p. X-50).
5) There is currently a lack of exposure-response
information on forest tree effects. In addition, there
is a broad range of uncertainty among scientists
regarding 03 effects on forest trees. Consequently
there is no consensus on the most important averaging
time for perennials or on the precise role of O3 vs.
other pollutants in causing forest decline. Therefore,
the staff concludes that a separate secondary standard
based on protection of forest trees is not warranted at
this time.
6) There appears to be no threshold level below which
materials damage will not occur; exposure of sensitive
materials to any non-zero concentration of O3
(including natural background levels) can produce
effects if the exposure duration is sufficiently long.
However, the slight acceleration of aging processes of
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XXX
materials which occurs at the level of the NAAQS is not
judged to be significant or adverse. Consequently, the
staff concludes that materials data should not be used
as a basis for adequately defining an averaging time or
concentration level for the secondary standard and that
the secondary standard should be based on protection of
vegetation.
7) Effects on personal comfort and well-being, as defined
by human symptomatic effects, have been observed in
clinical studies at O3 levels in the range of 0.12-0.16
for 1-2 hour exposures and at somewhat lower levels in
extended exposure clinical and epidemiological studies.
CASAC recommended that these effects be considered
health effects in developing a basis for the. primary
standard for 03.
Based on scientific and technical reviews, CASAC comments,
and policy considerations, the staff makes the following
recommendations with respect to secondary standards:
1) In consideration of the large base of welfare
information attributing effects to 03 exposure and the
limited evidence which demonstrates welfare effects
from exposure to ambient levels of non-03 photochemical
•oxidants, there appears to be little evidence to
suggest a change in chemical designation from O3 to
photochemical oxidants.
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2) Given the lack of effects data on forests and the
preliminary nature of the Lee et al. (1988c) results
regarding selection of the appropriate exposure
statistic for crops, the EPA staff concludes that it
may be premature at this point in time to change the
form of the standard and the averaging time. It is our
judgment that a 1-hr averaging time standard in the
range of 0.06-0.12 ppm represents the best staff
recommendation that could be made to the Administrator
at this time to close out the review of the screritific
data. This is consistent with CASAC comments (CASAC,
1987, 1988) urging EPA to consider a 1-hr averaging
time and to act on the existing state of science rather
than extend the review until a more exhaustive
assessment is made of alternative averaging times.
With this portion of the review complete, and after
considering CASAC's .views on all issues, the
Administrator will be in a position to make a
regulatory decision on how and when to best act on the
1-hr standard.
Alternatively, EPA could continue the standard review until
the information on alternative exposure indicators has matured.
Additional time for review and revision of Lee et al.•(1988c)
would allow the scientific community the opportunity to review
the alternative indicators and move toward a consensus regarding
selection of the most appropriate exposure indicator. The
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liability of this alternative is that it postpones action on the
secondary standard and thus fails to utilize new and existing
information to assess the most appropriate exposure statistic or
the protection afforded by the current 1-hr standard.
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X- 1
x- Assessment of Welfare Effects and Related Welfare Issues
Considered in Selecting Secondary Standardfs) for Ozone
Of the phytotoxic compounds commonly found in the ambient
air, 03 is the most prevalent, impairing crop production and
injuring native vegetation and ecosystems more than any other air
pollutant (Heck et al., 1980). Some of the effects of O3
reported in the literature occur at O3 levels at or below natural
background concentrations in many areas of the country (see
Section IV. for further discussion of background values). Ozone
has also been shown to damage elastomers, textile fibers and dyes
and certain types of paints. Other photochemical oxidants of
importance to effects on vegetation, ecosystems and materials are
nitrogen dioxide (NO2) and peroxyacetyl nitrates. Air Quality
Criteria for Oxides of Nitrogen (U.S. EPA, 1982) and Review of
the NAAQS for NO2: Assessment of Scientific and Technical
Information (U.S. EPA, 1984) previously assessed the phytoxicity
of NO2, and thus NO2 will not be discussed in this staff paper.
In addition, while at a given dose the peroxyacetyl nitrates are
more phytotoxic than 03 (p. X-22), they generally occur at
significantly lower ambient concentrations. Because phytotoxic
concentrations of peroxyacetyl nitrates are less widely
distributed than those of 03 (CD, p. 6-1), the focus of this
staff paper will be on the effects of 03.
The objective of this section of the staff paper is to
assess the current basis for the 63 secondary NAAQS as contained
in Chapters 6, 7 and 8 of the CD. In addition, the section will
summarize new analyses that address key issues of concern for the
secondary standard: relationships of various air quality
indicators, crop loss estimates, averaging times and forest
response to O3. Key new studies that relate to the issue of
averaging time(s) will also be discussed to determine whether new
effects information suggests any change in existing secondary
NAAQS for O3.
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