&EPA
United States
Environmental Protection
Agency
Office of Air and Radiation
Washington D.C. 20460
Assessing the Risks of
Trace Gases That Can
Modify the Stratosphere
EPA 400/1-87/001B
December 1987
Volume II:
Chapters 1 - 5
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Assessing The Risks of Trace Gases
That Can Modify The Stratosphere
Volume II: Chapters 1-5
Senior Editor and Author: John S. Hoffman
Office of Air and Radiation
U.S. Environmental Protection Agency
Washington, D.C. 20460
December 1987
U.S. Environmental Protection Agency
P. -ron 5, Library (5PL-1G)
?•• ! . B:.irborn St-eet, Room ItiYO
CI;i .3^0, 1L 60604
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ACKNOWLEDGEMENTS
Many people made this document possible.
A Science Advisory Board (SAB) panel chaired by Dr. Margaret Kripke and co-
chaired by Dr. Warner North conducted an extensive and constructive review of
this document. Members of the panel provided important insights and assistance
in the assessments development. Members of the panel are:
Dr. Martyn Caldwell (Utah State University)
Dr. Leo T. Chylack, Jr. (Center for Clinical Cataract Research)
Dr. Nien Dak Sze (A.E.R., Inc.)
Dr. Robert Dean
Dr. Thomas Fitzpatrick (Massachusetts General Hospital)
Dr. James Friend (Drexel University)
Dr. Donald Hunten (University of Arizona)
Dr. Warren Johnson (National Center for Atmospheric Research)
Dr. Margaret Kripke (Anderson Hospital and Tumor Institute)
Dr. Lester Lave (Carnegie-Melon University)
Dr. Irving Mintzer (World Resources Institute)
Dr. Warner North (Decision Focus, Inc.)
Dr. Robert Watson (National Aeronautics and Space Administration)
Dr. Charles Yentsch (Bigelow Laboratory)
Dr. Terry F. Yosie (U.S. Environmental Protection Agency)
The panel's contribution to the process of protecting stratospheric ozone has
been critical. We also want to thank Terry Yosie, Director of the Science
Advisory Board, for setting up and helping to run the panels, and Joanna
Foellmer for helping to organize meetings.
Other scientists and analysts, too numerous to name, provided reviews of
early drafts of the chapters.
Production assistance, including editing, typing, and graphics, was
provided by the staff of ICF Incorporated, including:
Bonita Bailey
Susan MacMillan
Mary O'Connor
Maria Tikoff of the U.S. Environmental Protection Agency, coordinated
logistical parts of this document.
The cover photograph was supplied by the National Aeronautics and Space
Administration.
Technical support documents (Volumes VI, VII, and VIII) have been published
along with the first five volumes of the Risk Assessment. These documents are
not part of the official Risk Assessment, and have not been reviewed by the
SAB. Their publication is simply to assist readers who wish more background
than available in the Risk Assessment.
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List of Contributors
Michael J. Gibbs
IGF Incorporated,
9300 Lee Highway,
Fairfax, VA 22031
Brian Hicks
IGF Incorporated,
9300 Lee Highway,
Fairfax, VA 22031
John B. Wells
The Bruce Company,
Suite 410, 3701 Massachusetts Ave., N.W.,
Washington, DC 20016
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TABLE OF CONTENTS
PAGE
VOLUME I
ACKNOWLEDGMENTS i
ORGANIZATION ES-1
INTRODUCTION ES-2
SUMMARY FINDINGS ES-5
CHANGES IN ATMOSPHERIC COMPOSITION ES-15
POTENTIAL CHANGES IN OZONE AND CLIMATE ES-23
HUMAN HEALTH, WELFARE, AND ENVIRONMENTAL EFFECTS ES-32
QUANTITATIVE ASSESSMENT OF RISKS WITH INTEGRATED MODEL ES-54
VOLUME II
ACKNOWLEDGEMENTS i
INTRODUCTION 1
The Rise of Concern About Stratospheric Change 1
Concern About Public Health and Welfare Effects of Global
Atmospheric Change 1
Need for Assessments 2
1. GOALS AND APPROACH OF THIS RISK ASSESSMENT 1-1
Analytic Framework 1-1
Supporting Documents and Analysis for this Review 1-2
Chapter Outlines 1-2
2. STRATOSPHERIC PERTURBANTS: PAST CHANGES IN CONCENTRATIONS
AND FACTORS THAT DETERMINE CONCENTRATIONS 2-1
Summary 2-1
Findings 2-3
Measured Increases in Tropospheric Concentrations of
Potential Ozone Depleters 2-4
Measured Increases in Tropospheric Concentrations of
Potential Ozone Increasers 2-13
Factors that Influence Trace Gas Lifetimes 2-21
Long-Lived Trace Gases 2-22
Trace Gases with Shorter Lifetimes 2-26
Carbon Dioxide and the Carbon Cycle 2-26
Source Gases for Stratospheric Sulfate Aerosol (OCS, CS2) 2-26
Appendix A: CFG Emissions-Concentrations Model 2-28
References 2-30
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TABLE OF CONTENTS
(Continued)
PAGE
3. EMISSIONS OF INDUSTRIALLY PRODUCED POTENTIAL OZONE MODIFIERS 3-1
Summary 3-1
Findings 3-3
Introduction 3-6
Chlorofluorocarbons 3-6
Chlorocarbons 3-58
Halons 3-59
References 3-66
Appendix A: Chemical Use Estimate Made Available
Since Publication of the Risk Assessment A-l
Appendix A: References A-10
4. FUTURE EMISSIONS AND CONCENTRATIONS OF TRACE GASES WITH
PARTLY BIOGENIC SOURCES 4-1
Summary 4-1
Findings 4-2
The Influence of Trace Gases on the Stratosphere and
Troposphere 4-4
Trace Gas Scenarios 4-4
Effects of Possible Future Limits on Global Warming 4-23
Conclusion 4-23
References 4-25
5. ASSESSMENT OF THE RISK OF OZONE MODIFICATION 5-1
Summary 5-1
Findings 5-3
Introduction 5-6
Equilibrium Predictions for Two-Dimensional Models 5-18
Time Dependent Predictions for One-Dimensional
Models for Different Scenarios of Trace Gases 5-32
Time Dependent Predictions for Two-Dimensional Models
with Different Scenarios of Trace Gases 5-40
Models Fail to Represent All Processes That Govern
Stratospheric Change in a Complete and Accurate Manner 5-61
The Implications of Ozone Monitoring for Assessing Risks
of Ozone Modification 5-80
References 5-104
VOLUME III
6. CLIMATE 6-1
Summary 6-1
Findings 6-2
The Greenhouse Theory 6-7
Radiative Forcing by Increases in Greenhouse Gases 6-8
Ultimate Temperature Sensitivity 6-15
The Timing of Global Warming 6-18
Regional Changes in Climate Due to Global Warming 6-22
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TABLE OF CONTENTS
(Continued)
PAGE
Effects on the Stratosphere of Possible Control of Greenhouse
Gases 6-26
Attachment A: Description of Model to be Used in Integrating
Chapter 6-28
Attachment B: Trace Gas Scenarios 6-32
References 6-33
7. NONMELANOMA SKIN TUMORS 7-1
Summary 7-1
Findings 7-2
Background on Solar Radiation and the Concept of Dose 7-5
Introduction 7-5
Biology of Nonmelanoma Skin Tumors: Links to UV-B 7-11
Epidemiological Evidence 7-27
Dose-Response Relationships 7-40
Attachment A 7-49
References 7-58
8. CUTANEOUS MALIGNANT MELANOMA 8-1
Summary 8-1
Findings 8-3
Introduction 8-7
Epidemiologic Evidence 8-11
Experimental Evidence 8-28
Dose-Response Relationships 8-29
References 8-41
9. UVR-INDUCED IMMUNOSUPPRESSION: CHARACTERISTICS AND POTENTIAL
IMPACTS 9-1
Summary 9-1
Findings 9-3
Introduction 9-5
Basic Concepts in Immunology 9-5
Salt: Skin-Associated Lymphoid Tissues 9-7
Effects of Ultraviolet Radiation on Immunological Reactions 9-8
Human Studies 9-14
Effects of Ultraviolet Radiation on Infectious Diseases 9-15
References 9-18
10. CATARACTS AND OTHER EYE DISORDERS 10-1
Summary 10-1
Findings 10-2
Cataracts 10-3
Potential Changes in Senile Cataract Prevalence for
Changes in UV-B 10-29
Other Eye Disorders 10-33
References 10-37
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TABLE OF CONTENTS
(Continued)
PAGE
11. RISKS TO CROPS AND TERRESTRIAL ECOSYSTEMS FROM ENHANCED
UV-B RADIATION 11-1
Summary 11-1
Findings 11-2
Introduction 11-5
Issues and Uncertainties in Assessing the Effects
of UV-B Radiation on Plants 11-5
Issues Concerning UV Dose and Current Action Spectra
for UV-B Impact Assessment 11-5
Issues Concerning Natural Plant Adaptations to UV Radiation 11-7
Issues Associated with the Extrapolation of Data from
Controlled Environments to the Field 11-10
Uncertainties in Our Current Knowledge of UV-B Effects on
Terrestrial Ecosystems and Plant Growth Forms 11-11
Uncertainties with the Ability to Extrapolate Knowledge to Higher
Ambient C02 Environment and Other Atmospheric Pollutants 11-13
Risks to Crop Yield Resulting from an Increase in
Solar UV-B Radiation 11-15
Risks to Yield Due to a Decrease in Quality 11-20
Risks to Yield Due to Possible Increases in
Disease or Pest Attack 11-20
Risks to -Yield Due to Competition with Other Plants 11-22
Risks to Yield Due to Changes in Pollination and Flowering 11-23
References 11-25
12. AN ASSESSMENT OF THE EFFECTS OF ULTRAVIOLET-B
RADIATION ON AQUATIC ORGANISMS 12-1
Summary 12-1
Findings 12-2
Introduction 12-4
Background on Marine Organisms and Solar Ultraviolet
Radiation 12-4
Effects of UV-B Radiation in Phytoplankton 12-9
Effects on Invertebrate Zooplankton 12-11
Effects on Ichthyoplankton (Fisheries) 12-23
Conclusions 12-28
References 12-29
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TABLE OF CONTENTS
(Continued)
PAGE
13. EFFECTS OF UV-B ON POLYMERS 13-1
Summary 13-1
Findings 13-2
Photodegradation of Polymers 13-4
Polymers in Outdoor Uses and the Potential for Degradation 13-7
Damage Functions and Response to Damage 13-16
Effect of Temperature and Humidity on Photodegradation 13-29
Future Research 13-31
References 13-32
14. POTENTIAL EFFECTS OF STRATOSPHERIC OZONE DEPLETION ON
TROPOSPHERIC OZONE 14-1
Summary 14-1
Findings 14-2
Introduction 14-3
Potential Effects of Ultraviolet Radiation and Increased
Temperatures on Urban Smog 14-5
Conclusions and Future Research Directions 14-9
References 14-14
15. CAUSES AND EFFECTS OF SEA LEVEL RISE 15-1
Summary 15-1
Findings 15-2
Causes of Sea Level Rise 15-5
Effects of Sea Level Rise 15-15
Conclusion 15-32
Notes 15-33
References 15-34
16. POTENTIAL EFFECTS OF FUTURE CLIMATE CHANGES ON FORESTS
AND VEGETATION, AGRICULTURE, WATER RESOURCES
AND HUMAN HEALTH 16-1
Summary 16-1
Findings 16-5
References 16-10
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TABLE OF CONTENTS
(Continued)
PAGE
17. MODELS FOR INTEGRATING THE ANALYSES OF HEALTH AND
ENVIRONMENTAL RISKS ASSOCIATED WITH OZONE MODIFICATION 17-1
Summary 17-1
Introduction 17-2
The Model as a Framework 17-2
Analysis Procedure 17-4
Model Limitations 17-9
References 17-11
Appendix A: Model Design and Model Flow A-l
Appendix B: Scenarios of Chemical Production, Population,
and GNP B-l
Appendix C: Evaluation of Policy Alternatives C-l
Appendix D: Emissions of Potential Ozone-Depleting Compounds D-l
Appendix E: Atmospheric Science Module E-l
Appendix F: Health and Environmental Impacts of Ozone
Depletion F-l
18. HUMAN HELATH AND ENVIRONMENTAL EFFECTS 18-1
Summary 18 -1
Findings 18-2
Introduction 18-6
Methods for Estimating Health and Environmental Risks 18-11
Description of Range of Production, Emissions, and Concentrations
Scenarios for Evaluating Risks 18-12
Sensitivity of Health and Environmental Effects to Differences
in Emissions of Ozone Depleters 18-18
Sensitivity of Results to Alternative Atmospheric Assumptions 18-23
Sensitivity of Effects to Uncertainty in Dose Response 18-54
Relative Importance of Key Uncertainties 18-61
Summary 18-62
References 18-65
VOLUME IV
Appendix A
Ultraviolet Radiation and Melanoma
VOLUME V
Appendix B
Potential Effects of Future Climate Changes on Forests and
Vegetation, Agriculture, Water Resources, and Human Health
VOLUME VI
Technical Support Documents
Appendix C
Projecting Production of Ozone Depleting Substances
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TABLE OF CONTENTS
(Continued)
VOLUME VII
Technical Support Document
Appendix D
Scientific Papers
VOLUME VIII
Technical Support Document
Appendix E
Current Risks and Uncertainties of Stratospheric Ozone Depletion
Upon Plants
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LIST OF EXHIBITS
Page
1-1 Relationships Among the Chapters 1-3
2-1 Measured Increases in Tropospheric Concentrations
of CFC-11 (CFC-13) 2-5
2-2 Measured Increases in Tropospheric Concentrations
of CFC-12 (CF2CL2) 2-6
2-3 Measured Increases in Tropospheric Concentrations
of HCFC-22 (CHC1F2) 2-7
2-4 Measured Increases in Tropospheric Concentrations
of CFC-113 (C2CL3F3) 2-7
2-5 Measured Increased in Tropospheric Concentrations
of Carbon Tetrachloride (CC14) 2-9
2-6 Measured Increases in Tropospheric Concentrations
of Methyl Chloroform (CH3CC13) 2-10
2-7 Measured Increases in Tropospheric Concentrations
of Halon-1211 (CF2ClBr) 2-11
2-8 Measured Increases in Tropospheric Concentrations
of Nitrous Oxide (N20) 2-12
2-9 Measured Increases in Tropospheric Concentrations
of Nitrous Oxide (N20) 2-14
2-10 Ice Core Measurements of Historical Nitrous Oxide
(N20) Concentrations 2-15
2-11 Measured Increases in Tropospheric Concentrations
of Carbon Dioxide (C02) 2-16
2-12 Ice Core Measurements of Historical Carbon Dioxide
(C02) Concentrations 2-17
2-13 Measured Increases in Tropospheric Concentrations
of Methane (CH4) 2-19
2-14 Ice Core Measurements of Historical Methane (CH4)
Concentrations 2-20
2-15a CFC-12: Constant Emissions 2-23
2-15b CFC-12: Atmospheric Concentrations 2-23
2-16a CFC-12: Emissions 2-24
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LIST OF EXHIBITS
(Continued)
Page
2-16b CFC-12: Atmospheric Concentrations 2-24
2-17 CFC-12: Atmospheric Concentrations from Different
Emission Trajectories 2-25
A-l Concentrations of Fluorocarbons 2-29
A-2 Locations of Stations 2-29
3-1 Selected Properties of CFCS 3-8
3-2 CFC Characteristics and Substitutes 3-10
3-3 Companies Reporting Data to CMA 3-11
3-4 Production of CFC-11 and CFC-12 Reported to CMA 3-13
3-5 Historical Production of CFC-11 and CFC-12 3-15
3-6 CFC-11 and CFC-12 Used in Aerosol and Nonaerosol
Applications in the EEC 3-16
3-7 Comparison of Estimated CFC-11 Use: 1985 3-18
3-8 Comparison of Estimated CFC-12 Use: 1985 3-19
3-9 Estimates of Production and Emissions of CFC-11
and CFC-12 3-21
3-10 Published Estimates of U.S.S.R. Production of CFC-11
and CFC-12 3-22
3-11 Historical Production of CFC-11 and CFC-12 in the U.S 3-24
3-12 EEC Production and Sales Data 3-25
3-13 The Bottom Up Approach 3-27
3-14 Range of Population and GNP Per Capita Projections 3-30
3-15 Summary of Demand Projection Estimates 3-32
3-16 Summary of Demand Projection Estimates
(Average annual rate of growth in percent) 3-34
3-17 Long Term Projections CFC-11 and CFC-12
World Production (2000-2050) 3-35
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LIST OF EXHIBITS
(Continued)
Page
3-18 Bevington's Projections for Use of CFCs in the EEC 3-38
3-19 Camm Projections of World Use 3-40
3-20 Summary, of EFCTC Projections 3-42
3-21 Global Population and GNP Scenarios Used in
Gibbs' Analysis 3-43
3-22 Gibbs Scenarios of World CFG Use 3-45
3-23 Hammitt Projections of World CFC Use 3-47
3-24 Summary of Hedenstrom Projections for Sweden 3-49
3-25 Knollys Projections 3-51
3-26 Summary of Kurosawa Projections for Japan 3-53
3-27 Nordhaus Scenarios of World Nonaerosol CFC Consumption .... 3-55
3-28 Summary of Sheffield Projections for Canada 3-57
(1984-2005)
3-29 Global Halon Projections for Quinn 3-62
3-30 Hammitt and Camm Global Halon Projections 3-64
A-la Global Annual Production in Millions of Kilograms A-4
A-lb U.S. Annual Production in Millions of Kilograms A-4
A-2 Assumptions for lEc Halon Projections A-5
A-3 lEc Projections of Sales and Emissions for Halon-1301
and Halon-1211 A-6
A-4 Global Halon-1301 and Halon-1211 Growth Rates A-7
A-5 Dupont Estimates of CFC per Capita Use A-8
4-1 Effects of Changes in Composition of Atmosphere 4-5
4-2 Historical Carbon Dioxide Emissions from Fossil Fuels
and Cement 4-7
4-3 A Schematic of the Carbon Cycle 4-8
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LIST OF EXHIBITS
(Continued)
Page
4-4 Projected Carbon Dioxide Emissions and Doubling
Time of Concentrations 4-10
12
4-5 Estimated CH4 Emission Sources (10 grams per year) 4-12
4-6 Two Ways That CH4 Concentrations Could Have Changed 4-14
4-7 Possible Changes in CH4 Sources and in
Emission Factors 4-15
4-8 Current Sources and Sinks of Carbon Monoxide
(1984 concentration of CO: 30-200 ppb) 4-17
4-9 Scenarios of Carbon Monoxide (CO) Emissions from
Combustion 4-18
4-10 Preliminary Scenario of Future Growth in N20
Emissions by Source 4-21
4-11 Projected Nitrous Oxide (N20) Concentrations 4-22
4-12 Summary of Standard Scenarios Proposed for Assessment 4-24
5-1 Temperature Profile and Ozone Distribution in the
Atmosphere 5-7
5-2 Steady-State Scenarios Used in International Assessment ... 5-10
5-3 Change in Total Ozone from Representative One-Dimensional
Models for Steady-State Scenarios Containing Clx
Perturbations 5-12
5-4 Change in Total Ozone at 40 Kilometers for Steady-State
Scenarios Containing Clx Perturbations 5-13
5-5 Change in Total Ozone for Steady-State Scenarios 5-14
5-6 Effect of Stratospheric Nitrogen (NOy) on Chlorine-Induced
Ozone Depletion 5-15
5-7 Effect of Doubled C02 Concentrations on Ozone
Temperature 5-16
5-8 Calculated Changes in Ozone Versus Altitude 5-17
5-9 Two-Dimensional Model Scenarios Used in International
Assessment 5-19
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LIST OF EXHIBITS
(Continued)
Page
5-10 2-Dimensional Model Results: Globally and Seasonally-
Averaged Ozone Depletion 5-20
5-11 Ozone Depletion by Latitude, Altitude, and Season for Clx
Increase of 6.8 ppbv (MPIC 2-D Model) 5-21
5-12 Ozone Depletion by Latitude, Altitude, and Month for Clx
Increase of 6.8 ppbv (AER 2-D Model) 5-22
5-13 Ozone Depletion by Latitude, Altitude, and Month for Clx
Increase of 14.2 ppbv (AER 2-D Model) 5-23
5-14 Ozone Depletion of Latitude, Altitude, and Month for Clx
Increase of 6.8 ppbv (GS 2-D Model) 5-24
5-15 Ozone Depletion by Latitude and Season for Clx Increase
of 6.0 ppbv (IS 2-D Model) (AER 2-D Model) 5-25
5-16 Change in Ozone by Latitude and Season for Clx
Perturbations (MPIC 2-D Model) 5-26
5-17 Change in Ozone by Latitude and Season for Clx
Perturbations (AER 2-D Model) 5-27
5-18 Latitudinal Dependence of AER and MPIC 2-D Models 5-28
5-19 Change in Ozone by Latitude, Altitude, and Month for
Coupled Perturbations (GS 2-D Model) 5-29
5-20 Changes in Ozone by Latitude, Altitude, and Season for
Coupled Perturbations (MPIC 2-D Model) 5-30
5-21 Changes in Ozone by Latitude and Altitude in Winter for
Coupled Perturbations (MPIC 2-D Model) 5-31
5-22 Models With Reported Time Dependent Runs 5-33
5-23 LLNL 1-D Model Versus Parameterization Fit 5-34
5-24 Trace Gas Assumptions for Results in Exhibit 5-25
(Brasseur and DeRudder 1-D Model, 1986) 5-35
5-25 Time-Dependent Change in Ozone for CFG Growth and Coupled
Perturbations (Brasseur and DeRudder 1-D Model) 5-36
5-26 Time-Dependent Change in Ozone for Constant CFG Emissions
and Growth in Other Trace Gases (Brasseur and DeRudder
1-D Model) 5-37
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LIST OF EXHIBITS
(Continued)
Page
5-27 Sensitivity of 1-D Models to Representation of Radiative
Processes (Brasseur and DeRudder 1-D Model) 5-38
5-28 Model Comparison: Time-Dependent Change in Ozone for CFC
Growth and Coupled Perturbations 5-39
5-29 Trace Gas Assumptions for Results in Exhibit 5-30
(AER 1-D Model, 1986) 5-41
5-30 Time-Dependent Change in Ozone for Various Scenarios of
Coupled Perturbations (AER 1-D Model) 5-42
5-31 Trace Gas Scenarios Tested in LLNL 1-D Model 5-43
5-32 Time-Dependent, Globally Averaged Change in Ozone for
Coupled Perturbations (LLNL 1-D Model) "Reference Case" ... 5-45
5-33 Time Dependent, Globally Averaged Change in Ozone for
Coupled Perturbations (LLNL 1-D Model) 5-46
5-34 Effect of Potential Greenhouse Gas Controls on Ozone
Depletion (Results from 1-D Parameterization) 5-47
5-35 Calculated Ozone Depletion for 1970 to 1980 Versus
Umkehr Measurements 5-49
5-36 Time-Dependent Globally and Seasonally Averaged Changes
in Ozone for Coupled Perturbations (IS 2-D Model) 5-50
5-37 Time-Dependent Globally and Seasonally Averaged Changes
in Ozone for Coupled Perturbations (IS 2-D Model) 5-51
5-38 Time-Dependent Seasonally Averaged Change in Ozone for
1980 CFC Emissions and Coupled Perturbations (IS 2-D
Model) 5-52
5-39 Time-Dependent Seasonally Averaged Change in Ozone for
1.2% Growth in CFC Emissions and Coupled Perturbations
(IS 2-D Model) 5-53
5-40 Time-Dependent Seasonally Averaged Change in Ozone for
3% Growth in CFC Emissions and Coupled Perturbations
(IS 2-D Model) 5-54
5-41 Time-Dependent Seasonally Averaged Change in Ozone for
3.8% Growth in CFC Emissions and Coupled Perturbations
(IS 2-D Model) 5-55
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LIST OF EXHIBITS
(Continued)
Page
5-42 Temperature Feedback Experiment: Time-Dependent, Globally
and Seasonally Averaged Change in Ozone for 3% Growth in
CFC Emissions and Coupled Perturbations (IS 2-D Model) 5-57
5-43a Two-Dimensional, Time-Dependent Simulation for Constant
CFC Emissions (AER 2-D Model) 5-58
5-43b Two-Dimensional, Time-Dependent Simulation for CFC Growth
of 62 Percent Per Year (AER 2-D Model) 5-59
5-44 Model Comparison for Coupled Perturbations Scenario 5-60
5-45 Calcualted Ozone -- Column Change to Steady-State for Two
Standard Assumed Perturbations 5-63
5-46 Latitudinal Gradients in Odd Nitrogen: Models vs
Measurements 5-65
5-47 Logical Flow Diagram for Monte Carlo Calculations 5-67
5-48 Histogram of Measurements for a Rate Constant 5-68
5-49 Recommended Rate Constants and Uncertainties Used in
Monte Carlo Analyses 5-70
5-50 Monte Carlo Results: Change in Ozone Versus Fluorocarbon
Flux 5-71
5-51 Monte Carlo Results: Change in Ozone Versus Fluorocarbon
Flux 5-72
5-52 Monte Carlo Results: Ozone Depletion for Coupled
Pertubations 5-73
5-53 A Monte Carlo Distribution of Column Ozone Changes
for Changes in CFC Production 5-74
5-54 Monte Carlo Results: Changes in Ozone by Altitude 5-76
5-55 Monte Carlo Results: Changes in Ozone by Column and
Altitude, Unscreen Data 5-77
5-56 Monte Carlo Analysis With the LLNL 1-D Model 5-78
5-57 Monte Carlo Results: Changes in Ozone by Altitude 5-79
5-58 Ozone Trend Estimates by Latitude 5-83
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LIST OF EXHIBITS
(Continued)
Page
5-59 Changes in Ozone from 1970 to 1980: Umkehr Measurements
and Model Calculations 5-85
5-60 SBUV Zonal Trends Estimates Versus "Umkehr Station
Blocks" 5-86
5-61 Ozone Trend Estimates and 95% Confidence Intervals 5-88
5-62 Ozone Balloonsonde Stations 5-90
5-63 Correction Factors for Balloonsonde Measurements 5-91
5-64 Ozone Trend Emissions (% per year) As Determined from
Balloon Ozonesondes Versus Those Determined from Dodson
Measurements (Tiao, et al., personal communication) 5-93
5-65 Monthly Means of Total Ozone at Halley Bay 5-96
5-66 Nimbus 7 Antarctic Ozone Measurements: 12-Day Sequence ... 5-97
5-67 Nimbus 7 Antarctic Ozone Measurements: Mean Total
Ozone in October 5-98
5-68 Global (60°N-60°S) Monthly Ozone Determined from
NOAA TOVS System 5-100
5-69 Preliminary Ozone Trend Data (Health versus 2-D Model
Results) (Isaksen) 5-102
6-1 Stratospheric Perturbants and Their Effects 6-9
6-2 Absorption Characteristics of Trace Gases 6-10
6-3 Radiative Forcing for a Uniform Increase in Trace Gases ... 6-11
6-4 Effects of Vertical Ozone Distribution on
Surface Temperature 6-13
6-5 Water Vapor, Altitude, and Radiative Forcing 6-14
6-6 Temperature Sensitivity to Climatic Feedback Mechanisms ... 6-16
6-7 Empirical Estimates of Climate Sensitivity are Sensitive
to Estimates of Historical Temperature Increases and
Trace Gas Concentrations 6-17
6-8 Relationship of Radiative Forcing, Ocean Heat Uptake,
and Realized and Unrealized Warming 6-20
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LIST OF EXHIBITS
(Continued)
Page
6-9 Transient Estimates of Global Warming 6-21
6-10 Expected Temperature Increases 6-23
6-11 Results of Transient Analysis Using a General
Circulation Model 6-24
6-12 Regions of U.S. : Change in Runoff 6-25
7-1 Variation in UV Radiation by Latitude as Percent of Levels
at the Equator on March 21 at Noon 7-6
7-2 UV Radiation by Month in Washington, D.C 7-8
7-3 Ratio of Instantaneous Flux Throughout the Day to
Flux at 5:15 a.m. in Washington on June 21 (Assumes
a Clear Day) 7-9
7-4 Average DNA-Damage Action Spectrum 7-10
7-5 Organization of the Adult Skin 7-12
7-6 Ultraviolet Absorption Spectra of Major Epidermal
Chromophores 7-14
7-7 Skin Types and Skin Tanning Responses 7-16
7-8 Ultraviolet Action Spectra for DNA Dimer Induction,
Lethality and Mutagenicity 7-19
7-9 Effectiveness of UVR at Inducing Pyrimidine Dimers
and Transformation 7-21
7-10 Action Spectrum for the Induction of Single-Strand Breaks
in DNA 7-24
7-11 Action Spectrum of Mouse Edema (MEE48) as Compared
to that of DNA Damage and the Robertson-Berger
Meter 7-26
7-12 Comparison of Age-Adjusted Incidence Rates Per 100,000
Persons for Squamous Cell Carcinoma (SCC) and Basal Cell
Carcinoma (BCC) Among White Males and Females in the
United States 7-29
7-13 Percentage of Tumors by Anatomic Site for Nonmelanoma
Skin Cancer Among White Males and Females in the United
States (1977-1978 NCI Survey Data) 7-31
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LIST OF EXHIBITS
(Continued)
Page
7-14 Distribution by Sex and Anatomic Site of Nonmelanoma
Skin Tumors: Canton of Vaud, Switzerland (1974-1978) 7-32
7-15 Annual Age Adjusted Incidence Rates for Basal and Squamous
Cell Carcinoma (1977-1978 NCI Survey Data) and Melanoma
(1973-1976 SEER Data) Among White Males 7-35
7-16 Annual Age Adjusted Incidence Rates for Basal and
Squamous Cell Carcinomas (1977-1978 NCI Survey Data) and
Melanoma (1973-1976 SEER Data) Among White Females 7-36
7-17 Estimated of Relative Risks of Basal and Squamous Cell
Carcinomas for 32 Combinations of Risk Factors 7-38
7-18 Relative Mutagenicity of UV-B as a Function of Wavelength . 7-46
A-l Correlation of Alternative Measurements of UV-B Radiation
for Ten Locations in the United States 7-51
A-2 Population Weights for Ten Locations in the United
States 7-52
A-3 Estimated Dose-Response Coefficeints (and t-Statistics) for
Basal and Squamous Cell Skin Cancers (UV-B Dose-Skin
Cancer Incidence) 7-53
A-4 Estimated Percentage Changes in UV-B Radiation in San
Francisco for a Two and Ten Percent Depletion in Ozone .... 7-55
A-5 Percentage Change in Incidence of Basal and Squamous Cell
Skin Cancers for a Two Percent Depletion in Ozone for
San Francisco 7-56
A-6 Percentage Change in Incidence of Basal and Squamous Cell
Skin Cancers for a Ten Percent Depletion in Ozone for
San Francisco 7-57
8-1 Location of Melanocyte in the Epidermis 8-8
8-2 Comparative Transmittance of UV Radiation 8-9
8-3 Increases in Incidence and Mortality Rates from
Malignant Melanoma in Different Countries 8-17
8-4 Anatomic Site Distribution of Cutaneous Malignant
Melanoma 8-19
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LIST OF EXHIBITS
(Continued)
Page
8-5 Anatomic Site Distribution of Cutaneous Malignant
Melanoma by Gender 8-20
8-6 Malignant Melanoma Risk Factors by Measures of Skin
Pigmentation Within the Caucasian Population 8-26
8-7 Multiple Ways in which UVR can Play a Role in Melanoma
Development 8-30
8-8 Summary Statistics for Regressions of Skin Cancer
Incidence and Mortality on Latitude 8-32
8-9 Estimated Relative Increases in Melanoma Skin Cancer
Incidence and Mortality Associated with Changes in
Erythema Dose 8-33
8-10 Summary of Fears, Scotto, and Schneiderman (1977)
Regression Analyses of Melanoma Incidence Dose-Response ... 8-35
8-11 Biological Amplification Factors for Skin Melanoma by
Sex and Anatomical Site Groups, Adjusting for Age and
Selected Constitutional and Exposure Variables 8-35
8-12 Biological Amplification Factors for Melanoma Incidence
by Sex and Anatomical Site Groups, Adjusting for Age
and Combinations of Selected Constitutional and
Exposure Variables 8-36
8-13 Percentage Increase in Melanoma Death Rates for a One
Percent Decline in Ozone 8-39
9-1 Action Spectra for Local Suppression of Contact
Hypersensitivity Assuming Either One-Hit or Multi-Hit
Mechanisms 9-11
9-2 Action Spectrum For Systemic Suppression of Contact
Hypersensivity 9-12
10-1 Cataract Prevalence by UV Zone 10-7
10-2 Comparison of Cataract Prevalence for Aborigines and
Non-Aborigines 10-7
10-3 Composite Transmittance Curves for the Rabbit 10-9
10-4 Calculated Total Transmittance of the Human Eye 10-10
10-5 Percent Transmissivity Through the Entire Rhesus Eye 10-11
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LIST OF EXHIBITS
(Continued)
Page
10-6 Transmittance of the Total Rabbit Cornea, the Total
Human Cornea, and the Rabbit Corneal Epithalium 10-12
10-7 Transmittance of the Anterior Ocular Structures of
the Human and Rabbit Eyes 10-13
10-8 UV Radiant Exposure Threshold Data for the Cornea
HQ, Lens HL Cataracts, and Retina IL
for the Rabbit and Primate 10-14
10-9 The Action Spectra for Photokeratitis and Cataracts
for the Primate and Rabbit 10-15
10-10 Free Radicals and Oxidation: Reduction Systems 10-17
10-11 Enzyme Systems Involved in Oxidation: Reduction 10-18
10-12 Standardized Regression Coefficients for Cataract 10-31
10-13 Estimated Relationship Between Risk of Cataract
and UV-B Flux 10-32
11-1 A Summary of Studies Examining the Sensitivity of Cultivars
to UV-B Radiation 11-8
11-2 Survey of UV Studies by Major Terrestrial Plant
Ecosystems (after Whittaker 1975) 11-12
11-3 Summary of UV-B and C02 Effects on Plants 11-14
11-4 Summary of Field Studies Examining the Effects of
UV-B Radiation on Crop Yields 11-16
11-5 Details of Field Study by Teramura (1981-1985) 11-17
11-6 Summary of Changes in Yield Quality in Soybean
Between the 1982 and 1985 Growing Seasons
(Teramura 1982-1985) 11-21
12-1 Solar Irradiance Outside the Earth's Atmosphere and at
the Surface of the Earth for a Solar Zenith Angle of 60°. .. 12-5
12-2 Relationship Between Ozone Depletion and Biological
Effectiveness of Increased UV-B Radiation 12-6
12-3 Solar Spectral Irradiance at the Surface of the Ocean
and at Four Depths 12-7
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LIST OF EXHIBITS
(Continued)
Page
12-4 Lethal Effects on Shrimp Larvae for Various Combinations
of UV-R, Dose-Rate, and Total Dose 12-13
12-5 Estimated Effective UV-B Solar Daily Dose at Various
Atmospheric Ozone Concentrations Based on a 4-Year
Mean of Medians, Manchester, Washington, 1977-1980 12-14
12-6 Estimated Biologically Effective UV-B Doses Leading to
Significant Effects in Major Marine Zooplankton Groups .... 12-17
12-7 Percentage of Total Dose Limit to be Reached on Any
Particular Day: Lethal Doses Accumulated Only After
Dose-Rate Threshold is Exceeded 12-20
12-8 Effect of Increased Levels of Solar UV-B Radiation on
the Predicted Loss of Larval Northern Anchovy from Annual
Populations, Considering the Dose/Dose-Rate Threshold
and Three Vertical Mixing Models 12-27
13-1 Wavelengths of UV Radiation and Polymers with Maximum
Sensitivity and Corresponding Photon Energies 13-4
13-2 Plastics Used in Applications Where Exposure of the
Material to Sunlight Might Be Expected 13-8
13-3 Modes of Damage Experienced by Polymers Used in
Outdoor Application 13-11
13-4 PVC Siding Compound Composition 13-13
13-5 UV Screening Effectiveness of Selected Pigments 13-14
13-6 Domestic Consumption of Light Stabilizers, 1984-85 13-15
13-7 Increased Stabilization Market (1970-2020) 13-18
13-8 Ozone Depletion Estimates 13-19
13-9 Cumulative Added Cost 13-20
13-10 Diagrammatic Representation of the Effect of
Pigment/Fillers as Light Shielders
(Monodisperse Spherical Filler) 13-22
13-11 Relative Damage Indices for Yellowing of PVC Under Miami
(March 22nd) Conditions, at Different Extents of
Ozone Layer Deterioration 13-25
13-12 Estimated Ranges of Factor Increase in Damage and the
Factor Increase in Stabilizer Needed to Counter the
Change of Yellowing of Rigid PVC Compositions 13-28
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LIST OF EXHIBITS
(Continued)
Page
13-13 PVC Damage with Ozone Depletion 13-29
13-14 Projections of Future Demand for Selected Years
(Thousands of Metric Tons) 13-30
14-1 Ozone Concentrations for Short-Term Exposure That
Produce 5% to 20% Injury to Vegetation Growth Under
Sensitive Conditions 14-6
14-2 Ozone Concentrations at Which Significant Yield
Losses Have Been Noted for a Variety of Plant
Species Exposed Under Various Experimental Conditions 14-7
14-3 Ozone Concentrations Predicted for Changes in
Dobson Number and Temperature for Three Cities (ppm) 14-10
14-4 Global Warming Would Exacerbate Effects of Depletion
on Ground-Based Ozone in Nashville 14-11
15-1 Snow and Ice Components 15-6
15-2 Worldwide Sea Level in the Last Century 15-8
15-3 Temperature Increase At Various Depths and Latitudes 15-10
15-4 Estimates of Future Sea Level Rise 15-13
15-5 Local Sea Level Rise 15-14
15-6 Evolution of Marsh as Sea Level Rises 15-17
15-7 Composite Transect -- Charleston, S.C 15-18
15-8 Louisiana Shoreline in the Year 2030 15-20
15-9 Distribution of Population in Bangladesh 15-21
15-10 The Bruun Rule 15-23
15-11 Percent of Tidal Cycles in Which Specified
Concentration is Exceeded at Torresdale During a
Recurrence of the 1960's Drought for Three Sea Level
Scenarios 15-28
15-12 Estimates of Flood Damages for Charleston and Calveston
Resulting From Sea Level Rise 15-30
16-1 Summary of Findings from the WMO/UNEP/ICSU Conference
on Global Climate Held in Villach, Austria, October 1985 .. 16-1
17-1 Modular Structure 17-3
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LIST OF EXHIBITS
(Continued)
Page
17-2 Major Model Input Choices 17-5
17-3 Effects Not Quantified 17-10
A-l Flow of Analysis Program A-4
A-2 Files Required to Specify a Run A-6
B-l Future Global Production Scenarios: Middle Scenario B-3
B-2 Regional Use Shares for CFC-11 B-4
B-3 U.S. End Use Shares for CFC-11 B-6
B-4 Middle U.S. Population Scenario B-7
B-5 Middle U.S. GNP Scenario B-7
B-6 User-Modified Scenario Specifying a Growth Rate of 2
Percent Annually for CFC-11 in the U. S B-9
B-7 A User-Modified Scenario: Production as a Function of
Population B-9
D-l Release Tables for CFC-11 D-2
D-2 Emissions from a Hypothetical 100 Million Kilograms of
Production in 1985 D-4
D-3 Emissions from Production Over a Series of Years
(Millions of Kilograms) D-5
D-4 Sample Table of Exogenously Specified Emissions D-6
E-l Trace Gas Assumptions Used to Develop the Ozone Depletion
Relationship E-2
E-2 Comparison of Total Column Ozone Depletion Results from
the 1-D Model and the Parameterized Numerical Fit E-3
E-3 Hypothetical Table of User-Specifled Ozone Depletion E-6
E-4 Example Ozone Depletion Scaling Factors E-7
F-l Cities Used to Evaluate Changes in UV Flux for the Three
Regions of the U.S F-3
F-2 States Included in the Three Regions of the U.S F-5
F-3 Percent Change in UV as a Function of Change in Ozone
Abundance for Three U.S. Regions F-6
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LIST OF EXHIBITS
(Continued)
Page
F-4 Age Distribution of the U.S. Population Over Time in the
North Region F- 8
F-5 Baseline Incidence for Nonmelanoma Skin Cancers F-10
F-6 Basal Incidence for Melanoma Skin Cancers F-12
F-7 Mortality Rates for Melanoma Skin Cancers F-14
F-8 Standardized Regression Coefficients for Cataract F-16
F-9 Estimated Relationship Between Risk of Cataract and UV-B
Flux F-17
F-10 Sample Table for Specifying Relative Weights for Exposure
During a Person's Lifetime F-19
F-ll Coefficients Relating Percent Change in UV to Percent
Change in Skin Cancer Incidence F-22
F-12 Coefficients Relating Percent Change in UV to Percent
Change in Melanoma Mortality F-23
F-13 Dose-Response Coefficients F-25
F-14 Damage Index and Increase in Stabilizer for Ranges of
Ozone Depletion F-29
18-1 Types of Human Health and Environmental Effects
Estimated 18-8
18-2A Real World Equivalent to the No-Growth Scenario in Risk
Assessment 18-15
18-2B Real World Equivalent to the 1.2% Growth Scenario in Risk
Risk Assessment 18-16
18-3 Global Average Ozone Depletion: Central Case 18-20
18-4 Additional Cases of Nonmelanoma Skin Cancer by Type of
Nonmelanoma 18-21
18-5 Additional Mortality From Nonmelanoma Skin Cancer by Type
of Nonmelanoma 18-22
18-6 Additional Cases of Melanoma Skin Cancer by Cohort 18-23
18-7 Additional Mortality From Melanoma Skin Cancer by Cohort .. 18-24
18-8 Additional Senile Cataract Cases by Cohort 18-25
18-9 Environmental Effects Estimated Quantitatively for the U.S. 18-26
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LIST OF EXHIBITS
(Continued)
18-10 Environmental Effects Based on Case Studies and Research
in Early Stages 18-27
18-11 Equilibrium Temperature Change for the Emissions Scenarios
Assuming 3°C Warming for Doubled C02 18-28
18-12 Global Average Ozone Depletion: Comparison to Results
with a 2-D Dimensional Atmospheric Model 18-30
18-13 Climate, and Other Effects: Sensitivity to Relationship
Between Climate Change and C02 Emissions 18-31
18-14 Summary of Effects of Greenhouse Gases on Ozone Depletion
and Global Equilibrium Temperature 18-33
18-15 Global Average Ozone Depletion: Scenario of Limits
to Future Global Warming 18-34
18-16 Human Health Effects: Scenarios of Limits to Future
Global Warming. Additional Cumulative Cases and Deaths
Over Lifetimes of People Alive Today 18-36
18-17 Human Health Effects: Scenarios of Limits to Future
Global Warming. Additional Cumulative Cases and Deaths
Over Lifetimes of People Born 1986-2029 18-37
18-18 Human Health Effects: Scenarios of Limits to Future
Global Warming. Additional Cumulative Cases and Deaths
Over Lifetimes of People Born 2030-2074 18-38
18-19 Materials, Climate, and Other Effects: Scenarios
of Limits to Future Global Warming 18-39
18-20 Global Average Ozone Depletion: Methane Scenarios 18-41
18-21 Human Health Effects: Methane Scenarios Additional
Cumulative Cases and Deaths Over Lifetimes
of People Alive Today 18-42
18-22 Human Health Effects: Methane Scenarios
Additional Cumulative Cases and Deaths Over Lifetimes
of People Born 1986-2029 18-43
18-23 Human Health Effects: Methane Emissions Cases
Additional Cumulative Cases and Deaths Over Lifetimes
of People Born 2030-2074 18-44
18-24 Materials, Climate and Other Effects: Methane Scenarios .. 18-45
18-25 Global Average Ozone Depletion: Sensitivity to
Relationship Between Ozone Depletion and Emissions 18-46
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LIST OF EXHIBITS
(Continued)
Page
18-26 Human Health Effects: Sensitivity to Relationship
Between Ozone Depletion and Emissions. Additional
Cumulative Cases and Deaths Over Lifetimes of People
Alive Today 18-48
18-27 Human Health Effects: Sensitivity to Relationship
Between Ozone Depletion and Emissions. Additional
Cumulative Cases and Deaths Over Lifetimes of People
Born 1985-2029 18-49
18-28 Human Health Effects: Sensitivity to Relationship
Between Ozone Depletion and Emissions. Additional
Cumulative Cases and Deaths Over Lifetimes of People
Born 2030-2074 18-50
18-29 Human Health Effects: Maximum Depletion of 95 Percent.
Additional Cumulative Cases and Deaths Over Lifetimes
of People Alive Today 18-51
18-30 Human Health Effects: Maximum Depletion of 95 Percent.
Additional Cumulative Cases and Deaths Over Lifetimes of
People Born 1986-2029 18-52
18-31 Human Health Effects: Maximum Depletion of 95 Percent.
Additional Cumulative Cases and Deaths Over Lifetimes of
People Born 2030-2074 18-53
18-32 Human Health Effects: Sensitivity to Dose-Response
Relationship. Additional Cumulative Cases and
Deaths Over Lifetimes of People Alive Today 18-55
18-33 Human Health Effects: Sensitivity to Dose-Response
Relationship Additional Cumulative Cases and
Deaths Over Lifetimes of People Born 1986-2029 18-56
18-34 Human Health Effects: Sensitivity to Dose-Response
Relationship Additional Cumulative Cases and
Deaths Over Lifetimes of People Born 2030-2074 18-57
18-35 Human Health Effects: Sensitivity to Relationship Between
Ozone Depletion and Action Spectrum. Additional Cumulative
Cases and Deaths Over Lifetimes of People Alive Today 18-58
18-36 Human Health Effects: Sensitivity to Relationship Between
Ozone Depletion and Action Spectrum. Additional Cumulative
Cases and Deaths Over Lifetimes of People Born 1986-2029 18-59
18-37 Human Health Effects: Sensitivity to Relationship Between
Ozone Depletion and Action Spectrum. Additional Cases and
Deaths Over Liftimes of People Born 2030-2074 18-60
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LIST OF EXHIBITS
(Continued)
18-38 Comparative Sensitivity of Mortality From Skin Cancer to
Various Factors 18-63
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INTRODUCTION
Ozone in the stratosphere helps protect humans, biological organisms, and
useful materials from harm by partially blocking ultraviolet radiation in
wavelengths from 295 nanometers to 320 nanometers (Ultraviolet-B; UVB) from
reaching the earth's surface. The vertical distribution of ozone in the
stratosphere and the relative dryness of that atmospheric region also play a
role in sustaining the current radiative balance of the planet; changes in
vertical distribution of ozone and stratospheric water vapor can influence the
average surface temperature of the earth and its weather and climate. Because
of these two roles, the composition and structure of the stratosphere are of
human concern.
THE RISE OF CONCERN ABOUT STRATOSPHERIC CHANGE
In the early 1970s, Johnston and others expressed concern that the exhausts
of the then proposed fleets of supersonic transports would deposit nitrogen
oxides and water vapor into the stratosphere where these substances could
decrease the abundance of ozone. In 1974, Rowland and Molina raised the concern
that chlorofluorocarbons (CFCs), used as aerosol propellants, in foam blowing,
as solvents, and as refrigerants, would pose a similar threat. Since then,
others have raised concerns about nitrous oxides produced from combustion, soil
processes, and fertilizers, about brominated compounds produced as fire
extinguishing agents, and about a variety of other substances, including carbon
dioxide (C02) and methane (CH4), which have the potential to perturb
stratospheric composition and structure.
An understanding of the role of infrared gases in maintaining earth's
climate developed much earlier. In 1861 Tyndall discovered that water vapor
absorbs infrared radiation. Not much attention was paid to infrared absorbing
gases because they were assumed more or less constant in the atmosphere. In
1957, accurate measurements of C02 started. Since then, concern about the rise
in the atmospheric level of greenhouse gases and their potential to warm the
earth and change its climate has steadily increased. In the last ten years,
measurements of many radiatively important trace species other than C02 have
been made and have further heightened concern about global warming. In
addition, recent studies have begun to consider how changes in the vertical
location of ozone could add to, or in some cases subtract from, a greenhouse
warming. As a result of these efforts, it has become clearer that
considerations of stratospheric modification must include the potential
contribution to the total greenhouse warming and the general circulation of
weather on earth.
CONCERN ABOUT PUBLIC HEALTH AND WELFARE EFFECTS OF GLOBAL ATMOSPHERIC CHANGE
Concern about the effects of ozone depletion first focused on skin cancers,
crops, and aquatic organisms during the Climate Impact Assessment Project in the
1970s. These concerns still exist and much has been learned about them since
then. In addition a number of new concerns have been added, including the
potential effect of UV radiation on materials useful to man, on ecosystems, on
air pollution problems like ground-based oxidants and acid rain precursors, on
the immune system of humans, and on cataracts and other eye problems. In fact,
there has been a general recognition that ultraviolet radiation can alter many
different kinds of "target" molecules and that changes at molecular levels could
ultimately perturb the dynamics of the ecosystems. Despite advances, however,
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our understanding of the possible effects of increased ultraviolet radiation on
the earth remains in its infancy.
Concern about the impacts of climate change, including sea level rise,
alterations in hydrology and ecosystems, and a variety of other human endeavors
has grown stronger since Revelle's famous statement that mankind is performing a
great uncontrolled experiment on the earth. Knowledge of specific effects of
climate change however, also remains rather limited.
NEED FDR ASSESSMENTS
Protection of the stratosphere is an environmental issue that differs from
other concerns. Most environmental problems are local or regional in scale.
Increases in ultraviolet radiation or changes in climate would produce effects
worldwide. Most environmental problems can be eliminated as quickly as
emissions can be reduced. For instance, the lifetime of particulates in the
atmosphere can be measured in days. Once a problem is perceived and action
decided upon, concentration will drop as quickly as reductions in source
emissions can be made. For stratospheric modification this is not true. The
lifetimes of many possible stratospheric perturbants are very long. If a
problem begins to be observed, it will not disappear immediately, even if
emissions are totally curtailed. In fact, even with a total termination of
emissions of the long lived gases, decades to centuries would pass before
concentrations declined to their original levels before humanity perturbed them.
In the case of CFCs, if depletion starts to occur, actions that did not
drastically curtail or reduce CFC and chlorine levels, in fact, would only tend
to slow the rate of depletion.
These two features, the global impact of change, and the difficulty in
preventing, slowing, or reversing change if it occurs, create a unique problem
for scientists and decisionmakers attempting to assess risks of continued
unrestrained emission of potential ozone modifiers. Errors may take decades or
more to correct. Complicating the assessment process is that fact unlike many
areas of risk assessment, experiments cannot be done to verify model
predictions. There is no experimental earth to test theories and models --. the
only experiment that can be done is the one now underway on the planet.
The Basis For This Assessment
Progress has been made, however, in the science of the stratosphere, the
scientific disciplines related to effects, and in the process of doing risk
assessments. Much has been learned since the Climate Impact Assessment Project
(CIAP) done in the early 1970's and later assessments. Not only has there been
a steady improvement in atmospheric science, but atmospheric science has reached
out to other geophysical systems to include analysis of biogenic inputs into the
atmosphere. During the past two years, under the leadership of Dr. Robert
Watson and with the joint sponsorship of many international bodies, including
the World Meterological Organization (WMO), the United Nations Environment
Programme (UNEP), the National Aeronautics and Space Administration (NASA), the
Federal Aviation Administration (FAA), the National Oceanic and Atmospheric
Administration (NOAA), the Commission of European Communities, and the
Bundesminsterium Fur Forschung and Technologic, the most comprehensive
assessment of atmospheric science ever conducted has been completed. This
review considered a wider range of issues, a greater number of scenarios of
trace gases, and more uncertainties than in any previous assessment. The
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-3-
atmospheric chapters in this Risk Assessment draw heavily from that document and
consequent documents developed by NASA from it.
Advances have also been made in health and welfare effects. In the field of
melanoma, major advances have been made by Holman, Armstrong, Scotto, and
Elwood. In materials, Androtti has significantly pushed the frontier forward.
In tropospheric air pollution, Whitten has opened new paths. In climate,
Hansen, Manabe, Washington, Ramanathan and others have greatly increased our
understanding. In crops and aquatics, Teramura, Caldwell, Tevini, Hoder,
Worrest and others have improved our understanding. In addition, the chapter on
cataracts represents a new assessment extracted from a group coordinated by
Morris Waxier of the Food and Drug Administration to understand that issue.
This risk assessment attempts to build on the work of these and other
scientists.
EXPLICIT INCORPORATION OF ECONOMICS AND THE INTEGRATION OF VARIOUS AREAS
The major way this assessment differs from prior assessments is that we
explicitly look at emissions scenarios based on economics and we explicitly
integrate consideration of production of trace gases, emissions, concentrations,
atmospheric response, and effects to understand the joint implications of
projected trends and system behavior through time. This approach has several
advantages. It allows realistic assessment of risks rather than purely
hypothetical cases such as "steady state emissions." It raises new scientific
questions by forcing us to consider the inter-relationships of "disparate"
disciplines. And it allows exploration of the joint implications of uncertainty
in different areas. Only by integrating the various disciplines can we provide
decision makers with a real understanding of the risks associated with emission
of ozone-depleting substances and other trace gases that can modify the
stratosphere.
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CHAPTER 1
GOALS AND APPROACH OF THIS RISK ASSESSMENT
Under Part B of the Clean Air Act, the Administrator of EPA "shall propose
regulations for the control of any substance, practice, process or activity (or
any combination thereof) which in his judgment may reasonably be anticipated to
affect the stratosphere, especially ozone in the stratosphere, if such effect in
the stratosphere may be reasonably anticipated to endanger public health or
welfare."
This risk assessment seeks to summarize the state of scientific knowledge so
that the Administrator can make a considered judgment about the need for
additional controls. Scientific evidence is therefore reviewed and evaluated
for two purposes:
(1) to assess the likelihood that different human activities
could alter the stratosphere in ways that altered
ultraviolet radiation reaching earth's surface or that
changed climate; and
(2) to assess the likelihood that changes in ultraviolet
radiation or climate due to modifications in column
ozone or stratospheric water vapor would have
detrimental effects on human health or welfare.
ANALYTIC FRAMEWORK
There are four key parts to this risk assessment.
o Part 1 (Chapters 2, 3, 4) assesses possible changes in
the composition of the atmosphere.
o Part 2 (Chapters 5, 6) assesses possible responses of
the stratosphere to such changes in atmospheric
composition.
o Part 3 (Chapters 7-16) assesses possible public health
and welfare to changes in the stratosphere.
o Part 4 (Chapters 17, 18) assesses the joint implications
of knowledge and uncertainties about atmospheric
composition, stratospheric modification, and effects, to
produce a range of outcomes consistent with current
knowledge.
Appendix A presents a separate volume on assessing the risks that the
incidence and mortality of melanoma will increase if stratospheric ozone levels
are modified. Appendix B presents a separate volume on the effects of climate
change. Every chapter tries to summarize the most likely science as well as the
implications of uncertainty. A variety of cases and sensitivity analyses are
analyzed and they examine how various uncertainties could affect the projection
of changes. For example, in the integrating chapter, six scenarios are
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identified, encompassing the range of likely trajectories of emissions, not just
the single best case growth estimate.
Each chapter begins with a summary description and then a set of general
findings the latter of which is more detailed than the summary. Following this
the relevant science is critically reviewed. The second to last chapter
integrates all the findings from the previous chapters into a comprehensive
modeling framework. The last chapter presents the joint implications of the
prior work in terms of risk. In this way the risk assessment attempts to
provide decisionmakers with a range of estimates of overall risk, based on
various combinations of the joint uncertainties, not just a single estimate.
SUPPORTING DOCUMENTS AND ANALYSIS FOR THIS REVIEW
As mentioned earlier, this assessment draws heavily for atmospheric science
from the WMO/UNEP assessment. Other documents that were used include those
produced by UNEP's Coordinating Committee on the Ozone Layer. In addition
analyses from the Fluorocarbon Program Panel of the Chemical Manufacturers
Association (CMA), which continues to fund research primarily related to
atmospheric modeling, were used. The climate change conference convened by WMO
in Villach, Austria in October 1985 also provided valuable information. Finally
a risk assessment supervised by Dr. Donald G. Pitts and Morris Waxier of FDA is
used for cataracts. All four documents should be consulted by those interested
in more detailed treatments of these subjects.
CHAPTER OUTLINES
Chapter 2 focuses on past changes in stratospheric perturbants (trace gases
that can change the structure and composition of the stratosphere). Chapter 3
reviews a variety of studies completed in the last two years on the future
emissions of trace gases that are solely produced by man, and constitute
potential ozone depleters. Chapter 4 centers on studies done to understand
future concentrations of trace gases at least partly on biogenic sources --
carbon dioxide, methane, and nitrous oxide.
Following chapters on how atmospheric composition might change, Part II
consists of Chapter 5 on stratospheric modification and Chapter 6 on climate
change.
The next part of the analysis examines the effects of stratospheric
modification on public health and welfare. In each chapter, the likelihood of
effects are evaluated and attempts made to identify the quantitative
relationships that relate atmospheric change to impact. Chapter 7 reviews basal
and squamous skin cancers, and Chapter 8 melanoma. Chapter 9 addresses immune
suppression and the diseases it might produce, Chapter 10 cataracts and other
eye impairments. Chapter 11 analyzes possible crop and terrestrial ecosystem
disruption, while Chapter 12 reviews potential damage to aquatic life. Chapter
13 covers materials damage while Chapter 14 completes the review of possible
UV-B induced damage by examining possible air pollution effects of ozone
modification. Chapter 15 then reviews possible effects of global warming on sea
•"- To the maximum degree possible this report directly used the results of
other assessments. In many places large sections of text are taken from those
reports. Such text has been put into BOLDFACE, to facilitate recognition of
their quotation.
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level rise and Chapter 16 summarizes Appendix B's review of the effects of
global warming and associated climate change.
The next part of the Assessment consists of two chapters. Chapter 17
explains the models used to integrate the analyses, so that a comprehensive time
dependent assessment of risks of stratospheric modification for conditions of
uncertainty can be developed. Chapter 18 summarizes the risk assessment by
presenting six scenarios of ozone depleting substances and estimates of possible
damages for a variety of conditions with regard to atmospheric evolution and
effects. Various emissions scenarios are used with different atmospheric models
to estimate changes in ozone and global temperatures. These outputs of the
atmospheric models are used in effects models that produce quantitative and
qualitative estimates of impacts. In addition, extensive sensitivity analysis
of the implications of many uncertainties is presented. The chapter integrates
all that has proceeded.
Exhibit 1-1 summarizes the relationships among the various chapters.
EXHIBIT 1-1
Relationships Among the Chapters*
Emissions
o Chapter 1
o Chapter 2
o Chapter 3
o Chapter 4
-> Atmospheric Response
o Chapter 5
o Chapter 6
-> Effects
o Chapter 7
o Chapter 8
o Chapter 9
o Chapter 10
o Chapter 11
o Chapter 12
o Chapter 13
o Chapter 14
o Chapter 15
o Chapter 16
The Range of
Year-by-Year
Impacts &
Cumulative
Impacts
o Chapter 18
* Chapter 17 develops model representations that integrate all components of
the analysis.
-------
1-4
REFERENCES
CMA (1986), Chemical Manufacturers Association, "Production, Sales, and
Calculated Release of CFC-11 and CFC-12 Through 1985," Washington, D.C.
Pitts DG, et al. (in press), "Optical Radiation and Cataracts," in Vicusal
Health and Optical Radiation. M. Waxier and V. Kitchens, eds., CRC Press,
Inc., Boca Raton, Florida.
World Meteorological Organization (WMO), (1985), Report of the International
Conference on the Assessment of the Role of Carbon Dioxide and of Other
Greenhouse Gases in Climate Variations and Associated Impacts. WMO - No.
661, Villich, Austria, 9-15 October, 1985.
World Meteorological Organization (WMO), (1985), Report of the International
Conference on the Assessment of the Role of Carbon Dioxide and of Other
Greenhouse Gases in Climate Variations and Associated Impacts Villich.
Austria. 9-15 October 1984. WMO - No. 661, International Council of
Scientific Unions, United Nations Environment Programme, and World
Meteorological Organization.
-------
CHAPTER 2
STRATOSPHERIC PERTURBANTS: PAST CHANGES IN CONCENTRATIONS
SUMMARY
Recent measurements of trace gas abundance demonstrate that the
concentrations of many trace gases are increasing throughout the lower
atmosphere (the troposphere). These gases can directly influence the upper
atmosphere (the stratosphere) when they are transported there and become
involved in chemical reactions. Or they can play an indirect role in
stratospheric issues by influencing the atmosphere's radiative balances
(temperatures) or dynamics.
Tropospheric concentrations of the two most important chlorofluorocarbons
(CFCs), CFC-11 and CFC-12, are growing at approximately 5 percent per year. In
the last ten years, their concentrations have more than doubled. Tropospheric
concentrations of other chlorine bearing perturbants are also growing. Measured
increases in concentrations of chlorofluorocarbons include HCFC-22 at 11 percent
per year and CFC-113 at 10 percent per year. Measured increases in
chlorocarbons include carbon tetrachloride (CC14) at 1 percent per year and
methyl chloToform (CH3CC13) at 7 percent per year.
Tropospheric concentrations of Halon-1211, a bromine bearing compound, are
increasing at 23 percent per year. Trends in the concentrations of Halon-1301,
another brominated compound, have not been reported.
Tropospheric concentrations of gases with some sources that are partially
biogenic have also been increasing: nitrous oxide (N20) at 0.2 percent per
year, carbon dioxide (C02) at 0.4 percent per year, and methane (CH4) at 0.017
ppm per year.
Trace gases vary in their atmospheric residence times. Lifetimes of
long-lived trace gases include 75 (+32/-17) years for CFC-11 and 111 years for
CFC-12;1 90 years for CFC-113; 50 years for CC14; 110 years for Halon-1301 and
25 years for Halon-1211; and 150 years for N20. Lifetimes of shorter-lived
trace gases include, for anthropogenic gases, 20 years for HCFC-22 and 6.5 years
for CH3CC13, and for the biogenic gas CH4, approximately 11 years.
After a gas is emitted, its fate depends on deposition processes, chemical
interactions and transport to the stratosphere. Gases with long lifetimes are
inert, being less influenced by chemical loss mechanisms and are thus more
likely to survive until they can affect the stratosphere. Since the loss rate
to the stratosphere is relatively slow, once concentrations of inert gases rise,
their influence will be long lasting. If a given level of ozone depletion
The uncertainty associated with CFC-11 is +32 and -17 years; for CFC-12
it is +289 and -46 years. Thus for 100 kilograms of CFC-11 released in 1987,
the best estimate is that 26 kilograms will still be in the atmosphere in 2087,
with 66 percent probability that this amount will be reached between 2060 and
2119.
-------
2-2
occurs, it will diminish slowly even if there are no new emissions. In fact,
unless new emissions are less than the quantity of molecules lost to the
stratosphere, concentrations and depletion would increase. The concentrations
of gases that are chemically active are more dependent on a continued renewal by
emissions. Thus their concentrations are subject to greater short term
perturbation. The difference between long and short lifetimes has implications
for the kinds of risks associated with rising concentrations of different trace
species. Long lived gases will produce concentrations of those gases which may
only be reversible over a period of decades or more.
-------
2-3
FINDINGS
1. MEASUREMENTS OF TROPOSPHERIC CONCENTRATIONS OF INDUSTRIALLY PRODUCED
POTENTIAL OZONE-DEPLETING GASES SHOW SUBSTANTIAL INCREASES.
la. Measurements of current global average concentrations of CFG-11 are 200
parts per trillion volume (pptv), CFC-12 are 320 pptv, CFC-113 are 32
pptv, carbon tetrachloride (CC14) are 140 pptv, and methyl chloroform
(CH3CCL3) are 120 pptv.
Ib. Based on measurements from a global monitoring network, worldwide
concentrations of chlorine-bearing perturbants (i.e., potential ozone
depleters) have been growing annually in recent years at the following
rates: CFC-11 and CFC-12 at 5 percent; CFC-22 (CHC1F2) at 11 percent;
CFC-113 at 10 percent; carbon tetrachloride (CC14) at 1 percent; and
methyl chloroform at 7 percent.
Ic. Limited measurements show that global tropospheric concentrations of
Halon 1211, a bromochlorofluorocarbon containing both chlorine and
bromine (which is potentially more effective at depleting ozone), have
been growing recently at 23 percent annually. Concentrations have been
measured as one pptv.
Id. Measurements of tropospheric concentrations of Halon 1301, another
brominated compound that is a potential ozone depleter, estimate that
concentrations are approximately one pptv. No trend estimates have been
published.
2. ALMOST ALL EMISSIONS OF CFC-11. -12. -113. HALON 1211. AND HALON 1301
PERSIST IN THE TROPOSPHERE WITHOUT CHEMICAL TRANSFORMATION OR PHYSICAL
DEPOSITION. AS A RESULT. MOST OF THESE EMISSIONS WILL EVENTUALLY BE
TRANSPORTED TO THE STRATOSPHERE.
2a. Gases which are photochemically inert accumulate in the lower
atmosphere. Their emissions migrate to the stratosphere slowly.
Estimates of their atmospheric lifetimes (generally calculated based
on the time when 37 percent of the compound still remains in the
atmosphere) are the following: CFC-11 is 75 years (107/58 years);
CFC-12 is 111 years (400/55 years); CFC-113 is 90 years; CC14 is 50
years; Halon 1211 is 25 years; N20 is 150 years; and Halon 1301 is
110 years. (Where provided, the range in parentheses shows one
standard deviation).
2b. Because of their long atmospheric lifetimes, the concentrations of
these gases are currently far from steady state and will increase
over time unless there is a large reduction in future emissions.
2c. Because of their long atmospheric lifetimes, these gases would
continue to contribute to possible future ozone depletion and climate
change (CFCs and other gases affecting ozone are also greenhouse
gases) long after they are emitted. Full recovery from any depletion
or climate change would take decades to centuries.
-------
2-4
MEASURED INCREASES IN TROPOSPHERIC CONCENTRATIONS OF POTENTIAL OZONE DEPLETERS
The tropospheric concentrations of many potential ozone-depleting trace
gases have been measured as increasing throughout the world. Due to the
strength of global circulation and the chemical stability of many of these
gases, they are rapidly well mixed in the troposphere. Gases with longer
lifetimes are more equally mixed between the Northern and Southern Hemispheres.
The longest-lived trace gas, N20, has the smallest interhemispheric mixing
ratio: 1.003; and CH3CC13, a gas with a short lifetime, has the greatest
interhemispheric ratio: 1.37 (Prinn et al. 1983). After ozone depleters are
transported to the stratosphere, they are photodissociated. The NOx, Clx, or
Brx released can then enter into catalytic cycles that would reduce
stratospheric ozone (see Chapter 5).
CFG-11
The global average concentration of CFG-11 (CFC13) is approximately 200
parts per trillion volume (pptv) (Prinn et al. 1983). Tropospheric
concentrations show little latitudinal variation, with a North/South
interhemispheric mixing ratio of 1.09 (Prinn et al. 1983). CFC-11 has been
measured at the five globally distributed sites of the Atmospheric Lifetime
Experiment program. Average tropospheric concentrations are increasing at
approximately 5 percent per year (WHO 1986). (Exhibit 2-1) In the last 10
years tropospheric concentrations have more than doubled (Rasmussen and Khalil
1986).
CFG-12
The global average concentration of CFC-12 (CF2CL2) is approximately 320
pptv and is increasing at approximately 5 percent per year (WMO 1986) . It has
been measured at the five Atmospheric Lifetime Experiment stations (Exhibit
2-2). Concentrations are globally well mixed, with a North/South
interhemispheric mixing ratio of 1.08 (Prinn et al. 1983). In the last ten
years tropospheric concentrations have more than doubled (Rasmussen and Khalil
1986).
HCFC-22
The global average concentration of HCFC-22 (CHC1F2) is approximately 52
pptv (NAS 1984). Concentrations have been measured in the Pacific Northwest and
at the South Pole. Global increases in tropospheric HCFC-22 concentrations have
averaged approximately 11.7 percent per year (Khalil and Rasmussen 1982)
(Exhibit 2-3).
CFG-113
The global average concentration of CFC-113 (C2C13F3) is approximately 32
pptv (NAS 1984). Recent increases in tropospheric CFC-113 concentrations,
measured at the South Pole and Pacific Northwest, have averaged approximately
ten percent per year (Rasmussen and Khalil 1982) (Exhibit 2-4).
-------
2-5
EXHIBIT 2-1
Measured Increases in Tropospheric
Concentrations of CFG-11 (CFC13)
CFCL, (PI ADRIGOLE. IRELAND
I 210'
a 200i
; 190 j
(3 180 <
,70.
I'll
1978 1979 1980 1981
1983 1984
CFCL, (P! CAPE MEARES, OREGON
O 180 •
I 170 I
1978 1979
1983 19M
CFCL, [P| RAGGED POINT. BARBADOS
j 210
1 200 i
g 190,
1 180 .
I 170 I
1978 1979
1983 19<4
CFCLj (PI POINT MATATULA. AMERICAN SAMOA
a 170 .
i 160'
1978 1979
1981 1982
1983 19B4
CFCL, (P) CAPE GRIM, TASMANIA
I 200 \
I 190 I
O
P 180 1
I ""I
i '"I
'"'l.nin'"""
1»7« 1979
1963 19
Average concentrations of CFG-11 are increasing at approximately five percent
per year. Data are from the Atmospheric Lifetime Experiment.
Source: World Meteorological Organization, 1986; Figure 3-2.
-------
2-6
EXHIBIT 2-2
Measured Increases in Tropospheric
Concentrations of CFG-12 (CF2CL2)
CF.CL, ADRIGOLE. IRELAND
I 3.0
I3"
< 320
c
O 300
II'1
J978 1979
1983 1984
CF.CL, CAPE ME ARES, OREGON
I 380
I 360
< 3*0
J 320
§300.
1978 1979
1983 1984
CF,CL. RAGGED POINT. BARBADOS
; 310
•
O 290
« 270
1978 1979
1983 1984
CF,CL, POINT MATATULA. AMERICAN SAMOA
S 330
| 310
I 290
O 270 •
| 250 it,<
1978 1979
1983 1984
CF,CL, CAPE GRIM, TASMANIA
a 330 •
I 310.
« 290-
C
O 270 •
z
8 250
1978 1979
1983 1984
Average concentrations of CFG-12 are increasing at approximately five percent
per year. Data are from the Atmospheric Lifetime Experiment.
Source: World Meteorological Organization, 1986; Figure 3-3.
-------
2-7
EXHIBIT 2-3
Measured Increases in Tropospheric Concentrations of HCFC-22 (CHCIF2)
a,
1975
1977 1979 1981 1983
Average concentrations of HCFC-22 are increasing at approximately
12 percent per year.
Source: Rasmussen and Khalil 1982.
EXHIBIT 2-4
Measured Increases in Tropospheric Concentrations of CFC-113 (C2CL3F3)
60 '
c§
•33
(0 -H
8 H
88,
8 w 20
I
•paci-
South
•pole
1975 1977 1979 1981
1983
Average concentrations of CFC-113 are increasing at approximately 10 percent per
year.
Source: Rasmussen and Khalil 1982.
-------
2-8
Carbon Tetrachloride
The global average concentration of carbon tetrachloride (CC14) is
approximately 140 pptv and is increasing at approximately one percent per year
(WHO 1986). It has been measured at the five Atmospheric Lifetime Experiment
stations. The North/South interhemispheric mixing ratio is 1.05 (Prinn et al.
1983) (Exhibit 2-5). In the last ten years, tropospheric concentrations in both
hemispheres have increased by more than a factor of 1.2 (Rasmussen and Khalil
1986) (Exhibit 2-5).
Methyl Chloroform
The global average concentration of methyl chloroform (CH3CC13) is
approximately 120 pptv and is increasing at approximately seven percent per year
(WHO 1986). It has been measured at the five Atmospheric Lifetime Experiment
stations (Exhibit 2-6). Because methyl chloroform has a relatively shorter
lifetime than the other halocarbons, concentrations show a greater geographic
variation. The North/South interhemispheric ratio is 1.37 (Prinn et al. 1983).
In the last ten years, tropospheric concentrations have more than doubled
(Rasmussen and Khalil 1986).
Halon-1301
The current concentration of Halon-1301 (CF3Br), measured at the South Pole,
is approximately one pptv (Khalil and Rasmussen 1985) . Because researchers have
only recently attempted to measure its concentration, no trend estimates are
available. Archived air exists, however, and it may be possible to use it to
establish trends for this species.
Halon-1211
The current concentration of Halon-1211 (CF2ClBr), measured at the South
Pole, is approximately one pptv. Increases in the tropospheric concentrations
measured at the South Pole have averaged 23 percent (Khalil and Rasmussen 1985)
(Exhibit 2-7).
Nitrous Oxide
The mean global concentration of nitrous oxide (N20) is approximately 300
parts per billion volume (ppbv). Weiss (1981) collected separate measurements
between 1976 and 1980 at several monitoring stations and aboard oceanographic
vessels in the major world oceans. His analysis demonstrated that the
tropospheric N20 concentration was increasing at approximately 0.2 percent per
year (Exhibit 2-8).
Recent data for N20 from the five Atmospheric Lifetime Experiment stations
are shown below. The results are consistent with Weiss (1981). The measured
trends at the five network stations were: 0.77, 0.27, 0.24, 0.09, and 0.18
percent (WHO 1986). While the rates of increase appear to be larger in the
northern hemisphere (0.25-0.7 percent per year) than in the southern hemisphere
(0.1-0.2 percent per year) (WMO 1986), there is little variation in actual
-------
2-9
EXHIBIT 2-5
Measured Increases in Tropospheric
Concentrations of Carbon Tetrachloride (CC14)
CCU ADRIGOLE. IRELAND
|1SO {
I140;
< 130 •
U 120 1
* 110 •
5
1978 1979
1980 19B1
1983 1984
CCL. CAPE MEARES. OREGON
I150!
£ 1401
5 uo:
|,20j
1978 1979 1980 1981
1983 1984
CCU RAGGED POINT. BARBADOS
\ I4°
£ 130
< 120
| 11.
* 100
1978 1979
1981 1982
1983 1984
CCU POINT MATATULA. AMERICAN SAMOA
£ 130 I
g'2°: ,,,,, ,, :>••> '" '""
« 110 • i i I i '
c
O 100 I
1978 1979
1981 1982
1983 1984
CCU CAPE GRIM, TASMANIA
5 110
oe i
O 100 I
1971 1979
1981 1982
1983 1984
Average concentrations of carbon tetrachloride are increasing at approximately
one percent per year. Data are from the Atmospheric Lifetime Experiment.
Source: World Meteorological Organization, 1986; Figure 3-5.
-------
2-10
EXHIBIT 2-6
Measured Increases in Tropospheric
Concentrations of Methyl Chloroform (CH3CC13)
CH.CCLi ADRIGOLE. IRELAND
I150' ill 11
{:": .,,li;ii!l,I!i|!!^!i!!i !':i •" '
1978 1979
1983 1984
CH.CCL, CAPE MEARES. OREGON
| 150.
i140;
; 130.
K
O 1201
5 1101
1978 1979
CH.CCL, RAGGED POINT. BARBADOS
1983 1984
1978 1979
1980 1981
CH.CCL, POINT MATATULA. AMERICAN SAMOA
1983 1984
1 «
i 70
1978 1979
CH.CCL, CAPE GRIM, TASMANIA
1983 1984
iiooj
O 90 I
I ""
1978 1979
1983 19«
Average concentrations of methyl chloroform are increasing at approximately
seven percent per year. Data are from the Atmospheric Lifetime Experiment.
Source: World Meteorological Organization, 1986; Figure 3-4.
-------
2-11
EXHIBIT 2-7
Measured Increases in Tropospheric
Concentrations of Halon-1211 (CF2ClBr)
cu-
0
n 1.2H
c
JL(H
p i
a
I i6H
i.
P ,2J
P
* .0
D 0
1979
1980
1981
1982
1983
1984
Measurements from South Pole. Average concentrations of Halon-1211 are
increasing at approximately 23 percent per year.
Source: Khalil and Rasmussen, 1985.
-------
2-12
EXHIBIT 2-8
Measured Increases in Tropospheric
Concentrations of Nitrous Oxide (N20)
300
304
302
300
208
206
1070
1077
1070
1070
1000
Measurements of tropospheric nitrous oxide concentrations. Data were collected
at several monitoring sites and aboard vessels in the major world oceans.
Concentrations are increasing at approximately 0.2 percent per year.
Source: Weiss, 1981.
-------
2-13
concentrations. The North/South interhemispheric mixing ratio is 1.003 (Prinn
et al. 1983). If statistically significant, this discrepancy may be due to a
growing imbalance between Northern sources and global sinks (WMO 1986) (Exhibit
2-9).
Pearman et al. (1986) measured N20 concentrations trapped in polar ice and
provided the first evidence of changing N20 concentrations over hundreds of
years. They found that "the ice data for recent times agree with modern
measurements" and that concentrations have increased by 6 ppbv per 100 years
over the last three centuries. They conclude that their recent trend estimate
of 0.5-1.8 ppbv per year is not characteristic of the 400-year ice record, but
results from an increase since the time of the Industrial Revolution (Exhibit
2-10).
MEASURED INCREASES IN TROPOSPHERIC CONCENTRATIONS OF POTENTIAL OZONE INCREASERS
Carbon dioxide (C02) and methane (CH4) may, in some cases, contribute to
increasing ozone abundance in the stratosphere (C02 and CH4) or in the
troposphere (CH4). They may also contribute to global warming. Atmospheric
measurements indicate that their concentrations of potential ozone increasers
are increasing.
Carbon Dioxide
Continuous and accurate measurements of C02 concentrations began in 1958 at
Mauna Loa Observatory in Hawaii (Keeling and GMCC/NOAA). The data show' an
increase of approximately ten percent since then (Exhibit 2-11).
Other measurements of the rise of C02 have been made and are consistent with
the Mauna Loa time series, each varying in seasonal amplitude depending on the
distance from annual biospheric sources (Keeling 1978; Keeling et al. 1976;
Peterson et al. 1982; and Sundquist and Broecker 1985).
Direct measurements of C02 concentrations were attempted as early as 1872
(Callendar 1958). Because they are subject to substantial error, their utility
is limited. Indirect methods, however, such as measuring the concentrations of
C02 trapped in polar ice (Oeschger et al. 1982; Neftel et al. 1982; and Delmas
et al. 1980), and analyzing the isotopic carbon ratios in tree rings (Freyer
1978; and Peng et al. 1983), show that C02 concentrations before 1850
(pre-industrial times), remained approximately constant at 270 ppm + 10 -- 25
percent lower than today. Recent ice core measurements (Pearman et al. 1986)
are consistent with the upper end of this range and indicate that as early as
the seventeenth and eighteenth centuries, the average C02 concentration was
approximately 281 ppm + 7 ppm (Exhibit 2-12).
Methane
Ambient atmospheric measurements in the last several decades show that the
concentration of methane is increasing (Rasmussen and Khalil 1984; Blake et. al.
1982; Eraser, Khalil and Rasmussen, 1984; Eraser et. al. 1981; and Ehhalt,
Zander, and Lamontague 1983). Estimates of the rate of increase vary.
-------
2-14
EXHIBIT 2-9
Measured Increases in Tropospheric
Concentrations of Nitrous Oxide (N20)
N,O ADRIGOLE. IRELAND
9310jl:,!nl
< 300<
|2»,
1978 1979 1980 1981 1982 1983 1984
N,O CAPE MEARES, OREGON
"> > |
a 330 I
5 i I
s 320' i
« 310- ,, ,,, , | ,,,,,,, | ,, MI II 111! !1! I Illilll! |H I I II! Illll I
°300: j
I290; j
1978 1979 1980 1981 1982 " 1983 1984
N,O RAGGED POINT, BARBADOS
I 330- I
g 320' i
J 310
0 3OO<
I 290i I
1978 1979 1980 1981 1982 1983 19S4
N,O POINT MATATULA. AMERICAN SAMOA
|32oi'|
i310- .,, ,,. = .,.,,, i,,i,,,,." '" !
S3oo.ir: ' j
!"•• - !
I»' -.
1978 1979 1980 1981 1982 1983 1984
N,O CAPE GRIM. TASMANIA
| 3201
S310 I . , .
i:i'i'ii ••'•
J300,. •
O 290 <
I
I 280 I
1978 1971 19*0 1981 1882 1M3 1
Rates of increase in tropospheric nitrous oxide at the five monitoring stations
above are: 0.77%, 0.27%. 0.24%, 0.09%, and 0.18%. While the rates of increase
appear to be larger in the Northern hemisphere than in the southern hemisphere,
there is little variation in actual concentrations. Data are from the
Atmospheric Lifetime Experiment.
Source: World Meteorological Organization, 1986; Figure 3-7.
-------
2-15
EXHIBIT 2-10
Ice Core Measurements
Nitrous Oxide (N2O) Concentrations
O 350
s§
O -H
«3 -H-
§lr
ffl
Q ft
8fl
300
25°
1600
1700
1800
1900
Ice core data show that nitrous oxide concentrations were relatively constant
until the time of the Industrial Revolution.
Source: Pearman et al., 1986.
-------
2-16
EXHIBIT 2-11
Measured Increases in Tropospheric
Concentrations of Carbon Dioxide (CO2)
J50
315
I 310
o
>
s
3 335
Z 330
5
UJ
<_>
5
325
320
315 -
310
1955
1960
1965
1970
1975
1980
Monthly measurements from Mauna Loa, Hawaii. Data collection began in 1958 with
the International Geophysical Year. Since that time, concentrations have
increased 10 percent.
Source: Keeling, C.D., and GMCC/NOAA, unpublished.
-------
2-17
EXHIBIT 2-12
Ice Core Measurements of Historical
Carbon Dioxide (CO2) Concentrations
320
o
O H 300
(0
280
C
•H
260
1600
1700
1800
1900
Ice core data show that carbon dioxide concentrations were relatively constant
until the time of the Industrial Revolution.
Source: Adopted from Pearman et al., 1986.
-------
2-18
Rasmussen and Khalil (1984) had computed an average annual Increase of 1.3
percent, which at current concentrations is an increase of 0.02 ppm per year.
Their recent work (Khalil and Rasmussen 1986), however, indicates that this
trend estimate was influenced by interannual variability which may be linked to
the effects of the El Nino-Southern Oscillation. Their corrected estimate of
the long-term rate of increase is about 0.016 ppm per year, or one percent
annually. Measurements of Blake et. al. (1982) are consistent with a linear
rise of 0.018 ppm per year. Recently, spectrographic analyses by Rinsland,
Levine and Miles (1985) indicate an annual growth rate since 1951 of 1.10
percent. Rowland (in NASA 1986) shows an increase of 0.017 ppm per year since
1977 (Exhibit 2-13).
The examination of methane trapped in ice cores reveals that its
concentration was relatively constant until approximately 150-200 years ago.
Since that time it appears to have roughly doubled (Pearman et al. 1986;
Rasmussen and Khalil 1984) (Exhibit 2-14).
Carbon Monoxide
Since CO emissions can influence methane concentrations they must be
considered. Information about past CO trends would allow models to be used to
estimate how CO and CH4 fluxes have changed in the past. The following is a
summary from the World Meteorological Organization's international assessment
(World Meteorological Organization 1986) (references cited refer to the WMO
document):
[... Khalil and Rasmussen (1984b,c) indicated CO increases
of about 5% yr at Cape Meares, Oregon between 1979 and
1982. Subsequent measurements at this site lowered the
estimated mean trend. Results presented by Dvoryashina et
al. (1984), based on spectroscopic measurements of CO over
the U.S.S.R. between 1971-1983, suggest a 1-2% increase
during that period. Rinsland and Levine (1985) deduced
values for CO over Switzerland in 1951 (from Migeotte's
plates), and they estimated [a] mean annual increase of
2% yr"1 between 1951 and 1981 at that site.
Mean concentration concentrations and variability are
smaller for CO in the Southern Hemisphere than in the
north. The dominant sources of CO in the south may be the
oxidation of CH4 and transport from the north. Comparison
of recent measurements of CO at Cape Point, South Africa
(1978-81) with shipboard data obtained in 1971-1972
indicates that CO in the Southern Hemisphere may have
increased by 0.5-1% yr"1 (Seiler et al., 1984b).
Measurements of CO taken at Tasmania and the South Pole do
not yet show statistically significant increases (Eraser
et al., 1984).
Unfortunately, the extent to which these measurements can be extrapolated
with confidence to estimate global CO change is unclear given the spatial and
temporal variability of CO. The importance of establishing a definitive trend
-------
2-19
EXHIBIT 2-13
Measured Increases in Tropospheric
Concentrations of Methane (CH4)
1.65
o
g
I
1.60
u
I
8
1.55
1.50
1977
1979
1981
1983
1985
Average concentrations of methane are increasing at approximately 0.017 ppm per
year.
Source: Rowland, in NASA, 1986; Figure 5.
-------
2-20
EXHIBIT 2-14
Ice Core Measurements of
Historical Methane (CH4) Concentrations
c c
o o
•H -H
-U rH
fO rH
1,400
§
8
en
oo
0..-0
1600
1700
1800
1900
Ice core data show that methane concentrations were relatively constant until
the time of the Industrial Revolution. Since that time, they have roughly
doubled.
Source: Adopted from Pearman et al., 1986.
-------
2-21
for CO concentrations is clear, however, since once the CH4 and CO trends are
both understood, the fluxes generating them can more easily be derived.
For example, modeling analyses by several investigators (Khalil and
Rasmussen 1985a; Levine, Rinsland, and Tennille 1985; Thompson and Cicerone
1986) imply increases in CH4 fluxes from 1850 to 1985 ranging from 15 percent to
70 percent, depending on the magnitude of assumed CO changes during that period.
Levine, Rinsland, and Tennille (1985) used their estimates of changes in CO and
CH4 concentrations (1 percent and 2 percent, respectively), to estimate a change
of 14 percent in methane fluxes and 86 percent in CO fluxes to reconstruct
observed atmospheric changes in these gases. The uncertainties in measurements
and atmospheric models, however, are still too large to rely upon.
FACTORS THAT INFLUENCE TRACE GAS LIFETIMES
Trace gas molecules, both natural and man-made, are released into the
atmosphere at the earth's surface. Unless some rapid process exists for their
removal, these molecules are soon distributed throughout the troposphere. The
time scale for local vertical mixing is a few weeks; that for east-west mixing
about the globe, a few months; and that for exchange between northern and
southern hemispheres, a year or two (NAS 1976).
Trace gases can be removed from the troposphere by a number of processes
that occur either at the earth's surface or in the atmosphere. Physical
processes, such as absorption in the oceans, can remove trace gases from the
atmosphere. This is an important process for C02. Chemical processes, such as
reactions with the OH radical, can also remove trace gases from the troposphere.
These processes are important for a wide array of gases, particularly methane,
HCFC-22, and methyl chloroform. Other trace gases, including CFC-11, CFC-12,
CFC-113, Halon-1211, and Halon-1301, are chemically inert. For these gases,
transport to the stratosphere is the only significant removal process (NAS
1983).
Transport of trace gases within and between the troposphere and stratosphere
involves the vertical motion of large air masses. It is thus independent of the
molecular weight or structure of the species involved (NAS 1976) . It is a slow
process because air exchange is inhibited by the temperature structure of the
atmosphere. The stratosphere sits as a permanent air inversion over the
troposphere with temperature rising with altitude rather than falling. The
troposphere is heated from the surface and is vertically unstable. This
inversion inhibits transport.
The average concentration of a trace gas in the troposphere is determined by
the balance between the source strength of the trace gas, its rate of chemical
transformation in tropospheric destruction, its deposition, and the net flux
through the tropopause.
The lifetime of a trace gas in the atmosphere can be defined as the average
time its molecules reside there. If at any time, the release of a particular
trace gas is suddenly terminated, the residence time, or atmospheric lifetime,
is the time required for the concentration to drop to 1/e (37%) of its value at
the time of termination (NAS 1976).
-------
2-22
LONG-LIVED TRACE GASES
Many stratospheric perturbants are relatively chemically inert in the
troposphere. Despite an intense ten year effort to search for alternative sinks
for these long-lived gases, their only known significant sink is transport to
the stratosphere (NAS 1976; and NAS 1984). Lifetimes for these gases are: 75
(+32/-17) years for CFC-11 and 111 (+2S9/-46) years for CFC-12 (WHO 1986); 90
years for CFC-113 (NAS 1984); 50 years for CC14 (WMO 1986); 110 years for
Halon-1301 and 25 years for Halon-1211 (NAS 1984); and 150 years for N20 (WMO
1986). Because loss to the stratosphere is slow relative to their current
source strength, long lived gases would be expected to accumulate in the
troposphere and increase in concentration.
Clearly the rise in concentrations of gases demonstrates this fact. Current
concentrations of these trace gases appear far from steady state, and given
their current emission levels, concentrations will continue to rise even if
emissions do not increase (that is, if emissions do not move further from
atmospheric steady state). Thus, if emissions are held constant, tropospheric
concentrations will continue to increase -- although ultimately the increase
will slow and concentrations will gradually reach equilibrium (steady state).
At steady state, the tropospheric concentration will exceed today's
concentration.
Neglecting atmospheric feedbacks, a simplified model (See Appendix A, this
chapter) of source and loss terms implies that if current CFC-12 emissions are
held constant (Exhibit 2-15A), the concentration in the year 2100 would be 1.9
ppbv (Exhibit 2-15B), almost four times higher than the current concentration.
To halt a rise in concentrations would require a large shift in emission rates.
A reduction of 85 percent in CFC-12 emissions would be required to prevent an
increase from current concentrations (Exhibit 2-16A). To hold tropospheric
concentrations of CFC-11 constant would require an 80 percent cut in current
emissions (Exhibit 2-16B).
Reductions in emissions less than 85 percent would only slow increases in
concentrations. Exhibit 2-17 shows the concentrations of CFC-12 associated with
different emission trajectories. For example, a 15 percent decrease in current
emissions of CFC-12 would imply a tropospheric concentration in 2100 of 1.6 ppb,
approximately 3.9 times higher than the current concentration. A 50 percent
decrease in current emissions of CFC-12 would still result in increases in
tropospheric concentrations, and by 2100 a concentration of 1.01 ppbv, 2.5 times
the current concentration.
The disequilibrium for these long-lived gases between current emissions and
tropospheric concentrations has implications for the certainty of estimating
future concentrations. Future tropospheric concentrations will depend heavily
on past emissions. Even total termination of additional emissions of long-lived
gases to the atmosphere would not greatly alter concentrations for decades. In
addition, with long lived gases, preventing rises in concentration will be
difficult because only large reductions will bring emissions and gases back into
equilibrium. Freezes or small reductions will allow concentrations to rise for
decades.
-------
2-23
EXHIBIT 2-15A
CFC-12: Constant Emissions
(mill kg)
500
400
300
200
100
0
1930
1985
2100
EXHIBIT 2-15B
CFC12: Atmospheric Concentrations
(ppbv)
1930
2100
If future emission of CFC-12 were held constant at today's levels (A),
atmospheric concentrations would continue to rise for over 100 years (B).
Computed with simplified model of source and loss terms. See Appendix to
Chapter 2.
Source: Hoffman, 1986.
-------
2-24
EXHIBIT 2-ISA
500
400
300 -
200 -
100 -
0
CFC-12: Emissions
(mill kg)
1930
1985
2100
EXHIBIT 2-16B
CFC-12 Atmospheri9 Concentrations
(ppbv)
0.40
0.30 -
0.20 -
o.io H
I '
0
1930
1985
2100
A reduction of 85% in CFC-12 emissions (A) would be required to hold
concentrations constant (B). Computed with simplified model of source and loss
terms. See Appendix to Chapter 2.
-------
2-25
EXHIBIT 2-17
CFC-12: Atmospheric Concentrations
from Different Emission Trajectories
•B 2
I
3
ft
i
i -
0
Constant
emissions
15% Cut
50% C\il
85% Cut
1930
1905
2100
For CFC-12, holding emissions constant at 85% of today's level (a 15 percent
cut), would allow concentrations to increase by a factor of four. Only an
emission cap at 15 percent of today's level (an 85 percent cut) could hold
concentrations constant. Computed with simplified model of source and loss
terms. See Appendix to Chapter 2.
Source: Hoffman, 1986.
-------
2-26
TRACE GASES WITH SHORTER LIFETIMES
Several other stratospheric perturbants have relatively shorter lifetimes.
Their concentrations will depend on emissions from relatively shorter time
periods. Among the anthropogenic trace gases, HCFC-22 and methyl chloroform
(CH3CC13) have lifetimes shorter than 50 years.
HCFC-22 and CH3CC13 are partially halogenated (i.e., they contain C-H bonds)
and react with OH, the hydroxyl radical, in the troposphere. This chemical
removal process is responsible for their shorter lifetimes: 20 years for HCFC-22
(NAS 1984), and 6.5 years for CH3CC13 (WMO 1986). These lifetimes are long,
however, compared with those of molecules like carbon monoxide (CO), which have
a 16-week average lifetime (Ramanthan et al. 1985).
Methane (CH4), a trace gas with both natural and anthropogenic sources, has
a lifetime of approximately 11 years (WMO 1986). The major documented removal
processes for methane is also reaction with OH. This removal process appears to
account for 98 percent of the total removal. The remaining 2 percent is
accounted for by consumption by aerobic soils.
The current concentrations of these trace gases are not as far from
equilibrium with current emissions as are gases like CFC-11 or 12.
Concentrations twenty or more years from now will rise at current rates only if
emissions increase or if chemical sinks decrease so as to lengthen chemical
lifetimes. Changes in emissions can, within a relatively shorter time, alter
future concentrations significantly.
CARBON DIOXIDE AND THE CARBON CYCLE
The carbon cycle controls the distribution of carbon dioxide (C02)
throughout the biosphere. Emissions from fossil fuels are only one part of this
complex combination of biogeochemical processes. Other components of the carbon
cycle are the uptake of carbon by the terrestrial biosphere and the uptake,
absorbtion, and outgassing of C02 in the oceans. The carbon cycle is discussed
in greater detail in Chapter 4 of this assessment. Interested readers may also
wish to consult the "state-of-the-art" report Atmospheric Carbon Dioxide and the
Global Carbon Cycle. recently issued by the U.S. Department of Energy (Trabalka
1985) and The Carbon Cycle and Atmospheric C02: Natural Variations Archean to
the Present (Sundquist and Broecker 1985).
SOURCE GASES FOR STRATOSPHERIC SULFATE AEROSOL
Stratospheric sulfate aerosols (OCS, CS2) and volcanically injected chlorine
can in some cases reach and perturb the stratosphere. While most sulfur gases
emitted into the troposphere from natural and anthropogenic sources are too
reactive and/or too soluble to reach the stratosphere, carbonyl sulfide (OCS) is
an important exception (Crutzen 1976; Sze and Ko 1979). Apart from volcanic
injection, the major source of sulfur to the stratosphere is OCS from the
troposphere.
OCS, the most abundant gaseous sulfur carrier in the atmosphere, has a
nearly uniform concentration in the free troposphere of 500 pptv and an
estimated lifetime of more than one year (WMO 1986). Current estimates of the
global sources and sinks of OCS have been derived by extrapolating a very
limited data base and are subject to large uncertainties. Natural sources
include oceans, soils, and coastal salt marshes and an important secondary
-------
2-27
Turco et al. (1980) conclude that "the total global source of DCS is 1 to 10
tg per year, and that a large fraction of this, as much as 50%, may result from
anthropogenic activities related both to fuel processing and consumption." They
note that the size of the DCS combustion source is sensitive to the use of
sulfur recovery systems: untreated stack gases have very low OCS
concentrations, while the use of sulfur recovery systems generates OCS.
Increases in the future use of scrubbers could thus increase OCS emissions.
A small contribution to OCS emissions may result from the use of catalytic
converters in automobiles, which occasionally generate large quantities of (H2S)
and OCS. Negligible anthropogenic sources include direct commercial production,
cigarette smoke, vapors from cooking grain mashes, and Kraft mills. Future
concentrations of OCS cannot now be reliably predicted due to a lack of research
in this area. Given the possible importance of aerosols in the stratosphere,
this deficiency needs to be remedied (Turco et al. 1980).
Volcanoes have long been recognized as dominant sources of stratospheric
sulfate and aerosol. It has also been clear for some time that they could also
be sources of stratospheric chlorine. Little research has been done to quantify
this source. The amount of volatile material in the pre-eruption magma varies
from volcano to volcano, the amount of chlorine in the volatile material varies
similarly, and soluble, polar compounds like hydrochloric acid (HC1) can be
removed during the rapid rise (and condensation) of a volcanic plume. Hence
volcanoes are sporadic sources not easily described by annual averages. It is
clear, however, that only a fraction of volcanic eruptions penetrate the
stratosphere (WMO 1986).
-------
2-28
APPENDIX A
CFG EMISSIONS-CONCENTRATIONS MODEL
A simplified atmospheric parameterization, taken from Rind and Lebedeff
(1984), can be used to relate future tropospheric CFC-11 and CFC-12
concentrations to their future surface emissions. Their documentation follows:
... we estimate these residence times t^ to be 75 years for
Fll and 150 years for F12.2 Thus, for the year m the
concentration C^(m) as a function of the annual release R^(m) is
given by:
m -(m-e)/t
Ck(m) - ffe S e Rfc(e). (A)
e=1940
According to our estimate the annual release for both
fluorocarbons during the year 1940 was zero. The constant f^
relates the mixing ratios C^ in ppbv of fluorocarbons to their
annual release R^ (in millions kg/year). These constants of
proportionality were determined by comparing the computed
concentrations with observed globally averaged values of Fll and
F12 for the years 1977-1979 as reported by NOAA (1979) and
(1980) in Geophysical Monitoring for Climatic Change No. 7 and
No. 8. Global average concentrations were computed from the
results of measurements of concentrations at five stations.
Locations of these stations and the measured values are
summarized in Tables 4 and 5 [Exhibits A-l and A-2, this paper].
We assumed the concentrations to be zonally uniform and fitted
expressions
5
C (A,*) = S ae sin6'1 ()
e=l
to the data in Exhibit 2-4. Here denotes latitude and A
longitude. The global averages are shown in the last column of
Table 4 (Exhibit A-l, this paper). The constants of
proportionality f^ were obtained by^fitting expressions (A) to
the data, yielding f ^ = 4.6395*10 and f±2 = 5.3279*10
ppb/millions/kg/year).
The Rind and Lebedeff method does not consider changes in atmospheric
processes that may occur as a result of potential stratospheric ozone depletion.
Results from one-dimensional (1-D) model calculations indicate that if
stratospheric ozone levels decrease, the increased ultraviolet radiation that
penetrates to the troposphere may reduce CFC-11 and CFC-12 lifetimes and hence
the growth in their tropospheric concentrations. This process is unlikely to be
significant in scenarios of low CFG growth (Stolarski, personal communication).
r\
*• While the Rand and Lebedeff estimate for the CFC-12 lifetime differs from
that of WMO (1986), the estimate is within the uncertainty band given by WMO.
-------
2-29
EXHIBIT A-l
Concentrations of Fluorocarbons (ppbv)
STATION
YEAR
BRW
NWR
MLO
SMO
SPO
GLOBAL
Fluorocarbon 11 (CC13F)
1977
1978
1979
0.159 0.155
0.172 0.168
0.182 0.175
0.148 0.140
0.162 0.153
0.174 0.164
0.139
0.154
0.175
0.145
0.159
0.171
Fluorocarbon 12 (CC12F2)
1977
1978
1979
0.292
0.302
0.301
0.275
0.296
0.301
0.270
0.291
0.296
0.256
0.273
0.276
0.248
0.271
0.306
0.262
0.282
0.290
EXHIBIT A-2
Locations of the Stations
NAME
ABREV.
LONGITUDE
LATITUDE
Point
Niwot
Mauna
Barrow
Ridge
Loa
American Samoa
South
Pole
BRW
NWR
MLO
SMO
SPO
130
105
155
170
24
.60
.63
.58
.56
.80
O
0
o
o
0
w
w
w
w
w
70.
40.
19.
14.
89.
32
05
53
25
98
O
0
o
o
0
N
N
N
S
S
Source: National Oceanic and Atmospheric
Administration (1979) Geophysical Monitoring
for Climate Change No. 7, Summary Report
1978, B.C. Bendonca, (ed.).
-------
2-30
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-------
CHAPTER 3
PROJECTIONS OF
EMISSIONS OF INDUSTRIALLY-PRODUCED
POTENTIAL OZONE MODIFIERS*
SUMMARY
Human activities are the only source of emissions for three important
classes of chemicals that may modify the amount of ozone in the atmosphere: (1)
chlorofluorocarbons (CFCs); (2) chlorocarbons; and (3) Halons. CFCs and
chlorocarbons release free chlorine into the stratosphere, and Halons release
free chlorine and/or bromine into the stratosphere (there are other natural
sources of chlorine in the atmosphere).
Historically, CFCs have contributed more to potential ozone modification
than have chlorocarbons and Halons. The most widely used CFCs are CFC-11 and
CFC-12, which account for 80 percent of today's CFC production worldwide.
CFC-113 and HCFC-22 are also commercially produced in large quantities. A
variety of specialty CFCs are produced in small quantities.
Due to their unique physical properties, CFCs are employed in a diverse set
of applications, including: aerosol propellants; refrigeration; air
conditioning; solvents; and foam production. Substitutes for CFCs or the CFC-
related product exist for many of these applications. In some applications
(such as refrigeration), the CFCs remain captured in the product for many years
before being released.
Data describing the historical production and use of CFCs for various parts
of the world have been collected by a variety of organizations. The most
comprehensive data on the production of CFC-11 and CFC-12 have been compiled by
the Chemical Manufacturers Association (CMA) from reports by CFC producers.
These data indicate that production of CFC-11 and CFC-12 peaked in 1974, and
subsequently declined through 1982. Combined CFC-11 and CFC-12 production since
1982 has increased each year.
The decline in the production of CFC-11 and CFC-12 from 1974 to 1982 is
attributable primarily to the reduction in their aerosol propellant use. The
United States implemented a ban on the use of CFCs in nonessential aerosol
applications in 1978. Several other countries and groups of countries have
instituted controls on aerosol applications with varying degrees of stringency.
During the period when aerosol applications were declining, nonaerosol
applications (refrigeration, air conditioning, solvents, foam production)
continued to increase. In 1978, nonaerosol usage exceeded aerosol usage, and by
1985 nonaerosol usage was in excess of 70 percent of total CFC applications.
Therefore, CFC usage is increasingly dominated by nonaerosol applications.
* Better information about estimates of the use of CFCs in different countries
and Halon projections became available in late summer of 1987. The body of this
chapter does not incorporate these changes; however, in the Appendix of this
Chapter these data are shown. The data shown in the Appendix of this chapter
are not used in the Risk Assessment.
-------
3-2
Long term projections of CFCs are needed for risk assessment because of
their long lifetimes. Projections of the potential future demand for CFCs were
presented at a UNEP economics workshop on CFCs in May of 1986, and are found in
the trade literature. Indications are that in the absence of additional
controls on production, use, or emission, total CFG production is expected to
increase in the foreseeable future. Underlying this growth of CFCs is the
expectation that aerosol applications will continue to decline and level off.
The future growth in production is expected to be driven by increases in
nonaerosol applications. However, long term projections of potential growth are
viewed as very uncertain. In Chapter 18, we define a series of "what if"
scenarios for testing the atmospheric impacts of continued emission of these
ozone depleters that span a wider range of possible emission futures than
discussed here. In this chapter, the focus is on what various economic analyses
show are the most likely emission trends.
The chlorocarbons (carbon tetrachloride and methyl chloroform) are used
primarily as solvents and chemical intermediates. In the United States carbon
tetrachloride is primarily used to make CFCs and only a small amount of this use
is emitted to the atmosphere. In developing countries carbon tetrachloride is
believed to be used as a solvent, resulting in considerable emissions. Methyl
chloroform is primarily used as a general purpose solvent worldwide. Future
demand for methyl chloroform is expected to grow at a rate similar to rates of
growth of economic activity. Future demand for carbon tetrachloride is expected
to grow at the same rate as the demand for CFCs.
Halons have been used in hand-held and total-flooding fire extinguishers
since the 1970s. Their unique properties make Halons valuable for protecting
delicate electronic equipment such as computers. Annual production has been
estimated as small (approximately 20,000 kilograms) and emissions have been
assumed, by some authors, to be very small because the Halons remain in the fire
extinguishers for many years. In the absence of industry led attempts to reduce
halons or government regulation, halon production and emissions are expected to
grow significantly over the next 15 years, although the potential for long-term
growth is uncertain.
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3-3
FINDINGS
1. HUMAN ACTIVITIES ARE THE ONLY SOURCE OF EMISSIONS FOR THREE CLASSES OF
POTENTIAL OZONE-DEPLETING CHEMICALS: CHLOROFLUOROGARBONS (CFCs):
CHLOROCARBONS (CARBON TETRACHLORIDE AND METHYL CHLOROFORM'): AND HALONS
(chapter 3)1.
la. Since their development in the 1930s, CFCs have become useful chemicals
in a wide range of consumer and industrial goods, including: aerosol
spray cans; air conditioning; refrigeration; foam products (e.g., in
cushions and insulating foams); solvents (e.g., electronics); and a
variety of miscellaneous uses.
Ib. CFC-11 (CC13F) and CFC-12 (CC12F2) have dominated the use and emissions
of CFCs, accounting for over 80 percent of current CFC production
worldwide. Because of increased demand for its use as a solvent,
CFC-113 (CC12FCC1F2) has become increasingly important as a potential
ozone-depleting chemical.
2. WHILE CFCs USED IN AEROSOLS DECLINED FROM 1974 UNTIL 1984. NONAEROSOL USES
OF CFCs HAVE GROWN CONTINUOUSLY AND APPEAR CLOSELY COUPLED TO ECONOMIC
GROWTH (chapter 3).
2a. From 1960 to 1974, the combined production of CFC-11 and CFC-12 from
both aerosol and nonaerosol applications grew at an average annual r;ate
of approximately 8.7 percent. Total global CFC-11 and -12 productirjn
peaked in 1974 at over 700 million kilograms.
2b. From 1976 to 1984, sales of CFC-11 and CFC-12 for aerosol applicat;ions
declined from 432 million kilograms to 219 million kilograms, an .'average
annual rate of decline of over 8 percent. During the same period sales
for nonaerosol applications grew from 318 million kilograms to 47 g
million kilograms, an average annual compounded growth rate of 5
percent. By 1986, total CFC-11 and -12 global production was riearly
that in 1974.
3. STUDIES OF FUTURE PRODUCTION OF CFCs-11 AND -12 PROJECT AN AVERAGE ANNUAL
GROWTH RATE OF APPROXIMATELY 1.0 TO 4.0 PERCENT OVER THE NEXT 15 TO 65 YEARS
(chapter 3).
3a. A large number of studies of future global demand for CFCs were
conducted by experts from six countries under the auspices; of the United
Nations Environment Programme. These studies used a variety
of methods for estimating both near- and long-term periods. In general
these studies assumed that: (1) demand for CFCs was driven by economic
factors; (2) no additional regulations on CFC use were inrposed; and (3)
consumers or producers do not voluntarily shift away fr6m CFCs because
of concern about ozone depletion. These studies pr~vide a range of
growth rates for developing alternative baseline scenarios of future CFC
use and emissions.
The chapter references refer to the main body of the visk assessment
-------
3-4
3b. In general, these studies projected that CFC aerosol propellant
applications would remain constant or decrease further in many
regions of the world.
3c. In the U.S. over the past four decades new uses of CFCs have
developed first in refrigeration, then in aerosols, then in foam
blowing, and then in solvents.
3d. Studies have projected that growth in developed countries for
nonaerosol applications is expected to be driven by increased use in
foam blowing (primarily for insulation) and as solvents, and by the
continued introduction of new uses. The wide range of estimates of
future growth reflects the large uncertainties related to population
and economic growth, and technological change.
3e. Studies suggest that future CFC use in developing countries will grow
faster (i.e., at a higher rate) than future CFC use in the developed
world. Nevertheless, the projected rates for the developing
countries are lower than the historical rates that have been
experienced in wealthier countries. While these studies were done
using aggregate relationships of GNP and CFC use, they made different
assumptions about how closely the pattern of CFC use in developing
nations would replicate the pattern in developed nations, generally
assuming lower use rates. However, evidence from one recently
completed study (not completed at the time of the UNEP workshop)
indicates that in developing countries the penetration of CFC-using
goods may be occurring faster than expected on the basis of the
historical relationship in developed nations. If that study is
correct, growth in developing nations would be larger than proj ected
in the above-mentioned studies, which generally assumed less
penetration in developing nations than had occurred in developed
nations.
3f Three long-term studies of CFC demand report annual average rates of
growth for CFC-11 and CFC-12 over the next 65 years ranging from 0.2
percent to 4.7 percent, with a median estimate of about 2.5 percent.
The "what if" scenarios used for quantitative risk assessment span a
wider range of growth, including one scenario with substantial
(iecline.
3g. Limited studies on CFC-113 and CFC-22 project that in the absence of
regulation or voluntary shifts away from these chemicals, their
growth will increase at a faster rate than CFC-11 and -12 as new
markets develop and existing ones expand (e.g., use of CFC-113 as a
solvent in metal cleaning).
4. THE CHLOROCARBONS (METHYL CHLOROFORM AND CARBON TETRACHLORIDE) ARE USED
PRIMARILY AS ~QLVENTS AND CHEMICAL INTERMEDIATES. ANALYSIS SUGGESTS
LIMITED FUTUR.: GROWTH FOR THESE CHEMICALS (chapter 3).
4a. Methyl chloroform is primarily used as a general purpose solvent.
Global use in 1980 was estimated at nearly 460 million kilograms.
Limited finalysis of future demand indicates that it is expected to
grow at the rate of growth of economic activity (as measured by GNP).
Factors affecting future demand include possible control on it or
other solvents due to their health effects. Thus, use of methyl
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3-5
its use could be increased if CFG-113 use is restricted. Because
methyl chloroform has a substantially shorter atmospheric lifetime than
CFG-113, it has relatively less potential for depleting ozone.
4b. Carbon tetrachloride is primarily used to make CFCs in the U.S. In
developing countries it is also sometimes used as a general purpose
solvent. In general, future production and emission of carbon
tetrachloride is expected to follow the pattern of production of CFCs.
5. HALONS. ON A PER POUND BASIS. POSE A GREATER THREAT (2-1/2 TO 12-1/2 TIMES')
TO OZONE DEPLETION THAN DO CFCs.
5a. Halons have been used in hand-held and total-flooding fire
extinguishers since the 1970s. Annual production has been limited
(approximately 20,000 kilograms) and emissions have been assumed to be
only a small fraction of production based on the assumption that the
halons remain inside the fire extinguishers. Recent research suggests
the proportion of Halons released may be substantially higher. In the
U.S., industrial response to concern about depletion from halons is
likely to lead to some voluntary steps to curtail emissions.
5b. A single study has projected future demand for Halons. It indicates
that near-term demand is growing rapidly and that production may double
by the year 2000. In that study, longer-term demand is judged
uncertain and may range from an average annual decline of 1 percent
from 2000 to 2050 to an annual increase exceeding 5 percent.
5c. The expected rate of Halon emissions is very uncertain. The one study
assumed most production would remain within fire extinguisher systems
as part of a growing Halon "bank." That study has been the basis for
scenarios used in this analysis.
5d. The historic growth in Halon 1211 concentrations (recently measured at
over 20% per year) is significantly higher than the rate assumed for
future years in the one existing study.
5e. Discussions with Halon users indicate that Halon 1301 emissions may be
underestimated in the study used for this risk assessment. A recent
survey showed that existing systems are undergoing widespread testing
and accidental discharge occurs more frequently than assumed in prior
studies.
5f. Additional analysis of Halon emission estimates are necessary to assess
more adequately the risks associated with this trace gas.
Since this risk assessment was completed, Halon users in the U.S. have
taken a variety of steps to reduce emissions. This step is not considered in
this Risk Assessment.
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3-6
INTRODUCTION
Man's activities are the primary source of emissions for several important
potential modifiers of stratospheric ozone, including:
o Chlorofluorocarbons (CFCs), including: CFC-11; CFC-12;
HCFC-22; and CFC-113;
o Chlorocarbons, including: methyl chloroform and carbon
tetrachloride; and
o Halons, including: Halon-1211 and Halon-1301.
The atmospheric concentrations of these gases are driven by their emissions, and
by the natural physical processes that destroy and transport them (thereby
removing them from the atmosphere). This chapter describes the historical use
and emissions of each of these three classes of potential ozone-modifying
substances as well as estimates of potential future use and emissions. A long
term perspective on emissions is essential for assessing the risks because of
the long lifetime of most of these chemicals.
CFCs are discussed first. Historically, these compounds have contributed
the most to potential modification of stratospheric ozone. Chlorocarbons are
next in importance (despite the fact that their production volume is larger than
CFCs), and are discussed second. Finally, the information on the relatively
small amount of Halon production and use is presented. Despite their relatively
small production volume, Halons are considered to be growing in importance due
to their strong potential for modifying stratospheric ozone.
CHLOROFUJOROCARBONS
CFCs are a class of man-made chemicals that contain chlorine, fluorine, and
carbon. There are four major CFCs that are produced in commercial quantities.
o CFC-11;
o CFC-12;
o HCFC-22; and
o CFC-113.
CFC-11 and CFC-12 account for the largest share of total CFC production,
approximately 80 percent in recent years.
CFCs are used in a variety of applications that require chemicals with a
^ The relative importance of the compounds in terms of stratospheric ozone
modification depends on a variety of factors relating to the chemical
composition of each substance. Camm et al. (1986) report the following relative
importance as of 1985: CFCs -- 77.8 percent; Chlorocarbons -- 16.7 percent; and
Halons - - 5.6 percent.
2 Other CFCs produced in limited quantities include: CFC-13, CFC-14,
CFC-21, CFC-23, CFC-114, CFC-115, CFC-142b, CFC-152a. (See Hoffmann and Klander
1978, p. 8). Other CFCs with potential applications that are not currently
available commercially include CFC-123 and CFC-134a.
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3-7
fairly unique set of physical properties. The properties of CFCs that make them
valuable include:
o CFCs can be used with a variety of materials, including
plastics;
o CFCs are safe to use, they are not flammable and they are
relatively nontoxic;
o CFCs have a low boiling point; this factor is important in
manufacturing foams and for refrigeration applications; and
o CFCs have good thermodynamic properties.
Exhibit 3-1 displays selected properties of three of the major CFCs.
These properties enable CFCs to be used in a variety of important
applications. Initially, CFCs displaced ammonia in early refrigeration
applications. Ammonia was used in refrigerators that were replacing ice boxes
in the early twentieth century. However, ammonia is more toxic and combustible
than CFCs, and consequently the switch to CFCs reduced the hazards of owning a
refrigerator.
In the 1950s, aerosol propellant uses of CFCs were first introduced. These
applications grew into large markets of personal care products such as hair
sprays and deodorants. Also during the 1950s, refrigeration and air
conditioning applications grew rapidly. By the 1960s, these applications were
well established.
Two new important uses for CFCs were introduced in the 1960s. During this
decade, CFC-11 was first used to make plastic foams. These foams are used as
seat cushions (such as in furniture and cars) and as carpet backings. The foams
are also used as insulation in appliances (such as refrigerators) and buildings.
The use of CFC-11 in these foam applications has grown so rapidly that this is
now the dominant nonaerosol use of CFC-11. The other major use introduced in
the 1960s is the application of CFC-12 to automobile air conditioners. In the
U.S., the market for automobile air conditioners has grown rapidly and now is an
important use of CFC-12.
The most recent market for CFCs is for applications that require a solvent.
In particular, the use of CFC-113 as a solvent in the manufacture of electronic
components and computer chips has been expanding rapidly. CFCs are preferred as
solvents in these applications because they are mild and are not toxic. Its
potential as a solvent for metal cleaning may also be large, but was not
explicitly analyzed in this chapter.
Exhibit 3-2 provides the following information about the four major CFCs
used by industry today; the major applications; the properties that make them
useful; the potential for non-CFC substitutes (there may be CFC-related chemical
substitutes such as CFC-123 and FC-134a that are not listed); and the
consequences of switching to the substitutes. For example, refrigeration
-------
EXHIBIT 3-1
Selected Properties of CFCs
CFC-11 CFC-12 HCFC-22 CFC-113
CFC-142b CFC-123
FC-134a
Chemical Formula
Molecular Weight
Boiling Point, °F
Freezing Point, °F
Vapor Pressure, psig
At 70°F
At 130°F
CC13F
137.4
74.8
-168
13.4*
24.3
CC12F2 CHC1F2
120.9
-21.6
-252
70.2
181.0
86.5
-41.4
-256
CC12FCC12F2 CH3CC1F2
187.4
117.6
-31
100.5
14.4
-204
122.5 21.2 (at 77°F) NA
300.0 NA NA
CHC12CF3
152.9
80.7
NA
NA
NA
CF3CH2F
102
-15.7 F
NA
NA
NA
Liquid Density, gm/cm
At 70°F 1.485 1.325
At 130°F 1.403 1.191
Atmospheric Lifetime, years 84 148
1.209 1.565 (77°F) 1.113 (77°F) 1.475 (at 60"F) NA
1.064 NA NA NA NA
33
88
NA
NA
6.4
OJ
CO
* psia.
Sources: Hoffmann, B.L., and D.S. Klander (1978), Final EIS Fluorocarbons: Environmental and Health Implications.
FDA, p. 9.
Connell, P.S. (1986), "A Parameterized Numerical Fit to Total Column Ozone Changes Calculated by the LLNL
1-D Model of the Troposphere and Stratosphere," Lawrence Livennore National Laboratory, Livermore,
California, p. 4.
WHO Criteria Document on Chlorofluorocarbons (1986), Draft Report, Environmental Criteria and Assessment
Office, U.S. EPA, Cincinnati, Ohio, p. 2-10.
Memo from Lynn Erikson, Radian Corporation to Neil Patel, EPA, July 1986.
Anderson, L.G. (1980), "The Atmosphere Chemistry of 1,1,1-2-tetrafluoroethane," General Motors Research
Laboratory, Warren, Michigan, GMR-3450.
-------
EXHIBIT 3-2
CFC Characteristics and Substitute!
Application
Refrigeration
Air Conditioning
Automobile Air Conditioning
Type of
CFC Used
CFC-11
CFC-12
CFC-22
CFC-11
CFC-12
CFC-22
CFC-113
CFC-12
Key Characteristics
of CFC Used
Thermodynamic properties
Safety
Cost
Thermodynamic properties
Safety
Cost
Thermodynamic properties
Safety
Cost
Potential Alternatives
Armenia
Sulphur Dioxide
Methyl Chloride
Ammonia
Sulphur Dioxide
Methyl Chloride
Ammonia
Sulphur Dioxide
Methyl Chloride
Potential
Consequences of Using
Alternatives
More toxic
Combustible
Corrosive
Explosive
Less energy efficient
More toxic
Combustible
Corrosive
Explosive
Less energy efficient
More toxic
Combustible
Corrosive
Plastic Foam
insulation
CFC-11
CFC-12
Thermoc
Safety
Cost
Explosive
Less energy efficient
None for high-efficiency insulation Less effective
Pentane (some foams) Combustible
Methylene Chloride (some foams) Processing difficulties
Toxicity
Solvents
Aerosol Propellents
CFC-11
CFC-113
CFC-11
CFC-12
Ability to displace all
contaminants
Chemically inert
Safety
Thermodynamic properties
Safety
Perchloroethylene
Trichlorethylene
Trichloroethane
Hydrocarbons
Carbon Dioxide
More toxic
Uses more energy
Combustible
Reduced product quality
CFCs are used in a diverse set of applications. Substitutes for CFCs have undesirable consequences in many applications.
Source: Alliance for Responsible CFC Policy (1980), "An Economic Portrait of the CFC-Utilizing Industries in the United States,"
Washington, D.C.
-------
3-10
applications use CFCs 11, 12, and 22. These compounds are used because of their
thermodynamic properties, safety, and low cost. Potential alternatives to these
compounds include- ammonia, sulfur dioxide; and methyl chloride. However, these
chemicals are more toxic, flammable, corrosive, explosive, and/or less energy
efficient than CFCs. Analogous descriptions are shown for the other
applications.
Historical Production and Emissions
Data on the production of CFC-11 and CFC-12 have been collected by:
o The Chemical Manufacturers Association (CMA) for the
years 1931 to 1985;
o The United States International Trade Commission (ITC);
and
o The European Economic Community (EEC).
The CMA data were supplied by 21 CFG-producing companies that operate plants
around the world. These companies and the locations of their plants are listed
in Exhibit 3-3. These reporting companies represent CFC production in almost
all of the world except for India, Argentina, the East Bloc countries, and
China. Production is known to take place in Argentina and India, but data on
their production is sparse, and the level of production is believed to be low.
The most recent report issued by the CMA is "Production, Sales, and
Calculated Release of CFC-11 and CFC-12 Through 1985," September, 1986. Exhibit
3-4 lists the historical production data for CFC-11 and CFC-12 reported to the
CMA. Exhibit 3-5 displays these data for CFC-11 and CFC-12 combined in a
graphical form for 1960 to 1985. As the exhibits show, total production
increased rapidly throughout the 1960s and early 1970s, reaching a maximum of
813 thousand metric tons in 1974. During this period, the combined production
of these two CFCs grew at an average rate of 14 percent per year.
However, beginning in the mid-1970s, public attention focused on the
potential for CFCs to deplete stratospheric ozone. In response to these
concerns, the United States, a major producer of CFCs, instituted a ban on the
use of CFCs in nonessential aerosol propellant applications in 1978. Several
other countries also imposed controls on the production and use of CFCs with
varying degrees of stringency. For example, the members of the European
Economic Community (EEC) agreed to reduce the use of CFCs in'aerosols to 70
percent of what they had been in 1976. The subsequent use of CFC-11 and CFC-12
in aerosols as reported by the EEC (1985) is displayed in Exhibit 3-6.
The effect of these controls on aerosol applications, as well as the public
perception of CFC dangers, is clearly evident; total production reported to CMA
began to decline in 1975. This decline was driven by reductions in the use of
CFC-11 and CFC-12 in aerosol propellant applications, which occurred in both the
U.S. and the EEC.
In contrast to the decline in production for aerosol propellant
applications, production of CFCs for nonaerosol applications reported to CMA
continued to increase throughout the 1970s and the 1980s (1976-1985) at an
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3-11
EXHIBIT 3-3
Companies Reporting Data to GMA
The following is a listing of the reporting companies inclusive of any
related subsidiaries and/or joint ventures that reported CFG production and
release data:
1. Akzo Chemie B.V. (Holland)
2. Allied Corporation (U.S.)
(a) Allied Canada Inc. (Canada)
(b) Quimobasicos, S.A. (Mexico)
3. Asahi Glass Co., Ltd. (Japan)
4. ATOCHEM, S.A. (France)
(a) Pacific Chemical Industries Pty. Ltd. (Australia)
(b) Ugimica S.A. (Spain)
(c) Produven (Venezuela)
5. Australian Fluorine Chemical Pty. Ltd. (Australia)
6. Daikin Kogyo Co., Ltd. (Japan)
7. Du Pont Canada, Inc. (Canada)
8. Du Pont Mitsui Fluorochemicals Co., Ltd. (Japan)
9. E.I. du Pont de Nemours & Company, Inc. (U.S.)
(a) Du Pont de Nemours (Netherlands) N.V.
(b) Ducilo S.A. (Argentina)
(c) Du Pont do Brasil S.A. (Brazil)
(d) Halocarburos S.A. (Mexico)
10. Essex Chemical Corporation (Racon) (U.S.)
11. Hoechst AG (West Germany)
(a) Hoechst Iberica (Spain)
(b) Hoechst do Brasil Quimica e Farmaceutics S.A.
12. Imperial Chemical Industries PLC (England)
African Explosives & Chemical Industries, Ltd.
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3-12
EXHIBIT 3-3 (Continued)
Companies Reporting Data to CMA
13. I.S.C. Chemicals Ltd. (England)
14. Kaiser Aluminum & Chemical Corporation (U.S.)
15. Kali-Chemie Aktiengesellschaft (West Germany)
16. Kali-Chemie Iberia SA (Spain)
17. Montefluos S.p.A. (formerly Montedison S.p.A.) (Italy)
18. Navin Fluorine Industries (India)
19. Pennwalt Corporation (U.S.)
20. Showa Denko, K.K. (Japan)
21. Societe des Industries Chimiques du Nord de la Grece, S.A. (Greece)
22. Union Carbide Corporation (U.S.)
(Union Carbide ceased production in 1977. CFCs resold by Union
Carbide are included).
Source: CMA (1986), "Production, Sales, and Calculated Release of CFC-11
and CFC-12 Through 1985," Schedule 1, Listing of Reporting Companies,
Washington, D.C.
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3-13
EXHIBIT 3-4
Production of CFC-11 and CFC-12 Reported to CMA
(millions of kilograms)
Years
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
CFC-11
-
-
-
-
0.1
0.1
0.1
0.1
0.2
0.3
0.3
0.4
0.4
0.4
0.7
1.3
3.0
4.5
6.6
9.1
13.6
17.3
20.9
26.3
32.5
33.9
29.5
35.6
49.7
60.5
78.1
93.3
111.1
122.8
141.0
159.8
183.1
217.3
238.1
CFC-12
0.5
0.1
0.3
0.7
1.0
1.7
3.1
2.8
3.9
4.5
6.3
5.9
8.2
16.7
20.1
16.6
20.1
24.8
26.1
34.6
36.2
37.2
46.5
49.1
57.6
68.7
74.2
73.4
87.6
99.4
108.5
128.1
146.4
170.1
190.1
216.2
242.8
267.5
297.3
321.1
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3-14
EXHIBIT 3-4 (Continued)
Production of CFG-11 and CFC-12 Reported to CNA
(millions of kilograms)
Years CFC-11 CFC-12
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
263.2
306.9
349.1
369.7
314.1
339.8
320.5
308.9
289.5
289.6
286.9
271.4
291.7
312.4
326.8
341.6
379.9
423.3
442.8
381.0
410.7
382.8
372.1
357.2
350.2
351.3
328.0
355.3
382.1
376.3
Source: CMA (1986), "Production, Sales,
and Calculated Release of
CFC-11 and CFC-12 Through
1985," Schedules 2 and 3,
Washington, D.C.
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3-15
EXHIBIT 3-5
Historical Production of CFC-11 and CFC-12
tc
o
o
o
w
o
900
800 -
700 -
600 -
500 -
TOTAL
NONAEROSOL
400 -
300 -
200 -
100
AEROSOL
1960
1965
YEAR
Total reported production of CFC-11 and CFC-12 increased rapidly throughout the
1960s and 1970s, reaching a maximum of 813 thousand metric tons in 1974.
Aerosol applications declined since the mid-1970s, while nonaerosol applications
continued to increase. (Note: aerosol/nonaerosol divisions prior to 1976 are
estimates.)
Source: CMA (1986), "Production, Sales, and Calculated Release of CFC-11 and
CFC-12 Through 1985,." Washington, D.C.
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3-16
EXHIBIT 3-6
CFG-11 and CFG-12 Used in Aerosol and
Nonaerosol Applications in the EEC
Aerosol Use
(millions of
Year kilograms)
1976
1977
1978
1979
1980
19813/
1982^/
1983s/
1984^
176.9
162.5
150.4
136.5
126.4
116.1
111.7
113.9
114.7
Aerosol Use
Relative to 1976
(percent)
100
92
85
77
71
66
63
64
65
Nonaerosol Use
(millions of
kilograms)
67.1
70.4
81.0
83.0
90.4
93.6
95.1
102.5
103.1
Nonaerosol Use
Relative to 1976
(percent)
100
105
121
124
135
139
142
153
154
Includes data for Greece, whereas the 1976 to 1980 data do not.
Source: EEC (1985), "Chlorofluorocarbons in the Environment: Updating the
Situation," Communication from the Commission to the Council.
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3-17
average rate of over five percent per year. Reported use of CFCs for nonaerosol
applications in the EEC has also increased during this period (see Exhibit 3-6).
The CMA reports that the largest nonaerosol use of CFG-11 is currently as a
blowing agent for making closed cell foam (CMA 1986, Schedule 5). In this
application, the CFCs not only help form the cells in the foam, but they also
increase the insulating properties of the foam. The CMA estimates that the use
of CFC-11 for this application currently accounts for approximately 36 percent
of total CFC-11 production, and that it more than doubled from 1976 to 1985,
growing at an annual average rate of over 9 percent. The second largest
nonaerosol application is reported by CMA to be as an auxiliary blowing agent in
the production of open cell foams, accounting for approximately 19 percent of
current CFC-11 production. Refrigeration is reported as accounting for 8.2
percent, and all other uses account for 5.7 percent.
Hammitt (1986) developed independent estimates of the shares of CFC-11
production going to each of the applications identified by the CMA. These
estimates were developed by estimating the intensity of use of CFCs in each of
its applications and then estimating the amount of production of each applica-
tion (e.g., foams, refrigerators, aerosol products, and miscellaneous).
Hammitt's results are very similar to the CMA estimates, and are compared in
Exhibit 3-7.
As shown in the exhibit, Hammitt's estimates conform closely with the CMA
numbers. However, Hammitt's method reportedly resulted in estimates of CFC-11
use that are eight percent less that the reported total production. This
discrepancy is listed by Hammitt under "unallocated" in Exhibit 3-7, and it
indicates that while there is general agreement on the approximate magnitudes of
the use of CFC-11 in its various applications, there is some difficulty in
accounting for the total production.
Similar work has been done to estimate the current use of CFC-12. The CMA
reports the largest current use to be in refrigeration applications, accounting
for 49 percent of the total production in 1985. Between 1976 and 1985 the use
of CFC-12 in refrigeration applications (reported to CMA) grew at an average
rate of 4.2 percent per year. Aerosol propellant applications are reported as
accounting for 32 percent, and the remaining nonaerosol uses are reported as
accounting for approximately 19 percent.
Hammitt's estimates for the share of CFC-12 going to various applications
are compared to the CMA estimates in Exhibit 3-8. Compared to CFC-11, there is
less agreement on the amount of CFC-12 currently being used in its various
applications. The primary difference between the CMA and Hammitt estimates is
that Hammitt has only 27 percent of the production going to refrigeration
applications, while CMA has 49 percent. This difference appears to be accounted
for by a 22 percent share listed as "unallocated" by Hammitt.
The differences in the Hammitt and CMA allocation estimates indicate that
there is some uncertainty regarding the current use of CFC-12.
Describing the allocation of CFG production across its possible applications
is required for assessing the current (and future) emissions of the compounds to
the atmosphere. Some applications emit their CFCs immediately upon use, and are
-------
3-18
EXHIBIT 3-7
Conpaxison of Estimated CFC-11 Use: 1985
Application
Aerosol Propellant
Foam Production:
Closed Cell
Open Cell
Refrigeration and
Air Conditioning
All Other Uses
Unallocated Use
Total
N/A = not applicable
Sources: Hammitt, J
Potential
Hananitt
Use
(103 kilograms)
93,700
115,800
57,000
9,900
N/A
23,600
300,000
•
.K. , et al. (1986)
(percent
of total)
31
39
19
3
0
8
100
, Product
Ozone -Depleting Substances.
CMA
Use
(103 kilograms)
100,500
117,300
63,500
26,900
18,600
N/A
326,800
(percent
of total)
31
36
19
8
6
0
100
Uses and Market Trends for
1985-2000. The RAND
Corporation, p. 5 and p. 94. CMA (1986), "Production, Sales, and
Calculated Release of CFC-11 and CFC-12 Through 1985," Schedule 5.
-------
3-19
EXHIBIT 3-8
Comparison of Estimated CFC-12 Use: 1985
Application
Aerosol Propellant
Foam Production:
Closed Cell
Open Cell
Refrigeration and
Air Conditioning
All Other Uses
Unallocated Use
Total
N/A = not applicable
Sources: Hammitt, J
Potential
Hammitt
Use
(103 kilograms)
115,600
42 , 800
98,300
25,400
82,900
365,000
.
.K. , et al. (1986)
Ozone -Depleting Su
(percent
of total)
32
12
27
7
22
100
. Product
bstances .
CMA
Use
(103 kilograms)
119,700
30,200
20,400
185,000
21,000
N/A
376,300
(percent
of total)
32
8
5
49
6
0
100
Uses and Market Trends for
1985-2000. The RAND
Corporation, p. 6 and p. 95. CMA (1986), "Production, Sales, and
Calculated Release of CFC-11 and CFC-12 Through 1985," Schedule 6.
-------
3-20
termed "prompt emitters." These applications include aerosol propellant,
production of open cell (or flexible) foam, solvent applications, and some
miscellaneous applications. Other applications store their CFCs for periods of
time, often years. These applications include refrigeration, air conditioning,
and the production of closed cell rigid insulating foams.
Estimates have been made of the duration for which CFCs are stored in these
products (see, for example, Quinn et al. 1986, Gamlen et al. 1986, McCarthy et
al. 1977, and Khalil and Rasmussen 1986). Exhibit 3-9 displays the estimates of
emissions for 1971 to 1985 developed by the CMA for CFC-11 and CFC-12 based on
their assessments of the allocation of production across the end uses and the
duration for which CFCs are stored in the various products. As shown in the
exhibit, because CFCs are stored in many products, emissions generally do not
equal production in any given year.
Data describing CFC production in the East Bloc countries and China are
sparse. Very little has been published about the historical and current rates
of production in these countries. Published estimates of production in the
U.S.S.R. are displayed in Exhibit 3-10 (these values are not included in the CMA
total production values shown in Exhibit 3-4). Data have not been reported that
divide these production figures into aerosol and nonaerosol applications.
Zhijia (1986) presented estimates of current CFC production in China at the
May 1986 UNEP Workshop on the Control of Chlorofluorocarbons. Zhijia reports
annual production of "18 thousand tons" for CFCs 11, 12, 13, 14, 21, 22, 112,
113, and 114. Half of this production "is used for high-molecular polymer as
raw materials; another half for the production of refrigerant, aerosol
propellant etc." (Zhijia 1986, p. 1).
Based on the data reported in Exhibit 3-10 and assumed rates of growth since
1975, Hammitt estimated the 1985 production of CFC-11 and CFC-12 in the
"communist" countries to be 41.5 thousand metric tons and 78.7 thousand metric
tons, respectively. Using Hammitt's assumption that 15 percent of total CFC-11
and CFC-12 production in these countries is outside the U.S.S.R., the implied
annual production for CFC-11 and CFC-12 in the U.S.S.R. is 105 thousand metric
tons, for an annual average growth rate from 1975 to 1985 of 10.3 percent. This
rate of growth is much lower than the average of 19.6 percent per year from 1968
and 1975. However, the growth rate for production relative to the growth rate
of GNP is similar for the two periods. From 1968 to 1975 real GNP in the USSR
grew at annual rate of approximately 4.3 percent (CIA 1983). The ratio of the
CFC rate of growth to the GNP rate of growth was approximately 4.6 during this
period. From 1975 to 1983 real GNP grew at about 2.5 percent per year (CIA
1983), for a ratio of about 4.1. Nevertheless, a recent oral report by Soviet
attendees at a UNEP meeting indicates that the current production capacity in
the U.S.S.R. may be 60,000 metric tons for CFC-11 and CFC-12.
Production data for the U.S. have been collected by the International Trade
Commission (ITC) in its annual series Synthetic Organic Chemicals. In the early
1960s, production in the United States accounted for over 70 percent of total
CFC-11 and CFC-12 production reported to the CMA. The U.S. share of production
dropped in the 1960s, and since 1975 it has dropped both as a share of total
production and in absolute terms. By 1984, the U.S. share of reported
production had dropped to 34 percent. Most of the absolute decline in
-------
3-21
EXHIBIT 3-9
Estimates of Production and Emissions of CFC-11 and CFG-12
for Reporting Companies
(millions of kilograms)
CFC-11
Year
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
Annual
Production
263
306
349
369
314
339
320
308
289
289
286
271
291
312
326
.2
.9
.1
.7
.1
.8
.5
.9
.5
.6
.9
.4
.8
.4
.8
Annual
Emissions
226
255
292
321
310
316
303
283
263
250
248
239
252
271
280
.9
.8
.4
.4
.9
.7
.9
.6
.7
.8
.2
.5
.8
.1
.8
CFC-12
Annual
Production
341
379
423
442
381
410
382
372
357
350
351
328
355
382
376
.6
.9
.3
.8
.0
.7
.8
.1
.2
.2
.3
.0
.3
.1
.3
Annual
Emissions
321
349
387
418
404
390
371
341
337
332
340
337
343
359
368
.8
.9
.3
.6
.1
.4
.2
.3
.5
.5
.7
.4
.3
.4
.4
Source: CMA (1986), "Production, Sales, and Calculated
Release of CFC-11 and CFC-12 Through 1985,"
Table 3.
-------
3-22
EXHIBIT 3-10
Published Estimates of U.S.S.R. Production of CFC-11 and CFC-12
(millions of kilograms)
Year
Production
1968
1969
1970
1971
1972
1973
1974
1975
11.2
14.4
16.0
19.1
22.2
24.2
32.1
39.2
Source: Borisenkou, U.P., and Kazakou,
Y.E., 1980, "Effect of Freons
and Halocarbons on the Ozone
Layer of the Atmosphere and
Climate," Tr. Gl. Geofiz Obs.
1980 438, pp. 62-74, as
reported in CMA (1986).
-------
3-23
production in the U.S. can be attributed to the 1978 U.S. ban on nonessential
aerosol propellant uses of CFCs. Data on U.S. production of CFC-11 and CFC-12
are displayed in Exhibit 3-11. Because of the ban on nonessential aerosol
propellant applications of CFC-11 and CFC-12 in the U.S., nearly all of the
current production of these CFCs in the U.S. is used for nonaerosol'
applications.
The EEC publishes data on the production and sales of selected CFCs by EEC
producers. Exhibit 3-12 displays these EEC data. As shown in the exhibit,
total EEC production of CFC-11 and CFC-12 has remained below the reported 1976
value. Also of note is that a large fraction (approximately one-third) of all
CFC-11 and CFC-12 production in the EEC is exported. Unlike the decline in
CFC-11 and CFC-12 production since 1976, the data in Exhibit 3-12 indicate a
strong increase in the production of CFG-113 and CFG-114 in the EEC.
Less information is available on the historical production and use of other
CFCs. Relative to CFC-11 and CFC-12, the quantities produced are small.
CFG-113 is an important solvent used in the manufacture of electronic
components. Hammitt (1986) estimated the current world production of this CFG
at approximately 158 thousand metric tons (due to the lack of data, this
estimate is recognized as somewhat uncertain, however). Of note is that the
production of this CFC is believed to be growing rapidly, in part in support of
the recent growth of the computer industry.
HCFC-22^ is used in air conditioning applications (particularly in home air
conditioners) and in the production of fluoropolymers. When HCFC-22. is used to
make fluoropolymers, it is destroyed, and is consequently not emitted to the
atmosphere. Gibbs (1986a) reports the production of HCFC-22 in the U.S. to be
approximately 110 thousand metric tons in 1983, and that approximately 25 to 35
percent of the production is used in fluoropolymer production. Gibbs also
reports production in the OECD countries in 1975 at approximately 75 thousand
metric tons. This is the most recent estimate for the OECD countries reported.
No estimate is available for the entire world at this time.
Of note is that the trade literature recently reported that a major CFC
producer has plans to double the CFC-113 capacity and add 75 percent to its
HCFC-22 capacity in Japan. These increases in capacity may indicate
expectations of continuing demand for these CFCs.
Other specialty CFCs are produced in small quantities (e.g., CFC-114,
CFC-115). Comprehensive information on these CFCs is not available at this
time.
Projections of Future Demand for CFCs
A series of studies has examined the potential future demand for CFCs in
various parts of the world, 11 studies were submitted to the UNEP Workshop on
the control of chlorofluorocarbons (Rome, Italy, May 1986). Most of these 11
Of note is that HCFC-22 has a much lower ozone-depleting potential than
CFC-11, CFC-12, and CFC-113.
4 Chemical Marketing Reporter. March 10, 1986, p. 3.
-------
3-24
EXHIBIT 3-11
Historical Production of CFG-11 and CFG-12 in the U.S.
(millions of kilograms)
Year
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
CFG -11
32.8
41.3
56.6
63.6
67.4
77.3
77.3
82.7
92.7
108.2
110.9
117.0
135.9
151.4
154.7
122.3
116.2
96.4
87.9
75.8
71.7
73.8
63.7
73.1
84.0
73.8 p
CFC-12
75.5
78.7
94.3
98.6
103.4
123.1
129.9
140.5
147.7
166.8
170.3
176.7
199.2
221.7
221.1
178.3
178.3
162.5
148.4
133.3
133.8
147.6
117.0
135.4
154.1
127.9 ]
p = preliminary estimate.
Source: ITC (1986), Synthetic
Organic Chemicals.
-------
3-25
EXHIBIT 3-12
EEC Production and Sales Data
(millions of kilograms)
CFC-11 and CFC-12
Year Production a/
1976
1977
1978
1979
1980
1981 b/
1982
1983
1984
326.4
319.1
307.0
304.2
295.7
300.1
289.0
310.2
322.2
EEC Sales
244.0
233.0
231.4
219.6
216.8
209.7
206.8
216.4
217.7
Exports
83.6
81.2
82.2
81.6
79.4
88.2
82.0
91.2
103.4
CFC-113 and CFG -114
Production
23.5
23.9
N/A
N/A
N/A
N/A
N/A
N/A
53.6
EEC Sales
17.6
19.3
N/A
N/A
N/A
N/A
N/A
N/A
38.6
Exports
5.2
5.7
N/A
N/A
N/A
N/A
N/A
N/A
12.9
a/ Includes imports. Production may not equal EEC sales plus exports.
b/ Data for 1981 to 1984 include Greece; previous years do not.
N/A = Not available.
Source: EEC (1985), "Chlorofluorocarbons in the Environment: Updating the
Situation," Communication from the Commission to the Council,
Annex I.
-------
3-26
studies analyzed CFC-11 and CFC-12 demand over the next 10 to 15 years. Only
three studies examined the potential demand beyond 2000. The general
conclusions from the studies can be summarized as follows:
o Future global production and emission of CFCs are
expected to increase over the next 15 to 65
years.
o Aerosol propellant applications are expected to remain
constant or decrease in many portions of the world.
o Growth in nonaerosol applications is expected to be
driven by uses for making foams and electronic equip-
ment.
o Key uncertainties include technological changes over the
long term and the patterns of use in developing
countries.
This section first describes the methods that were used to project demand, and
then summarized the key findings of the studies.
Methods Used for Projecting Future Demand
Two complementary methods have been used to project the future demand for
CFCs: (1) a "bottom up" approach; and (2) a "top down" approach. Although the
specifics of each author's method vary, the two approaches can be characterized
as follows:
o Bottom Up. The bottom up approach relies on a detailed
specification of all the products that use CFCs or are
made with CFCs (such as aerosols, foams, electronic
equipment, and refrigerators). Each of the products is
examined to identify its expected future demand and the
potential for changes in the intensity with which CFCs
are used in the products (i.e., changes in the amount of
CFCs required to produce the given product, such as
foam). The potential future demand for each of the
products is driven by a variety of factors (such as
population growth, economic growth, government
regulation, and technological change). The intensity of
use of CFCs in the identified products may change (i.e.,
increase or decrease) due to technological change or
changes in the relative prices of substitutes. The
projection of future CFG demand is compiled by adding
the estimates of demand for CFCs in each product.
Exhibit 3-13 shows graphically the bottom up approach.
o Top Down. The top down approach does not rely on
detailed specifications of the products that use CFCs.
Instead, an aggregate relationship between CFG use and
general descriptors of overall demand for goods and
services is used. These relationships vary, but are
-------
EXHIBIT 3-13
The BottCB Dp Approach
Aerosol
Propellants
Rigid
Foams
End Use
Products
r~
Furnilun
Be
^
1
i Carpet
Underlay
riding
Aulon
Se
1
Dash-
boards
Pack
mobile
als
Journals, Company
I
Others
aging
CFC-1 1
Flexible
Foams
I
Substitute
Products
Spr
Pliable
Plastics
ngt Pa
Prod
jer
lucls
o
Refrigeration
Substitute
Technologies
1
i
Melhylene CO2
Chloride (High Density)
<•
Miscellaneous
Technologi
Innovatioi
cal
i
i i
Alternative Other
Blowing
Process
(Belgium)
Estimates, Market Studies, Conversations with Experts.Trade Associations
ro
-j
Source: "Overview Paper for Topic #2: Projections of Future Demand," UNEP Workshop, May 1986,
-------
3-28
generally of the form where CFG use is related to overall
economic activity (such as gross national product (GNP) or
GNP per capita). The relationships may be defined on a
chemical-specific basis (e.g., CFC-11 versus CFC-12), and
may differentiate between different classes of uses (e.g.,
aerosol versus nonaerosol applications). Historical data
and statistical methods are generally used to specify these
relationships. A range of adjustments to the relationships
may be made based on a range of assumptions about future
changes in the underlying factors affecting the demand for
CFCs. The projection of future CFG demand is compiled by
applying the (adjusted) relationships to a projection (or
set of projections) of the descriptors of overall economic
activity (e.g., GNP).
The strength of the bottom up approach is that it examines the details of
the demand for products that use CFCs. This detailed examination may reveal
recent or impending changes in technology or demand patterns for these products.
These changes or ongoing trends can be reflected in the projections of CFC
demand made using the bottom up approach (the top down approach will not reflect
impending changes and may not discern recent trends if they are small).
The weaknesses of the bottom up approach can be characterized as follows:
o Data Intensity. The bottom up approach requires
considerable data on every product that uses CFCs. The
data may be difficult to obtain or verify for certain
products or parts of the world, thereby limiting the
applicability of this approach.
o Bias. The bottom up approach tends to be limited to
examining existing products that use CFCs. The
potential demand for new (as yet unknown) products
generally is difficult to estimate. By omitting
potential new products (while including the potential
displacement of existing products), the approach is
biased toward underestimating future demand.
Additionally, data limitations may limit the ability to
project future demand for known products. For example,
the inability to allocate all of current production to
existing uses shows the potential difficulty in
implementing the bottom up approach.
o Time Frame. The detailed data needed to implement the
bottom up approach necessarily limit it to the short run
(10 to 15 years). Detailed estimates of demand for the
individual products that use CFCs are generally not
feasible beyond this time frame.
The major strengths of the top down approach are that it is much less data
intensive than the bottom up approach, and it can be used to produce projections
of demand beyond the short term. The ability to produce long-term projections
is particularly important for the analysis of stratospheric protection because
potential ozone-modifying substances (such as CFCs) remain in the stratosphere
for very long times (up to 100 years or longer). Consequently, choices
regarding what level of stratospheric protection to adopt necessarily require
-------
3-29
trade offs between short-term and long-term uses of substances like CFCs.
Therefore, long-term projections are required.
The top down approach reflects the potential for product innovation and
displacement, albeit in an implicit manner. The historical data upon which the
method is based include new product introduction, product maturation, and
product displacement. For example, during the 1960s and 1970s the use of CFCs
for producing foams grew rapidly (product introduction). During the 1970s, the
use of CFCs in certain refrigeration applications matured and leveled off in the
developed countries. Aerosol propellant applications of CFCs have matured or
declined since the mid-1970s. The top down approach implicitly assumes that
these types of product introduction, maturation, and displacement (or some
adjusted representation of these) will continue into the future.
The top down approach also allows the uncertainty in the long-term role of
CFCs to be reflected. Using short-term detailed analyses as a guide, the
long-term projections based on the top down approach may be adjusted to
reflect alternative assumptions regarding how the key factors affecting future
demand may unfold (such as technological change, changes in relative prices,
changes in consumer tastes, and changes in regulations). Because these factors
are very uncertain over the long term, and may be very different from current
conditions, long-term projections based on the top down approach must use a
range of assumptions to identify the possible paths of future CFCs use that may
be expected.
The weaknesses of the top down approach can be characterized as follows:
o Reliance on Other Projections. Because the top down
approach relates CFG demand to overall indicators of
economic activity (such as GNP), the method must rely on
projections of these overall indicators. Although these
aggregate indicators may be easier to project into the
long term than more detailed factors, they will
necessarily be somewhat uncertain, particularly in the
out years. Therefore, the CFC demand projections using
this method can only be as good (and as precise) as the
economic and population projections upon which they are
based. Exhibit 3-14 shows the range of population and
economic projections used in these studies.
o Bias. The top down approach will be biased if the
period of historical data upon which the method is based
is not representative of the future. In the case of
CFCs, the recent historical data cover a period that
includes new product introduction (e.g., foam blowing),
product displacement (reduction in the use of aerosol
propellants, in part due to government regulation) and
product improvements. If the relative rates of
introduction and displacement during this period are not
expected to continue into the future, then the top down
approach may be biased either upward or downward.
-------
EXHIBIT 3-14
Range of Population and GUP Per Capita Projections
Population Projections
Economic Projections
12
10
8
Population
(Billions)
0
1985 1995 2005 2015 2025 2035 2045
9000
8000
7000
Real 6000
GNP
Capita 500°
(Dollars/
person) 4000
3000
2000
1000
0
1 1 •—r— 1 • r-
1985 1995 2005 2015 2025 2035 2045
Source: "Overview Paper for Topic #2: Projections of Future Demand," UNEP Workshop, hlay 1986.
-------
3-31
The strengths and weaknesses of the two methods make them natural
complements. The bottom up approach provides valuable information about current
and ongoing trends, which allows short-term projections to be made. Although
these projections may be biased downward, they are useful for calibrating the
long-term projections based on the more aggregate top down approach. Together
the two approaches provide a rich set of information that indicates the likely
range of future CFG demand.
Of note is that both methods are subject to uncertainty. With three
exceptions, the papers reviewed did not explicitly quantify the range of
uncertainty surrounding their projections. Nevertheless, the uncertainty
exists, in part due to uncertainty regarding future economic and population
growth (even in the short term), and uncertainty in the future role that CFCs
will play in existing and potential new products.
Summary of CFG Projections
Exhibit 3-15 summarizes the methods used in the 11 papers reviewed that
contain projections of future demand of CFCs. As shown, six authors used the
bottom up approach, four used the top down approach, and one author used a mixed
approach. Also shown in the exhibit are the CFCs covered by each author, the
portion(s) of the world covered, and the time period analyzed (short term or
long term).
Exhibit 3-16 summarizes the estimates of potential future demand for CFCs
from all the authors. The exhibit is divided into short-run and long-run
estimates. The short-run estimates are divided into aerosol applications of
CFC-11 and CFC-12, nonaerosol applications of CFC-11 and CFC-12, nonaerosol
applications of HCFC-22, and nonaerosol applications of CFC-113. Within each of
these categories, projections of future demand for various portions of the world
are listed.
The long-term estimates portion of the exhibit reports on all the
applications of CFC-11 and CFC-12 for the entire world. The uncertainties in
these long-term estimates are listed. Exhibit 3-17 shows the long term
projections made.
The short-term projections listed in Exhibit 3-16 show distinct themes.
Aerosol applications of CFCs are expected to decline or remain constant in
several portions of the world (EEC, U.S., Sweden). The growth in aerosol
applications in other portions of the world is generally expected to be slight
(Japan, 1.5 percent per year, and "Western" Countries, an average of less than
1.0 percent per year). Gibbs (1986a) reports a large rate of increase for the
non-U.S. use of CFC-11 and CFC-12 in aerosols, but his aerosol estimates are
higher than the other authors' estimates and are not considered representative
of the overall aerosol projections.
These projections of aerosol applications also indicate an important point.
Since the middle 1970s, the total use of CFCs in the Western Countries category
(including the U.S.) has declined and remained fairly flat. This decline and
subsequent flattening out of total use was driven by substantial reductions in
aerosol applications, which balanced off increases in nonaerosol applications
-------
EXHIBIT 3-15
Sunmary of Demand Projection Estimates
BEVINGTON
COMPOUNDS COVERED;
AEROSOL APPLICATIONS;
CFC-11 YES
CFC-12 YES
NONAEROSOL APPLICATIONS:
CFC-11 YES
CFC-12 YES
CFC-22 NO
CFC-113 YES
REGIONS COVERED:
EEC
PERIOD COVERED:
SHORT TERM YES
LONG TERM NO
METHOD USED;
BOTTOM
UP
CAMM EFCTC
YES YES
YES YES
YES YES
YES YES
NO NO
YES NO
a/
WORLD VARIOUS
S/
YES YES
YES NO
e/
MIX BOTTOM
UP
GIBBS HAMMITT OSTMAN
YES YES YES
YES YES YES
YES YES YES
YES YES YES
YES NO NO
YES YES YES
b/ c/ a/
WORLD WORLD SWEDEN
YES YES YES
YES NO NO
TOP BOTTOM BOTTOM
DOWN UP UP
KNOLL YS
YES
YES
NO
NO
NO
.NO
EEC
YES
NO
BOTTOM
UP
KUROSAWA
YES
YES
YES
YES
NO
NO
JAPAN
YES
NO
BOTTOM
UP
NORDHAUS
YES
YES
YES
YES
NO
NO
d/
WORLD
YES
YES
TOP
DOWN
PERSKY
NO
NO
YES
YES
NO
NO
U.S.
YES
NO
TOP
DOWN
SHEFFIELD
NO
NO
YES
YES
YES
YES
CANADA
U)
YES l*»
Ni
NO
TOP
DOWN
a/ Camro and Hammitt break their world estimates into the following regions: (1) U.S.; (2) Other Reporting Countries; and (3)
"Communist" Countries.
b/ Regions covered by EFCTC include: (1) Western Europe, South Africa, Australia, and New Zealand; and (2) the "Rest of the World,"
excluding North America (Canada, U.S., Mexico), Japan, East Bloc countries, and Peoples Republic of China.
£/ Gibbs reports results separately for: (1) U.S.; (2) non-U.S. OECD countries; and (3) the "Rest of the World."
d/ Nordhaus reports results separately for the U.S. and the Rest of the World.
e/ Camm's projections prior to 2000 are based on the bottom up approach results reported in Haranitt. The post-2000 estimates are based
on the top down approach results reported in Quinn (1986).
Sources: Bevington 1986; Camm et al. 1986; EFCTC 1985; Gibbs 1986a; Hammitt et al. 1986; Ostman, Hedenstrom, and Samuelsson, 1986;
Knollys 1986; Kurosawa and Imazeki 1986; Nordhaus and Yohe 1986; Persky, Weigel, and Whitfield 1985; Sheffield 1986 (see
references for complete source).
-------
EXHIBIT 3-16
Sumary of Demand Projections
(Average annual rate of growth in percent)
a/ b/
BEVINGTON CAW EFCTC GIBBS HAM1ITT OSIMAN KNOLLYS KUROSAWA NORDHAUS PERSKY SHEFFIELD
Aerosol Applications of CFC-11 and CFC-12:
EEC -0.6
Japan
Sweden
U.S.
"Western" Countries d/
World
SHORT-TERM PROJECTIONS: APPROXIMATELY 1985 TO 1995/2000
£/
-0.6 0.0 -3.9
0.2
0.0
2.5
4.0
-0.6
0.0
0.0
0.1
1.7 e/
1.5
2.2
Nonaerosol Applications of CFC-11 and CFC-12:
Canada
EEC c/ 2.1 .. 2.1
Japan
Sweden
U.S.
"Western" Countries d/ .. .. 2.5
World
4.5
4.3
4.7
4.2
2.5
3.3
3.3 e/
4.9
3.2
3.7
3.4
4.4-7.9
Nonaerosol Applications of CFC-22:
Canada
World
5.1
4.2-5.1
Nonaerosol Applications of CFC-113:
Canada
EEC 7.5
Sweden
U.S.
"Western" Countries d/
World
5.3
5.3
5.4
5.9
7.1
6.5
2.5
4.5-8.9
Not reported. Only "base case" or "middle" values are listed here for Cam, Gibbs, and Nordhaus.
-------
EXHIBIT 3-16 (Continued)
Sunmary of Demand Projections
(Average annual rate of growth in percent)
a/ b/
BEVINGTON CAMM EFCTC GIBBS HAMMITT OSTMAN KNOLLYS KUROSAWA NQRDHAUS PERSKY SHEFFIELD
LOKG-TERM PROJECTIONS: APPROXIMATELY 2000 TO 2050
All Applications of CFC-11 for the World:
Lower Bound .. 0.5 .. 1.8
Low .. 1.6 .. 2.4 .. .. .. .. 0.8
Medium .. 2.4 .. 3.1 .. .. .. .. 3.6
High .. 3.2 .. 3.4 .. .. .. .. 3.6
Upper Bound .. 4.3 .. 4.0
All Applications of CFC-12 for the World:
Lower Bound .. -0.4 .. 1.6
Low .. 1.6 .. 2.0 .. .. .. .. 1.0
Medium .. 2.4 .. 2.6 .. .. .. .. 3.6
High .. 3.2 .. 2.8 .. .. .. .. 3.9
Upper Bound .. 4.4 .. 3.4 .. .. .. .. .. .. ..
a/
Canrn's short-term projections are based on Hammitt, and are therefore not listed here separately.
b/
Values listed under long-term projections are for the 25th, mean, and 75th percentile.
£/ EFCTC projection includes Western Europe, South Africa, Australia, and New Zealand.
d/ Coverage varies by author. Approximate coverage includes non-U.S., non-East Bloc countries. EFCTC also excludes Japan, Canada,
Mexico.
e/ Assumes that one-half of East Bloc country use reported in Haimitt is in aerosol applications.
Sources: Bevington 1986; Canrn et al. 1986; EFCTC 1985; Gibbs 1986a; Hammitt et al. 1986; Ostman, Hedenstrom, and Samuelsson, 1986;
Knollys 1986; Kurosawa and Imazelci 1986; Nordhaus and Yohe 1986; Fersky, Weigel, and Whitfield 1985; Sheffield 1986 (see
references for complete source).
-------
CAMM
GIBBS1
NORDHAUS
-i.o
3-35
EXHIBIT 3-17
Long Term Projection
CFG-11 and CFG-12 -- World Production
(2000-2050)
0.0
.- • r r r 7 rfr.,'//," 7
- CFC-12 f/y///s
_ ^ , ^ _ ^_ ^fj r'^_
—i—
1.0
—i—
2.0
—i—
3.0
—i—
4.0
Annual Rate of Change (%)
5.0
6.0
Source: "Overview Paper for Topic #2: Projections of Future Demand," UNEP
Workshop, May 1986.
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3-36
during this time. The projections of flat or slight growth for aerosol
applications in the Western Countries indicate that: (1) as aerosol
applications become a smaller share of total use, further aerosol application
reductions will be less effective in balancing off growth in nonaerosol
applications; and (2) future large reductions in aerosol applications are not
anticipated under current regulations. Together, these two points indicate that
the total use of CFG-11 and CFG-12 will increasingly be driven by expected rates
of growth in nonaerosol applications.
The short-term nonaerosol applications of CFC-11 and CFC-12 show a trend
that is different than the trend for aerosol applications. All estimates
indicate continued strong growth in nonaerosol applications during the short
term. The estimates range from 2.1 percent per year in the EEC (Bevington 1986;
EFCTC 1985) to 7.9 percent per year in Canada (Sheffield 1986, upper bound). No
estimates of declines or flat demand were reported. These estimates are
consistent with a recent trade journal projection of growth of 4 percent to 5
percent per year through 1990. •*
It is interesting to note that the underlying patterns of demand reported by
the various authors show considerable similarity. The bottom up estimates all
reported that the largest nonaerosol application growth is expected in the
production of foams, both flexible and rigid. The important insulating
properties of CFCs used in the production of insulating rigid foams were often
cited as the driving factor behind this growth. Refrigeration and air
conditioning applications were generally reported as being fairly mature, with
only small growth anticipated in the short term. Due to changing workplace
practices and modifications to equipment, future use of CFCs in some air
conditioning applications was projected to decline (Hammitt et al. 1986, p. 56).
Overall, foam production is expected to account for the majority of nonaerosol
applications of CFC-11 and CFC-12 in the future.
The estimates do not include detailed evaluations of developing countries
(e.g., Africa, portions of Asia). The pattern of future use of CFCs in
developing countries may differ from the pattern in developed countries because
the refrigeration and air conditioning markets in these countries may not be as
mature. Because the developing countries have fairly large populations, the
potential growth in the demand for CFCs for refrigeration and air conditioning
applications in these countries may be significant.
The several estimates of future demand for HCFC-22 and CFC-113 are also
shown in Exhibit 3-16. All estimates show strong growth. The demand for
CFC-113 is reportedly driven by expected strong growth in solvent applications,
particularly in solvents used for cleaning electronic components. Although
these CFCs are expected to grow rapidly in the short term, their overall level
of use will remain well below the level of use of CFC-11 and CFC-12 (less than
half).
Exhibit 3-16 also displays long-term demand projections by Camm et al.,
Gibbs, and Nordhaus and Yohe. These projections are necessarily more uncertain
than the short-term estimates, and consequently the full range of estimates
provided by each author is listed. As one check on the validity of these
long-term projections, one should note that in the short term (through 2000)
5 Chemical Marketing Reporter. March 10, 1986, p.54.
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3-37
they are consistent with the range of short-term estimates provided by the other
authors.
As shown in Exhibit 3-16, the overall picture of long-term demand for CFCs
is one that may range from modest growth (on the order of 1.0 percent per year
or less), to sustained strong growth (nearly 4.0 percent per year). The only
possibility that appears to have been considered unlikely by the authors is
substantial declines in the use of CFCs over the long term. As the authors
caution, however, currently unforeseen technological advances could produce a
situation where use declines (or increases) considerably, as unforeseen
applications develop. Although the likelihood of either a considerable decline
or increase is difficult to quantify at this time, it is believed to be very
small.
The specific methods used by the individual authors varied. Each paper is
summarized in turn.
Bevington (1986): Projections of Production Capacity. Production and Use of
CFCs in the Context of EEC Regulations.
Bevington presents projections for the demand of CFC-11, CFC-12, CFC-113,
and CFC-114 in EEC countries from 1984 to 1995. The bottom up approach was
used, with various trade associations providing estimates of expected rates of
growth in particular product markets (associations listed include: EFCTC; FEA;
BING; and EUROPUR). Products examined include: aerosols; rigid foams; flexible
foams; solvents; and other.
Exhibit 3-18 summarizes Bevington's projections for the EEC. Aerosol
applications of all the CFCs are projected to continue to decline. The most
rapidly growing nonaerosol applications of CFC-11 and CFC-12 are expected to be
foams (both rigid and flexible). Refrigeration applications are expected to
grow more slowly, and are projected to account for less than 12 percent of CFC-
11 and CFC-12 use by 1995.
The CFC-113 and CFC-114 use is dominated by the solvent applications of CFC-
113. Use in this application is projected to grow significantly over the period
examined, producing an average increase of 6.7 percent per year for all CFC-113
and CFC-114 uses.
Camm et al. (1986): Joint Emission Scenarios for Potential Ozone Depleting
Substances.
Camm presents projections of the demand for seven potential ozone-modifying
substances: CFC-11; CFC-12; CFC-113; methyl chloroform; carbon tetrachloride;
Halon-1301; and Halon-1211. This summary includes only the CFCs. A range of
projections are provided for the entire world and for two time periods: 1985 to
2000 and 2000 to 2040. The projections are based on scenarios of potential
future demand developed using the bottom up approach for 1985 to 2000 reported
in Hamntitt (1986) and the top down approach for 2000 to 2040 reported in Quinn
(1986). The range of projections in both the short and long term reflect
uncertainties in the rate of economic growth and the role that CFCs will play
-------
3-38
EXHIBIT 3-18
BEVINGTON'S PROJECTIONS FOR USE OF CFCs IN THE EEC
(Annual average rate of change for 1984 to 1995)
RATE OF CHANGE (%)
CFG-11 and CFG-12:
Aerosol Applications -0.6%
Nonaerosol Applications 2.1%
Total 0.8%
CFG-113 AND CFG-114:
Aerosol Applications -0.6%
Nonaerosol Applications 7.5%
Total 6.7%
Source: Bevington (1986), p. 10-11.
-------
3-39
in its various applications. Exhibit 3-19 summarizes the projections of global
demand for each of the compounds individually. A total of five estimates are
presented for each compound, for each time period.
As shown in the exhibit, CFC-113 is projected to grow the fastest, followed
by CFC-11, and then CFG-12. The range between the Low and High scenarios is
estimated by Camm to reflect a 50 percent confidence interval (i.e., the
likelihood of the result actually falling in this range is estimated as 0.5).
The range between the Lower Bound and the Upper Bound is reportedly a 90 percent
confidence interval. The base case economic growth rate assumptions are 3.3
percent per year for the period 1985 to 2000 and 2.4 percent per year for 2000
to 2040.
Comparing these growth rate assumptions to the values in Exhibit 3-19
indicates that: the use of CFC-11 is expected to grow at approximately the rate
of economic growth in the Medium case in both the short and long term; the use
of CFC-12 is expected to grow more slowly than the rate of economic growth
through 2000, and at approximately the rate of economic growth after 2000; and
the use of CFC-113 is expected to grow more rapidly than economic growth through
2000, and at approximately the rate of economic growth after 2000. The range of
uncertainty includes growth of all the chemicals both exceeding or being less
than the rate of growth in economic activity.
The differential patterns of growth and decline across various applications
and regions of the world are not reported in Camm. However, the detailed
projections in Hammitt (summarized separately), upon which the Camm estimates
prior to 2000 are based, indicate that patterns vary across uses and regions of
the world. The estimates for post-2000 are based on top down estimates from
Quinn (1986), which do not explicitly report changing mixes of CFC applications.
The work by Camm makes an important contribution to the development of
scenarios of future demand because it not only provides detailed scenarios of
the future use of each of the CFCs, but it is the only method that attempts to
reflect a convolution of uncertainties across chemical compounds. Camm
correctly asserts that taking the fifth fractile estimate of demand for each
potential ozone-depleting substance at the same time does not necessarily
produce the fifth fractile estimate of ozone-depleting potential. Because
ozone-depleting potential is the key policy variable of interest, Camm et al.
developed a method for identifying joint scenarios across a group of compounds
that convolute each compound's uncertainties in conjunction with each compound's
ozone-depletion potential.
The results of this approach for creating joint scenarios are scenarios of
chemical production that have narrower uncertainties than the independent
scenarios for each compound (reported in Exhibit 3-19). This result is expected
when the uncertainty across compounds is not perfectly correlated (a reasonable
assumption). The degree of correlation among the uncertainties is unknown, and
the Camm assumption of complete independence across the chemicals (except for
the common driving factor of economic growth) may be extreme. Nevertheless, the
general result of their work is indicative that the scenarios of production used
for policy analysis should possibly be narrower in uncertainty than the
scenarios estimated for each compound separately.
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3-40
EXHIBIT 3-19
CAMM PROJECTIONS OF WORLD USE
(Annual average growth rate in percent)
Chemical
CFC-11
CFG -12
CFG -113
Period
1985-2000
2000-2040
1985-2000
2000-2040
1985-2000
2000-2040
Lower
Bound
0.81
0.47
-0.29
-0.43
1.19
-0.06
Low
2.27
1.61
1.21
1.59
5.19
1.39
Medium
3.29
2.40
2.27
2.40
6.55
2.40
High
4.31
3.19
3.32
3.21
7.93
3.41
Upper
Bound
5.78
4.33
4.83
4.37
9.89
4.86
Source: Camm (1986).
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3-41
European Fluorocarbon Technical Committee (EFCTC) (1985), Halocarbon Trend
Study 1983-1995.
The EFCTC provides projections of the consumption of CFG-11 and CFC-12 for
the following uses: aerosols; refrigeration; rigid foam; flexible foam; and
other (food freezant, sterilizing gas, fire-fighting chemicals, vapor-pressure
control instruments, wind tunnels, solvent applications, and flotation
processes). The projections cover the period 1983 to 1995 and are divided
into two regions: (1) Western Europe, South Africa, Australia and New Zealand;
and (2) "Rest of World," excluding: North America (U.S., Canada, Mexico),
Japan, East Bloc countries, and Peoples Republic of China.
The bottom up approach was used to prepare these forecasts. Forecasts
were made by individual CFG producers, and collated and averaged in a
confidential manner. Each projection was weighted equally, and the average
was adopted by the EFCTC as "representing the best view of the European CFC
producers on the future use of chlorofluorocarbons 11 and 12" (p. 1). Exhibit
3-20 summarizes the EFCTC projections for the two regions identified above.
As shown in Exhibit 3-20, aerosol use is projected to increase slightly
for CFC-11 and decrease slightly for CFC-12. Nonaerosol applications of both
CFCs are projected to grow between two and three percent per year.
Gibbs (1986): Scenarios of CFC Use: 1985 to 2075.
Gibbs presents scenarios of the potential future use of CFC-11, CFC-12,
HCFC-22, and CFC-113 in aerosol and nonaerosol applications. Estimates are
provided for four time periods (1985-2000; 2000-2025; 2025-2050; and 2050-
2075) and for three parts of the world (U.S.; non-U.S. OECD; and the Rest of
the World).
Gibbs developed relationships between per capita CFC usage and per capita
GNP based on historical data, controlled for the price of CFCs, and included
estimates for OECD countries. Ordinary least squares regression was used, and
serial correlation reportedly biased downward the estimates of the standard
deviations of the coefficients.
Gibbs applied these relationships to the OECD countries using a range of
population and GNP scenarios from published sources. The ranges used were
quite large, resulting in wide ranges of potential CFC demand in the future.
Population varied by a factor of nearly two by 2075, and GNP per capita varied
by nearly a factor of five. Gibbs' population and GNP scenarios are
summarized in Exhibit 3-21. In his highest and lowest scenarios, Gibbs also
adjusted the coefficients by one standard deviation to reflect potential
technological innovation. The potential implications of innovation were not
explicitly evaluated.
Gibbs estimated demand in the non-OECD countries by assuming that per
capita demand in these countries by the end of the projection period (2075)
would be the ratio of (1) the GNP per capita in the non-OECD countries to (2)
the current GNP per capita in the OECD countries times the current use per
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3-42
EXHIBIT 3-20
SUMMARY OF EFCTC PROJECTIONS
ANNUAL AVERAGE RATE OF CHANGE (%)'
1983-1990 1990-1995 1983-1995
CFG-11 CONSUMPTION
Aerosol Applications 0.4% 0.4% 0.4%
Nonaerosol Applications 2.5% 2.1% 2.3%
Total CFG-11 1.6% 1.4% 1.5%
CFG-12 CONSUMPTION
Aerosol Applications -0.1% 0.2% 0.0%
Nonaerosol Applications 2.7% 2.9% 2.8%
Total CFG-12 1.4% 1.7% 1.5%
Source: EFCTC (1985) Appendix IV.
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3-43
EXHIBIT 3-21
Global Population and GNP Scenarios Used in Gibbs' Analysis
GLOBAL POPULATION SCENARIOS (millions)
Year
1985
2000
2025
2050
2075
Lowest
4536
5377
6505
7324
7131
Low
4745
5901
7384
7664
7944
Medium
4745
5901
7384
8223
8491
High
4835
6147
8160
9496
9960
Highest
5000
6500
9500
12100
13600
GLOBAL GNP PER CAPITA SCENARIOS
(1975 U.S. $)
Year
1985
2000
2025
2050
2075
Source:
Lowest
1900
2206
2499
2831
3051
Gibbs ,
Low
1900
2375
3201
4105
5264
Michael J.
Medium
1900
2447
3729
5683
8662
(1986),
High
1900
2557
4195
6883
11292
Scenarios
Highest
1900
2752
5102
9458
17535
of CFC Use:
1985 to 2075. IGF Incorporated, prepared for U.S.
Environmental Protection Agency, Washington, D.C.
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3-44
capita in the OECD countries. Between 1985 and 2075 Gibbs fitted an
"S-shaped" curve that reflects the standard product lifecycle.
This method of projecting non-OECD demand has a large influence on the
overall results produced by Gibbs because the non-OECD countries account for a
large fraction of the total growth in demand (nearly 50 percent). The
potential bias of the method is ambiguous. Differences between the OECD and
non-OECD countries (in terms of culture, climate, and other factors) could
produce different patterns of CFG use relative to OECD countries, even at
similar levels of per capita GNP. Whether the levels would be higher or
lower, is unknown.
There is some indication that Gibbs' method may produce estimates of
demand in the non-OECD countries that are biased downward, because evidence
indicates that at the same level of income per capita, later developing
countries tend to have higher levels of consumption of industrial products
when compared to the countries that developed first. The explanation given is
that product penetration into the market place generally proceeds faster in
later developing countries. whether this would be the case for CFCs in
non-OECD countries is unknown, although evidence indicates it may have been
true in the non-U.S. OECD countries as compared to the U.S.
Gibbs presents five scenarios of future demand that reflect a wide range
of assumptions about the potential future rates of growth in GNP per capita
and population. The scenarios were not adjusted to reflect potential changes
in the structure of the CFC markets. Exhibit 3-22 presents the Gibbs
scenarios for the entire world, for both aerosol and nonaerosol applications.
As shown in the exhibit, each of the compounds is expected to grow more
rapidly in the short term than in the long term. CFC-113 is projected to grow
most rapidly, followed by HCFC-22, CFC-11 and then CFC-12. Compared to the
assumed growth rates for global GNP, the scenarios display CFC growth in
excess of economic growth for all the scenarios; the increment over the rate
of economic growth is lower in the long term.
The overall patterns of growth shown in Exhibit 3-22 include differential
rates of growth of aerosol and nonaerosol applications in different regions of
the world. In the U.S. and EEC countries, aerosol use is assumed to remain
constant throughout the period examined. Aerosol applications in other
regions are permitted to grow. Nonaerosol applications are projected to grow
at rates that exceed the assumed rates of economic growth in all regions. The
analysis by Gibbs does not incorporate assumptions about specific nonaerosol
uses of CFCs. Also, confidence intervals or probabilities are not assigned to
Gibbs' scenarios. Consequently, although a range is presented, the likelihood
of future demand falling in particular portions of the range cannot be
computed.
5 Gibbs (1986b), p. 17.
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3-45
EXHIBIT 3-22
GIBBS SCENARIOS OF WORLD CFC USE
(Annual average growth in percent)
Chemical
CFC -11
CFC -12
HCFC-22
CFC- 113
GNP
GROWTH
Period
1985-2000
2000-2075
1985-2000
2000-2075
1985-2000
2000-2075
1985-2000
2000-2075
1985-2000
2000-2075
Lower
Bound
3.2
1.8
2.8
1.4
4.1
1.2
4.1
1.1
2.1
0.8
Low
4.0
2.4
3.7
2.0
4.7
1.8
5.0
1.7
2.9
1.5
Medium
4.5
3.1
4.4
2.6
5.1
2.6
5.4
2.5
3.1
2.2
High
5.6
3.4
6.0
2.8
6.2
2.9
6.4
2.9
3.5
2.7
Upper
Bound
6.5
4.0
6.7
3.4
6.7
3.6
7.0
3.6
4.1
3.5
Source: Gibbs (1986) Exhibit 8, and Exhibit E-2.
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3-46
Hammitt et al. (1986): Product Uses and Market Trends for Potential
Ozone Depleting Substances: 1985-2000.
Hammitt presents projections of the use of seven potential ozone-modifying
substances: CFC-11; CFG-12; CFG-113; methyl chloroform; carbon tetrachloride;
Halon 1301; and Halon 1211. This summary includes only the CFCs. The
projections are developed for the period 1985 to 2000 using the bottom up
approach and the following CFC applications: aerosol propellants; rigid foams;
flexible foams; refrigeration and air conditioning; miscellaneous uses of CFC-
11 and CFC-12 (sterilants, fast food freezing, other); and solvents (CFC-113
only). Each application is examined in detail, and projections are presented
separately for the following three regions: U.S.; other "non-communist"
countries (referred to in the report as other countries that report production
to the Chemical Manufacturers Association); and "communist" countries.
The base case Hammitt projections for the world are presented in Exhibit
3-23 along with upper and lower bounds. As shown in the exhibit, CFC-113 is
anticipated to grow most quickly during this period, averaging 6.5 percent per
year in the base case. CFC-11 has a base case estimate of 3.3 percent per
year, and CFC-12 has a base case estimate of 2.3 percent.
Within these global figures, some applications are expected to decrease in
their use of CFCs (e.g., aerosol applications of CFCs in EEC countries), some
are expected to remain approximately constant (e.g., aerosol applications in
the U.S.), and some are expected to increase (e.g., solvent applications of
CFC-113 and CFC-11 and CFC-12 foam blowing applications). Patterns of change
are not uniform across all portions of the world. In total, however, global
use in relation to global economic growth (assumed in the study to be 3.3
percent per year in the base case) is expected to be as follows:
o CFC-11: 40 percent to 160 percent of base economic growth, with a
base case of 100 percent of economic growth.
o CFC-12: 9 percent to 130 percent of base economic growth, with a base
case of 70 percent of economic growth.
o CFC-113: 120 percent to 280 percent of base economic growth, with a
base case of 200 percent of economic growth.
These ranges of uncertainty reportedly reflect an 80 percent confidence
interval (meaning that the actual result is expected to fall in this range
with a likelihood of 0.8), and include the possibility of economic growth
being higher or lower than the base case. Additionally, they reflect the
potential for technological change and changing market structure.
The Hammitt paper is the only one reviewed that explicitly considered the
potential implications of technological innovation in a detailed manner.
Additionally, the explicit quantification of uncertainty provides guidance as
to the likelihood of the different scenarios. The shortcomings of the method
are that:
o it was unable to associate all current production with
an application --a significant portion of production
remained unallocated across applications, implying
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3-47
EXHIBIT 3-23
HAMMITT PROJECTIONS OF WORLD CFC USE
(Average annual growth rate for 1985 to 2000 in percent)
CFC -11
CFC -12
CFC -113
Base Case
3.3%
2.3%
6.5%
Lower Bound
1.4%
0.3%
3.9%
Upper Bound
5.2%
4.5%
9.2%
Source: Hammitt (1986), Table S.I.
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3-48
that better information on specific uses could be
obtained, and that the method may underestimate future
demand; and
o the assumption of normally-distributed uncertainty may
be unrealistic, given evidence from the results by
Nordhaus and Yohe that indicate that a skewed result
may be possible.
Ostman, Hedenstrom and Samuelsson (1986): Projections of CFG Used in
Sweden.
Ostman provides a detailed bottom up analysis of CFC-11, CFC-12, and CFC-
113 uses in Sweden. Recent and ongoing trends in current uses and
technologies are described. Special attention is paid to expected changes in
these trends, including saturation in key markets or applications that have
grown rapidly in the past. Projections are provided for the period 1984 to
1994 covering the following uses: flexible foams; rigid foams (polyurethane
in refrigerators/cooling and other, and extruded polystyrene); cooling and
heating (cooling, service, heat pumps, heat pump service); degreasing and
cleaning; and other. Of note is that projections are reported for the use on
CFCs in these products that are consumed in Sweden, including products that
are imported into Sweden.
Exhibit 3-24 summarizes Ostman's projections across all the uses examined
(including net imports). Overall, strong growth is projected for total CFC-11
and CFC-12 use. The largest growth is projected in rigid foams, particularly
extruded polystyrene. These foams are used as "insulation in houses,
insulation in the ground and packaging material" (p. 11). "Despite the low
new production activity within the building industry an increase in insulation
and panel demand is expected" (section 4). These foams account for over 75
percent of the increase in CFC-11 and CFC-12 use projected between 1984 and
1994.
Modest growth is projected for heating and cooling applications, mostly in
the area of service. New installations are not expected to grow significantly
because these markets are well saturated. The authors note that recovery of
CFCs during service could have a "marked effect on the emissions of CFCs from
this sector" (p. 12).
As shown in Exhibit 3-24, CFC-113 is also expected to increase in use,
although not as rapidly as CFC-11 and CFC-12. Ostman reports that CFC-113's
"... higher prices (compared to possible substitutes) are holding them back
and for larger consumers of degreasing agents for more "general" purposes they
are not yet attractive" (p. 13). Also noted is the possibility that CFC-113
growth could be larger if its substitutes are subjected to further health
restrictions.
This study is distinguished as the only regional study that explicitly
estimated the amount of CFCs contained in products that are imported and
exported. CFCs are imported to Sweden in bulk as well as in finished products
(such as refrigerators). Sweden does not produce CFCs.
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3-49
EXHIBIT 3-24
SUMMARY OF HEDENSTROM PROJECTIONS FOR SWEDEN
(Average ammal rate of growth for 1984-1994)
GROWTH RATE (%")
CFG-11 and CFG-12 4.1%
Nonaerosol applications 4.2%
Aerosol applications 0.0%
CFC-113 2.5%
Source: Hedenstrom (1986), Table 3.
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3-50
Not included in the Ostman study (or in any other study) are the regional
CFG demand implications of trade in products that do not retain their CFCs
after manufacture (e.g., flexible urethane foam). The methods generally used
for estimating demand for CFCs assigns the demand to the country of
manufacture of the foam, not to the country that uses the foam. The extent to
which the incorporation of this factor would modify the current perception of
regional CFC demand is not known at this time. Flexible foam products (cars,
furniture) and electronic components (cleaned with CFC-113 solvent) are traded
extensively on the world market.
Knollys (1986): Fluorocarbon Use in Aerosols -- A Trend Study 1984-1995
in Member Countries of the European Economic Community.
Knollys projects the use of CFCs in aerosols in the member countries of
the EEC from 1984 to 1995. Although not explicitly stated, it is assumed for
this summary that the projection applies to CFC-11 and CFC-12. The bottom up
method was used, where "member associations representing the aerosol
industries in countries in the European Economic Community ... prepare(d)
forecasts of aerosol production for the years 1990 and 1995 and ... compare(d)
these with actual production estimates for 1984" (p. 14). Forecasts covering
13 separate aerosol categories were received from countries that represent 54
percent of 1984 EEC production. To create an aggregate forecast, these
forecasts were adjusted to reflect the share that these countries have of the
market for each of the product categories, and then aggregated. From the data
presented it is not possible to identify the range of coverage within each of
the 13 categories.
The projection provided by Knollys is summarized in Exhibit 3-25. As
shown, EEC aerosol production is expected to increase, as is the quantity of
the contents of the aerosol packages. However, the amount of CFCs in the
packages is expected to decrease by an average of 0.75 percent per year from
1984 to 1990, and by 0.40 percent per year from 1990 to 1995. The explicit
factors driving these results are not reported.
Of the 13 categories analyzed, only two are projected to have declines in
aerosol production packs and contents between 1984 and 1995 (hairspray and
insecticides). The other 11 categories are projected to have increases (hair
mousse, deodorant/anti-perspirant, body spray, shave foam, household cleaners,
air fresheners, automotive products, industrial products, paint, food, and
others). In terms of CFC propellant use in aerosols, only four categories are
projected to have increases (shave foam, automotive products, industrial
products, and others). These four categories account for 24.5 percent of
aerosol propellant applications in 1984, and are projected to increase by less
than one percent per year from 1984 to 1995.
Assumptions regarding economic growth are not reported, so it is not
possible to relate these projections to future growth. Although the
uncertainty of the projection is not quantified, Knollys states that the
general direction of the trend is reasonable (p. 15).
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3-51
EXHIBIT 3-25
KNOLLYS PROJECTIONS
ANNUAL AVERAGE RATE OF CHANGE (%)
1984-1990 1990-1995 1984-1995
EEC AEROSOL PRODUCTION (Packs) 1.3% 1.6% 1.4%
EEC AEROSOL PRODUCTION (Contents) 1.1% 1.1% 1.1%
EEC USE OF CFCs IN AEROSOLS -0.75% -0.4% -0.6%
Source: Knollys (1986), tables 4, 5, and 6.
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3-52
Kurosawa Imazeki (1986): Projections of the Production Use and Trade of
CFCs in Japan in the Next 5-10 Years.
Kurosawa provides projections for CFC-11 and CFG-12 production in Japan
for 1985 to 1995 for the following uses: refrigerant; aerosol propellant;
blowing agent; and export. The bottom up approach was used, with the
prospects for continued development in these products and exports examined
individually. As shown in Exhibit 3-26, growth is anticipated throughout the
period. Blowing agents account for most of the projected growth in production
between 1985 and 1995 (51 percent); refrigerants account for 32 percent of the
growth; exports account for 12 percent; and aerosols account for 5 percent.
The blowing agent growth is reportedly driven by increases in the
production of automobiles. Refrigeration uses are driven by the demand for
building air conditioners, automobile air conditioners, and demand for
refrigerators for export. Kurosawa reports that CFCs in aerosol propellant
applications (expected to grow slightly) "have become an essential element as
a flammability suppressant" (p. 3). Finally, exports from Japan to its East
and Southeast Asian neighbors are expected to increase because these nations
do not currently produce CFCs.
Nordhaus and Yohe (1986): Probabilistic Projections of Chlorofluorocarbon
Consumption: Stage One.
The approach used by Nordhaus, called probabilistic scenario analysis,
explicitly considers uncertainty and is based on statistical analyses of
historical data. This method was originally designed by the authors to
investigate the problem of forecasting carbon dioxide emissions and
concentrations from an economically consistent model of future energy markets.
The method provides not only a best-guess estimate, but a quantified range of
uncertainty, built up from uncertainty regarding the individual factors
affecting demand.
Using statistical methods and historical data, Nordhaus and Yohe specified
the relationship driving the intensity of use of CFC-11 and CFC-12 over time
in the U.S. A family of logistic curves is fit to the data to describe the
manner in which the use of CFCs approaches what is called a "frontier" over
time. The frontier represents the total possible use of CFCs at a given level
of wealth, and it changes over time. A family of curves is used to represent
the uncertainty in the location of the frontier, which is not known with
precision.
This method is able to capture the implicit effects of product
introduction, innovation, and maturity. It reflects the uncertainty in our
ability to estimate (from historical data) the relative importance of these
factors. Because data are not available for performing this analysis on the
rest of the world outside the U.S., the authors assume that the rest of the
world will develop in a pattern similar to the lead provided by the U.S., but
more slowly.
The relationships developed using this method are used to project future
demand. First, the basic building blocks of the relationships, the rate of
change of the frontier, the increase in labor productivity, and population
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3-53
EXHIBIT 3-26
SUMMARY OF KUROSAWA FROJECTIONS FOR JAPAN
(Average annual rate of growth 1985-1995)
RATE OF GROWTH (%")
CFG-11 and CFG-12 4.4%
Nonaerosol applications 4.9%
Aerosol applications 1.5%
Exports 6.1%
Source: Kurosawa (1986), Table 1.
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3-54
growth are projected. The future values- for labor productivity and population
are derived from probability distributions. The distributions are based on
the range of published estimates, and studies that indicate that ranges of
published estimates often understate true uncertainty. As recognized by the
authors, however, the distributions are considered to be subjective.
Estimates of the future growth or decline of the frontier for CFC use have
not been published. Nordhaus and Yohe write that a reasonable range for
industrially demanded goods is between a 2 percent per year average decline to
a 2 percent per year average increase. A decline in the frontier implies that
the amount of CFCs that can be used at a given level of economic activity
(e.g., measured as gross national product or GNP) is declining over time. In
other words, due to technological innovation, product displacement, or other
factors, the intensity with which CFCs would be used per dollar of GNP is
simulated to decrease. An increase in the frontier implies the opposite, an
increase in intensity. This range of a 2 percent decrease to a 2 percent
increase is used in the study.
Given the relationships based on historical data and the probability
distributions for the future values for population, labor productivity, and
the CFC frontier, a Monte Carlo analysis is performed by drawing from the
distributions using pseudo-random numbers, and inserting the drawn values into
the relationships. A number of independent trials are performed, the results
of which form a distribution. This distribution of results reflects the
uncertainty in each of the steps of the method.
The strengths of this approach include its statistical analysis of
historical data and its explicit consideration and modeling of uncertainty.
Of interest is that the results indicate that the potential for future demand
for CFC-11 and CFC-12 does not have a symmetrical range of uncertainty. The
possibilities for values that are much larger than the median appear to exceed
the possibilities that the values will be far below the median. Also, there
does not appear to be a significant likelihood that CFC-11 and CFC-12 demand
will decrease from current levels (in the absence of regulation), even though
a decline in the CFC frontier is modeled as being equally likely as an
increase.
The shortcoming of the analysis is the lack of detail with which the use
of CFCs is modeled in countries outside the U.S. Applying the U.S.-based
relationships may over- or understate demand in these countries; the bias is
ambiguous.
The nonaerosol results obtained by Nordhaus are presented in Exhibit 3-
27. Estimates are provided for the 25th and 75th percentiles and for the
mean. The percentile estimates may be interpreted as meaning that the result
is expected to fall below the 25th percentile 25 percent of the time, between
the 25th and 75th percentiles 50 percent of the time, and above the 75th
percentile 25 percent of the time. The mean represents the average of all
possible outcomes.
Exhibit 3-27 shows that CFC-11 is expected to grow more rapidly than CFC-
12. Also, the rate of growth of both the CFCs exceeds the rate of economic
growth in the near term for all the projections presented. In the long term
(post 2000), the rate of growth in the consumption of the chemicals may be
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3-55
EXHIBIT 3-27
NORDHAUS SCENARIOS OF WORLD NONAEROSOL CFC CONSUMPTION
(Annual average rate of growth in percent)
Compound
CFC -11
CFC -12
ECONOMIC
GROWTH
Period
1980-2000
2000-2050
1980-2000
2000-2050
1980-2000
2000-2050
25th Percentile
3.2
1.2
3.0
1.1
3.1
1.7
75th Percentile
5.4
3.6
4.8
2.9
4.0
2.5
Mean
4.6
3.5
4.0
3.1
3.6
2.2
Source: Nordhaus (1986) Table III-3 and Table III-4.
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3-56
greater than (75th percentile and the mean) or less than (25th percentile) the
rate of economic growth.
Persky, Weigel, and Whitfield (1985): A Review of the Study: "Projected
Use. Emissions, and Banks of Potential Ozone Depleting Substances" (Rand
Report No. 2483-3-EPA1.
Persky examined the draft Rand Report Projected Use. Emissions, and Banks
of Potential Ozone Depleting Substances by Quinn (1985), the revised version
of which formed the basis for the long-term projections presented in Camm
(1986). Persky raised questions regarding the data and assumptions used in
Quinn (1985) and the model used to project future demand. In doing the
review, Persky presented an alternative estimate of future demand for CFC-11
and CFC-12 in nonaerosol applications in the U.S. from 1985 to 2010. The top
down approach was used, where historical CFC use in the U.S. was related to
historical GNP per capita in the U.S. The projected growth rates were 3.5
percent per year and 3.4 percent per year for CFC-11 and CFC-12 respectively,
for the period 1985 to 2010. The underlying assumptions about economic growth
and population growth were not reported.
It should be noted that the focus of the Persky paper is a critique of
Quinn (1985); its primary objective was not to develop an independent
projection of CFC demand.
Sheffield (1986): Canadian Overview of CFC Demand Projections to the Year
2005.
Sheffield provides two projections of the potential nonaerosol use of CFC-
11, CFC-12, HCFC-22, and CFC-113 in Canada from 1984 to 2005. A top down
approach is used where CFC use per capita in several applications is related
to GNP per capita and a time trend variable. The applications examined
include: CFC-11 and CFC-12 in foams, CFC-11, CFC-12, and HCFC-22 in
refrigeration, and CFC-113 in solvents. Two projections were developed: one
using an exponential model to fit parameters to the historical data, and a
second using a linear model. The exponential model produces much larger
projections than does the linear model, and Sheffield states that "... we can
rest reasonably assured that the actual use in the year 2005 will probably
fall somewhere" between the two projections (p. 11).
Exhibit 3-28 displays the overall results reported by Sheffield. Strong
growth is projected for all the compounds examined. Solvent applications of
CFC-113 are anticipated to grow at the fastest rate. Foam applications of
CFC-12 are projected to account for the largest share of future growth (22 to
58 percent, depending on the projection). Refrigeration applications display
the slowest rates of growth.
Despite the diversity of the methods used by the various authors to
project possible future demand, the results presented above indicate a
considerable degree of similarity and consensus. The overall picture of
long-term demand for CFCs is one that may range from modest growth (on the
order of 1.0 percent per year or less) to sustained strong growth (nearly 4.0
percent per year). The only possibility that appears to have been considered
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3-57
COMPOUND
CFC-11
CFC-12
HCFC-22
CFC-113
EXHIBIT 3-28
SUMMARY OF SHEFFIELD PROJECTIONS FOR CANADA 1984-2005
(Annual average growth rates in percent)
LINEAR MODEL
4.4%
4.4%
4.2%
4.5%
EXPONENTIAL MODEL
6.4%
8.5%
5.1%
8.9%
Source: Sheffield (1986), p. 16.
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3-58
unlikely by the authors is substantial declines in the use of CFCs over the
long term.
Of note is that potential constraints on future production were
investigated in two studies, Gibbs and Weiner (1986) and Mooz, Wolf, and Canm
(1986). Both studies investigated the potential for the supply of fluorspar
to constrain future CFG production. Fluorspar is the primary source of
fluorine used in the production of hydrofluoric acid (HF), which is used to
make CFCs. It is considered a strategic mineral because it is also used in
the production of steel, and HF is also used to make aluminum. Although not
mined extensively in the U.S., fluorspar is abundant in Mexico, South Africa,
China, Mongolia, and portions of Southeast Asia (Gibbs and Weiner 1986).
To assess whether fluorspar availability would likely constrain future CFC
production, Gibbs and Weiner and Mooz, Wolf and Camm compared U.S. Bureau of
Mines estimates of fluorspar resources to the potential requirements of future
production implied by the demand scenarios developed in Gibbs (1986a) and Camm
et al. (1936). Both studies found that currently identified economic reserves
would be sufficient to supply expected fluorspar demand (from all
applications) for the next 20 years. The high quality of the ore currently
being mined (e.g., in Mexico and Southeast Asia) and the fact that fluorspar
has historically been abundant indicate that it is likely that sufficient new
reserves will be available to meet demand far beyond the next 20 years. Gibbs
and Weiner found that the rate at which new reserves would have to be added in
order to meet demand over the next 65 to 90 years was less than the rate of
addition to reserves over the last 20 years. Additionally, Mooz, Wolf, and
Camm point out that the abundance of fluorine in other forms (such as
phosphate rock) could provide a potentially large source of fluorine.
However, it is expensive to recover fluorine from these sources.
Mooz, Camm, and Wolf also examined possible constraints posed by the
availability of production capacity. Although current production capacity may
be reached by approximately the year 2000, they found that in the absence of
government regulation, increases in capacity would likely take place.
These two studies indicate, therefore, that currently there do not appear
to be supply constraints that would limit the ability to meet the future
demand for CFCs.
CHLOROCARBONS
Two chlorocarbons have been identified as potentially important ozone
depleters:
o carbon tetrachloride (CC14); and
o methyl chloroform (CH3CC13).
Carbon tetrachloride is an excellent solvent in many applications, and was
once used extensively as a solvent and grain fumigant in the U.S. Because of
its toxicity, it is only used in small amounts in such applications today
(Hammitt et al. 1986). The major use of carbon tetrachloride in the U.S. is
in the manufacture of CFC-11 and CFC-12. During the manufacturing process,
almost all of the carbon tetrachloride is consumed or destroyed; very little
is emitted.
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3-59
Hammitt et al. (1986) estimate current U.S. production of carbon
tetrachloride at 280 thousand metric tons, and world production at 870
thousand metric tons (this estimate does not include production in East Bloc
countries). Hammitt et al. and Camm et al. project the future demand for
carbon tetrachloride to remain closely tied to the demand for CFG-11 and
CFG-12. Consequently, the future rates of growth in demand for of this
compound are expected to be approximately the same as the rates of growth in
the demand for these CFCs. Of note is that the uses of carbon tetrachloride
as a solvent and grain fumigant may persist in other countries. The
projections of demand for those compounds are therefore uncertain.
Methyl chloroform is produced in large quantities around the world, and is
used as a cleaning solvent in vapor degreasing and cold cleaning applications.
Small amounts are also used in adhesives, aerosols, and coatings (Hammitt et
al. 1986). Hammitt et al. estimate 1985 U.S. production at 270 thousand
metric tons and world production at 545 thousand metric tons (Hammitt et al.
1986, p. 80).
Hammitt et al. (1986) and Camm et al. (1986) estimate a range of future
growth in the demand for methyl chloroform. These growth rates reflect alter-
native assumptions regarding the influence on use and recycling of the
expected land disposal ban on chlorinated solvents (including methyl
chloroform). These annual rates range from 0.4 percent to 4.7 percent for the
period 1985 to 2040. Due to the lack of data on the production and use of
methyl chloroform outside the United States, these estimates of production and
emissions are recognized as uncertain.
HALONS
Halogenated extinguishing agents are made from hydrocarbons in which one
or more hydrogen atoms have been replaced by halogen atoms. The common
halogen elements are fluorine, chlorine, bromine, and iodine. These
extinguishing agents include:
Chemical Name
Methyl bromide
Methyl Iodide
Bromochloromethane
Dibromodifluoromethane
Bromochlorodifluoromethane
Bromotrifluoromethane
Carbon tetrachloride
Dibromotetrafluoroethane
Formula
CH3Br
CH3I
BrCH2Cl
Br2CF2
BrCClF2
BrCF3
CC14
BrF2CCBrF2
Halon No.
1001
10001
1011
1202
1211
1301
104
2402
Use
Fixed
Hand
Fixed a/
Fixed/Hand b/
Fixed b/, d/
Hand
Hand c/
a/ Declining use in the United States Air Force applications.
b/ Recognized by NFPA Standards.
c/ Limited use in Italy and Russia, no U.S. use.
d/ Halon-1301 is also mixed with Halon-1211 in small hand-held extinguishers.
Halon-1301 and Halon-1211 have excellent flame extinguishment properties
and acceptable toxicity under favorable circumstances. However, there are
significant health risks if the fire is not quickly extinguished. Halons
undergo pyrolysis when subject to flame or surface temperatures greater than
480°C. The extent of pyrolysis depends on length of exposure to high
temperatures, the Halon concentration, and the degree of mixing. Halon-1301
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3-60
decomposition products are halogen acids-, hydrogen fluoride (HF) , hydrogen
bromide (HBr), the free halogens (Br2), and small amounts of carbonyl halides
(COF2), COBr2). Halon-1211 has the same decomposition products as Halon-1301
plus hydrogen chloride (HCl), chlorine gas (C12), and phosgene (COC12) (NFPA
1986).
Halon-1301 and Halon-1211 are the only halogenated extinguishing agents
recognized by the National Fire Protection Association (NFPA) for use in the
United States. They have a combination of desirable characteristics:
o low toxicity in occupied spaces (in most circumstances);
o low electrical conductivity;
o high visibility during use;
o little corrosive or abrasive residue; and
o high effectiveness per pound of chemical.
In stationary or fixed applications the gaseous Halon-1301 is widely used
while the liquid Halon-1211 is preferred in portable applications, where
liquid range is desirable.
These chemicals were not used extensively in fire protection until the
1970s. Although these compounds are currently produced in small quantities,
they are of major concern to ozone protection because use is growing rapidly
and because they are believed to be as much as ten times more potent per pound
in depleting stratospheric ozone.
Halon-1301 use has increased rapidly for applications like computer
centers and art collections because: (1) it can be discharged in an occupied
space without significant risk to occupants; (2) it does not damage chemically
sensitive contents of the space; and (3) it is very effective against many
types of fires. These advantages reduce the financial consequences of
accidental extinguisher discharge and allow faster extinguisher deployment
since evacuation need not precede discharge. In contrast, extinguishing
agents like carbon dioxide (C02) can reduce oxygen so quickly that the
occupants of the area may be endangered. The absence of residue not only
protects property against damage, but allows quicker return to work spaces.
The future demand for Halon-1211 and Halon-1301 will depend on the need
for fire extinguishers with their unique properties. The choice depends on
property value, fire and fire fighting consequence, probability of fire, the
consumer awareness, and product marketing.
The expected continued growth in the use of computing and other expensive
electronic equipment indicates that the use of the Halon-1301 may be expected
to grow rapidly. The backlog of property with substantial value such as art,
antiques, and business records offers large new markets for Halon use.
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Military uses, including routine preemptive releases in situations of high
fire danger, could drastically increase use.
Studies that Project Halon Emissions
Analysis by the RAND Corporation experts (Hammitt et al., 1986; Camm et
al., 1986; and Quinn et al., 1986) present preliminary estimates of the U.S.
and world production of these two compounds (estimates do not include
production in East Bloc countries). Current U.S. production of Halon-1301 is
estimated at 5.4 million kilograms with historic growth rates of 15 to 30
percent per year and world production is estimated at 10.8 million kilograms
(Hammitt et al. 1986).
Hammitt (1986) presented the limited information and simplifying
assumptions that were used to build the RAND projections:
o U.S. Halon-1301 production was from industry sources.
o World Halon-1301 production was thought to be about twice U.S.
production.
o Halon-1211 production was thought to be about the same as
Halon-1301 production.
o Future growth rates were based primarily on electronics expansion,
not included was an assessment of all property that could be
effectively protected by Halon systems.
o Emissions from Halon-1301 systems are based on:
19% for initial system testing;
1%/year for filling and servicing;
0.1%/year for leaks;
1%/year for false discharge;
1%/year fire discharge; and
-- Recycle of Halon-1301 at 40 year intervals.
o Emissions from Halon-1211 portable extinguishers are assumed to be
the same as the emissions from fixed Halon-1301 systems excluding
recovery.
Exhibit 3-29 presents a range of global Halon projections from Quinn
(1986). Three cases are shown for Halon-1301. The Base Case (which uses the
assumptions described above) shows considerable near-term growth. The rate of
growth slows, and there is a decline in production as recovery of Halon-1301
from retiring systems is used to meet growing demand. Because the average
size of new units is also assumed to decline, the net result is a temporary
drop in production. Following the decline, production in the Base Case
resumes its growth.
Two alternative Halon-1301 cases are also shown in the exhibit. If
recovery is assumed not to take place, production grows more rapidly following
the year 2000, and there is no decline. If new systems are assumed to decline
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EXHIBIT 3-29
Global Halon Projections from Qulnn (1986)
(millions of kilograms)
Halon-1301
Year
Base Case
Use Emissions
Without Recovery
Use Emissions
Low Charge
Use Emissions
1985
2000
2025
2050
2075
11
28
25
38
53
3
9
15
22
33
11
28
33
50
73
3
9
23
35
54
7
12
7
13
19
2
4
6
8
12
Halon-1211
Year
Low Use
Use
Emissions
Source: Quinn et al. (1986)
High Use
Use Emissions
1985
2000
2025
2050
2075
2
6
7
10
15
1
2
5
7
11
11
28
33
50
73
3
9
23
35
54
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in size more rapidly than assumed in the Base Case (the Low Charge Case), then
use grows more slowly.
Quinn's Halon-1211 scenarios are based on scant information (Quinn 1986,
p. 85). The two cases shown in Exhibit 3-29 are based on the assumption that
Halon-1211 use is 20 percent of (Low Case) or equal to (High Case) the Halon-
1301 Base Case projection. For both of the Halon-1211 cases shown, it is
assumed that no recovery is undertaken.
Hammitt et al. (1986) and Camm et al. (1986) built upon Quinn's work to
develop a range of production projections for the Halons. The uncertainty
analysis used to develop these projections is described above in the section
on CFC scenarios. Exhibit 3-30 presents the full range of projections
presented by the authors. A range of scenarios is presented based on
subjective quantile estimates. Because the uncertainty ranges are subjective,
it is not possible to associate the low or high values with specific events
such as no recovery or low charge. Of note is that these projections assume
that Halon-1211 production is comparable to Halon-1301 production, and not 20
percent of the value as potentially indicated by Quinn.
Although the RAND effort is a contribution to our understanding of the
potential significance of Halons to stratospheric ozone depletion, there are
reasons to believe that the estimates presented below understate the
emissions, perhaps by substantial amounts.
For Halon-1301 systems RAND assumes a 1 percent per year accidental
discharge and a 1 percent per year fire discharge. No basis is given for
these estimates in the RAND Study. if the actual accidental release was as
much as ten times higher and the probability of a fire in a Halon protected
space ten times lower (one in a thousand or less), the actual total emissions
would increase by more than three hundred percent over those estimated by
RAND. In addition, RAND assumed that the volume of Halon protected space
would decrease as a result of computer downsizing. RAND made no adjustment
for the possibility that other nations will rapidly computerize, thus
accelerating the world rate of growth in Halon systems.
Other factors not included in these estimates could lead to even higher
releases. For example, the National Fire Protection Association (NFPA)
Halon-1301 technical committee has proposed that all new systems be tested
with a full-scale release of Halon-1301. This would increase emissions of
Halon-1301 by over four hundred percent.
RAND assumed that Halon-1211 use for portable fire extinguishers is about
the same as use of Halon-1301 in fixed systems and that it will grow at a
similar rate. The product uses are quite different. Halon-1211 is used
primarily in hand-held fire extinguishers and U.S. Air Force rapid
intervention crash trucks (Hammitt et al. 1986, p. 68). The sizes of these
devices reportedly range from 14 ounces to 150 pounds (Quinn et al. 1986, p.
86). Because the devices are small, it is unlikely that significant
quantities will be recovered from disposed or deactivated systems. Portable
Halon-1211 units are not subject to the same testing by discharge. However,
Halon-1211 units are now being marketed as relatively low-cost consumer
products. Their superior performance in particular circumstances means that
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EXHIBIT 3-30
Hanraitt and Cam Global Halon Projections
(millions of kilograms)
Quantile
Halon- 1301
1985
2000
2040
Halon-1211
1985
2000
2040
0.05
11
11
7
11
11
8
0.25
11
16
21
11
16
25
0.50
11
20
44
11
20
53
0.75
11
26
92
11
26
111
0.95
11
37
259
11
37
315
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3-65
they may face rapid growth, particularly if they are specified for commercial
buildings and other business applications or if they are aggressively
marketed. Furthermore, it is unlikely that the average useful life of
hand-held extinguishers will be as long as 40 years as assumed by RAND.
-------
3-66
REFERENCES
Alliance for Responsible CFC Policy (1980), "An Economic Portrait of the
CFC-Utilizing Industries in the United States," Washington, D.C.
Bevington, C.F.P. (1986), Projections of Production Capacity. Production and
Use of CFCs in the Context of EEC Regulations. Metra Consulting Group Ltd.,
London, U.K., prepared for the European Economic Community.
Camm, Frank et al. (1986), Joint Emission Scenarios for Potential Ozone
Depleting Substances. The RAND Corporation, prepared for the U.S.
Environmental Protection Agency, Washington, D.C.
Camm, F., J. Hammitt, and K. Wolf (1986), Reaction to DRI Critique of
Unpublished RAND Working Draft: "Projected Use. Emissions, and Banks of
Potential Ozone-Depleting Substances." The RAND Corporation, Santa Monica,
California.
CMA (1986), Chemical Manufacturers Association, "Production, Sales, and
Calculated Release of CFC-11 and CFC-12 Through 1984," Washington, D.C.
Chemical Marketing Reporter. "Chemical Profile," March 10, 1986, Vol. 229, pp.
3 and 54.
CIA (1983), Handbook of Economic Statistics. 1983. Directorate of
Intelligence, Central Intelligence Agency, Washington, D.C.
Connell, P.S. (1986), "A Parameterized Numerical Fit to Total Column Ozone
Changes Calculated by the LLNL 1-D Model of the Troposphere and Stratosphere,"
Lawrence Livermore National Laboratory, Livermore, California.
Department of Environment, Ministry of Science, Technology and Environment,
Malaysia (Malaysia) (1986), Country Report. Chlorofluorocarbon Chemicals in
Malaysia.
DuPont (1986), Corporate Policy Statement.
EEC (1985), European Economic Community, "Chlorofluorocarbons in the
Environment: Updating the Situation," Communication from the Commission to
the Council.
Erickson, Lynn (1986), Memo to Neal Patel, EPA, Radian Corporation, Houston,
Texas.
European Fluorocarbon Technical Committee (EFCTC) (1985), Halocarbon Trend
Study 1983 - 1995. EFCTC (a CEFIC Sector Group).
Gamlen, P.H., et al. (1986), "The Production and Release to the Atmosphere of
CC13F and CC12F2 (Chlorofluorocarbons CFC-11 and CFC-12), Atmospheric
Environment. pp. 1077-1085.
-------
3-67
Gibbs, Michael J. (1986a), Scenarios of CFG Use: 1985 to 2075. IGF
Incorporated, prepared for the U.S. Environmental Protection Agency,
Washington, D.C.
Gibbs, Michael J. (1986b), "Summary of Historical Chlorofluorocarbon
Production," Presented at UNEP Economic Workshop on the Control of Chloro-
fluorocarbons, Rome, Italy, May 1986.
Gibbs, Michael J., and Robin Wiener (1986), Assessment of the Availability of
Fluorine for the Production of Chlorofluorocarbons. IGF Incorporated, prepared
for the U.S. Environmental Protection Agency, Washington, D.C.
Hammitt, James K., et al. (1986), Product Uses and Market Trends for Potential
Ozone Depleting Substances: 1985 - 2000. The RAND Corporation, prepared for
the U.S. Environmental Protection Agency, Washington, D.C.
Henderson, L.G. (1980), "The Atmosphere Chemistry of 1,1,1-2-tetra-
fluoroethane," General Motors Research Laboratory, Warren, Michigan, GMR-3450.
Hoffman, B.L. and D.S. Klander (1978), Final EIS Fluorocarbons: Environ-
mental and Health Implications. U.S. Federal Drug Administration, Washington,
D.C.
ITC (1986), U.S. International Trade Commission, Synthetic Organic Chemicals.
ITC, Washington, D.C.
Khalil, M.A. and R.A. Rasmussen (1986), "The Release of Trichlorofluoromethane
from Rigid Polyurethane Foams," JAPCA. pp. 159-163.
Knollys, R.C. (1986), Fluorocarbon Use in Aerosols -- A Trend Study 1984-1995
in Member Countries of the European Economic Community, prepared on behalf of
The Federation of European Aerosol Associations.
Kurosawa, Kimio, and Katsuo Imazeki (1986), Projections of the Production Use
and Trade of CFCs in Japan in the Next 5-10 Years. Japan Fluoride Gas
Association and the Japan Aerosol Association.
McCarthy, R.L., et al. (1977), "The Fluorocarbon -- Ozone Theory -- I.
Production and Release: World Production and Release of CC13F and CC12F2
(Fluorocarbons 11 and 12) through 1975, Atmospheric Environment, pp. 491-497.
Mooz, W.E., K.A. Wolf, and F. Camm (1986), Potential Constraints on Cumulative
Global Production of Chlorofluorocarbons. The RAND Corporation, prepared for
the U.S. Environmental Protection Agency, Washington, D.C.
National Fire Protection Association (1986), National Fire Protection
Handbook. 14th Edition, Boston, MA.
Nordhaus, William D., and Gary W. Yohe (1986), Probabilistic Projections of
Chlorofluorocarbon Consumption: Stage One. Yale University and Wesleyan
University, prepared for the U.S. Environmental Protection Agency, Washington,
D.C.
-------
3-68
Orfeo, S. Robert (1986), "Response to questions to the panel from Senator John
H. Chafee," Ozone Depletion, the Greenhouse Effect, and Climate Change.
Hearings before the Senate Subcommittee on Environmental Pollution of the
Committee on Environment and Public Works, Washington, DC: US G.P.O., pp.
189-192.
Ostman, Anders, Olle Hedenstrom, and Sture Samuelsson (1986), Projections of
CFG Use in Sweden, prepared for Statens naturvardsverk, Sweden.
Persky, Susan, C. Miles Weigel, and Ronald M. Whitfield (1985), A Review of
the Study: "Projected Use. Emissions, and Banks of Potential Ozone Depleting
Substances" (Rand Report No. 2483-3-EPA). prepared by Data Resources, Inc.,
Washington, D.C., at the request of E.I. duPont de Nemours.
Quinn, Timothy H., et al. (1985), Projected Use. Emissions, and Banks of
Potential Ozone Depleting Substances. draft working paper by The RAND
Corporation, prepared for the U.S. Environmental Protection Agency,
Washington, D.C.
Quinn, Timothy H., et al. (1986), Projected Use. Emissions, and Banks of
Potential Ozone-Depleting Substances. The RAND Corporation, prepared for the
U.S. Environmental Protection Agency, Washington, D.C.
Sheffield, A. (1986), Canadian Overview of CFG Demand Projections to the Year
2005. Commercial Chemicals Branch, Environmental Protection Service,
Environment Canada, Ottowas, Canada.
Strobach, Donald (1986), "A Search for Alternatives to the Current Commercial
Chlorofluorocarbons," in Protecting the Ozone Layer: Workshop on Demand and
Control Technologies. Washington, DC: U.S. Environmental Protection Agency.
UNEP (1986), Report of the First Part of the Workshop on the Control of
Chlorofluorocarbons. UNEP/WG.148/2, Nairobi, Kenya.
Weigel, C.M., and R.M. Whitfield (1986), Reply to the RAND Corporation's
Response to DRI' s Review of RAND's Working Draft. "Projected Use. Emissions.
and Banks of Potential Ozone-Depleting Substances." Data Resources, Inc.,
Washington, D.C.
WHO Criteria Document on Chlorofluorocarbons (1986), Draft Report,
Environmental Criteria and Assessment Office, U.S. EPA, Cincinnati, Ohio, p.
2-10.
Yarrow, G.K. (1986), The Reliability of Very Long Run Forecasts of
Chlorofluorocarbon Production and Emissions. Hertford College, Oxford.
Zhijia, W. (1986), "Country Paper for Topic I: UNEP Workshop on the
Protection of the Ozone Layer," National Environmental Protection Agency of
the People's Republic of China.
-------
APPENDIX A
CHEMICAL USE ESTIMATES MADE AVAILABLE SINCE PUBLICATION
OF THE RISK DRAFT ASSESSMENT1
Since the publication of the October 1986 Draft of this Risk Assessment,
several new estimates have been made concerning global production and use of
CFCs, Chlorocarbons, and Halons. Some of these estimates are revisions to
previously published estimates. These new data are discussed below:
Nordhous and Yohe (1986) present revised estimates of U.S., Rest of
the World, and Global CFC-11 and CFC-12 production. Projected
estimates for nonaerosol applications and the annual growth rates
implied by these projections are presented in Exhibit A-l.
Short term mean global growth rates for CFC-11 and CFC-12 are
approximately the same, 3.8 and 3.6 percent respectively. Long term
rates are also similar (3.7 percent). Projected U.S. growth for the
mean is slower than the global average. In 2050 mean global estimates
for CFC-11 and CFC-12 are about five times larger than the 25th
percentile estimates. Global estimates in 2050 for the 75th
percentile are approximately 20 and 50 percent higher than mean
estimates for CFC-11 and CFC-12 respectively.
In the U.S., the mean estimates for 2050 are equal to (CFC-11) or
greater than (CFC-12) the 75th percentile estimates. This result
indicates that a skewed distribution of outcomes is expected, with the
mean values exceeding the median value (i.e., 50th percentiles) by
substantial amounts.
lEc (1987) estimated U.S. and global Halon-1301 and Halon-1211 use and
emissions for fire extinguishing applications through the year 2050.
This report estimated historical U.S. use based on industry sources
and published reports (Camm and Hammitt 1986; Quinn 1986). lEc
developed a computational model that projects Halon stocks and
emissions based on release rates, equipment life, and system testing
parameters constructed from industry sources. Projections of Halon-
1301 were based on projections of the growth of total flooding fire
extinguishing systems. Halon-1211 projections were based on the
growth of portable fire extinguisher use. lEc (1987) presented nine
Halon-1301 and six Halon-1211 projections for the U.S. that alter
chemical demand and control technology assumptions. Global estimates
are presented for only one baseline scenario. After the publication
of this report, lEc revised some of their assumptions for the U.S. and
provided projections for "Rest of World" Halon use and emissions to
provide a "Best Guess" scenario. This scenario is the only one
considered in this summary.
These results are not used in the RISK ASSESSMENT; they are presented
for informational purposes only.
r\
zIEc projects "sales" in millions of kilograms. Sales are defined as new
production adjusted for imports and exports.
-------
A-2
The assumptions used by lEc to project Halon use and emissions are
presented in Exhibit A-2. "Initial Charge Emissions" occur during the
construction and activation of fire extinguishing units or systems.
"Bank Emissions" occur annually from stored chemical in existing
systems. "Recovery at Disposal" indicates the percent of chemical
that is reused and not emitted from a retiring system. Systems
charged with Halon-1301 emit a larger percentage of their initial
change when compared to units using Halon-1211. However, disposal
recovery rates were greater for Halon-1301 systems.
Exhibit A-3 shows projected U.S. and global Halon use and the implied
growth rates over time for the lEc "Best Guess" scenario. Halon-1301
use in the U.S. is projected to be flat until 2000 and then grow
approximately three percent annually until 2050. Global use is
projected to grow slowly in the short term and then accelerate after
2000. Halon-1211 use for the U.S. and the world is expected to grow
rapidly in the short term (5.7 and 8.8 percent respectively) and then
slow to rates similar to long term growth for Halon-1301 (about 3
percent annually). Growth rates for emissions are significantly
higher than sales for both compounds because of the slow release rates
of Halons from fire extinguisher applications.
lEc projections differ significantly from previously published
estimates in Camm and Hammitt (1986) and Quinn (1986). Exhibit A-4
shows the short and long term growth rates for these reports and lEc
(1987). lEc short term projections for Halon-1301 are lower than
almost all other previous projections. Short term projections for
Halon-1211 are higher than all previous short term projections. lEc
long term projections for both Halon-1301 and Halon-1211 are higher
than the "Middle" estimates for Camm and Hammitt (1986).
United States
o ITC (1987) provides revised 1985 U.S. production estimates of 79.7 and
136.9 million kilograms for CFC-11 and CFC-12, respectively. This
publication also presented preliminary 1986 estimates of 91.3 and
146.2 million kilograms for CFC-11 and CFC-12. The implied growth of
combined production from 1985 to 1986 is 9.6 percent.
EEC
EFCTC (1986) estimates 1985 EEC use of CFC-11, CFC-12, and combined
CFC-113 and CFC-114. Use is reported as 135.9, 92.6 and 43.7 million
kilograms for these compounds, respectively. For combined CFC-11 and
CFC-12 use, this reflects a 5.0 percent growth from 1984 to 1985.
CFC-113/CFC-114 growth is 13.3 percent for the same time period.
Araki (1986) estimates 1986 CFC-113 production in Japan as 51.5
million kilograms.
-------
A-3
USSR
Tirpak (1986) summarizes the results of the Global Climate Change Work
Group VIII's conference in the USSR. In these meetings Soviet sources
reported 1986 USSR CFG-11 and CFC-12 production of 103.0 million
kilograms. In addition, these sources indicated that annual
production capacity would increase for CFG-11 and CFC-12 to 140
million kilograms by 1990. Assuming production capacity is fully
utilized, this implies an 8.0 percent annual increase in production of
CFC-11 and CFC-12 through 1990.
Canada
Buxton (1987) estimates total 1986 Canadian CFG production as 20
million kilograms.
o Dupont (1987) estimates per capita CFC consumption for 72 countries.
This source divides these countries into four groups:
-- less than 0.1 kilograms per capita;
-- 0.1 to 0.2 kilograms per capita;
-- 0.2 to 0.5 kilograms per capita; and
-- greater than 0.5 kilograms per capita.
A range of estimated use for each country is calculated by multiplying
1985 population by estimated use per capita for each country. These
use estimates are presented in Exhibit A-5.
-------
A-4
EXHIBIT A-l
GLOBAL ANNUAL PRODUCTION IN MILLIONS OF KILOGRAMS
(Ammal Average Growth Rate in Percent)
Non-Aerosol CFC-11
1980
2000
2050
Non-Aerosol CFC-12
1980
2000
2050
25th Percentile
193.3 (1.8)
275.0 (1.0)
446.5
249.1 (1.6)
345.5 (1.1)
600.3
75th Percentile
193.3 (4.9)
506.5 (3.7)
3,045.6
249.1 (4.9)
651.2 (4.1)
4,802.2
Mean
193.3 (3.8)
405.2 (3.7)
2,470.3
249.1 (3.6)
503.1 (3.7)
3,071.7
U.S. ANNUAL PRODUCTION IN MILLIONS OF KILOGRAMS^/
(Annual Average Growth Rate in Percent)
Non-Aerosol CFC-11
1980
2000
2050
Non-Aerosol CFC-12
1980
2000
2050
67.6 (1.4)
89.4 (0.0)
90.3
128.3 (1.1)
160.5 (0.3)
190.3
67.6 (4.1)
151.8 (2.3)
471.0
128.3 (4.4)
301.6 (2.4)
983.9
67.6 (3.2)
127.3 (2.6)
470.2
128.3 (3.2)
239.7 (3.0)
1,030.9
a/ Non-aerosol compound growth accounts for essentially all growth in the U.S.
SOURCE: Nordhaus and Yohe (1986).
-------
EXHIBIT A-2
ASSUMPTIONS FCS lEc HALOH HJOJECTIGRS
Halon-1301
Halon-1211
U.S.
Initial Charge Emissions
3.7X
Manufacturing/Installation
Discharges:
New Filling Related Discharges: 3.8X
Discharge Testing: 12.6X-5.0X3
Bank Emissions
Service Discharges:
Unwanted Discharge:
Training Discharges:
Fire Discharges:
Percent of Fire Discharges
Destroyed:
Recovery at Disposal:
Other Assumptions
Assumed System Life:
0.6X-0.3X /year a/
1.3X-1.2X /year a/
0.3X /year
1.5X /year
1.0% /year
67.5X-85.5X b/
25 yrs
Rest of World
3.7X
U.S.
Rest of World
1.6X
1.6X
3.8X
12. 6X
0.6X /year
1.3X /year
0.3X /year
1.5X /year
l.OX /year
.7.5X
1.4X-5.0X
d/
0.4X-0.3X /year a/
l.OX /year
1.3X /year
10. OX /year
15.0X-52.0X c/
d/
1.4X
d/
0.4X /year
2.6X /year
1.3X /year
10. OX /year
15. OX
25 yrs
20 yrs
20 yrs
a/ This range reflects the change in assumptions from 1985 to 1990. The value on the right of the range is used after 1990.
b/ This range reflects the change in assumptions from 1985 to 1992. The value on the right of the range is used after 1992.
£/ This range reflects the change in assumptions from 1985 to 1995. The value on the right of the range is used after 1995.
d/ lEc does not estimate these categories.
SOURCE: lEc (1987).
-------
EXHIBIT A-3
IBC EBQJBCTIOBS OF SALES AND HUSSIONS FOR
HALGB-1301
AHD HALGN-1211
TEC Halon-1301 Estimates
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
2020
2025
2030
2035
2040
2045
2050
USA
Total Use
Halon-1301
(Mill KG)
0.0
0.1
0.6
1.8
3.5
4.6
4.6
3.9
4.7
5.7
6.7
7.5
8.4
10.0
11.8
13.7
15.7
17.9
USA
Emissions
Halon-1301
(Mill KG)
0.0
0.0
0.1
0.3
1.0
1.4
1.8
2.1
2.7
3.3
4.0
4.4
4.8
5.8
6.9
8.1
9.1
10.3
World
Total Use
Halon-1301
(Mill KG)
0.0
0.2
1.2
3.6
7.0
9.5
9.7
8.2
10.2
12.5
14.7
16.4
18.1
21.7
25.8
30.2
34.3
38.9
Growth Bates for
World
Emissions
Halon-1301
(Mill KG)
0.0
0.0
0.2
0.6
2.0
3.1
4.0
4.7
6.2
7.8
9.3
10.2
10.8
13.3
16.0
18.8
21.2
23.6
1965
1970
1975
1980
1985
1990
1995
2000
2005
2010
2015
2020
2025
2030
2035
2040
2045
2050
USA
Total Use
Halon-1211
(Mill KG)
0.0
0.1
0.3
0.9
2.8
4.1
5.5
6.4
7.2
7.5
8.9
10.3
12.1
13.7
16.1
18.6
21.7
24.8
IEC Halon-1211 Estimates
USA
Emissions
Halon-1211
(Mill KG)
0.0
0.0
0.0
0.1
0.4
0.8
1.4
2.2
3.5
4.4
5.4
6.2
7.3
8.1
9.7
11.1
13.1
14.8
World
Total Use
Halon-1211
(Mill KG)
0.0
0.2
1.2
3.6
7.0
14.6
20.3
24.7
27.1
31.6
37.9
43.8
49.1
57.7
68.1
78.8
89.6
104.7
World
Emissions
Halon-1211
(Mill KG)
0.0
0.0
0.1
0.6
1.5
3.3
6.4
10.5
14.5
21.3
26.0
30.0
33.0
39.1
46.6
53.8
60.6
71.1
Sales and Emissions for Halon-1301 and HaLon-1211
(Percent)
Halon-1301
1985-2000
2000-2050
1985-2050
0.7
3.1
2.5
5.0
3.2
3.6
1.1
3.2
2.7
5.9
3.3
3.9
1985-2000
2000-2050
1985-2050
5.7
2.7
3.4
Halon-1211
12.0
3.9
5.7
8.8
2.9
4.2
13.9
3.9
6.1
-------
A-7
EXHIBIT A-4
GLOBAL HALON-1301 AND HAUON-1211 GROWTH RATES
(Percent)
Halon-1301
Short Term Growth: 1985-2000
lEc (1987) Canun and Hanmitt (1986) a/
Lower Bound
Low Bound
Middle
High Bound
Higher Bound
Halon-1211
Lower Bound
Low Bound
Middle
High Bound
Higher Bound
0.0
2.5
1.1 4.1
5.9
8.4
0.0
2.5
8.8 4.1
5.9
8.4
Ouinn (1986) b/
3.6
6.4
6.4
7.6
6.4
Halon-1301
Long Term Growth: After 2000
lEc (1987) c/ Camm and Hammitt (1986) c/
Lower Bound
Low Bound
Middle 3.2
High Bound
Higher Bound
Halon-1211
Lower Bound
Low Bound
Middle 2.9
High Bound
Higher Bound
-1.1
0.6
2.0
3.2
5.0
-0.8
1.1
2.5
3.7
5.5
Ouinn (1986) d/
0.9
1.3
2.0
1.0
1.2
a/ Estimates represent 5th, 25th, 50th, 75th, and 95th percentiles.
b/ Estimates represent Low Charge (Low Bound), Base Case (Middle), and Without Recovery
(High Bound) scenarios for Halon 1301. Halon 1211 estimates represent Low and High
Use scenario. Note Halon 1211 growth rates for the Low Bound exceed rates in the
High Bound case even though absolute production is much lower .
c/ Projections are from 2000 to 2050.
d/ Quinn projections for the long term are from 2000 to 2040.
SOURCE: lEc (1987); Camm and Hammitt (1986); and Quinn (1986).
-------
A-8
EXHIBIT A-5
DUPONT ESTIMATES OF CFG PER CAPITA USE
1985
Population a/ Range of Implied Country Use
Country (thousands) (thousands of metric tons)
Belize
Bolivia
Brazil
Chile
Colombia
Costa Rica
Dominican Republic
Ecuador
Egypt
El Salvador
Fiji
Gabon
Guatemala
Honduras
India
Indonesia
Iran
Iraq
Ivory Coast
Kenya
Morocco
Nicaragua
Paraguay
Peoples Republic of
Peru
Philippines
Senegal
Thailand
Togo
Uruguay
Zimbabwe
Algeria
Argentina
Liberia
Malaysia
Mexico
Panama
South Korea
Taiwan
Tunisia
Turkey
U.S.S.R.
(Countries with <0.
0.2
6.4
135.6
12.1
28.4
2.6
6.4
9.4
48.5
4.8
0.7
0.8
8.0
4.4
765.1
162.2
44.6
15.9
10.1
20.4
21.9
3.3
3.7
China 1 , 040 . 3
18.6
54.7
6.6
51.7
3.0
3.0
8.4
(Countries with 0.1 to
21.9
30.5
2.2
15.6
78.8
2.2
41.1
19.1
7.1
50.2
277.4
1 kg/cap consumption)
b/ <0 . 02
<0.64
<13.56 c/
<1.21
<2.84
<0.26
<0.64
<0.94
<4.85
<0.48
b/ <0 . 07
b/ <0.08
<0.08
<0.44
<76.51 c/
<16.22 c/
<4.46
<1.59
<1.01
<2.04
<2.19
<0.33
<0.37
<104.03 c/
<1.86
<5.47 c/
<0.66
<5.17 c/
<0.30
<0.30
<0.84
0.2 kg/cap consumption)
2.19-4.38
3.05-6.10
0.22-0.44
1.56-3.12
7.88-15.76
0.22-0.44
4.11-8.22
1.91-3.82
0.71-1.42
5.02-10.04
27.74-55.48
-------
A-9
EXHIBIT A-5 (Continued)
DUPONT ESTIMATES OF CFG PER CAPITA USE
1985
Population a/ Range of Implied Country Use
Country (thousands) (thousands of metric tons)
(Countries with 0.2 to 0.5 kg/cap consumption)
Bahrain 0.4 b/ 0.08-0.20
Norway 4.2 0.84-2.10
Portugal 10.2 2.04-5.10
Puerto Rico 3.3 b/ 0.66-1.65
Saudi Arabia 11.5 2.30-5.75
South Africa 32.4 6.48-16.20
Spain 38.6 7.72-19.30
Sweden 8.4 0.84-4.20
Venezuela 17.3 3.46-8.65
Yugoslavia 23.1 4.62-11.55
(Countries with >0.5 kg/cap)
Australia 15.8 >7.90
Austria 7.6 >3.80
Belgium 9.9 >4.45
Canada 25.4 >12.20 d/
Denmark 5.1 >2.55
Ireland 3.6 >1.80
Finland 4.9 >2.45
France 55.2 >27.60 d/
Greece 9.9 >4.45
Israel 4.2 >2.10
Italy 57.1 >28.55
Kuwait 1.7 >0.85
Netherlands 14.5 >7.25
Singapore 2.6 >1.30
Switzerland 6.5 >3.25
U.A.E. 1.4 >0.70
United Kingdom 56.5 >28.25 d/
United States 239.3 XL19.65 d/
West Germany 61.0 >30.50 d/
a/ Most population estimates from (excepted indicated by b/) The World Bank (1987), The
World Development Report 1987. Oxford University Press.
b/ 1984 population estimated from The World Bank (1986), The World Bank Atlas. The World
Bank Press.
c/ Developing countries with large population may have much less use than this benchmark
estimate suggests.
d/ Some developed countries may have much more use than this benchmark estimate
suggests.
SOURCE: Dupont (1982).
-------
A-10
REFERENCES
Araki, Ichiro (1986), Ministry of International Trade and Industry, Basic
Industries Bureau Chemical Products Division, unclassified telegram to U.S.
Department of State, Washington, D.C.
Buxton (1987), personal communication.
Camm, Frank and James K. Hammitt (1986), "An Analytic Method for Constructing
Scenarios from a Subjective Joint Probability Distribution," The RAND
Corporation, prepared for the U.S. Environmental Protection Agency,
Washington, D.C.
Dupont (1987), "Estimated Per Capita Consumption of CFCs," Exhibit prepared
for UNEP International Conference for a Protocol to Prevent Global Ozone
Depletion, Montreal Canada.
EFCTC (1986), European Fluorocarbon Technical Committee, presented at "UNEP
Workshop on Protection of the Ozone Layer," Rome, Italy.
lEc (1987), Industrial Economics, Inc. "Historical and Projected Growth of
Halons Bank and Emissions," prepared for the U.S. Environmental Protection
Agency, Cambridge, Massachusetts. The numbers presented are revised from the
original paper.
ITC (1987), U.S. International Trade Commission, Synthetic Organic Chemicals,
ITC, Washington, D.C.
Nordhaus, William D. and Gary W. Yohe (1986), Probabilistic Projections of
Chlorofluorocarbon Consumption: Stage One. Yale University and Wesleyan
University, prepared for the U.S. Environmental Protection Agency, Washington,
D.C.
Quinn, Timothy H. et. al. (1986), "Projected Use, Emissions, and Banks of
Potential Ozone-Depleting Substances," The RAND Corporation, prepared for the
U.S. Environmental Protection Agency, Washington, D.C.
Tirpak, Dennis (1986), U.S. Environmental Protection Agency, memorandum
summarizing the outcome of Global Climate Change Work Group VIII conference in
theU.S.S.R., Washington, D.C.
World Bank, The (1986), The World Book Atlas. The World Bank Press.
World Bank, The (1987), The World Development Report 1987. Oxford University
Press.
-------
CHAPTER 4
FUTURE EMISSIONS AND CONCENTRATIONS OF TRACE GASES
WITH PARTLY BIOGENIC SOURCES
SUMMARY
Assessment of the risks of stratospheric modification must be based on
realistic projections of atmospheric change. Because the stratosphere can be
perturbed by many gases simultaneously, models that attempt to simulate such
changes require projections of future concentrations of all relevant trace
gases, including those that are wholly industrially produced and those that are
partly biogenic.
This chapter summarizes evidence, gathered by a variety of researchers, on
past emissions and possible future changes in the concentrations of three
gases: carbon dioxide (C02), methane (CH4), and nitrous oxide (N20) -- all
potentially important stratospheric perturbants. Future concentrations of
these gases, particularly methane, are difficult to project for several
reasons: current emission sources are not well understood; estimates of the
growth in activities that produce emissions depend on future economic,
political, and physical forces; future emissions for different activities or
natural systems may change as the environment changes; and our understanding of
the biogeochemical cycles that control the fate of emissions both now and in
the future is incomplete. Together these difficulties make precise projection
of future concentrations of trace gases impossible.
Despite these uncertainties, however, atmospheric modelers have generally
settled on a narrow range of standard scenarios. While recommending the use of
a scenario consistent with prior decisions of the "atmospheric" community in
this risk assessment, this chapter also suggests additional sensitivity
scenarios useful for examining the range of possible futures of these gases.
The standard scenario adopted is as follows: for C02, the 50th percentile
scenario prepared for the National Academy of Sciences is recommended (doubling
of pre-industrial C02 concentrations in 2065); for CH4, a 0.017 parts per
million (ppm) increase per year, the average growth per year based on historic
changes, is suggested; for N20, a scenario of continued growth in
concentrations of 0.2 percent per year is proposed.
Additional sensitivity scenarios are suggested which will improve our
understanding of the range of risks that we face. It should be noted that the
"standard scenarios" do not reflect the possibility that governments may
attempt to limit "greenhouse warming" by controlling the concentrations of
these gases (C02, CH4, or N20). The assumption that has been implicitly made
by extrapolating past rates of growth of these trace gases indefinitely into
the future is that future decision makers will never decide to limit global
warming (e.g., regardless of the amount the earth warms, greenhouse gases will
be allowed to grow). In Chapter 18, the implications of alternative
assumptions are analyzed.
-------
4-2
FINDINGS
1. FUTURE CONCENTRATIONS OF STRATOSPHERIC PERTURBANTS THAT HAVE AT LEAST"SOME
BIOGENIC SOURCES. CARBON DIOXIDE. METHANE. AND NITROUS OXIDE. ARE DIFFICULT
TO PROJECT (chapter 4).
la. The size of existing source terms (wetland areas, for example) is not
known with certainty today for all these trace species. Greatest
uncertainty exists for methane, least for C02. To estimate future
emissions reliably requires estimating the growth of source terms
(e.g., acreage of rice paddies, wetlands area), which will be
determined by many technical, political, environmental, and social
factors.
Ib. Current emission factors for each source term must be estimated; some
are not known today or have not been reliably estimated (emissions from
soils, for example).
Ic. Possible changes in emission factors due to changes in the environment
must be projected. Projection of changes is difficult because the
underlying physical or biological processes that determine emissions
are not well understood and because changes in the environment that
could alter emissions are not easy to project.
Id. Biogeochemical cycles that control the fate of emissions once released
into the atmosphere must be understood to determine future
concentrations of these trace species; severe limitations to our
current understanding of these cycles limits our capacity to determine
the consequences of changing emissions in the future.
le. Possible changes in these biogeochemical cycles due to changes in-the
environment must be projected; again deficiencies in existing knowledge
makes this task difficult.
2.. DESPITE THE UNCERTAINTIES ASSOCIATED WITH EACH OF THESE FACTORS.
RESEARCHERS HAVE DEVELOPED SCENARIOS FOR THREE GASES WHICH ARE COMMONLY
USED. IN THIS RISK ASSESSMENT A SCENARIO CONSISTENT WITH ONES USED IN THE
ATMOSPHERIC COMMUNITY'S WILL BE ADOPTED. AS WELL AS SEVERAL SENSITIVITY
SCENARIOS TO EXAMINE THE SENSITIVITY OF ATMOSPHERIC EVOLUTION TO THE
SCENARIOS (chapter 4).
2a. The scenarios used in this risk assessment are consistent with that
commonly used by the atmospheric community and assume the following
changes in trace gas concentrations:
o for C02, a scenario developed by the National Academy of
Sciences (its 50th percentile, i.e., pre-industrial C02
concentrations doubling by about 2065);
o for CH4, a linear increase in concentrations of 0.017 ppm
per year;
o for N20, concentration increases of 0.2 percent per year.
-------
4-3
2b. Additional scenarios used to analyze risks will include:
- for C02
o NAS 25th percentile (pre-industrial concentrations
doubling by 2100)
o NAS 75th percentile (pre-industrial concentrations
doubling by 2050)
- for CH4
o 0.01275 ppm per year growth in concentrations (75
percent of the historically observed 0.017 ppm per
year increase)
o 0.02125 ppm per year growth in concentrations (125
percent of the historically observed 0.017 ppm per
year increase)
o 1 percent compound growth per year in concentrations
o 1 percent compound growth per year in concentrations
from 1985 to 2010, followed by constant
concentrations at 2.23 ppm
o 1 percent compound growth per year in concentrations
from 1985 to 2020, growing to 1.5 percent compound
annual growth by 2050 and thereafter
- for N20
o 0.15 percent per year compound growth in
concentrations
o 0.25 percent per year compound growth in
concentrations
DECISION MAKERS SHOULD BE MADE AWARE THAT THE MOST COMMONLY USED SCENARIOS
IN STRATOSPHERIC MODELING IMPLICITLY ASSUME THAT FUTURE DECISION MAKERS
NEVER TAKE ACTION TO LIMIT THE RISE IN CONCENTRATIONS OF CARBON DIOXIDE.
METHANE. AND NITROUS OXIDE. THREE GASES CONTRIBUTING TO THE GREENHOUSE
WARMING (chapter 4).
3a. The standard assumption in most atmospheric modeling has been, by
default, that greenhouse gases will be allowed to increase without
limit regardless of the level of global warming that occurs or is
projected.
3b. In order to provide decision makers with adequate information to
assess the risks of ozone modification due to rising CFCs and
Halons, alternative assumptions about the future of greenhouse gases
need to be examined. Two scenarios are examined:
limiting global warming to 2°C.
limiting global warming to 3°C.
-------
4-4
THE INFLUENCE OF TRACE GASES ON THE STRATOSPHERE AND TROPOSPHERE
Rising concentrations of C02, CH4, and N20 may influence a number of
natural atmospheric and environmental processes (see Exhibit 4-1). Increases
in C02 concentrations have three major effects: (1) C02 is an important
greenhouse gas (Ramanathan et al. 1985); (2) C02 affects the physiological
development of plants, enhancing photosynthesis, decreasing gas exchange and
transpiration (water loss), and altering the morphological and biochemical
development of plants (Strain and Cure 1985); and (3) C02, by cooling the
stratosphere, increases ozone abundance there (World Meteorological
Organization 1986).
CH4 concentrations have two important effects on the stratosphere: (1) CH4
decreases column ozone destruction at lower altitudes; (2) CH4 adds water vapor
to the stratosphere, which amplifies global warming and climate change. In the
troposphere, CH4 will increase tropospheric ozone, resulting in a further
enhancement of the greenhouse effect and possibly an increase in oxidants that
affect surface processes (World Meteorological Organization 1986) . Carbon
monoxide (CO) is considered in this chapter because its abundance, in part,
controls and is, in part, controlled by the abundance of CH4 (Thompson and
Cicerone 1986; Levine, Rinsland, and Tennille 1985). By altering the abundance
of OH, which is a sink for CH4, increases of CO will indirectly increase CH4;
decreases in CO will have the opposite effect (Levine, Rinsland, and Tennille
1985).
Increasing tropospheric concentrations of N20 are a major source of global
warming (Ramanathan et al. 1985). By itself, an increase in stratospheric N20
would also decrease stratospheric ozone abundance. However, in tandem with
increasing chlorine, N20 may interfere with chlorine's catalytic cycle. The net
effect depends on the exact scenario (Stolarski, personal communication).
The fact that C02, CH4, and N20 are all gases that contribute to global
warming is important. To the extent that global warming becomes a concern,
future emissions of these gases may depend on whether governments undertake
policies to directly or indirectly alter these atmospheric concentrations.
Nations may, for example, undertake policies to limit carbon monoxide emissions
in order to lower CH4 concentrations and reduce global warming. Similarly,
nations may control emissions in order to prevent the buildup of oxidants in the
troposphere. Future policies may play an important role in determining the
emissions and concentrations of these gases. As Mintzer and Miller (1986) note,
"[if] restraints were imposed on the buildup of C02, CH4 and N20 in order to
control their contribution to global warming, the role of these gases as
moderators of potential ozone depletion in high CFC emission scenarios could be
severely limited."
TRACE GAS SCENARIOS
The remainder of this chapter reviews scenarios that researchers have
developed to describe possible trends in concentrations of CH4, C02, and N20.
Efforts to measure past and current concentrations were discussed in Chapter 2;
here we examine the current understanding of source terms and fluxes for each
gas or its precursors and how these might change over time. This review
-------
EXHIBIT 4-1
EFFECTS OF CHANGES IN COMPOSITION OF AIM3SPHEKE
RISING
LEVELS
EFFECT ON PLANTS
EFFECT ON
SURFACE CLIMATE
EFFECT ON
TROPOSPHERIC CHEMISTRY
EFFECT ON
STRATOSPHERIC COMPOSITIOH
AND STRUCTURE
C02 Changes physiology;
increases photo-
synthesis; changes
water relations
(Strain and Cure
1985)
Greenhouse gas
(Ramanathan et al.
1985)
No direct effect
Cools stratosphere, increasing ozone level
by slowing destruction processes
(NAS 1984)
CH4
None
Greenhouse gas
(Ramanathan et al.
1985)
Creates ozone (NAS 1984);
alters OH abundance
(Khalil and Rasmussen
1985a), increases CO abun-
dance (Thompson and
Cicerone 1986). Effect
is latitudinally depen-
dent, decreasing with
distance from equator
(Isaksen and Stordal
1986).
o Interferes with catalytic destruction by
chlorine, thereby increasing ozone
(NAS 1984)
o Alters vertical distribution of ozone,
increasing greenhouse effect and possibly
changing circulation patterns (World
Meteorological Organization 1986)
o Creates additional greenhouse effect in
stratosphere by adding water, adding to
tropospheric greenhouse warming normally
considered (World Meteorological
Organization 1986).
N20
Greenhouse gas
(Ramanathan et al.
1985)
No direct effect
Contributes odd nitrogen to stratosphere:
-- can, in some cases, interfere with
chlorine catalysis of ozone
(Stolarski, personal communication)
CO
None
Indirectly
increases C02 and
03, two green-
house gases (World
Meteorological
Organization 1986).
Alters OH abundance
thereby increasing
methane abundance
(Thompson and Cicerone
1986)
-- by itself, acts as catalyst to ozone
destruction
(Stolarski, personal communication)
Does not reach stratosphere in significant
quantity; indirect
-------
4-6
concentrates on the scenarios generally in use in the atmospheric community.
However, other scenarios, which will be used in later chapters in analyzing
risks of stratospheric change, are described here as well.
Carbon Dioxide (C02)
Measured Increases in C02 Concentrations
Chapter 2 summarizes historical changes in the concentrations of C02:
relatively constant concentrations until the onset of the Industrial Revolution,
followed by continuous increases (Pearman et al. 1986; Keeling and GMCC/NOAA
1985).
Historical C02 Emissions
In the century before the beginning of the industrial revolution the natural
losses of C02 roughly balanced natural emissions, leading only to a seasonal
cycle visible each year. After 1850 and the onset of the Industrial Revolution,
the heavy use of coal and other fossil fuels (and possibly massive
deforestation) led to a large increase in C02 emissions. Rotty and Marland
(1984) have analyzed historical records of fossil fuel use and reconstructed the
emissions profile shown in Exhibit 4-2. While fossil fuels are the major source
of emissions, such activities as forest clearing and deforestation may have
redistributed C02 from biomass sinks to the atmosphere. However, estimates of
the amount of C02 emitted to the atmosphere as a result of deforestation have
declined substantially in recent years (Houghton et al. 1983; Brown and Lugo
1981).
The Carbon Cycle: Estimates of the Current Budget
Emissions from fossil fuels are only one part of the biogeochemical
processes known as the carbon cycle. Other components of the carbon cycle are
the uptake of carbon by the terrestrial biosphere and the uptake, absorption,
and outgassing of C02 in the oceans (Trabalka 1985). Exhibit 4-3 provides a
schematic of these components. Understanding the carbon cycle presents an
enormous scientific challenge to which much effort has been devoted. The
Department of Energy has recently issued a state-of-the-art report Atmospheric
Carbon Dioxide and the Global Carbon Cycle. which interested readers should
consult for more information (Trabalka 1985). Suffice it to say, even after
decades of study there are significant uncertainties in this cycle and
disagreement still exists about the size of various sources and sinks and the
current fraction airborne.
Projections of Future C02 Emissions
Future concentrations of C02 will depend on the quantity of C02 emissions,
the future operation of the carbon cycle, and its impact on the fraction
airborne. Consequently, predictions of future C02 levels are subject to
uncertainty. Several researchers have used long-term energy models to represent
the socioeconomic factors that contribute to energy use and C02 emissions.
While models differ, in some fashion each model relates world economic
production and population growth to energy use and economic efficiency. By
making different assumptions about future population and economic growth, the
-------
4-7
EXHIBIT 4-2
Historical Carbon Dioxide Emissions from Fossil Fuels and Cement
8 r
Carbon dioxide emissions have risen rapidly since the outset of the Industrial
Revolution.
Source: Rotty and Marland 1984.
-------
4-8
EXHIBIT 4-3
A Schematic of the Carbon Cycle
Atmosphere
1
711
•
(335 ppm of C02)
1
5 56 56 2
12.000
(7.500
ultimately
recoveraOle)
1
1.760
.
t
3 90 90
.
Fossil fuels Terrestrial
| |
eon
38.400
Oceans
\
ourtace
Intermediate
and deep
and shales biosphere
Reservoirs in 10 metric tons
Fluxes in 10 metric tons/year
The stocks of carbon in each natural reservoir and the annual flows that take
place among reservoirs are shown. Taken together, these stocks and flows
constitute the carbon cycle. Carbon distributed through this cycle plays an
important role in the ecological balance of the atmosphere, biosphere, and
oceans.
Source: Council on Environmental Quality 1981.
-------
4-9
modelers generate projections of future energy use and fuel mix. They then
apply average carbon content ratios to compute the associated C02 emissions
(Edmonds and Reilly 1985a).
Perhaps the most widely accepted set of projections was developed for the
National Academy of Sciences by Nordhaus and Yohe (1983). In the most likely
scenario, C02 emissions rise from 5 gigatons per year in 1975 to nearly 20 by
the year 2100. Other researchers with published projections of CO2 emissions
include Seidel and Keyes (1983) and Edmonds et al. (1984). Exhibit 4-4 shows
the low, medium, and high projections of each group.
Projections of Future C02 Concentrations
As future C02 emissions increase, the fluxes between compartments of the
carbon cycle may change. For example, some researchers believe that the ocean's
absorption of C02 may change as the ocean becomes more saturated with C02 and as
ocean circulation patterns are modified. (Emmanuel, Kilbugh, and Olson 1981;
Baes, Jr., Bjoerkstroem, and Mulholland 1985.) Photosynthesis may also
increase, leading plants to store additional carbon standing biomass, thereby
reducing the percentage of C02 emissions that remains in the atmosphere (Gates,
Strain, and Weber 1983). Respiration may increase with warming, altering C02
emissions from previously inactive storage compartments (Woodwell et al. 1983).
Thus, both rising C02 emissions and an increasing airborne fraction should
contribute to future increases in C02 concentrations.
A widely adopted measure of concentration projections is the "doubling
time," the year in which C02 concentrations reach twice their pre-industrial
level. Exhibit 4-4 shows that mid-range projections estimate that a doubling of
C02 could occur as early as 2050 or as late as 2065, assuming a 'well behaved'
carbon cycle. If there is, however, a large change in the carbon cycle due to
changes in increased or decreased respiration or photosynthesis, these estimates
could change.
Standard Scenario Proposed for Assessing Risks and Later Policy Testing
A scenario that will be used for assessing risks of ozone depletion due to
increases in CFCs, halons, and other chemicals, will be the NAS 50th Percentile
(Nordhaus and Yohe 1983), which is generally consistent with that used in most
atmospheric modeling (Ramanathan et al. 1985; Wuebbles, MacCracken, and Luther
1984; World Meteorological Organization 1985). The NAS 50th Percentile Scenario
projects the following C02 concentrations from 1975 to 2100:
Concentration
(ppm)
1975 340
2000 366
2025 422
2050 508
2075 625
2100 770
This scenario assumes that no efforts are made in this period to limit
greenhouse warming by limiting C02.
-------
4-10
EXHIBIT 4-4
Projected Carbon Dioxide Emissions and Doubling Time of Concentrations
Cai-bon Dioxide Pro j ec t i on« :
Emissions and Doubling Tixe
t*r* 2000
C02 emission projections are shown for EPA (Seidel and Keyes 1983), NAS
(Nordhaus and Yohe 1983), and Edmonds (Edmonds et al. 1984). The brackets
indicate the approximate time at which concentrations reach twice the
pre-industrial level.
-------
4-11
In addition, the following 25th and 75th percentile scenarios will be
examined (these scenarios also assume approximately 50 percent airborne).
NAS 25th NAS 75th
Percentile Percentile
(ppm) (ppm)
1975 340 340
2000 359 380
2025 391 456
2050 434 568
2075 477 735
2100 579 910
Methane (CH4)
Measured Increases in CH4 Concentrations
Chapter 2 summarizes historical changes in CH4 concentrations: relatively
constant levels until approximately 150 to 200 years ago, followed by increases
that now approximate 0.017 ppm per year (Khalil and Rasmussen 1986).
Historical CH4 Emissions
The extent of scientific agreement on the probable sources and quantities of
CH4 emissions (Exhibit 4-5) is quite limited (World Meteorological Organization
1986). In fact, the discrepancies shown in the exhibit probably underestimate
uncertainty -- not reflecting, for example, questions emerging about the
potential magnitude of tundra as a source of emissions. Our understanding of
past changes is limited. Expanded human activities, such as rice cultivation,
agriculture, raising cattle, and the use of oil and natural gas, may have
increased fluxes from these sources (World Meteorological Organization 1986).
Decreases in wetlands may have reduced fluxes from this source. However,
because the size of change in each source is uncertain (e.g., rice acreage
added), and the flux associated with different conditions for each source is
unclear (for example, emissions from different types of rice cultivation vary),
we cannot directly estimate past changes in CH4 fluxes through time.
CH4 Photochemistry and Biogeochemical Cycling
Changes in CH4 concentrations depend on changes in CH4 fluxes and the many
physical and chemical processes that control the fate of CH4 emissions.
CH4 emitted to the atmosphere (1) combines with the OH radical to form C02
and water vapor, (2) is reabsorbed by soils and water, and (3) is transported to
the stratosphere where it is oxidized to add water vapor and other compounds in
that relatively dry region (Thompson and Cicerone 1986).
The key factor controlling the fate of CH4 once it is in the atmosphere is
its reaction with OH (Khalil and Rasmussen 1985b). OH concentrations in turn
-------
4-12
EXHIBIT 4-5
Estimated, CH4 Emission Sources
(10 grans per year)
Enteric fermentation
(livestock)
Rice paddies
Wetlands
Biomass burning
Freshwater lakes
Oceans
Tundra
Anthropogenic/
fossil fuel
Other
TOTAL
a/
COLUMN I
100-200
- 280
190-300
1-25
1-17
0.3-3
16-50
--
586-825
b/
COLUMN II
100-150
100 ± 50
150 + 50
10 - 60
—
—
10-150
390-765
Q
Column I is taken from Ehhalt (1974) and Ehhalt and
Schmidt (1978).
Column II is taken from Khalil and Rasmussen (1983).
Source: World Meteorological Organization (1986).
-------
4-13
are determined by CH4, CO, and possibly non-methane hydrocarbons on a localized
scale. As such, OH provides a close coupling between CO and CH4: CO
concentrations must be considered when interpreting the behavior of CH4 in the
atmosphere. One possible cause for a temporal increase in CH4 concentrations is
a declining supply of OH brought about by increasing CO (Khalil and Rasmussen
1985b; Levine, Rinsland, and Tennille 1985).
An example of the interaction between CO and CH4 appears in Exhibit 4-6 from
Thompson and Cicerone. Note that increases in CO emissions, by decreasing the
OH abundance, increase the CH4 lifetime and concentrations; decreasing CO will
tend to have the opposite effect. Unfortunately, there are two factors that
complicate analysis of actual CO and CH4 trends and predictions of future
changes in these trace gases. The first is that atmospheric CO trends are
harder to discern than are CH4 trends, although there is accumulating evidence
that at least in some locations CO is increasing (see below) (Rinsland and
Levine 1985; Khalil and Rasmussen 1983). The second is that measurements of OH
are nearly nonexistent and both present-day and historical OH can only be
deduced from model calculations. Calculations show that there are numerous
factors besides concentrations of CH4 and CO that determine OH concentrations,
and hence methane lifetimes (Thompson and Cicerone 1986). These include 03,
water vapor distributions, the amount of sunlight and concentrations of soluble
OH end-product gases that can be rained out (e.g., HN03, H202). All of these
factors vary widely in time and with locality and season. Reactive non-methane
hydrocarbons (presumably both those emitted by human activities and those
occurring naturally from vegetation) may control OH more effectively than CO and
CH4 in areas where their concentrations are high. Ozone and NOx (NOx = NO +
N02) levels are critical to OH concentrations since 03 is the precursor species
for OH, For example, at low NOx concentrations, increasing CO and CH4
suppresses OH almost uniformly throughout the troposphere, but at high NOx (as
would be found in a continental or urban environment), increasing CH4 or CO
contributes to photochemical ozone formation and increases OH near the ground
and in the upper troposphere (Hameed, Pinto, and Stewart 1979; Thompson and
Cicerone 1985).
Consequently, if one were to estimate future CH4 concentrations from models
one would need to estimate not only future CH4 fluxes, but future fluxes of many
other gases, as well as a variety of environmental conditions, none of which can
be precisely forecast at this time.
Projections of Future Emissions of Methane
If CH4 emissions are to continue to grow, increases in source terms and/or
emission rates would be required. Empirical work on this subject is limited,
although certain educated guesses may be possible (Hoffman and Wells 1986) (see
Exhibit 4-7).
Consequently, as Exhibit 4-7 outlines, it is possible that CH4 emissions
will cease growing (if they are growing now). This could happen if increases in
the size of various sources slow (rice acreage, for example), if source terms
are eliminated (forests, for example), or if emissions factors decline (from
rice paddies, for example, if C02 reduces transport by changing stomatal
resistance). However, it is also possible that increases in temperature or
changes in hydrology will increase emissions factors for some sources (from
tundra, for example), compensating for, or overwhelming any decreases in
source-term quantities (Hoffman and Wells 1986).
-------
4-14
EXHIBIT 4-6
Two Ways That CH4 Concentrations Could Have Changed
1.5 20
CO FLUX (Normalized)
2.5
1.0 1-5 2.0
CH4 FLUX (Normalized)
As a consequence of coupling between CO and CH4, due to their reactions with OH,
concentrations of CH4 can increase both through increases in CO fluxes (a) and
CH4 fluxes (b) .
Source: Thompson and Cicerone 1985.
-------
4-15
EXHIBIT 4-7
Possible Changes in CH4 Sources and in Emission Factors
SOURCE TERMS
POSSIBLE CHANGE IN LEVEL
OF SOURCE TERMS
POSSIBLE CHANGE IN EMISSION
FACTOR FOR SOURCE TERMS
Rice
Livestock
Deforestation
Wetlands
Mining
Tundra
To slow and then stabilize
with population
To slow and then stabilize
To slow, then disappear
Loss of wetlands should
increase, then slow and
stabilize
Increasing
None
Decline possible if:
o increased C02 reduces
emissions by reducing
transport through plants
o cultivars shift
o cropping practices remove
wastes
Increases possible if warmer
temperatures raise emissions
per unit biomass
Possible decrease with
biotechnology to reduce
methanogenesis and "wasted"
energy
Possible increase with
temperature/decrease with
C02
No information available
Changes are possible:
o Increase with rising
temperature if
methanogenesis increases
o Decrease with rising
temperature if several
microorganisms are
cold-tolerant and subject
to adverse selection if
warming occurs
Source: Hoffman and Wells 1986
-------
4-16
Projections Of other Gases Influencing Future CH4 Concentrations
Future concentrations of CH4 will be influenced by the OH radical and the
trace gases such as CO, NOx, and non-methane hydrocarbons that help determine
its concentration. In this section, we summarize our current understanding of
these gases:
1) Measured Trends in CO Concentrations. Chapter 2 summarizes measurements
of atmospheric CO concentrations: annual increases of approximately 1 percent
to 2 percent since the 1950s.
2) Current and Historical CO Emissions. Information about past and current
CO emissions is sparse. Logan (1985) has made estimates of the current sources
and sinks of CO emissions (Exhibit 4-8). Estimates of past global CO emissions
have not been made, except by use of models that make assumptions about
concentrations of CH4 and CO. Kavanaugh (1986) has recently completed a study
of historical CO emissions from combustion. He estimates that from 1960 to
1975, emissions of CO from fossil fuel combustion increased at a rate of 1.7
percent per year.
3) Future Emissions of CO. Estimates of future emissions of CO require
projecting changes in all source terms and their associated emission factors. A
search of the literature revealed no published literature of future CO emissions
from natural sources. Kavanaugh (1986), however, argues that there is likely to
be a substantial reduction in future CO emissions from combustion.
Exhibit 4-9 shows three such scenarios. The cause of the expected decline
in CO emissions is the penetration of efficient engines into world vehicle
markets, the substitution of ethanol, diesel, and unleaded gasoline for leaded
gasoline, and the adoption of pollution-reduction equipment in some parts of the
world's transportation sector (Kavanaugh 1986).
Furthermore, to the extent that CO emissions stem from forest clearing, this
source of emissions can be expected to slow and eventually terminate, as the
supply of clearable forest areas becomes exhausted.
4) Past, Current, and Future Emissions of NOx, OH, and Non-Methane
Hydrocarbons. NOx and non-methane hydrocarbons, through their effect on OH and
CO, play a role in determining CH4 concentrations. Unfortunately, there is
little historical information on these- compounds and even present-day ambient
data are uneven in quality and spatial resolution. An evaluation of past NOx
and non-methane hydrocarbon combustion sources is underway (Dignon and Hameed
1986; Hameed, personal communication to Anne Thompson, 1986). These gases are
also relevant to the formation of tropospheric ozone, which may be increasing
(Logan 1985).
Scenarios for GH4 Proposed for Assessing Risks and Later Policy Testing
Current information about sources, future source size, emission rates and
future emission rates has not yet been integrated to develop projections of CH4
concentrations based on modeling from 'the ground up.' In absence of anything
better, a reasonable approach to projecting future methane concentrations would
be to extrapolate past increases of 0.017 ppm indefinitely into the future.
Research should focus on all of the areas discussed earlier in this chapter,
including the following: how the CH4 sources would change over time (how much
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4-17
EXHIBIT 4-8
Current Sources and Sinks of Carbon Monoxide
(1984 Concentrations of CO: 30-200 ppb)
SOURCE GASES
Atmospheric burden (10^ tons as carbon) 200
Sinks + Accumulation (10" tons per year as carbon)
Reaction with OH 820+300
Soil uptake 100
Accumulation (5.5%/yr.) 10
TOTAL 940+330
Sources (10 tons per year as carbon)
Fossil fuel combustion 190
Oxidation of anthropogenic hydrocarbons 40
Wood used as fuel 20
Oceans 20
Oxidation of CH4 260
Forest wild fires (temperate zone) 10
Agricultural burning (temperate zone) 10
Oxidation of natural hydrocarbons (temperate zone) 100
Burning of savanna and agricultural land (tropics) 100
Forest clearing (tropics) 160
Oxidation of natural hydrocarbons (tropics) 150
TOTAL 1060
Tropical Contribution
Burning 100
Forest clearing 160
Oxidation of hydrocarbons 150
TOTAL 410
Source: Logan et al. (1981), updated by Logan et al. (private
communication, 1984), as reported in World Meteorological
Organization (1986).
-------
4-18
EXHIBIT 4-9
Scenarios of Carbon Monoxide (CO) Emissions fron Combustion
9OO
BOO -
700 -
600 -
300 -
Future carbon monoxide emissions from combustion, as projected by Kavanaugh
(1986). The case of the expected decline is the penetration of efficient
engines into world markets, the substitution of cleaner fuels, and the
increased use of pollution reduction equipment in transportation.
Source: Kavanaugh (1986).
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4-19
more rice paddies and cattle, how much less wetland area, etc.); how emission
rates (e.g., emissions per acre of rice) would change because of alterations
in temperature, water, cultivation practices, and atmospheric C02; how CO,
NOx, and non-methane hydrocarbon emissions will change; and how tropospheric
chemical balances will change as a result. The time to attempt such an
effort is clearly upon us.
Because future methane concentrations are uncertain, the following wide
range of sensitivity scenarios of CH4 concentrations are suggested for use in
Chapter 18:
o Case 1. CH4 concentrations increase by 0.01275 ppm per year (75
percent of the historically observed 0.017 ppm per year
increase).
o Case 2. CH4 concentrations increase by 0.02125 ppm per year (125
percent of the historically observed 0.017 ppm per year
increase).
o Case 3. CH4 concentrations increase by 1 percent per year from
1985 to 2010, followed by constant concentrations at 2.23 ppm.
This scenario, proposed by Hoffman and Wells (1986), attempts to
reflect the slowing or cessation of deforestation, a source of CO
and CH4 fluxes.
o Case 4. CH4 concentrations increase by 1 percent per year from
1985 to 2020, followed by a 1.5 percent per year increase after
2050. This scenario, recommended by Hoffman and Wells (1986),
asserts that temperature increases overwhelm other forces that
would tend to reduce the growth of CO and CH4 fluxes.
These scenarios can help illuminate the effects of uncertainty about CH4 on
column ozone abundance.
Nitrous Oxide (N2O)
Measured Increases in N20 Concentrations
Chapter 2 summarizes that historical changes in N20 concentrations have
increased approximately 6 ppb over the last 300 years (Pearman et al. 1986).
Currently, concentrations are increasing at about 0.2 percent per year (WHO
1986).
Historical N20 Emissions
The major sources of N20 are emissions from soils, fossil fuel combustion,
and fertilizer use (McElroy and Wofsy 1984). Researchers estimate that fossil
fuel combustion currently accounts for between 20 percent and 30 percent of the
emissions, with fertilizers and natural sources contributing the remainder
(McElroy and Wofsy 1984). However, the change in global emissions may be mostly
attributable to fossil fuel burning.
N20 and the Biogeochemical Cycle
The only known sink for N20 is stratospheric photolysis and reaction with
singlet atomic oxygen. Both processes occur only in the upper atmosphere, and
the atmospheric residence time of N20 is consequently long -- approximately 100
-------
4-20
to 175 years (World Meteorological Organization 1986). As with the CFCs, the
long lifetime means that curtailing the growth of N20 emissions so that N20
emissions are held constant would not prevent an increase in N20 concentrations
for many decades, since N20 is far from the equilibrium value with its current
emissions.
Projections of Future N20 Emissions and Concentrations
Future emissions of N20 will primarily depend on fossil fuel combustion,
natural emissions, and agricultural activity. Estimates of future N20 emissions
from energy combustion were prepared by Kavanaugh (1986). Kavanaugh used the
Institute for Energy Analysis/Oak Ridge Associated Universities Long-Term Global
Energy Model to project fossil fuel use (Edmonds and Reilly 1985b). He compiled
current emission factors and considered possible changes in emission factors
(from increased adoption of catalytic converters, for example). Kavanaugh found
large increases in N20 emissions from combustion: "a doubling in emissions from
1975 to 2000 and a 44% increase from 2000 to 2025." He stated that the "driving
force in these changes is rapid economic and population growth in [the rest of
the world] and China."
Weiss (1981) developed a simplified atmospheric model that computes
atmospheric N20 concentrations from increases in N20 emissions. Input to the
Weiss model is the aggregate emissions growth rate in each time period. To
compute this aggregate growth rate, emissions from all sources must be
projected. Estimates for future changes in the flux of agricultural and natural
emissions have not been developed, however.
To conduct a preliminary analysis of future N20 concentrations, we developed
simplified scenarios for each source term. The combustion source was assumed to
contribute 31 percent of the total (McElroy and Wofsy 1984). Projections of
combustion were taken from Kavanaugh (1986). The agricultural source was
assumed to contribute 58 percent of the total (McElroy and Wofsy 1984). In the
absence of independent projections, it was assumed that the agricultural source
would increase at the same rate as world population. The population
projections, consistent with those in the energy model, were based on the work
of Keyfitz and are discussed in Gibbs (1986). Natural fluxes, assumed to
contribute 11 percent of total emissions (McElroy and Wofsy 1984), were held
constant.
Using the baseline distribution of source terms and the projected increases
in each source, aggregate growth rates were computed. Exhibit 4-10 presents the
growth in emissions from each source and the aggregate growth rate.
These increases in N20 emissions were used as inputs to the Weiss (1981)
model. Exhibit 4-11 shows that the computed concentrations for this preliminary
scenario are consistent with the N20 concentrations scenarios generally used by
the atmospheric modeling community.
Standard Scenario Proposed for Assessing Risks and Later Policy Testing
Because our preliminary emission-concentrations analysis gives results
consistent with the scenario commonly used by the atmospheric modeling
community, we propose using this scenario -- 0.20 percent growth per year -- for
the standard case for risk assessment. The standard scenario assumes no effort
is made to limit emissions caused by human activity. Sensitivity tests of 0.15
percent and 0.25 percent will also be examined.
-------
4-21
EXHIBIT 4-10
Preliminary Scenario of Future Growth in
N2O Emissions by Source
PERCENT ANNUAL GROWTH RATE
SOURCE (% of total)
Combustion (31)
Agricultural (58)
Natural (11)
AGGREGATE (100)
1975-2000
2.9
1.6
0.0
1.9
2000-2025
1.6
0.9
0.0
1.1
2025-2050
1.6
0.4
0.0
1.0
2050-2075
1.6
0.1
0.0
1.0
Sources: McElroy and Wofsy (1984)
Kavanaugb (1986)
Edmonds and Reilly (1985b)
-------
4-22
EXHIBIT 4-11
Projected Nitrous Oxide (N02) Concentrations
0
m
o
0.
400
380 -
360 -
.25% annual increase
in concentrations
§. 340 -
32O -
300
Preliminary emissions
concentrations model
1980
2OOO
2020
2040
2060
2O80
-------
4-23
EFFECTS OF POSSIBLE FUTURE LIMITS ON GLOBAL WARMING
C02, CH4, and N20 are radiatively active trace gases that may contribute to
future global warming (Ramanathan et al. 1985; Cicerone and Dickinson 1986;
Wang, Wuebbles, and Washington 1985). To the extent that decision makers become
concerned about global warming, governments may take action to limit the rise in
the concentrations of these trace gases.
Mintzer and Miller (1986) suggest that several measures are available to
reduce greenhouse gases -- either directly, by limiting their emissions, or
indirectly, by manipulating their atmospheric loss terms. To reduce C02
emissions from biogenic sources, they suggest reforestation efforts. To control
CH4 concentrations, they suggest regulations to limit emissions and natural gas
pipelines, coal mines, and oil fields. Buildup in the atmosphere, they contend,
could also be limited by efforts to reduce CO emissions, which, as this chapter
discussed earlier, may deplete OH concentrations, which are a major loss term
for CH4. A recent workshop report indicated that N20 might be controlled
through better combustion practices (EPA 1986).
It is beyond the scope of this chapter to evaluate the likelihood of
successful government action to limit greenhouse gas increases. No one knows
how future decision makers will respond to greenhouse warming. The default
assumption of the standard scenarios has been that no response will develop.
That assumption constitutes one bound of possibility. Another bound might be
that major efforts are undertaken to stabilize global atmospheric
concentrations. In between these extremes, a range of possibilities exists. In
order to provide decision makers with an assessment of the risks of ozone
depletion for various emission scenarios of ozone-depleting substances, Chapter
18 will analyze scenarios in which total global warming is limited to 2°C or 3°C
(plus or minus 50%, the uncertainty attached to any radiative forcing by the
National Academy of Science evaluations on climate change -- see Chapter 6).
CONCLUSION
Because N20 and C02 are long-lived gases, their concentrations are likely to
rise despite significant uncertainties about future emissions trends. Future
concentrations of CH4 are another matter, however. CH4 has a relatively short
lifetime and the factors that determine its production and loss terms are quite
difficult to predict. Its future is more difficult to project reliably.
Exhibit 4-12 presents the combined scenarios proposed for use in risk
assessment analysis. In Chapter 18, alternative scenarios are examined, which
examines how risks would change if future decision makers decide to limit global
warming to 2°C or 3°C.
-------
4-24
EXHIBIT 4-12
Summary of Standard Scenarios Proposed for Assessment
Carbon dioxide (C02) concentrations (ppm)
Reference
YEAR
1975
2000
2025
2050
2075
2100
NAS 50th Percentile
340
366
422
508
625
770
Sensitivity Cases
NAS 25th
Percentile
340
359
391
434
477
579
Source: Nordhaus and Yohe (1983).
Methane (CH4) concentrations (ppmv)
REFERENCE
SENSITIVITY CASES
Case 1 Case 2 Case 3 Case 4 Case 5
1980
1990
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100
1.65
1.84
2.01
2.18
2.35
2.52
2.69
2.86
3.03
3.20
3.32
3.54
3.71
1.65
1.82
1.95
2.07
2.20
2.33
2.46
2.58
2.71
2.84
2.97
3.09
3.22
1.65
1.86
2.07
2.29
2.50
2.71
2.92
3.14
3.35
3.56
3.77
3.99
4.20
1.65
1.82
2.28
2.23
2.23
2.23
2.23
2.23
2.23
2.23
2.23
2.23
2.23
1.65
1.82
2.28
2.23
2.46
2.79
3.16
3.56
4.16
4.83
5.62
6.53
7.58
Nitrous oxide (N2O) concentrations:
Standard Sensitivity
NAS 27th
Percentile
340
380
456
568
735
910
0.20% annual increase
0.15% annual
increase
0.25% annual
increase
-------
4-25
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CHAPTER 5
ASSESSMENT OF THE RISK OF OZONE MODIFICATION
SUMMARY
Models project that the average global column of ozone will deplete slightly
for a time if emissions of chlorofluorocarbons (CFCs) and other chlorine and
bromine bearing compounds grow from current levels even if the greenhouse gases
that counter ozone depletion continue to grow at current rates. For latitudes
greater than 40°N, column depletion is projected even for scenarios in which the
emissions of chlorofluorocarbons and other chlorine- bearing substances are
reduced to their 1980 levels and emissions of Halons are eliminated. At 60°N,
two-dimensional models project that the depletion for this latter scenario would
exceed 3 percent by 2030. Depletion would be larger if emissions of ozone-
depleting substances grow.
Some uncertainty exists about the validity of model predictions. Although
models do a good job of explaining the distribution and abundance of most
chemical species in the atmosphere, discrepancies between model predictions and
apparent observations of the current atmosphere lower confidence in model
predictions.
Another source of uncertainty is that laboratory measurements provide
inexact values for various inputs to the models, such as rate constants or cross
sections. Over the past 15 years, better laboratory estimates of rate constants
and cross sections have produced several alterations in depletion estimates. In
order to understand the likelihood that estimates will change again with new
laboratory measurements, formal analyses have been done to determine the
sensitivity of model projections of ozone depletion to the currently accepted
set of best estimates for such inputs. Based on these analyses, depletion
appears likely if concentrations of CFCs grow, although a small possibility
exists that no depletion would occur.
Formal uncertainty analyses take into account only some of the factors that
could alter model predictions. Existing models may omit processes important to
determining the future evolution of the stratosphere. No method exists to
quantitatively evaluate the impacts of such potentially missing factors.
Clearly, the possibility exists that models have omitted a key process and that
their predictions under- or overestimate the depletion levels that would be
associated with any scenario of trace gas emissions.
The WMO 1986 assessment of stratospheric ozone concluded that from 1970 to
1980 ground-based and balloon monitoring of ozone in the stratosphere shows
depletion roughly predicted by models at high and low stratospheric altitudes,
as well as the small increases that would generally be expected in the
troposphere. Models have failed, however, to predict the observed rapid
springtime depletion of ozone that has occurred over and adjacent to Antarctica.
In addition, recent satellite measurements from Nimbus 7 appear to show a
decrease in global ozone greater than that simulated in models or that observed
by many ground-based systems. However, significant uncertainty exists about
these measurements. The atmospheric science community is intensively reviewing
this information about both Antarctica and global trends. Until such reviews
are concluded, the implications of these results cannot be determined.
Consequently, in this risk assessment, we assume that the Antarctic hole and
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5-2
global trends have no implications for assessing future global risks and do not
bring current model projections into question. Future risk assessments will
revisit this issue.
Most model projections, including those presented above, have assumed that
the atmospheric growth of carbon dioxide (C02), methane (CH4), and nitrous oxide
(N20) will go unchecked for the period being examined. Since these gases add
ozone to the atmosphere or prevent ozone depletion from occurring, growth in
their concentrations counters ozone depletion that CFCs and halons are predicted
to cause. Future efforts to limit emissions and concentrations of these gases,
which might be taken in order to reduce the greenhouse warming, would make the
stratosphere significantly more vulnerable to depletion from CFCs and Halons.
Thus, the assessment of column depletion risks associated with CFCs and other
depleters depends strongly on the assumptions made about whether future decision
makers will act to limit increases in emissions and concentrations of those
greenhouse gases in the future.
In conclusion, current knowledge indicates that average global ozone will
deplete if chlorine continues to grow at current rates and that depletion over
much of the United States will exceed the global average. The risk of depletion
is higher if the emissions and concentrations of carbon dioxide, methane, and
nitrous oxide are reduced as a result of concern over global warming.
-------
5-3
FINDINGS
STRATOSPHERIC MODELING PROJECTS THAT THE COMBINED EFFECTS OF A VARIETY OF
TRACE GASES (CHLOROFLUOROCARBONS. NITROUS OXIDE. CARBON DIOXIDE. HALONS. AND
METHANE) ARE LIKELY TO REDUCE THE COLUMN DENSITY OF OZONE UNLESS EMISSIONS
OF OZONE DEPLETERS ARE PREVENTED FROM GROWING.
la. Photochemical theory continues to support the conclusion that chlorine,
nitrogen, and hydrogen can catalytically destroy ozone in the
stratosphere, thus depleting column levels.
Ib. One-dimensional (1-D) models currently predict a 5-9 percent depletion
for the equilibrium concentrations of chlorine that would result from
constant emission of CFCs at 1977 levels. While useful for
intercomparing models, these values cannot be used to assess the risks
of depletion in an atmosphere in which other gases are also changing.
Ic. One-dimensional (1-D) models predict average column ozone will decrease
if global emissions of CFCs and other ozone depleters continue to rise
from current levels, even if concentrations of methane, carbon dioxide,
and nitrous oxide continue to grow at past rates. For a 3 percent
growth of CFCs, models predict over a 25 percent depletion by 2075 if
the other gases continue to grow.
Id. Two-dimensional models (2-D) used in steady state multi-perturbant
studies that include chlorine, methane, and nitrous oxide project
depletion higher than global averages at latitudes greater than 40°N,
especially in the spring.
le. Time-dependent simulations of stratospheric change in which 2-D models
are used predict that depletion over 4 percent will occur at some
latitudes for all cases of positive growth in CFG emissions. Such
models even predict ozone depletion of up to 3 percent at inhabited
latitudes for a scenario in which emissions of chlorine-bearing
substances are reduced from current to 1980 levels and in which halon
emissions are eliminated, but in which the greenhouse gases that
counter depletion are allowed to grow at historical rates.
If. Time-dependent simulation with one 2-D model, with CFCs growing at 3
percent, methane rising at 1 percent, nitrous oxide at 0.25 percent and
carbon dioxide growing at 0.6 percent, projects annual average
depletion at 40°N of approximately 1.1 percent by 2000 and 5.2 percent
by 2030. At 50°N, depletion is projected to be 1.5 percent by 2000 and
6.5 percent by 2030. At 60°N, depletion is projected to be 2.1 percent
by 2000 and 8.1 percent by 2030. Springtime depletion would be higher.
Ig. Time-dependent simulation with one 2-D model, with CFC-11 and -12
emissions rolled back to 1980 levels, CFC-113 capped, other chlorinated
emissions and bromine emissions eliminated, methane rising at 1
percent, nitrous oxide at 0.25 percent, and carbon dioxide at 0.6
percent, projects depletion by 2030 of about 0.5 percent at 40°N, 0.7
percent at 50°N, and 1.1 percent at 60°N (these depletion values are
from 1985 levels). If carbon dioxide concentrations are prevented from
growing from current levels, depletion would be anticipated to be
higher.
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5-4
Ih. Time-dependent simulations with two other two-dimensional models show
roughly comparable results to those reported here, with a slightly less
latitudinal gradient. However, these models also project latitudinal
gradients from equatorial to polar and regions.
li. Because of possible increases in the emissions of bromine molecules
(see Chapter 4), Halons present a more important risk for stratospheric
depletion than has generally been appreciated.
2. CURRENT THEORY AND MODELS FAIL TO REPRESENT ALL OBSERVATIONAL MEASUREMENTS
OF THE ATMOSPHERE AND PROCESSES THAT WILL INFLUENCE STRATOSPHERIC CHANGE IN
A COMPLETE AND ACCURATE MANNER.
2a. While accurately reproducing many measurements in the current
atmosphere, current models fail to reproduce some measurements; the
amount of ozone at 40 kilometers is underestimated, for example.
2b. While including representations of most atmospheric processes, current
models fail to include all the processes that influence stratospheric
composition and structure in a realistic manner. Transport processes,
for example, are represented in a simplified manner that does not
encompass all the complications of movement in the real atmosphere.
2c. The inability of models to wholly reproduce measurements of the current
atmosphere lowers our confidence in them to predict the future; it is
possible that models are over- or under-predicting future depletion.
3. UNCERTAINTY ANALYSES THAT CONSIDER A RANGE OF POSSIBLE VALUES FOR CHEMICAL
AND PHYSICAL INPUTS CRITICAL FOR MODEL ESTIMATION OF DEPLETION INDICATE THAT
DEPLETION IS LIKELY IF CFCS CONTINUE TO GROW.
3a. Uncertainty analyses conducted with one-dimensional models predict
depletion for a variety of CFG levels.
3b. Uncertainty analyses using different sets of kinetics and cross
sections have not been tested in two-dimensional models. However,
different 2-D models have used different approaches for transporting
species. This provides a useful test of the sensitivity of model
predictions to the uncertainty of how transport actually works. While
differing somewhat in the latitudinal gradients of depletion, the
models with different transport both predict depletion that increases
with distance from the equator.
3c. Not all uncertainties can be tested in the modeling process. The
possibility that missing factors may lead to a greater or lesser
depletion than indicated in formal uncertainty analyses cannot be
excluded.
4. OZONE MONITORING SHOWS CHANGES IN OZONE ROUGHLY CONSISTENT WITH MODEL
PREDICTIONS. WITH TWO EXCEPTIONS.
4a. Measurements by balloons and Umkehr show 3 percent depletion at
mid-latitudes in the upper atmosphere, 1.3 percent depletion in the
lower stratosphere, and 12 percent increases in the lower troposphere.
Uncertainty exists about the accuracy of all these observations. These
results, however, are roughly consistent with the expectations
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5-5
generated by one-dimensional and two-dimensional models. The ground
based measurement system covers only a small part of the Earth and is
limited at high latitudes.
4b. Nimbus 7 measurements appear to show a decrease in global ozone,
especially at both poles. However, the decrease in Arctic ozone from
1978 to 1984 may have occurred only in the last several years. Concern
exists about calibration problems, which make an exact determination of
the absolute magnitude of depletion difficult. However, the
latitudinal variations in depletion seem to indicate that a real
phenomenon is being observed, not just instrumental drift.
4c. The cause of these apparent ozone decreases measured by Nimbus 7 has
not been sufficiently analyzed to determine whether the changes (if
they are real) can be attributed to manmade chemicals. Other possible
explanations include natural variations caused by solar cycles or other
processes. The latitudinal gradients of the changes, are, however,
roughly consistent with those projected by 2-D model results, although
the magnitude is substantially larger than models predict. Until
further analysis is performed to determine whether depletion is
actually occurring and whether it can be attributed to man-made
chemicals, models to assess risks to the stratosphere should not be
revised.
4d. Measurements in the Antarctic spring show that the gradual depletion
that occurred in the mid-1970s over and near Antarctica has given way
to a steep non-linear depletion from 1979 to 1985. The ozone maximum
outside Antarctica (between 50°S and 70°S) appears to be showing a
decline. The depletion of all areas south of 80°S appears to be 16
percent.
4e. Models with conventional chemistry do not predict "the Antarctic ozone
hole." Care should be exercised in interpreting the meaning of the
phenomenon. Several hypotheses have been put forward, including a
chemical explanation that attributes the loss of ozone to manmade
sources (bromine and chlorine), a chemical explanation that attributes
the loss to natural sources (NOx, solar cycle), or an explanation that
claims the phenomenon is entirely due to the change in climate
dynamics. Until more is understood about the true causes of the hole,
it is impossible to determine whether the hole is a precursor of
atmospheric behavior that will occur in other regions of the world.
Until a better understanding of the mechanisms creating the depletion
is obtained, the existence of the Antarctic ozone hole should not be
used as a basis for making regulatory decisions.
4f. This risk assessment will assume that Antarctic ozone and global trends
have no implications for global projections. Future reviews should
update this conclusion as necessary.
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5-6
INTRODUCTION1
The ozone layer has a continuous distribution with a peak concentration in
the lower stratosphere between about 20 and 25 kiloneters altitude. [Exhibit
5-1] illustrates the standard definitions of the troposphere, stratosphere and
mesosphere in terns of the profile of tenperature with altitude and shows an
average ozone distribution .... (NASA, 1986) Because the stratosphere
constitutes a permanent inversion of air, with relatively low mixing of air with
the troposphere below, the two must be viewed as two separate but related zones.
Ultraviolet solar radiation produces ozone in the atmosphere. Wave- lengths
of less than 242 nm [nanometers] possess sufficient energy to dissociate
molecular oxygen, O2, into its component O atoms. These 0 atoms in turn react
rapidly with O2 to form ozone, O3. The O3 formed can subsequently absorb
ultraviolet radiation in the 200-320 nm wavelength region, dissociating into an
O atom and an O2 molecule. Ozone is also dissociated, by visible and near
infrared radiation, although to a much lesser extent. These processes form a
long chain in which the oxygen atom alternately attaches itself to an O2 to form
O3 and then is detached, until finally, the O atom and an O3 molecule react to
re-form two 02 molecules .... (NASA, 1986)
According to this very simple model, the ozone concentration is controlled
by its production and loss rates. The ratio of the frequency of the ozone loss
to production rate is directly dependent on the effective length of the chain
(catalytic efficiency) and thus, the 03 concentration depends directly on the
chain length .... (NASA, 1986)
There are chemical processes which can shorten this chain. Among these are
the catalytic processes of the nitrogen, chlorine and hydrogen oxides (NOx,
ClOx, HOx). These processes have the same net effect as the direct reaction of
O and O3. For example, the simplest catalytic cycle for involving ClOx is the
two-reaction set:
Cl + 03 —> CIO + 02
CIO + 0 —> Cl + 02
Net 0+03 —> 02 + 02
for NOx:
NO + 03 —> N02 + 02
N02 + 0 —> NO + 02
Net 0+03 —> 02 + 02
These sets (or cycles) are catalytic because, at the end, the Cl atom or NO
molecule is again available to continue converting O and O3 back to O2. (NASA,
1986)
Bold-face textual material is directly quoted from the source listed.
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5-7
EXHIBIT 5-1
Temperature Profile and Ozone Distribution in the Atmosphere
OZONE CONCENTRATION (cm-1)
ui
O
10'
10'
10'
140
120
100
80
60
40
20
THERMOSPHERE
100
200
300
400
10"
500
TEMPERATURE (K)
The ozone layer has a peak concentration in the lower stratosphere between
about 20 and 25 kilometers altitude. In the troposphere, temperature
decreases with altitude. In the stratosphere, temperature increases with
altitude.
Source: NASA (1986).
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5-8
The significance of the catalytic cycles is that small amounts of the
catalytic species can affect ozone in a substantial manner .... We now find
that an even smaller amount of the catalytic oxides (in the part per billion
range) are significant in controlling the amount of ozone. (NASA, 1986)
Modeling Stratospheric Change
To estimate the stratosphere's response to increasing concentrations of
stratospheric perturbants requires modeling the physical and chemical forces
that will bear on the catalytic cycles that control ozone abundance. Chemical
interactions between gases are controlled by their rate of combination and
dissociation. These reactions are controlled by kinetic rate coefficients.
NASA has established an extensive program and review procedure to establish the
database of rate coefficients. While subject to continual update and
improvement, this database has been progressively strengthened by many years of
laboratory experiments.
Radiation is also a driving force on the structure and evolution of the
stratospheric system, playing an important role in chemistry as well as in the
dynamics that transport various species from region to region. Uncertainties
exist in some of the cross sections of various molecules as well as the energy
received from the sun at different wavelengths. We refer interested readers to
Chapter 7 of Atmospheric Ozone 1985 by the World Meteorological Organization
(1986) for details about these uncertainties.
Transport determines how various species move from one area to another. We
study species transport in an attempt to understand how the distribution and
abundance of species is changed by motions of the atmosphere.
[Ideally models would simulate the actual] structure of the stratosphere,
[which includes the] complex interplay among radiative, dynamical and chemical
processes [described. Such a model would have a] relatively complete
description of all of the relevant processes in a three-dimensional
time-dependent manner. This is not yet possible, both because of limitations in
computer resources and limitations in the complete understanding of all of the
relevant processes. Thus, the problem of understanding the complete
stratosphere is attacked with a hierarchy of models which vary in complexity and
vary in completeness of description of each of the major aspects of the
atmospheric system. (NASA, 1986)
One convenient method of classifying stratospheric models is according to
their dimensionality. A zero-dimensional model considers chemistry in a box,
i.e., at single points in the atmosphere decoupled from all other points. Such
models (or sub-models) allow a detailed description of the chemical evolution of
the system. They generally consider situations in which a chemically dominated
system is driven from equilibrium. One example is the diurnal variation of the
solar input which can be isolated from the complexity of the overall system so
that the problem of diurnal correlation of reacting species can be evaluated.
This leads to accurate computation of the modification of the effective diurnal
average rate of reaction as compared to that computed from average constituent
concentrations. With zero-dimensional models, the impact of changes in rate
coefficients or reaction mechanisms on the chemical system are readily
evaluated. Of course, care must be taken to apply these models only to
chemically dominated regions of the atmosphere. (NASA, 1986)
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5-9
The next: level of complexity in atmospheric models is the one-dimensional
model which considers variations in the vertical dimension. In this type of
model, transport in the vertical dimension is parameterized as Fickian diffusion
in which the same diffusion coefficient is used for each chemical species. In
general, optimal values for the diffusion coefficient vs. altitude are obtained
by fitting the distribution of one or more of the source gases. [Since the
atmosphere exists in more than one dimension, there are various ways to
interpret the output of one-dimensional models.] ... In one sense, ...
one-dimensional models represent the globally and annually averaged
stratosphere, in that the diffusion representation of transport attempts to
account for globally averaged motions in which all horizontal motions average
out ... in another sense, the models purport to represent a specific latitude
(30°N) and a specific time of year (equinox) in that they use a diurnal march of
zenith angles for the Sun appropriate to those conditions. Thus, the
photochemical driver is not globally averaged properly, and the models represent
a hybrid situation. (NASA, 1986)
The next level of complexity in the dimensionality of atmospheric models are
two-dimensional models. These models attempt to simulate the latitudinal and
seasonal variations in atmospheric structure. Some of these models use
specified two-dimensional transport dynamics while others seek to model the
evolution of the transport by zonally averaged meridional and vertical dimen-
sions. A characteristic difficulty with such models is how to rationally
specify the transport effects of asymmetric motions. (NASA, 1986)
Three different broad classes of two-dimensional photochemical models are
presently in use. These are models in which transport is accomplished by
specified diffusion coefficients which are quite large. There are also those
two-dimensional models with either specified or internally computed advective
circulations with specified small diffusion coefficients; and finally, there are
some models in which an effort is being made to use a consistent formulation of
the advective and diffusive transports. (NASA, 1986)
Two-dimensional models do allow latitudinal and seasonal variations of
constituents to be calculated. Thus, these features may be tested against
observations for models of present-day conditions. These models also allow
predictions of the latitudinal and seasonal effects of constituent scenarios to
be made. Many present two-dimensional models include quite complete chemical
schemes. In fact, in several cases, the chemical scheme being used
in a two-dimensional model is identical to the one being used in a
one-dimensional model by the same group. (NASA, 1986)
No three-dimensional (3-D) models with complete chemistry yet exist (NASA,
1986). Efforts to use general circulation models to test transport of species
have been performed, but no assessments have been made with them. Thus for the
purposes of this assessment, no further mention will be made of 3-D models.
Equilibrium Predictions of One-Dimensional Models
In the World Meteorological Organization (1986) assessment, a series of
steady-state calculations were done with a variety of one-dimensional models.
These experiments were not intended to represent simulations of future
atmospheres, but to test the sensitivity of models to different changes in gases
across a range of possible values. Exhibit 5-2 shows the atmospheric
-------
5-10
EXHIBIT 5-2
Steady-State Scenarios Used in International -Assessment
*SO: Definition of 1980 reference, ambient atmosphere:
Assumptions
C02 = 340 ppm, N20 - 300 ppb, CH4 - 1.6 ppm,
CO = 100 ppb, CH3C1 = 0.7 ppb, CC14 = 100 ppt,
CFC-11 = 170 ppt, CFC-12 = 285 ppt, CH3CC13 = 100 ppt.
CHSBr = 20 ppt (assumed only stratospheric source of bromine),
CFG-11 flux = 309 Gg/yr = 8.4E6/cm2/sec,
CFC-12 flux = 433 Gg/yr = 1.34E7/cm2/sec.
SOA: Definition of background chlorine, circa 1960 atmosphere: Same as above
without CFC-11, CFC-12, CH3CC13.
Scenario
S1A: CFC-11 and -12 in steady state in 1980 fluxes.
*S2A: Clx = 8 ppb (approx: from CFC-11 = 0.8 ppb, CFC-12 = 2.2 ppb).
*S2B: Clx = 8 ppb plus 2 x CH4 (concentration), 1.2 x N20.
S2C: Clx = 8 ppb plus 2 x CH4, 1.2 N20 and 2 x C02.
*S3A: Clx = 15 ppb (approx: from CFC-11 = 1.6 ppb, CFC-12 = 4.4 ppb).
*S3B: Clx = 15 ppb plus 2 x CH4 (concentration), 1.2 x N20.
S3C: Clx = 15 ppb plus 2 x CH4, 1.2 x N20, and 2 x C02.
S4: 1980 with 2 x CH4 concentration.
S5: 1.2 x N20.
S6: 2 x CO.
S7: 2 x C02.
S8: NOx injection from stratospheric aircraft 1,000 molec cm-3S-l or 2,000
molec cm-3S-l at 17 km and 20 km.
S9: Bromine increase from 20 ppt to 100 ppt.
* Also used as 2-D model scenario.
A set of scenarios for the future evolution of the atmosphere was
selected by the World Meteorological Organization for 1-D and 2-D model
simulations of stratospheric ozone. Each scenario has a label. For
instance, S1A refers to the scenario in which equilibrium
concentrations are reached for CFC-11 and -12 without increases in
other gases.
Source: Adapted from World Meteorological Organization (1986).
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5-11
concentrations used in various "steady-state scenarios" of different trace gas
levels. Exhibits 5-3, 5-4, and 5-5 show the effect of these trace gas levels on
globally averaged ozone depletion. Exhibits 5-6, 5-7, and 5-8 show the
importance of odd nitrogen on projected ozone depletion, the effects of doubled
carbon dioxide on temperature, and the changes in vertical distribution of
ozone. The following conclusions can be made based on those modeling
experiments:
o different models of ozone depletion are roughly consistent
in projections of ozone depletion.
o projections of ozone depletion resulting from chlorine
increases are decreased when carbon dioxide, methane, and
nitrous oxide are added to future atmospheres.
o projected ozone depletion at 40 kilometers is much higher
than column average.
o even if chlorine levels are held to 8 ppb and other gases
increase, the abundance of ozone at different altitudes
would be fundamentally changed, with ozone increases at
lower altitudes and decreases in upper altitudes.
o carbon dioxide concentration increases are expected to cool
the stratosphere, reducing ozone depletion.
o uncertainties in odd nitrogen in the stratosphere have
critical importance in estimating projected depletion.
Bromine
. . . Although bromine chemistry is in many respects similar to that for
chlorine, there are also significant differences. Dissociation and reactions of
CH3Br and other important bromine sources occur at lower altitudes than for the
major chlorine sources. While the reaction of Cl with CH4 to produce HC1 limits
the abundance of active chlorine radical species in the stratosphere, the
reaction of Br with'CH4 is endothermic and therefore negligibly slow. Also, the
photolysis of HBr is more rapid than that of HC1, and the reaction of OH with
HBr is more rapid than its rate with HCl. Consequently, the majority of BrX is
present as the active species BrO. On a molecule for molecule basis, bromine is
a much more efficient sink for stratospheric odd oxygen than chlorine. (World
Meteorological Organization, 1986)
The bromine . . . sensitivity test considered is an increase in surface
mole fraction of CH3Br from 20 to 100 pptv. As seen in [Scenario S9 of Exhibit
5-5] the LUNL model was the only model used to calculate the perturbation. It
gave a total ozone change of -3% (without temperature feedback), in good
agreement with the -4% calculated change in total ozone for the same scenario by
Prather et al. (1984). The major contribution to the change in the ozone column
occurs around 20 km. The largest relative change in ozone (7% decrease) is at
15 km with a secondary peak at about 40 km. (World Meteorological Organization,
1986)
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5-12
EXHIBIT 5-3
Change in Total Ozone from Representative One-Dimensional Models for
Steady-State Scenarios Containing Clx Perturbations
Change in Total Ozone (%)
LLNL Harvard AER DuPont IAS MPIC
Scenario (Wuebbles) (Prather) (Sze) (Owens) (Brasseur) (Bruehl)
S1A CFC 1980 Flux -7.0 -5.3 -5.3 -4.9
only (-7.2) (-6.1) (-7.9) (-9.4)
S2A 8 ppbv Clx -5.1 -2.9 -4.6
only (-5.7) (-4.1) (-9.1)
S2B 8 ppbv Clx -3.4 -3.0 -3.3 -3.1
+ 2 x cm (-2.3) (-6.0)
+ 1.2 x N20
S2C 8 ppbv Clx (+0.2) (-1-4) (0.0) (-5.2)
+ 2 x CH4
+ 1.2 x N20
+ 2 x C02
S3A 15 ppbv Clx -12.2 -17.8 -15.
only (-12.4) (-8.8) (-22.0)
S3B 15 ppbv Clx -7.8 -8.2 -8.8 -7.2
+ 2 x CH4 (-7.2) (-5.6) (-13.7)
+ 1.2 x N20
S2C 15 ppbv Clx (-4.6) (-3.5) (-13.6)
+ 2 x CH4
+ 1.2 x N20
+ 2 x C02
Calculated ozone changes from six modeling groups participating in international
assessment. Results are from 1-D models and are relative to an atmosphere with
about 1.3 ppb background Clx and with no CFCs (Scenario # SOA). Numbers in
parentheses refer to calculated changes when including temperature feedback.
Source: World Meteorological Organization (1986).
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5-13
EXHIBIT 5-4
Change in Total Ozone at 40 kilometers for Steady-State
Scenarios Containing Clx Perturbations
Scenario
Change in 40 km Ozone (%)
LLNL Harvard AER
(Wuebbles) (Prather) (Sze)
DuPont IAS MPIC
(Owens) (Brasseur) (Bruehl)
S1A CFG 1980 Flux -63
only (-56)
-64
-62 -62
(-57) (-81) (-59)
S2A 8 ppbv Clx -55
only (-50)
S2B 8 ppbv Clx -50
+ 2 x CH4 (-45)
+ 1.2 x N20
S2C 8 ppbv Clx (-35)
+ 2 x CH4
+ 1.2 x N20
+ 2 x C02
S3A 15 ppbv Clx- -74
only (-68)
S3B 15 ppbv Clx -69
+ 2 x CH4 (-64)
+ 1.2 x N20
S2C 15 ppbv Clx
+ 2 x CH4
+ 1.2 x N20
+ 2 x C02
(-58)
-57
-50
-78
-73
-56
-49
-77
-64
-58
-74
(-67) (-57)
(-62) (-50)
(-49) (-55) (-45)
(-83) (-76)
(-81) (-71)
(-78) (-67)
Calculated changes in upper stratospheric ozone (40 kilometers) from six
modeling groups participating in international assessment. Results are from 1-D
models and are relative to an atmosphere with about 1.3 ppb Clx and with no CFG
(Scenario # SOA). Numbers in parentheses refer to calculated changes when
including temperature feedback.
Source: World Meteorological Organization (1986).
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5-14
EXHIBIT 5-5
Change in Total Ozone for Steady-State Scenarios
Change in Total Ozone (%)
Scenario
S4 2 x CH4
S5 1.2 x N20
S6 2 x CO
S7 2 x C02
LLNL
(Wuebbles)
+2.0
(+2.9)
-2.1
(-1.7)
+1.1
(+1.1)
(+3.5)
Harvard
(Prather)
+0.3
-2.6
+0.3
AER
(Sze)
+0.9
-1.8
+0.6
(+2.6)
DuPont
(Owens)
+1.7
-2.3
+0.8
(+2.8)
IAS
(Brasseur)
(+1.6)
(-1-1)
(+3.1)
MPIC
(Bruehl)
(+1.4)
(-1.2)
(+0.8)
(+1.2)
S8a NOx, injection -1.8
17 km, 1,000 (-1.3) (-1.4)
molec. cm-3s-l
S8b NOx, injection -5.7
17 km, 2,000 (-3.4)
molec. cm-3s-l
S8c NOx, injection -5.7
20 km, 1,000 (-4.6) (-3.9)
molec. cm-3s-l
S8d NOx, injection -12.2
20 km, 2,000 (-8.8)
molec. cm-3s-l
S9 Brx -3.0
20 to 100 pptv
Calculated ozone changes from six modeling groups participating in international
assessment. Results are from 1-D models and are relative to the present
atmosphere (Scenario #SO), except for the AER and DuPont calculations, which are
relative to a background atmosphere with no CFCs (Scenario #SOA). Numbers in
parentheses refer to calculated changes when including temperature feedback.
Source: World Meteorological Organization (1986).
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5-15
EXHIBIT 5-6
Effect of Stratospheric Nitrogen (NOy)
on Chlorine-Induced Ozone Depletion
z
3
O
u
O
z
UJ
O
4
X
U
24.1 ppbv NOy
2 x CH4
20.8 ppb NO
10 12 14 16 18 20
CHANGE IN Clx (ppbv)
Results from Owens and Fisher of Dupont. Calculated ozone change is
presented as a function of stratospheric Clx for different values of
stratospheric NOy (NO, N02, N03, N205, C10N02, NH04, and HN03). For
large background NOy (about 30 ppb) the decrease of ozone is small and
very nearly linear with increasing Clx, but for small background NOy
(13 ppb), ozone is strongly and non-linearly reduced by Clx.
Source: World Meteorological Organization (1986).
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EXHIBIT 5-7
Effect of Doubled C02 Concentrations on Ozone Temperature
One -Dimensional
Models
LLNL (Wuebbles)
AER (Sze)
DuPont (Owens)
IAS (Brasseur)
MPIC (Bruehl)
Ozone
Column
(Percent)
+3.5
+2.6
+2.8
+3.1
+1.2
Ozone
at 40 km
(Percent)
+19.3
+9.4
+11.5
+18.8
+13.0
Temp.
at 40 km
(Kelvin)
-8.0
-8.4
-7.4
-9.0
-7.1
Percentage changes in total ozone column, ozone at 40
km, and temperature at 40 km are shown for a doubling
of carbon dioxide (Scenario #S7), relative to the
present atmosphere, as calculated by 1-D models.
Source: World Meteorological Organization (1986).
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EXHIBIT 5-8
Calculated Changes in Ozone Versus Altitude
LLNL 1-D MODEL
COMBINED STEADY STATE
SCENARIOS (S2B. C AND S3B. C)
FIXED TEMPERATURE
- TEMPERATURE FEEDBACK
-80 -70 -60 -50 -40 -30 -20 -10 0 10 20
CHANGE IN LOCAL OZONE 1%)
Changes in vertical distribution of ozone for steady-state changes in
ozone as calculated by the LLNL 1-D model for the following scenarios:
S2B: Clx = 8 ppb plus 2 x CH4 (concentration), 1.2 x N20
S2C: Clx = 8 ppb plus 2 x CHA, 1.2 x N20, and 2 x CO 2
S3B: Clx = 15 ppb plus 2 x CH4, 1.2 x N20
S3C: Clx = 15 ppb plus 2 x CH4, 1.2 x N20, and 2 x C02.
Source: World Meteorological Organization (1986).
-------
5-18
Because current increases in concentrations of Halon 1211 are at 23 percent
per year, and, in the absence of regulation, emissions may increase greatly,
bromine from Halon molecules constitute a larger risk for stratospheric
depletion than generally recognized.
EQUILIBRIUM PREDICTIONS FOR TWO-DIMENSIONAL MODELS
In recent years, many detailed photochemical and dynamical two-dimensional
models of the stratosphere have been developed. These have achieved a measure
of success in simulating the zonally and seasonally averaged distribution of
constituents influenced both by photochemistry and transport in the
stratosphere, such as methane and nitrous oxide (see Miller et al., 1981; Gidel
et al., 1983; Garcia and Solomon, 1983; Jones and Pyle, 1984; Guthrie, et al.,
1984; Ko et al., 1984, 1985). Ozone densities below about 20-25 km are
predominantly controlled by transport of ozone from the middle and upper
stratosphere. Since most of the ozone column abundance at extra-tropical
latitudes is located in this dynamically dominated region, it is important to
examine ozone perturbations using multi-dimensional models that include at least
a first order representation of transport in the meridional (height-latitude)
plane. Such studies reveal latitudinal variations in ozone depletions, which
are of importance for ozone monitoring programs and they provide insight beyond
that obtained with comparable one-dimensional model studies. (World
Meteorological Organization, 1986)
Here the results of four two-dimensional models are examined. The model
referred to here as MPIC is that of Gidel et al. (1983); the calculations were
done by Schmailzl and Crutzen. The model (GS) is that of Garcia and Solomon
(1983) and Solomon and Garcia (1984). The model (AER) is that described by Ko
et al. [1985] . The photochemical reaction rates used were those of JPL/NASA
(1985) [Appendix 1], and the solar flux, oxygen and ozone cross sections were
taken from Chapter 7 [of the WMO, 1986, publication], but the authors used
different methods in the treatment of the Schumann-Runge bands and used
different boundary conditions. A fourth model that is examined (IS) is that of
Isaksen and Stordal (1986). It has been added to the analyses in Exhibit 5-9
which shows the scenarios used in each model. (World Meteorological
Organization, 1986)
These experiments were again intended to test the results of the models
across a range of species values, not to simulate the atmosphere in any given
year. Exhibits 5-10 through 5-21 provide detailed results of these experiments.
The conclusions are briefly summarized here:
o 2-D models get roughly the same global depletion for the
same inputs.
o 2-D models agree in projecting more depletion near the poles
than at the equator, but vary in the strength of this
latitudinal effect.
o Winter and Spring are the seasons of greatest projected
depletion.
-------
5-19
EXHIBIT 5-9
Two-Dimens ional Model Scenarios Used in International Assessment
Clx/opb
Scenario #
S2A
S2A
S3A
S2C
SMA
-
-
SMB
SMC
IS
Total
8.
8.2
15.5
8.
9.5
2.7
9.5
9.5
18.
7.2
Reference
1
1
1
1
2
1
1
2
2
1
.3
.3
.3
.3
.7
.3
.3
.7
.7
.0
Increase
6
6
14
6
6
1
8
6
15
6
.7
.9
.2
.7
.8
.4
.2
.8
.3
.2
2xCH4
1.2xN20 Model Symbol
no Garcia and Solomon GS
(1983)
no Ko et al. (1985) AER
no AER
yes Garcia and Solomon GS
(1983)
no Gidel et al. (1983) MPIC
no MPIC
no MPIC
yes MPIC
yes MPIC
no Isaksen and Stordal IS
(1986)
Scenarios used for 2-D model simulations of stratospheric ozone. The GS, AER, and
MPIC models were used in the WHO international assessment. The IS model has been
added for this analysis.
Source: Adapted from World Meteorological Organization (1986).
-------
5-20
EXHIBIT 5-10
2-Dimensional Model Results:
Global and Seasonally-Averaged Ozone Depletion
Clx/DDbv
Initial
1.3
2.7
1.3
2.7
2.7
1.3
1.3
1.0
Final
2
9
9
9
18
8
15
7
.7
.5
.5
.5
.2
.5
.2
Increase
1
6
8
6
15
6
14
6
.4
.8
.2
.8
.3
.9
.2
.2
2 x CH4
1.2 x N20
no
no
no
yes
yes
no
no
no
% Ozone
Decrease
1.
7.
9.
4.
11.
8.
18.
7.
9
2
1
5
1
5
1
Model
Sensitivity
-%/ppbv Model
1
1
1
0
0
1
1
1
.36
.06
.11
.66
.73
.23
.27
.16
MPIC
MPIC
AER
IS
Results for 2-D models used in international assessment. Model sensitivity
of ozone to Clx is percent ozone decrease divided by ppb Clx increase.
Source: World Meteorological Organization (1986).
-------
5-21
EXHIBIT 5-11
Ozone Depletion by Latitude, Altitude, and Season
for Clx Increase of 6.8 ppbv
(MPIC 2-D Model)
500
80
Results from MPIC 2-D model, for scenario #SMA, relative to reference
atmosphere with 2.7 ppb Clx (see Exhibit 5-9). Panel a shows percent
change in ozone in winter; panel b in spring.
Source: World Meteorological Organization (1986).
-------
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5-26
EXHIBIT 5-16
Change in Ozone by Latitude and Season for Clx Perturbations
(MPIC 2-D Model)
_ a
Steady-state changes In ozone by latitude and season as calculated by
tbe MPIC 2-D model for the following scenarios:
Panel A, Scenario SMA: Clx =9.5 ppbv
Panel B, Scenario SMB: Clx =9.5 ppbv plus 2 x CH4, 1.2 x N20
Panel C, Scenario SMC: Clx =18.0 ppbv plus 2 x CH4, 1.2 x N20
Changes are relative to reference atmosphere with 2.7 ppbv.
Source: World Meteorological Organization (1986).
-------
5-27
EXHIBIT 5-17
Change in Ozone by Latitude and Season for Clx Perturbations
(AER 2-D Model)
90 °N
30°N
EQ
30 «S
60 °S
90 °S
-16
-14" ., '-'\ -14
' -6 -,
.-8
JFMAMjjASOND
MONTH
90 °N
60 °N
30°N
EQ
30 °S
60 °S
90 «S
/ 19 / .--24. / ••' I
! .-' •• .-• \ ' -28/
..... / I 1'---..'\" -30 \-28~"'--.,-.^"'--
"I i ' i i ' i " i 1 i '-i !''
JFMAMJJASONO
MONTH
Steady state changes in ozone by latitude and season as calculated by
the AER 2-D model for the following scenarios:
Panel A, Scenario S2A: Clx = 8.2 ppbv
Panel B, Scenario S3B: Clx =15.5 ppbv
Changes are relative to reference atmosphere with 1.3 ppbv Clx. The
global average ozone changes are -8.5 percent and -18 percent,
respectively.
Source: World Meteorological Organization (1986).
-------
5-28
EXHIBIT 5-18
Latitudinal Dependence of AER and MPIC 2-D Models
20
IU
CO
Ul
S 12
s
3 8
O
U
ui
O
N 4
O *
-80
-60
-40
S
-20
0
LATITUDE
20
40
60
80
Ozone column decrease in April for Clx increase of about 7 ppbv. The
AER 2-D model shows more variation with latitude than the MPIC model.
This difference can be attributed to differences in transport,
especially the rate of horizontal mixing.
Source: World Meteorological Organization (1986).
-------
5-29
EXHIBIT 5-19
Change in Ozone by Latitude, Altitude, and Month
for Coupled Perturbations
(GS 2-D Model)
COUPLED CH..IM.O
DECEMBER
-90 -70 -50 -30 -10 10 30 50 70 90
S LATITUDE N
MARCH
90 -70 -50 -30 -10 10 30 50 70 90
Steady-state changes in ozone by latitude and altitude as calculated
by the GS 2-D model. For Scenario S2C: Clx = 8 ppbv plus 2 x CH4 and
1.2 x N20. Top panel shows results for December, bottom panel for
March. Changes are relative to reference atmosphere with 1.3 ppbv
Clx.
Source: World Meteorological Organization (1986).
-------
5-30
EXHIBIT 5-20
Changes in Ozone by Latitude, Altitude, and Season
for Coupled Perturbations
(MPIC 2-D Model)
iOO
-60 -40
S
-20 0 20
LATITUDE
40
N
60
80
Steady-state changes in ozone by latitude and altitude as calculated
by the MPIC 2-D model. For Scenario SMB: Clx =9.5 ppbv plus 2 x CH4
and 1.2 x N20. Panel a shows results for winter, panel b for spring.
Changes are relative to reference atmosphere with 2.7 ppbv Clx.
Source: World Meteorological Organization (1986).
-------
5-31
EXHIBIT 5-21
Changes in Ozone by Latitude and Altitude in Winter
for Coupled Perturbations
(MPIC 2-D Model)
50
45
— 500
Steady-state changes in ozone by latitude and altitude in winter as
calculated by the MPIC 2-D model for Scenario SMC: CIO -15.3 ppbv
plus 2 x CH4 and 1.2 x N20. Changes are relative to reference
atmosphere with 2.7 ppbv CIO.
Source: World Meteorological Organization (1986).
-------
5-32
o multi-species perturbations in which methane concentrations
are increased in addition to the chlorine increases still
result in column ozone depletion, but with the loss of ozone
varying at different altitudes and by different amounts in
different models.
TIME-DEPENDENT PREDICTIONS FOR ONE-DIMENSIONAL MODELS FOR DIFFERENT SCENARIOS
OF TRACE GASES
Tine-dependent calculations including multiple-species perturbations are
regarded as the most nearly realistic of the one-dimensional model assessments.
Several studies have considered such tine-dependent multiple-species scenarios
(e.g., Vuebbles et al., 1983; Callis, Natarajan, and Boughne, 1983; Sze et al.,
1983; DeRudder and Brasseur, 1984; Owens et al., 1984; Owens et al. 1985;
Brasseur et al., (1985). (World Meteorological Organization, 1986) Exhibit
5-22 shows a list of 1-D and 2-D models used for time- dependent runs that have
been reported in this analysis. Recent studies by Connell using a parameterized
version of the Lawrence Livermore National Laboratory (LLNL) model have added to
the available analysis of 1-D runs. See Chapter 17 and Connell (1986) for
details of the parameterization. Exhibit 5-23 shows the fit between the Connell
parameterization and the LLNL 1-D model results.
Several time-dependent runs have recently been done using the models of
Brasseur, AER, and Connell with greater levels of trace gases. Exhibit 5-24
shows the Brasseur scenario and Exhibit 5-25 the results (Brasseur and DeRudder,
1986). The run shows global ozone depletion increasing to around 5 percent by
2040 and to 30 percent by 2080. Note that these runs assumed methyl chloroform
and carbon tetrachloride are capped in 1986, and that Halon-1211 and -1301 and
HCFC-22 are essentially eliminated. Brasseur also ran scenarios of constant CFC
emissions, other chlorine emissions at 1985 levels (and Halons eliminated). The
results (Exhibit 5-26) show depletion increasing to almost 2 percent before the
increase in carbon dioxide (0.5 percent), methane (1 percent), and nitrous oxide
(0.25 percent) overwhelm increases in chlorine concentrations (Brasseur and
DeRudder, 1986).
In the same paper, Brasseur and DeRudder demonstrate a very important
sensitivity of the models to representation of radiative processes. Exhibit
5-27 summarizes the results. Clearly, the different radiative codes produce
different depletion estimates. Brasseur points out that the differences in
radiative code may explain differences in 1-D model calculations in the World
Meteorological Organization (1986) report. In Exhibit 5-28, the results of
Connell's parameterization and Brasseur's model are presented. Connell's
results, which are lower, are based on a model that uses an assumption of fixed
equilibrium temperature for regions above 14 km and fixed temperature below. It
is possible that Brasseur may be correct in his assertion that differences in
model results may stem from this assumption. In general, one might expect the
approach used by Brasseur in the model C.I (that is, not assuming fixed
equilibrium temperatures) to be more likely to describe the real world, since
radiative equilibrium is not likely to prevail in that region with ozone
changes. Brasseur does point out, however, that both radiative models do as
well in explaining the current atmosphere.
-------
5-33
EXHIBIT 5-22
Models With Reported Time-Dependent Runs
Wuebbles (Lawrence Livermore National Laboratory [LLNL] Model) 1-D
Connell (Parameterization of Lawrence Livermore National Laboratory) 1-D
AER Model 1-D, partly funded by Chemical Manufacturers Association
Brasseur 1-D, Belgium (partly funded by European Community)
Isaksen 2-D, Norway
-------
5-34
EXHIBIT 5-23
LLNL 1-D Model versus Parameterized Fit:
c
0)
u
c_
01
0.
ID
I
O
-10
-15 -
uj -20 -
o
rsi
o
o
o
LOW CFC SCENARIO
PARAMETERIZED
HIGH CFC SCENARIO
-25 -
-30 -
-35 -
-40
0
30 40 50
TIME FROM PRESfcNT
Time-dependent change in ozone as calculated by LLNL 1-D model and
parameterized fit for two divergent scenarios of growth in CFCs and
other trace gases. "Differences between the parameterization and the
full 1-D model are generally less than one percent except at very
large depletions."
Source: Connell (1986).
-------
5-35
EXHIBIT 5-24
Trace Gas Assumptions for Results in Exhibit 5-25
(Brasseur and DeRudder 1-D Model, 1986)
CHLOROFLUOROCARBON EMISSIONS OTHERS
(mill kg/year)
CFG- 11 CFC-12
1985
1990
1995
2000
2010
2020
2030
2040
2050
2060
2070
2080
2090
2100
Average % growth ,
1985-2000
2000-2100
279.5
253.5
298.0
347.7
455.8
615.3
830.5
1121.1
1513.3
2042.8
2757. 4
3722.1
5024.4
6782.2
1.5
3.0
397.0
396.2
450.6
514.8
665.7
898.6
1213.0
1637.4
2210.2
2893.5
4027.3
5436.2
7338.1
9905.4
1.7
3.0
CFC-113 Compound
148.4 C02
198 . 6 CH4
265.7 N20
347.7 CC14
465.8 CH3CC13
615 . 3 Halons
830.5
1121.1
1513.3
2042 . 8
2757.4
3722.0
5024.4
6782.2
5.8
3.0
Growth Rate
(%/year)
-0.5
1.0
0.25
constant
constant
Not included
Source: Brasseur and DeRudder (1986).
-------
5-36
EXHIBIT 5-25
Time-Dependent Change in Ozone for CFC Growth
and Coupled Perturbations
(Brasseur and DeRudder 1-D Model)
C
-------
5-37
EXHIBIT 5-26
Time-Dependent Change in Ozone for Constant CFG Production and
Growth in Other Trace Gases
(Brasseur and DeRudder 1-D Model)
c i
u
5 o
UJ
O
u
UJ
P
<
_j
o:
-i
-2
-3
-4
-5
i r
J I
I I
1
j I
1 I
1950
2000
2050
2100
Time-dependent change in ozone as calculated by Brasseur and DeRudder,
(1986) for constant CFC-11, CFC-12 and CFC-113 production at the 1985
level. Does not include Halons. Growth in other trace gases is:
Compound
CH4
N20
C02
Growth Rate in Concentrations
(%/year)
1.0
0.25
-0.5
Depletion increases to almost two percent before the effects of
increasing CH4, N20, and C02 concentrations overwhelm the effects of
increased chlorine.
Source: Brasseur and DeRudder (1986).
-------
5-38
EXHIBIT 5-27
Sensitivity of 1-D Models to Representation
of Radiative Processes
(Brasseur and DeRudder 1-D Model)
0)
£
0)
^
LU
X
o
UJ
-I
LJ
OZONE
Total column
Model C.I
- Model C.2
1950
2000
2050
2100
YEAR
Time-dependent changes in ozone as calculated for two trace gas
scenarios with two different model representations of radiative
processes. Solid lines represent a treatment with radiative code,
that is, run iteratively until radiative equilibrium conditions are
reached in the stratosphere (above approximately 14 km). Below 14 km
a convective adjustment is performed such that the lapse rate never
exceeds -5.9 K/km. The dashed lines show the case where the radiative
code has fixed equilibrium temperatures at the surface.
Scenario "3C" assumes constant production of CFC-11 and CFC-12 at 1985
levels. Scenario "5C" assumes that CFC-11 and CFC-12 production grows
at 3 percent per year and is capped at a level of 1.5 times current
production. In both scenarios it assumed that CFC-113 grows at 6
percent per year but is not allowed to exceed the production level of
CFC-11. Does not include Halons.
Source: Brasseur and DeRudder (1986).
-------
5-39
EXHIBIT 5-28
Model Comparison: Tine-Dependent Change in Ozone
for CFC Growth and Coupled Perturbations
o>
o
6
c
I
Q.
-10 -
-20 -
-30
1980 2000 2020 2040 2060 ?flRO 2100
Time-dependent change in ozone, as calculated by the 1-D model of
Brasseur and DeRudder (1986) and Connell's parameterization of the
LLNL 1-D model. Trace gas assumptions are shown in Exhibit 5-30 and
may be summarized as:
Compound
CFC-11
and CFC-12
CFC-113
CC14
CH3CC13
CH4
N20
C02
Halons
Growth Rate (%/vear")
1.5% to 2000, 3% from 2000 to 2100 (production)
1.0% to 2000, 3% from 2000 to 2100 (production)
constant
constant
1.0
0.25
-0.50
(production)
(production)
(concentrations)
(concentrations)
(concentrations)
Not included
Note that Connell's parameterization produces lower results than
Brasseur's 1-D model.
Sources: Brasseur and DeRudder (1986); Connell (1986).
-------
5-40
The time-dependent AER scenarios are shown in Exhibit 5-29, and the results
in Exhibit 5-30. They are roughly consistent with Brasseur's runs, indicating
that global average depletion over 1 percent will occur even if greenhouse gases
are not limited, unless CFCs and other depleters do not grow in concentration
beyond current levels.
The LLNL 1-D model has been used to estimate global average changes in ozone
over time (Connell and Wuebbles, 1986). Exhibit 5-31 shows trace gas emissions
over time for three scenarios in which concentrations of methane grow at 1
percent per year, nitrous oxide at 0.25 percent per year, carbon dioxide at
approximately 0.6 percent per year and halocarbon emissions vary in each
scenario: a "reference case" ("2.5 percent growth), "low growth" (-1.4 percent
growth), and "high growth" (~4.1 percent growth). Exhibit 5-32 shows the
results for the reference case and Exhibit 5-33 for the low and high cases.
Exhibit 5-34 shows the results of a run using the Connell parameterization
in which, instead of assuming greenhouse gases grow without limit, it is assumed
that emissions from these gases are eventually limited (Gibbs, 1986). In that
run, it is assumed that carbon dioxide, methane, and nitrous oxide are halved
from the growth rate assumed in other scenarios starting in the year 2000. As
the results show, the limits still allow a large greenhouse warming (the change
in temperature equilibrium for the earth for these scenarios is estimated using
the equations of Lacis, modified by coefficients from Ramanathan [see Chapter 6]
[Hoffman, Wells, and Titus 1986]). Clearly, assumptions about future greenhouse
warming are critical. Unless one assumes no efforts are ever made to reduce the
greenhouse warming by limiting carbon dioxide, nitrous oxide, or methane, model
runs that merely extrapolate the growth of these gases from past increases in
concentrations will seriously underestimate ozone depletion.
TIME-DEPENDENT PREDICTIONS FOR TWO-DIMENSIONAL MODELS WITH DIFFERENT SCENARIOS
OF TRACE GASES
Isaksen and Stordal have conducted two sets of time-dependent runs using
their two-dimensional model. Sze and Brasseur have also performed time-
dependent 2-D runs. The two sets of Isaksen runs differ in one important
respect. In one set of model runs, temperature feedback is not considered and
carbon dioxide was implicitly assumed not to grow. In the second set of runs,
however, the radiative cooling for rising carbon dioxide is considered using
values for carbon dioxide cooling obtained from the Goddard Institute for Space
Studies general circulation model. Sze's runs ignore the effects of carbon
dioxide on stratospheric temperatures.
For the period 1960-1980, Isaksen used CFC release rates from Cunnold et al.
(1983a, CFC13), Cunnold et al. (1983b, CF2C12), Prim et al. (1983b, CH3CC13)
and Simntonds et al. (1983, CC14). The atmosphere was assumed to initially
(1960) contain 0.6 ppb of CH3C1 and 0.1 ppb of CC14, resulting in a 1 ppb
content of stratospheric chlorine. The CH3C1 surface flux needed to obtain the
1960 mixing ratio was kept constant in all the computations. For the CFC13,
CF2C12 and CH3CC13, the integrations were started in 1960 with zero abundances
and releases corresponding to amounts accumulated in the years prior to I960,
which is a reasonable assumption since the releases were small before 1960.
(Stordal and Isaksen, 1986)
-------
5-41
EXHIBIT 5-29
Trace Gas Assumptions for Results in Exhibit 5-30
(AER 1-D Model, 1986)
CH4* CFG**
SCENARIO 1960-2020 After 2020 1985-2008 After 2008
1A
2A
3A
3B
4A
4B
1
1
1
1
1
1
.0
.0
.0
.0
.0
.0
1
1
1
0
1
0
.0
.0
.0
.5
.0
.5
No CFG Emission
Constant at 1984 Rates
3.0 Constant
2008 rate
3.0 Constant
2008 rate
3.0 Constant
1984 rate
3.0 Constant
1984 rate
at
at
at
at
* Methane growth rate is in percent per year for the periods
1960-2020 and after year 2020.
** Assumed CFC release rates after year 1985. Prior to 1985,
historic release data are used. The emission rate at the year
2008 corresponds to double the present-day CFC production if 3
percent annual growth were maintained through 1985-2008.
Does not include CFC-113, methyl chloroform, CCL4 or Halons.
Source: Chemical Manufacturers Association (1986).
-------
5-42
EXHIBIT 5-30
Time-Dependent Change in Ozone for
Various Scenarios of Coupled Perturbations
(AER 1-D Model)
I960 1980 2000 2030 2040 2060
-4
I960 1980 2000 2020 2040 206O
Time-dependent change in ozone as calculated by the AER 1-D model for
several scenarios of growth in trace gas emissions and concentrations,
shown in Exhibit 5-29. The results indicate that global average
depletion over one percent will occur if growth in CFCs and other
potential ozone depleters continues.
Source: Chemical Manufacturers Association (1986).
-------
5-43
EXHIBIT 5-31
Trace Gas Scenarios Tested in LLNL 1-D Model
(Bnissions in millions of kg/year)
CFC-113
Year
1985
1990
1995
2000
2005
2010
2015
2020
2025
2030
2035
2040
2045
2050
2055
2060
2065
2070
2075
CFC-11
Reference
325
428
553
717
870
1024
1173
1322
1480
1637
1826
2006
2237
2468
2702
2937
3188
3440
3711
(CFC13)
Low
324
422
476
522
558
594
626
657
691
725
762
798
837
876
918
960
1006
1053
1104
High
594
1184
1486
2428
5456
8485
17422
26358
35841
45323
47666
50009
51790
53570
54795
56020
57044
58068
69555
CFC-12
Reference
449
528
625
746
870
995
1130
1266
1415
1564
1742
1919
2131
2342
2556
2770
2998
3226
3472
(CF2
Low
446
519
573
611
647
683
723
763
808
853
902
951
1004
1058
1118
1177
1245
1312
1386
C12)
High
527
722
1042
1406
1997
2587
3483
4378
5219
6058
6499
6940
7299
7658
7890
8122
8278
8434
8547
(CF2
High
102
142
210
277
311
344
378
411
445
493
540
588
635
683
753
823
893
963
1033
C1CFC12)
Low
102
142
157
180
202
224
245
267
289
320
351
381
412
443
489
534
580
625
671
HCFC-22
High
52
84
122
167
221
273
332
394
463
541
626
715
807
900
998
1097
1195
1292
1387
1495
(CHF2C1)
Low
54
71
89
107
127
137
148
155
163
170
178
187
196
205
216
226
238
250
263
276
-------
5-44
EULLblT 5-31 (cootlnued)
Trade Gas Scenarios Tested in LLHL 1-D Model
(Emissions In •llUnm. of kg/year)
CC14 106
Year
1985
1990
1995
2000
2005
2010
2015
2020
2025
2030
2035
2040
2045
2050
2055
2060
2065
2070
2075
Reference
and High Low
153
188
206
226
250
275
300
325
350
384
419
454
489
524
576
628
680
732
784
131
41
45
49
54
59
64
70
76
83
91
99
107
115
126
137
148
160
172
CH3CC13
(methyl chloroform)
Reference, Low,
and High
510
569
634
708
793
878
963
1049
1135
1256
1377
1499
1621
1743
1922
2101
2280
2459
2638
HALOH 1301
(CF3Br)
Reference,
High Low
2
3
4
6
9
12
16
19
22
25
29
32
36
39
43
47
51
55
59
1
2
2
3
4
5
7
9
11
12
14
16
18
20
21
23
25
27
29
HALON 1211
(CF2BrCl)
Reference,
High Low
0
1
1
1
1
2
3
4
5
5
6
7
8
9
9
10
11
12
13
0
0
0
1
1
1
2
2
2
2
3
3
4
4
4
5
5
6
7
Biogenic Trace Gases: CH4 concentrations at IX per year, N20 at 0.25Z per year, and C02 at
approximately 0.6% per year.
Source: Connell and WuebbLes (1986).
-------
5-45
EXHIBIT 5-32
Tine-Dependent, Globally Averaged Change in Ozone
for Coupled Perturbations
(LLNL 1-D Model)
"Reference Case"
c
•i
u
c.
V
a
UJ
(9
UJ
O
M
O
z
a
u
-5
-10
-15
-20
-25
1990 2000 2010 2020 2030 2040 2050 2060 2070 2080.
Total column ozone change for "reference case" scenario of trace
gases: ~2.5 percent growth in CFG emissions, concentrations of CH4 at
1 percent, N20 at 0.25 percent, and carbon dioxide at ~0.6 percent.
Source: Connell and Wuebbles (1986).
-------
5-46
EXHIBIT 5-33
Tine-Dependent, Globally Averaged Change in Ozone
for Coupled Perturbations
(LLNL 1-D Model)
c
at
o
t.
9)
a
ui
e>
<
a
tu
z
o
Z
ID
_)
O
O
_J -pn -
O
1990
2000 2010 2020 2030 2040 2050 2060 2070 2080
Total column ozone change for "low" and "high" scenarios of trace
gases:
CFCs
CH4
N20
C02
Low
1.4
1.0
0.25
-0.6
High
4.1 (emissions)
1.0 (concentrations)
0.25 (concentrations)
~0.6 (concentrations)
Source: Connell and Wuebbles (1986)
-------
5-47
EXHIBIT 5-34
Effect of Potential Greenhouse Gas Controls
on Ozone Depletion
(Results from 1-D Parameterization)
0.0
-2.0
Global
Ozone -4. 0
Depletion
a) -6. o
-8.0-
-10.0-
-12.0-
CONTROL OPTION 1
CONTROL OPTION 1 WITH
THE GROWTH RATES OF
CONCENTRATIONS OP OTHER
TRACE GASES REDUCED By
50 PERCENT STARTING
IN 2000
1980 2000 2020 204Q
2060
Source: Gibhs(1986). "Analysis of the Importance of
Various Design Factors in Determining
the Effectiveness of Control Strategy Options."
UNEP Workshop
Change in global average ozone as calculated by a parameterized
version of the LLNL 1-D model (see Connell, 1986). Control option 1
is:
CFCs
CH4
N20
C02
2.5% (emissions) until CFCs double
1.0% (concentrations)
0.25% (concentrations)
~0.6% (concentrations)
In "Half Trace Gas" curve, action is simulated in the year 2000 to cut
the growth rates in half for concentrations of CH4, N20, and C02.
The temperature equilibrium uses 3°C as the temperature sensitivity
for doubled C02. Actual equilibrium temperatures could be plus or
minus 50 percent.
Source: Gibbs (1986).
-------
5-48
In looking at the time period in which actual measurements exist, the
IS model performs well in comparison to Umkehr measurements (Exhibit 5-35).
Estimates with temperature feedback (curve 1) give upper stratospheric
ozone depletion larger than what is deduced from Umkehr observations. We
have, however, also done one model study where we included temperature
changes between 1979 and 1980. The stratospheric temperature decrease
adapted for this period is taken from one-dimensional, model studies by
Brasseur, DeRudder, and Tricot (1985). Their calculations are based on a
combined scenario, where temperature decreases in the 1970-80 period are a
result of increases in CO2 and other trace species. We have assumed that
approximately one-third of the estimated change up to 1983 given by
Brasseur, DeRudder, and Tricot (1985) takes place between 1970 and 1980.
This gives temperature decreases of approximately 1°C in the 45-50 km
region and less than 1°C below 35 km. When the temperature feedback is
considered (curve 2) ozone depletion becomes approximately two-thirds of
the estimated depletion when no temperature effect is considered. (Stordal
and Isaksen, 1986)
Four scenarios were run with the IS 2-D model with temperature
feedback. In scenario IT, CFC-11 and -12 are rolled back to 1980 levels,
CFC-113 is assumed to grow at the same rate as CFC-11 and -12 and to have
the characteristics of CFC-12, halon emissions do not occur, methyl
chloroform concentrations and CC14 rise, as in Quinn (1985), at about a 2
percent rate, methane concentrations rise at 1.0 percent, carbon dioxide at
0.6 percent, and nitrous oxide at 0.25 percent yearly. Scenario 2T allows
CFC-11 and -12 to grow at 1.2 percent, Scenario 3T has 3.0 percent, and
Scenario 4T has 3.8 percent, with all other assumptions the same as IT.
Exhibit 5-36 shows the globally and seasonally averaged change in ozone
calculated for these four scenarios.
Scenarios 1WT, 2WT, 3WT, 4WT are scenarios without temperature
feedback, assuming essentially that carbon dioxide does not grow. These
scenarios may be thought of as the case in which greenhouse warming is
limited, although it is unlikely that carbon dioxide would be reduced to no
growth and nitrous oxide and methane allowed to grow. The main value of
these scenarios is that they demonstrate the additional susceptibility of
the stratosphere to depletion if greenhouse warming is limited by reducing
carbon dioxide or other greenhouse gases. Of course, the effects of
limiting nitrous oxide or methane would be quantitatively somewhat
different than limiting carbon dioxide, but would still exacerbate
depletion at some latitudes. Exhibit 5-37 shows the results for global
averages.
The results of the various scenarios that include the stratospheric
cooling (temperature feedback) associated with rising carbon dioxide are
included in Exhibits 5-36, 5-38, 5-39, 5-40, and 5-41. Several important
results are clear from these runs. If CFCs grow at 3.8 percent, while
Halons are eliminated, and methane grows at 1 percent and nitrous oxide at
0.25 percent, depletion will exceed 4 percent (from a 1985 base) at 50°N
before the year 2010. Since near-term growth estimates do not preclude
growth at 3.8 percent (see Chapter 3), these results are particularly
important. For growth of 3.0 percent for CFC-11 and -12 (with all other
assumptions about limiting depleters and allowing greenhouse gases to
grow), depletion will exceed 4 percent at 60°N by 2015. For
-------
5-49
EXHIBIT 5-35
Calculated Ozone Depletion for 1970 to 1980
vs. Umkehr Measurements
MB
1-2
2-4
4-8
8-16
16-32
UmkeHR
Layer
_l L.
-1 =6^4^ -2 0
OECAOAL OZONE CHANGES
"Calculated ozone depletion between 1970 and 1980 without (curve 1)
and with (curve 2) temperature changes from radiatively active gases
in the stratosphere. The adapted temperature change is taken from a
1-D model study by Brasseur, DeRudder, and Tricot (1985). Estimated
global trends (Reinsel et al. 1983; Reinsel et al. 1984) are based on
Umkehr data (triangles with error bars). A one-dimensional model
calculation by Wuebbles, Luther, and Penner (1983) is included (3)."
Source: Stordal and Isaksen (1986).
-------
5-50
EXHIBIT 5-36
Time-Dependent Globally and Seasonally Averaged
Changes in Ozone for Coupled Perturbations
(IS 2-D Model)
OZODQ
Doplotjon
1960 1970 1980 1990 2000 2010 2020 2030
For four scenarios of trace gas growth results show:
Scenario
IT
2T
3T
4T
CFC-11 and CFG-12
1980 levels
1.2% growth
3.0% growth
3.8% growth
Assumptions for other trace gases are the same in each scenario:
emissions of CFC-113 parallel CFC-12 and are treated identically,
constant CC14 and CH3CC13 emissions, zero emissions of halons, 1
percent growth per year in CH4, and 0.25 percent growth per year in
N20. C02 concentrations grow at 0.5 percent. Temperature Feedback
considered in model.
Source: Isaksen, personal communication.
-------
5-51
EXHIBIT 5-37
Time-Dependent Globally and Seasonally Averaged
Changes in Ozone for Coupled Perturbations
(IS 2-D Model)
1wt
1980 1990 2000 2010 202O
4wt
-10
2O3O
TRACE GAS ASSUMPTIONS
CFG-11 and CFG-12
Scenario IT: Constant emissions at 1986 levels
Scenario 21:
CFC-11 assumed to grow at an 'average' annual rate of 1.4%
(5% from 1980 to 1990; 1.1% from 1990 to 2000; 1.0% from 2000
to 2040, and 0.9% from 2040 to 2075). This scenario is taken
from Quinn et al., (1986), Scenario II "Slow Growth"
Scenario 3T: Growth of 3% per year.
Scenario 4T: CFC-11 and CFC-12 increase at approximately 3.5% per year and
5% per year until 2000, after which growth gradually declines
to 2% per year by 2075. This scenario is the average of
Scenario VI "Later Market Maturation" and Scenario VII "New
Markets" from Quinn et al., (1986).
Assumptions for other trace gases are the same in each scenario: emissions
of CFC-113 grow at the same rate as CFC-12 and are treated identically,
constant CC14 and CH3CC13 emissions, zero emissions of halons, 1 percent
growth per year in CH4 and 0.25 percent growth per year in N20. C02
concentrations are held constant. Temperature Feedback not considered in
model.
Source: Isaksen (1986).
-------
5-52
EXHIBIT 5-38
Tine-Dependent Seasonally Averaged Change in Ozone
for 1980 CFC Emissions and Coupled Perturbations
(IS 2-D Model)
I960
1980
20dO
2020
Results shown from constant CFC emissions at the 1980 level
(approximately 10 percent less than current emissions); CH4
concentrations at 1 percent per year, N20 concentrations at 0.25
percent per year, and C02 concentrations at approximately 0.5 percent
per year. Methyl chloroform and CC14 are essentially capped; halons
eliminated. Changes shown for 40°N, 50°N, and 60°N. Temperature
feedback considered in model.
Source: Isaksen (personal communication)
-------
5-53
EXHIBIT 5-39
Time-Dependent Seasonally Averaged Change in Ozone
for 1.2% Growth in CFG Emissions and Coupled Perturbations
(IS 2-D Model)
I960
2020
Results shown for 1.2 percent growth per year in CFG emissions, 1
percent growth in CH4 concentrations, 0.25 percent growth in N20
concentrations, and approximately 0.5 percent growth in C02
concentrations. Methyl chloroform and CC14 are essentially capped;
halons eliminated. Changes shown for 40°N, 50°N, and 60°N.
Temperature feedback considered in model.
Source: Isaksen (personal communication)
-------
5-54
EXHIBIT 5-40
Time-Dependent Seasonally Averaged Change in Ozone
for 3% Growth in CFG Emissions and Coupled Perturbations
(IS 2-D Model)
-1O
I960
1980
2000
Results shown for 3 percent growth per year in CFG emissions, 1
percent growth in CH4 concentrations, 0.25 percent growth in N20
concentrations, and approximately 0.5 percent growth in C02
concentrations. Changes shown for 40°N, 50°N, and 60°N. Temperature
feedback considered in model.
Source: Isaksen (personal communication)
-------
5-55
EXHIBIT 5-41
Time-Dependent Seasonally Averaged Change in Ozone
for 3.8% Growth in CFG Emissions and Coupled Perturbations
(IS 2-D Model)
-12 -
i960
1980
Results shown for 3.8 percent growth per year in CFC emissions; 1
percent growth in CH4 concentrations; 0.25 percent growth in N20
concentrations, and approximately 0.5 percent growth in C02
concentrations. Changes shown for 40°N, 50°N, and 60°N. Temperature
feedback considered in model.
Source: Isaksen (personal communication)
-------
5-56
CFG-11 and -12 growth of 1.20 percent (and other assumptions limiting
depleters and allowing greenhouse gas growth), 2 percent depletion will be
exceeded at 50°N in 2015. Even if CFC-11 and -12 emissions are reduced 10
percent to 1980 levels (with other depleters limited and greenhouse gases
growing), 1 percent depletion will be reached at 50°N by 2015, although the
ozone layer would cover if greenhouse gases grow thereafter.
Examining the shape of the depletion curves is also instructive. In
Scenario IT, the rollback case, the rise of carbon dioxide and methane
eventually limits depletion to 50°N. In scenario 3T, with moderate CFG-11
and CFC-12 growth, a turnaround never comes -- depletion continues to
increase at an accelerating rate.
Globally and seasonally averaged ozone changes for scenario 3WT
(moderate CFG growth) are shown in Exhibit 5-42. Also shown in this
exhibit are the results for model calculations in which carbon dioxide
cooling and temperature feedback are excluded.
Clearly, carbon dioxide plays an important role in countering
depletion. The risks of depletion will be increased if decisionmakers in
the future decide not to accept global warming of the magnitude that would
be implied by allowing carbon dioxide to rise at 0.6 percent, nitrous oxide
to rise at 0.25 percent, and methane to rise at 1.0 percent for the rest of
the next century. More discussion on this point is presented in Chapter
18.
The Isaksen runs underestimate depletion because they do not consider
all depleting chemicals. CFC-113, which is not explicitly represented in
the model, was predicted to grow at 3 percent and was assumed to have an
effect equal to that of adding CFC-12 emissions to the atmosphere because
of the similarity between the photochemical characteristics of both CFCs
(NASA/IPC, 1985). Clearly, CFC-113 is likely to grow faster than CFC-12
(see Chapter 3). As mentioned earlier, brominated compounds (Halon 1211
and 1301) are omitted in the Isaksen runs, thus making all runs equivalent
to an assumption that emissions will be prohibited. (Currently,
concentrations of Halon-1211 are growing at 23 percent (Khalil and
Rasmussen, 1985). If bromine compounds grow at current or faster rates,
depletion would be greater than predicted by these model runs (see earlier
discussion on bromine).
Sze's time-dependent simulations show results quite similar to
Isaksen's, although latitudinal gradients and seasonality are somewhat
different (Exhibit 5-43) (Sze, 1987). Brasseur's time-dependent 2-D runs
are also quite similar (Brasseur, personal communication).
A Comparison of Results of One-Dimensional and Two-Dinensional Models
One-dimensional and two-dimensional models differ in their treatment
of transport. One-dimensional (1-D) models, at best, project average
global depletion. Two-dimensional (2-D) models project depletion by
latitudes, which, of course, can be averaged together to estimate average
global depletion. Exhibit 5-44 shows the averaged global depletion results
-------
5-57
EXHIBIT 5-42
Temperature Feedback Experiment:
Time-Dependent, Globally and Seasonally Averaged Change
in Ozone for '3% Growth in CFC Emissions and Coupled Perturbations
(IS 2-D Model)
WITH TEMP. FEEDBACK
c
-------
PRESSURE (MB)
PRESSURE (MB)
00
o
o
fB
CO
N
CD CD
w 3
to p.
O O
**1 P
O M
r>
o>
ca
m
o
O ^3
3 (B
W l-i
rt O
fu fD
3 3
rt rt
n>
*H L^
H' fD
in in
in T3
H- fD
O O
3 rt
O I-1
ro i-1
P
fB rt
3 fD
P. p.
en
01 T3
P- fD
O »-!
3 O
W 0>
3
p) rt
P. O
§ §
3 3
W (B
(B
W H)
hi
H« O
3 3
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ffi vo
^" 0s*
o
CD
3 rt
qu O
o 3 a N>
hi o ro o
O I—' O ^>
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o p. o
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M P W
u> rt rt
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003
tc o
B> O *T]
tn t-1
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P i-( 3
SOP,
p. fD
rt
APPROX. ALTITUDE (KM)
PERCENT CHANGE
APPROX. ALTITUDE (KM)
Ul
CX3
-------
5-59
EXHIBIT 5-43b
Two-Dimensional, Time-Dependent Simulation
for CFG Growth of 62 Percent Per Year
(AER 2-D Model)
LJ
5
CO
CO
UJ
o:
Q.
0.1
60S 30S EQ 30N SON 90N
LATITUDE
CD
UJ
0 _ '"-40-'-
,,--,
'/. r_-"- 20 ,:
'--~^:— --—_in— -—-^ .
60
•50
40
•20
HO
905 60S SOS EQ 30N 60N 90N
LATITUDE
UJ
Q
:D
<
x
0_
0_
i960
1980
2000 2020
YEAR
204O
206C
Calculated percent changes in ozone from 1960 to 2060 for projected 1.2 percent
per year growth in emissions of CFG-11 and CFG-12, and annual increases in CH4
and N20 concentrations of 1 percent and 0.25 percent, respectively. Model does
not include CFC-113 or Halons, and assumes constant emissions of CC14 and methyl
chloroform.
Source: Sze, Ko and Weisenstein, 1986.
-------
5-60
EXHIBIT 5-44
Model Comparison for Coupled Perturbation Scenario
-0.5
Ozone
Depletion
(%)
1985
1995
2005
2015
2025
Global average change in total column ozone as calculated by several
modeling groups for a common scenario of:
Compound
CFCs
CH4
N20
C02
Growth Rate (% per year)
3.0 (emissions)
1.0 (concentrations)
0.25 (concentrations)
"0.60 (concentrations)
Results shown for 2-D models of Isaksen and AER, 1-D models of
Brasseur and Wuebbles, and Cornell's parameterization of the LLNL 1-D
model.
Source: Chemical Manufacturers Association (1986); World
Meteorological Organization (1986); Connell (1986); Brasseur
and DeRudder (1986); and Isaksen and Stordal (1986).
-------
5-61
of Isaksen's and AER's 2-D models, Brasseur's 1-D model, and the Connell
parameterization of the Lawrence Livermore 1-D model for very similar
scenarios. The outcomes are relatively similar, indicating that the 1-D
models and Isaksen's 2-D models do not differ in their fundamental
projections for global results, and that Isaksen's model distributes
depletion in a manner consistent with total global depletion from 1-D
projections. The higher estimate from Isaksen's 2-D model is to be
expected. In model comparisons done in the World Meteorological
Organization (1986) assessment, the 2-D model of AER exhibited similar
behavior to Isaksen's. The global average for AER's 1-D model, with
exactly the same chemistry and an almost identical perturbation study, was
20 percent higher. While much remains to be learned about 2-D models, it
is clear that they offer more information for monitoring, for validation
(and invalidation), and for impact analyses than do 1-D models. The World
Meteorological Organization (1986) report stated "In summary, While 1-D
models remain useful assessment Cools for assessment, it is becoming clear
that 2-D models provide a much more detailed picture of atmospheric
response to perturbations.
MODELS FAIL TO REPRESENT ALL PROCESSES THAT GOVERN STRATOSPHERIC CHANGE IN
A COMPLETE AND ACCURATE MANNER
Current models fail to represent all the processes that will influence
stratospheric change in either a complete or an accurate manner. While the
models can reproduce many of the measurements that describe today's
atmosphere, they fail to reproduce some observations very accurately.
This, by itself, lowers our confidence in current model predictions,
suggesting the need for careful sensitivity testing for various
uncertainties and assumptions. In addition, theory suggests that models do
not describe all processes in a completely accurate manner, suggesting the
possibility that missing factors or simplified processes could undermine
the accuracy of model proj ections.
The Nature of Model Validation for Geophysical Systems
In many science disciplines, the predictive power of theories and
models can be confirmed by doing and redoing experiments. In this way
experimenters can gain confidence by actually manipulating the system under
study. For geophysical systems, this approach generally cannot be taken --
there is no experimental earth on which to conduct tests. Thus modelers
attempt to validate their models by comparing them to the actual
atmosphere. Such tests impose strong restrictions on models in the sense
that there are many variables to be predicted, and fixing one aspect of a
model's deficiencies often results in the emergence of a new deficiency.
Even if a model reproduces the current world with complete fidelity,
however, it may have substantial problems. There may be several models
that reproduce existing conditions, yet projections of change from each
could diverge. Models that 'fit well' may lack adequate power to predict
the effects of perturbations if factors are missing from the model that are
not critical in describing current conditions, but will be critical in
describing future conditions. There always exists the possibility that
some factor is missing, that some relationship that now holds will be
invalid under future conditions. Without an experimental earth to use for
model validation, it will always be impossible to eliminate that
possibility.
-------
5-62
Nevertheless, there are mechanisms for testing models and their
robustness. Past assessments have reported changes in the prediction of
ozone depletion (Exhibit 5^45) for the same scenarios. At first glance,
these changes, in themselves, might be taken to reduce our confidence in
the models. An examination of the cause of those changes, however, reveals
that most occurred primarily as a product of new estimates in rate
constants or cross sections from the laboratory. While it was impossible
for laboratory kineticists to predict the changes that occurred in their
laboratory estimates, kineticists certainly were not surprised that changes
occurred, nor that they had implications on model outputs. Even today,
after enormous improvements in laboratory procedures, uncertainty about
kinetics and cross sections still exist. Clearly then, to avoid surprise
in changes in the estimates of depletion in the future, we must examine a
range of rate constants and cross sections to determine the extent to which
model results depend on a unique set of inputs. Furthermore, it is
instructive to consider the fact that chlorine increases constant with
steady state for CFC has always produced depletion.
Another source of uncertainty that needs to be considered is transport.
Chemical interactions may be described quite well by models, but if
molecules do not move to areas to which they are expected to move, the
outcome of models may be inaccurate.
To address these concerns, this section considers these three
questions:
(1) How well do models reproduce the current atmosphere?
(2) How dependent are model predictions on a narrow range of
kinetics and cross sections?
(3) How dependent are models on a single formulation of
transport?
By answering these questions, it should be possible to establish a range of
concern that should govern judgments about model reliability.
Agreements and Deficiencies In Model Representations of the Current Atmosphere
The extent to which models reproduce observed concentrations will have a
bearing on the confidence we place in them. There are a few discrepancies
between model predictions and the observed atmosphere, which lowers our
confidence in the predictions of one- and two-dimensional models. One
discrepancy is that there is an inconsistency between modelled (using both one-
and two-dimensional models) and measured (by both ground-based and satellite
instrumentation) ozone abundances above 35 km by as much as 30-50%. [For some] ,
it is particularly troubling that this problem occurs in an altitude region in
which the ozone concentrations are photochemically controlled. [Others feel
that because this is a region with low ozone, the discrepancy is not that
important.] Furthermore, if the observed ozone concentrations are used in
-------
5-63
EXHIBIT 5-45
Calculated Ozone -- Column Change to Steady-State
for Two Standard Assumed Perturbations
ut
13
-------
5-64
radiative models of the upper stratosphere, the predicted tenperatures are
higher than measured. Another problem is that there are considerable
differences in the distribution of odd nitrogen species that are computed by the
models of different groups ([Exhibit 5-46]). This is true for both one- and
two-dimensional models. This disagreement is understandable for the
two-dimensional models given the differences in their formulations of transport,
but is very disturbing for the one-dimensional models in which these differences
cannot be attributed to differences in transport. One source for these
differences in odd nitrogen distributions are the differing treatments for the
penetration of solar radiation in the Schumann-Runge bands. However, models
with similar radiation schemes still show significant differences in odd
nitrogen. We do not presently understand the source of these different odd
nitrogen distributions. They are important, however, since nitrogen species
interfere with chlorine catalysis of ozone destruction and also because of the
important catalytic role of the odd nitrogen species themselves. (NASA, 1986)
Except for ozone, the data base of oxygen species is very limited and,
therefore, not adequate to critically test these models. For comparisons with
other species the reader is referred to WHO 1986.
In summary, models can reproduce many, but not all atmospheric measurements.
Uncertainty in the reliability of atmospheric measurements hampers this effort.
Nevertheless, the fact that there are cases in which models do not reproduce
apparent observations lowers our confidence in the predictive ability of models.
uncertainties in Chemical and Photochemical Parameters
Clearly, there are uncertainties in the chemical and photochemical rate
parameters and in the mechanisms involved in the atmospheric chemistry. They
are one of the major factors in limiting the accuracy of model calculations of
species concentrations and ozone perturbations in the atmosphere. Most of the
changes in the predicted ozone depletion due to chlorofluoromethanes that have
occurred in recent years have resulted from changes in the values of kinetic
parameters used in model calculations. (World Meteorological Organization,
1986)
The uncertainty in the kinetic parameters for the key atmospheric reactions
has been reduced greatly over the last 10-15 years due mainly to the rapid
development of the techniques used for the direct measurement of radical species
in the gas phase and for investigation of their reaction kinetics. Whereas 20
years ago the rates of most radical-molecule reactions were only known to within
a factor of 10, today the room temperature rate constants of atmospherically
important reactions of this type can be measured within an accuracy of + 10%.
Moreover, the number of reactions for which good kinetic data are available have
increased tremendously. The consistency in the experimental measurements gives
confidence in the data base. There remain problems in reaction rate theory
which is not able to explain some of the observed temperature and pressure
dependencies. Although there is improved reliability of the data, it should be
recognized that the errors in the rate coefficients increase as the temperature
diverges from room temperature and that certain reactions, e.g., radical +
radical reactions, are intrinsically more difficult to study and consequently
are always likely to carry more uncertainty than straightforward radical +
molecule reactions. (World Meteorological Organization, 1986)
-------
5-65
EXHIBIT 5-46
Latitudinal Gradients in Odd Nitrogen:
Models vs Measurements
3mb SUMMtft
- 48 - 64
30 mb SUMMER
LIMS DATA
-32
LATITUDE
"There are considerable differences in the distribution of odd
nitrogen species that are computed by models of different groups."
Source: NASA (1986).
-------
5-66
Difficulties also arise in the study of very slow reactions between
radicals and molecules, due to complications such as those arising from
heterogeneous effects. (World Meteorological Organization, 1986)
The uncertainty in the rate coefficients for atmospheric reactions
results primarily from systematic errors arising from the chemical systems
and the techniques used for their determination rather than measurement
error of a statistical nature. Consequently, it is not straightforward to
assign uncertainties to preferred values given in an evaluation. Errors
quotes in the NASA or CODATA evaluations are assessments based on such
factors as the number of independent determinations made and the number and
reliability of the different techniques employed. Furthermore in most
cases, the probability of an error of a given magnitude falls off more
slowly than a normal Gaussian function. (World Meteorological
Organization, 1986)
For the key elementary reactions identified as being important for the
stratosphere many of which are radical + radical reactions, the prospect of
reducing uncertainties in the rate coefficients to less than -I- 10% cannot
be considered realistic. Some reduction in uncertainty can be expected
from further temperature and pressure dependence studies, and a further
understanding of product channels and reaction mechanisms can be
anticipated in the future. (World Meteorological Organization, 1986)
For a Range of Testable uncertainties, Models Project Depletion
The depletion predicted by earlier models uses a single set of input
values for kinetics, cross sections, and transport. As discussed above,
significant uncertainty exists about the value of these inputs. Past
changes in these inputs that occurred with improved laboratory experiments
have significantly changed estimates of ozone depletion. Given past
history, it makes sense to test a range of kinetic and cross-section
inputs, rather than relying solely on best-case estimates.
Fortunately, such uncertainty analyses have been conducted, by
Stolarski and Douglass (1986) and by Grant et al. (1986). These analyses
recognizing the uncertainties in reaction rate coefficients, absorption
cross sections, solar fluxes and boundary conditions, have sampled from a
range of different inputs, using the probability of the value for each
input as a selection criteria. By doing this many times and for a variety
of emission scenarios, these modelers have essentially explored the
robustness of the model predictions to these uncertainties. The approach
to doing the uncertainty analyses is illustrated in Exhibit 5-47. None of
the uncertainty analyses included higher levels of C02. Different sampling
strategies have been used, and different CFC levels analyzed.
Exhibit 5-48 is included in order to give readers a better feel for the
nature of this analysis; that is, how uncertainty ranges are derived for
rate constants. It shows a histogram of all of the individual measurements
of the room temperature rate coefficient of the reaction O + NO2 - O2 + NO
by three different groups (Remand et al., 1974; Slanger et al., 1973 and
Davis et al., 1973). These 62 data points form a distribution that is fit
well by either a Gaussian or a log-Gaussian distribution with parameters
given by DeMore et al. (1985). These are a central value of 9.4 x 10"^
-------
5-67
EXHIBIT 5-47
Logical Flow Diagram for Monte Carlo Calculations
NASA Codate Panel
For Given Fluxes of
CFCS, N,O. CH4
Range & Probability
of Kinetics & Cross Sections
Sampling Strategy
(n cases where n
was large enough
to develop a
reasonable measure
of the distribution)
Run 1 Dimensional
Model n Times
Output Range of
Depletion Numbers
Screening System
(Must Meet Current
Atmospheric Measurements
fo X Variables)
Probabilities of
Various Levels of
Depletion without Screening
Probabilities of
Various Levels of
Depletion with Screening
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5-69
and a one- sigma uncertainty of +10%. Also shown in the [exhibit] is a
vertical line representing the Bean value which is normally used in a
photochemical model. This is not a complete representation of the known
information on this reaction. (Stolarski and Douglass, 1986)
In the uncertainty analysis, rather than using a single value for the rate
coefficient described above, different values are used. Some modelers used the
Monte-Carlo method, to choose coefficients, others used other sampling methods.
.. .Of course, a well-measured reaction was chosen for this illustration. Other
reactions have only been measured a few times (or only the mean of the actual
runs were reported), and the measurements may disagree with one another by
substantial amounts. For these cases, it is not obvious how much improvement is
obtained by attempting to represent an entire distribution (Stolarski and
Douglass, 1986).
Most of the reactions used in the Stolarski and Douglass model used the
chemical kinetic and cross section data and the 1-sigma uncertainties from
evaluation 7 of the NASA Panel In Data Evaluation (DeMore et al., 1985). For 02
dissociation, the 1-sigma uncertainty is assumed to be 20% with the Schumann
Runge bands and the Herzberg continuum treated independently. The 1-sigma
uncertainties in the boundary conditions and assumed dissociation rates are
given in [Exhibit 5-49], (World Meteorological Organization, 1986)
Stolarski and Douglass then applied the Monte-Carlo technique to this model
... to generate a total of 329 cases of varied inputs for calculation of the
atmosphere without fluorocarbons, with enough fluorocarbons to give a reasonable
steady-state representation of the present atmosphere and with the sequence of
increasing fluorocarbon perturbation to investigate the model response to large
chlorine amounts. [Exhibit 5-50] shows the calculated change in the column
content of ozone compared to the no fluorocarbons case as a function of the
injected fluorocarbon flux shown in units of the present flux of fluorocarbons
11 and 12 (PFF). The solid curve, labeled the base case, gives the results
using the mean values for each input parameter. The dashed curve is the mean
ozone depletion obtained from the 329 cases. The mean curve is significantly
more linear than the base case curve. (Stolarski and Douglass, 1986)
Stolarski and Douglass (1986) used current observations to screen their
model runs. None of the 329 runs was able to satisfy all the constraints posed
by all the observations. Exhibit 5-51 shows the results for the equilibrium
values of various levels of CFCs alone. For current emissions, the most common
depletion is 3 percent. For 1-sigma deviation (64 percent probability),
depletion always occurs. The shaded areas are those cases that passed all the
screens except 03 in the upper atmosphere. Note that the screens reduce the
variation of results substantially. For a CFC flux of 2 times present values,
the screen reduces the range of total column depletion from (+ 1 percent to -60
percent) to (+ 1 percent to -24 percent). Exhibit 5-52 shows the distribution
of runs for equilibrium concentrations of 3.5 x current CFC, 1.2 x N20, and 2 x
current CH4. Note that distribution is weighted towards higher values more than
lower, and that the worst cases are eliminated if only the cases meeting the
screens are used. Exhibit 5-53 represents the change in depletion that would
occur for moving from 3.5 x CFC to 3x, from 3x to 2.5x, etc. This exhibit shows
that any reduction in emissions of one half of current emissions (that is, from
3x to 2.5x, from 2.5x to 2x, etc.) is likely to lead to less ozone being
-------
5-70
EXHIBIT 5-49
Recommended Rate Constants and Uncertainties
Used in Monte Carlo Analyses
No.
1.
2.
3.
4.
5.
6.
Reaction
CIO + 0 = Cl + 02
Cl + CH4 = HC1 + CH3
OH + HC1 = Cl + H20
OH + HN03 = H20 + N03
OH + HN04 = H20 + 02 + N02
0(1D) + M = 0(3P) + M
Experimental
Sensitivity Factors Uncertainty
+1 -1 Av. Factor
+0
-0
+0
-0
-0
+0
.60
.48
.56
.51
.16
.60
+0
-0
+0
-0
-0
+0
.68
.46
.79
.56
.33
.63
+0
-0
+0
-0
-0
+0
.64
.47
.68
.53
.25
.62
1
1
1
1
2
1
.43
.16
.32
.30
.20
.32
Error
Contribution
Factor
+0
-0
+0
-0
-0
+0
.23
.07
.19
.14
.20
.17
7. 0(1D) + N20 = 2 NO
= N2 + 02 -0.51 -2.00 -1.26 1.30 -0.33
8. CIO + N02 + M = C10N02 + M -0.31 -0.37 -0.34 1.56 -0.15
9. 02 + hn (S-R) = 2.0 -0.58 -0.85 -0.72 1.40 -0.24
Rate constants recommended in evaluation 7 of the NASA Panel In Data
Evaluation. Also shown are the 1 sigma uncertainty bands.
Source: World Meteorological Organization (1986).
-------
5-71
EXHIBIT 5-50
Monte Carlo Results:
Change in Ozone Versus Fluorocarbon Flux
2
O
U
O
z
O
U
6"
-40 -
1
FACTOR TIMES PRESENT
FLUOROCARBON FLUX
The calculated change in total column ozone as the fluorocarbon flux
increases. The sold line shows the base case, which uses the mean
value for each input parameter. The dashed line shows the mean
depletion from the 329 model runs. The vertical bars show the 1-sigma
uncertainty limits.
Source: Stolarski and Douglass (1986).
-------
5-72
EXHIBIT 5-51
Monte Carlo Results:
Change in Ozone Versus Fluorocarbon Flux
-60 -« -20 0
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5-75
depleted. The distributions of changes in the ozone column look quite
similar; for example, going from 3.5 x current to 3.0 x current (panel e)
produces very similar distribution as going from 3.Ox to 2.5x (panel d).
The average amount of depletion prevented by reducing emissions by 0.5
current emissions is about 5 percent. The benefits of a shift in 1/2
current CFG flux are relatively stable across the absolute level of CFCs.
Even in the case of going from .5x current emissions to current emissions
(panel a), the mean gain in column ozone is close to 4 percent.
And the distribution shows that there is little chance that a 0.5 current cut in
CFCs will not produce a thickening of the ozone column. In addition, the common
shape of the distribution shows that expected change in column ozone is
relatively independent of the absolute depletion across the range of input
uncertainties Stolarski and Douglass investigated.
Grant et al. (1986) performed two uncertainty analyses. One used 15 ppb
Clx, 2 x methane, 1.2 x nitrous oxide and NASA/CODATA kinetics distribution
similar to Stolarski and Douglas; the other assumed that all uncertainties in
kinetics were reduced to 10 percent, the level the panel has suggested is the
practical limit for improving kinetic estimates. Exhibit 5-54 shows the changes
in ozone with altitude due to the uncertainty tests (as a percent). Exhibit
5-55 shows the results for unscreened data. When only cases meeting all
observational screens are used, uncertainty is reduced to 7.7 ± 6 percent. It
is relevant to note that at least eight sets of kinetics and cross sections
adequately describe all the apparent observations of the atmosphere.
Exhibit 5-56 shows the cumulative probability of various depletion levels.
Approximately 10 out of 100 cases were at around 0.2 percent depletion. For an
approximately equal number of cases, depletion was equal to or greater than 20.2
percent. Exhibit 5-57 demonstrates that even if a low level of uncertainty is
achieved about kinetics (i.e., +10 percent), uncertainty will still exist about
outcomes.
The results of the two studies indicate that across a wide range of CFC
scenarios and current uncertainties about kinetics, cross sections and solar
flux, average global depletion can be reasonably anticipated for cases in which
CFCs grow. Stolarski and Douglass demonstrated that the change in column ozone,
for a fixed reduction in CFCs, will vary very little. Thus, even though there
is uncertainty about the absolute depletion for any given level of CFCs, there
is less uncertainty about how much the column will thicken for reductions in
CFCs. This means that the change in column ozone obtained by cutting back
emissions is less uncertain than the absolute depletion caused by any level of
CFCs.
Uncertainty Analysis of Two-Dimensional Models
To date, the computation costs of performing uncertainty analysis for two-
dimensional models have prevented such studies from being undertaken. However,
because two-dimensional modelers have used very different transport mechanisms,
they have, in effect, created a way to look at the sensitivity of 2-D models to
transport uncertainties. Exhibit 5-21 shows the results of the AER and MPIC
models; clearly transport makes some difference. The quantity of depletion
varies at different latitudes, with the AER model predicting greater depletion
further from the poles and the MPIC model predicting greater depletion towards
the equator. Both, however, have a gradient of increasing depletion as one
-------
5-76
EXHIBIT 5-54
Monte Carlo Results:
Changes in Ozone by Altitude
C«»«
— R«ea«Mnd*d uncertainty Fietari
101 Unetrtiinty Ftctort
-80
-60 -50 -40 -30 -20 -10
Ozone cnnMM (-3)
10
20
30
Results from Monte Carlo analysis of uncertainties regarding rate
constants. Solid line shows calculated changes in ozone by altitude
for mean values of input parameters. Dashed lines show calculated
changes for recommended uncertainty factors. Dotted lines show
calculated changes for uncertainties which have been reduced to 10
percent. Perturbations are: 15 ppbv Clx, 2x CH4, and 1.2x N20.
Source: Grant, Connell, and Wuebbles (1986).
-------
5-77
EXHIBIT 5-55
Monte Carlo Results:
Changes in Ozone by Column and Altitude, Unscreened Data
Distribution of Percent Oiont Cheng*
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-37.0 -32.0 -27.0 -tt.O -17.0 -lt.0 -7.0 -t.O 3.0 0.0 13.0 10.0
Distribution of Percent Ozone Change
*•
n
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IT
^
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1
1
1
1
1
1
*/
y
X
[ v
I
I
Percent Change at 25 km
TIM* 1.0E»001
Percent Change at 32 km
Distribution of Percent Ozone Change
Distribution of Percent Ozone Change
*»•
n
D **'
EC
•J
1 »•
X
O
0
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S K
1
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.
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48
m
tr
a
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c
w
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I
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i
i
I
y\
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I
1 -1.Z -7.7 -7.Z -«.7 -«.Z -J.7 -3.1 -4.7 -4.!
Percent Change at 40 k«
-33.2 -30.2 -23.2 -20.2 -13.2 -10.2 -3.2 -0.2 4.B 9
Percent Change for Total Column
Frequency distributions of Monte Carlo model results for changes in
ozone. Top left panel shows results for 25 km, top right for 32 km,
bottom left for 40 km, and bottom right for total column ozone.
Perturbations are: 15 ppbv Clx, 2x CH4, and 1.2x N20.
Source: Grant, Connell, and Wuebbles (1986).
-------
5-78
EXHIBIT 5-56
Monte Carlo Analysis With the LLNL 1-D Model
1OO
9O -
BO
z: vo H
5
X
3
3
O
6O -
50 -
4O -
3O -
2O -
1O -
O
Scenario analyzed;
15 ppbv C1X
1.25 x present cone, of
2 x present cone, of CH.
>30
>25
r
>2O
>o
TOTAL COLUMN OZONE DEPLETION (PERCENT)
SOURCE; Adopted from K.E. Grant et al. (1986) "Monte Carlo Uncertainty Analysis of
Stratospheric Ozone in Ambient and Perturbed Atmospheres", LLNL.
The cumulative probability of ozone depletion cases unscreened for meeting
current atmospheric measurements is shown above. For example, the chance of a
depletion greater than 10 percent occurring is about 50 percent. The dashed
line indicates the value of depletion predicted for current kinetics and other
inputs.
Source: Adapted from Grant, Connell, and Wuebbles (1986).
-------
5-79
EXHIBIT 5-57
Monte Carlo Results:
Changes in Ozone by Altitude
Dlatr of Ozone X Change for 10X Uncertainty
i
1
1
I
Y\
fj
i
i
i
i
i
i
i
i
i
r
i
i
i
-37 0 -32.0 -TT.9 -7J.9 -17. tf -«*.0 -7.9 -2.9 3.9 9.9 19.0 li.O
Dlstr of Ozone » Change for 10> Uncertainty
41
n
§ 40.
tr
~
1 *
X
Numder from 100
3 H
1
1
1
1
1
I
I
i
i
i
i
i
i
i
i
en
L
-5.0 -4.S -4.0 -3.5 -3.0 -8.5 -J.O -1.5 -1.0 -0.5 0.0 0.5
Percent Change at 25 km
TlMt I.Of-001
Percent Change at 32 km
Distr of Ozone X Change for 10X Uncertainty
Dlstr of Ozone X Change for 10X Uncertainty
i
\
\
0
I
i
i
i
i
i
i
i
i
i
i
VA &7\
-•7 -• 2 -7.7 -7.1 -».7 -«.Z -S. 7 -S.I -4.7 -4.1
Percent Change at 40 km
c
3
(T
E
3
Z
i
„ I
Vf
//
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I —
i
i
I
r
i
i
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-35 3 -30 t -23.3 -20 2 -I5.Z -!«.» -5.2 -O.Z 4.» ».
Percent Change for Total Column
Frequency distributions of Monte Carlo model results for changes in
ozone, when uncertainties in input parameters are reduced to 10
percent. Top left panel shows results for 25 km, top right for 32 km,
bottom left for 40 km, and bottom right for total column ozone.
Perturbations are: 15 ppbv Clx, 2x CH4, and 1.2x N20.
Source: Grant, Connell, and Wuebbles (1986).
-------
5-80
moves away from the equator. Thus, while the uncertainty in transport
clearly produces different gradients, at least for these models, the
results robustly predict depletion.
Missing Factors
The possibility of missing factors in the models used to project future
ozone levels is a difficult one. The most likely "missing factor" is some
heterogenous chemical reaction. Several reactions have been suggested in
recent years for such reactions and several of the hypotheses put forth to
explain the Antarctic ozone hole include heterogenous reactions. Another set
of "missing factors" that could be important are "dynamic or transport" changes
induced by climate or ozone change. Clearly, the possibility of missing
factors exists and always will exist. Nevertheless, it is imperative to try to
encompass all factors that suggest themselves as possibly important.
Consequently, it is important to undertake research into the possibility that
aerosols in the stratosphere are providing a place for heterogenous reactions
to occur. The search for other potentially missing factors should also be
continued and intensified.
THE IMPLICATIONS OF OZONE MONITORING FOR ASSESSING RISKS OF OZONE MODIFICATION2
Monitoring can do several things: it can validate or invalidate models; it
can suggest a path for future stratospheric change; and it can serve as a
warning system that helps initiate action. Monitoring of ozone is currently
done with a variety of ground-based and satellite systems. This section
analyzes research based on ground-based measurements of total and upper
atmosphere ozone trends, balloon measurements, and satellite measurements. The
first part of the analysis focuses on total column ozone as measured by
ground-based instruments. Observations made with ground-based instruments
appear roughly consistent with one-dimensional model predictions. The second
part of this section reviews ozone measurements for different altitudes as
measured with ground-based instruments, which also appear to show depletion
roughly consistent with models. The third section reviews altitude data
collected by balloons, which apparently shows depletion inconsistent with one
dimensional models, but consistent with two-dimensional models. The fourth
part reviews ground-based and satellite data for Antarctica, which appear
inconsistent with models. Finally, satellite data for total column ozone for
the globe and different latitudes is reviewed. This data shows decreases in
ozone greater than models predict.
^ The scientific description in this section of the risk assessment is
severely out of date. Major reassessments on Antarctic ozone and global trends
are underway in the scientific community. EPA plans to issue a risk assessment
on these areas in 1988. Readers may wish to skip this section since it is not
reflective of current thinking. It is left in this document for the purpose of
demonstrating what assessment was made of this data in the 1986-1987
timeframes. Discussion of the policy implications of monitoring data and
Antarctica remains the same; however, EPA has assumed that current models are
accurate for decisionmaking and that it is premature to argue that Antarctica
or global trends invalidate current models.
-------
5-81
Analyses of Global Total Ozone with Ground Based Instruments
Analyses of total column ozone using Dobson instruments must convert the
irradiances received by the spectrometer into a total column ozone reading.
Reading from each station must be combined to represent seasonal and yearly
averages for that location. To develop global averages, station values must be
locally weighted and averaged. At each one of these stages, assumptions and
choices must be made which can influence the outcome of the analysis.
Ground Based Global Ozone Depletion Estimates Appear Consistent with One
Dimensional Model Predictions
Over the past several years there have been several studies conducted in an
attempt to detect any evidence of a total ozone trend (e.g. Hill et al., 1977;
Reinsel, et al., 1981; St. John et al., 1982, Angell and Korshover, 1983;
Bloomfield et al., 1983). Most recent statistical analyses have adopted a time
domain approach to estimating a global trend. The ozone value Xt,j at time t
and observing station j is represented by Xt,j = Ij ht + et,j where ht
represents a predicted global trend ... at station j; and et.j represents an
error process to account for other influences on ozone. The et,j series is
typically assumed to be an autoregressive process (e.g., Hill et al., 1977;
Reinsel et al., 1981; St. John et al., 1982). This model is fit separately to
the ozone record from each station, and a global trend estimate is obtained by
combining the station values ej. Bloomfield et al., (1983), on the other hand,
introduce a frequency domain statistical model. This model extends
variance-components analysis to the time series case and incorporates both
temporal and spatial association found in the ozone data. A key feature of
this model is the inclusion of a common global term representing natural global
variations in ozone. (World Meteorological Organization, 1986).
Reinsel et al., (1981) found an increase of 0.28% in global total ozone
over the period 1970-1978 with a standard error of 0.67%, while St. John et
al., (1982) found an increase of 1.5% with a standard error of 0.5% from
'70-'79 and Bloomfield et al., (1983) found an increase of 0.1% for the same
period with a standard error of 0.55%. Thus there is little overall support
for the suggestion of a statistically significant trend in total ozone. (World
Meteorological Organization, 1986) .
Reinsel et al. , (1985 - personal communication) have recently extended the
analysis using data through 1983. Time series models were used to obtain a
trend estimate for each station, where level shifts to account for instrument
recalibration were also included in the model for five stations
(Mt. Louis, Mt. Abu, Lisbon, Buenos Aires, and Hradec Kralove). The overall
trend estimate for total ozone change over the entire period 1970-1983, with
associated 95% confidence limits, is (-0.003 + -1.12) % per decade. (World
Meteorological Organization, 1986).
Trend analyses were also performed using the flO.7 solar flux series and
the sunspot number series separately as explanatory variables for the total
ozone series at each station. Results were quite similar in both cases, and
the overall total ozone trend estimates for the period 1970-1983 are summarized
as follows, (World Meteorological Organization, 1986):
(-0.00 + 1.12) % per decade with no solar effect in model
(-0.17 + 1.10) % per decade with flO.7 solar flux in model
(-0.14 + 1.08) % per decade with sunspot series in model
-------
5-82
The £10.7 solar flux series (as well as the sunspot series) was found to be
mildly related to total ozone overall, with the estimated effect of flO.7 solar
flux on total ozone (averaged over 36 stations) equal to (0.63 -I- 0.53)% ozone
change per 100 units of F10.7 solar flux. This estimate corresponds to about a
one percent change in total ozone from solar cycle minimum to maximum. (World
Meteorological Organization, 1986).
These analyses all indicate no significant overall trend in total ozone
during the fourteen year period 1970-1983, and suggest a mild relation between
total ozone and flO.7 solar flux. The trend estimates are about 0.2% per
decade more negative with the inclusion of data for 1983 than comparable
estimates based on data through 1982. (World Meteorological Organization,
1986).
A major question of the statistical analyses has been the general lack of
global coverage of the ground-based observations suggesting possible spatial
biases. For the most recent trend estimates given above by Reinsel et al.,
(1985, personal communication). [Exhibit 5-58] shows a plot of the trend
estimates as a function of latitude. Altogether, there does not seem to be any
latitudinal effect, but if we examine this diagram by region we see an
interesting pattern. For example, all of the North American stations are below
the Indian network as are 6 of 7 European stations. While the analysis of
Reinsel et al., (1981) takes this type of regional networking into
consideration, it suggests that more consideration should be given to the
representativeness of the data set. (World Meteorological Organization, 1986).
In addition, it is clear that there is very poor coverage in northern
latitudes, with no stations in the sample significantly above 60°N. Coverage
in the southern hemisphere is worse.
Analysis of Ozone Trends at Different Altitudes with Ground Based
Ins truments
Although there have been several recent analyses of Umkehr data (eg Angel
and Korshover, 1983b; Reinsel et al., 1983; Bloomfield et al., 1982), these
have been limited in that they did not consider the impact of stratospheric
aerosols on the observations. This has been discussed by Deluisi (1979) and
Dave et al., (1979) and it has been concluded that aerosols tend to induce
significant negative errors in the Umkehr measurements in the uppermost layers
7-9, with the largest percentage error occurring in layer 9. (World
Meteorological Organization, 1986).
Based on this, Reinsel et al., (1984) have completed a statistical analysis
of the Umkehr data where atmospheric aerosols are taken into account. In the
statistical trend analysis, time series models have been estimated using
monthly averages of Umkehr data over the past 15 to 20 years through 1980 at
each of 13 Umkehr stations and at each of the five highest Umkehr layers, 5-9,
which cover an altitude range of approximately 24-48 km. The time series
regression models incorporate seasonal, trend, and noise factors and an
additional factor to explicitly account for the effects of atmospheric aerosols
on the Umkehr measurements. At each Umkehr station, the explanatory series
used in the statistical model to account for the aerosol effect is a 5 month
-------
5-83
EXHIBIT 5-58
Ozone Trend Estimates by Latitude
I
i
0
0.4
0
ooo
0 0.2
oooo
o
oooooo
00000 QQ
00
oooo
00 -02
ooo
0
-0.4
oo
-
1
A
*
'• !
1 J N
H** *%E
N
A S E E N
E
N
N NE E
H
A
1 1 11 1 1 L
60 -40 -20 0 20 40 60 80
LATITUDE
A AUSTRALIA 1 INDIA N NORTH AMERICA H HAWAII
E EUROPE J JAPAN S SOUTH AMERICA
Recent ozone trend estimates from ground-based observation networks.
Horizontal axis shows latitude of measurement. Legend identifies each
site. Vertical axis shows histogram of trend estimates.
Source: World Meteorological Organization, (1986).
-------
5-84
running average of the monthly atmospheric transmission data at Mauna Loa,
Hawaii, the only long running aerosol data available. A random effects
model is used to combine the 13 individual station trends for each Umkehr
layer. The analysis indicates statistically significant trends in the
upper Umkehr layers 7 and 8 of the order of -0.2 to -0.3% per year over the
period 1970-1980, with little trend in the lower layers 5 and 6. (World
Meteorological Organization, 1986).
The results are [repeated here and] shown graphically in [Exhibit
5-59] (Reinsel et al., 1983) where we have added, for comparison numerical
model calculations from Wuebbles et al., (1983). We see that there is
substantive agreement between the observations and the model calculations.
(World Meteorological Organization, 1986). Readers may also wish to refer
back to Exhibit 5-35 for a 2-D comparison.
There are several points to be raised on these results of the Umkehr
analysis. The first is that the results, including the sign, are very
sensitive to the inclusion of a stratospheric aerosol impact (i.e. Reinsel
et al., 1983, 1984). For this data record, the major impact is due to the
volcanic eruption at Mt Agung in 1963 and to lesser extent that of Tierra
Del Fuego in 1974 and possibly Mt. St. Helens in 1980. The use of a single
station such a Mauna Loa to account for the aerosol on a global basis is
fraught with difficulty and great care must be taken on the interpretation
of the results. This was evidenced most recently by the events of the
volcanic eruption of El Chichon. Attempts (DeLuisi, personal
communication) to consider this even within the framework of the previous
analysis have not been free of difficulty. One suggestion by DeLuisi is
that there existed an actual decrease of ozone associated with the volcanic
debris, possibly due to heterogeneous chemistry or injected chlorine, but
this is still quite uncertain. Considerably more work will be required
before we will be able to utilize the Umkehr data through the El Chichon
event with some confidence. (World Meteorological Organization, 1986).
Another point for consideration is the global representativeness of
the 13 station network, an element touched on in the total ozone trend
section. For the Umkehr data, Reinsel et al., (personal communication)
have examined the spatial sampling by examining the approximate 4 year
period of the global SBUV data. Their results are presented in [Exhibit
5-60] where the trends over the period November '78 - April "82 have been
determined from SBUV zonal averages. Superposed on these curves are the
values determined in 10° x 10° longitude/latitude boxes from the SBUV data
that includes the Umkehr site. In layer 8, for example, we see that the
North American and European stations are biased on the high side of the
curve and that Japanese stations tend to bring the overall average into
line. Thus, the overall results can be very sensitive to the availability
of tiie stations. This is taken to extreme in the Southern Hemisphere where
we see that the Australian station happens to coincide with the relative
peak in the zonal average. Because of this fortuitous sampling the overall
station average is rather close to the total SBUV area weighted trend.
That the ground-based results are so sensitive to the spatial sample is, of
course, precisely why the NOAA operational satellite ozone measurement
program was initiated. This will be discussed further below. (World
Meteorological Organization, 1986).
-------
5-85
EXHIBIT 5-59
Changes in Ozone from 1970 to 1980:
Umkehr Measurements and Model Calculations
LYH
MB
9 H
REINSEL ET AL. (1984)
WUEBBLES £7" XU. 11983)
A REINSEL ET AL. (1984)
1-2
24
4-8
8-16
16-32
-6 -5 -4 -3 -2 -1
Changes in ozone by altitude for 1970 to 1980. The data "analysis
indicate statistically significant trends in the upper Umkehr layers 7
and 8 of the order of -0.2 to -0.3 percent per year over the period
1970-1980, with little trend in the lower layers 5 and 6.
Source: World Meteorological Organization, (1986).
-------
5-86
EXHIBIT 5-60
SBUV Zonal Trends Estimates Versus "Umkehr Station Blocks'
LAYER 9
0.0
g-os
H-vo
- 1 5
-20
1 0
§ 0.5
s
/-OS
-1.5
-80
1 0
05
0 0
0 5
1.0
- 80 - 60
1 0
0 5
0 0
-0 5
- 1 0
A AUSTRALIA
E EUROPE
N N
^^ — ~N~
-40 -20
0
LAYER 5
20
40
60
J
-90 -60 -40 -20 0 20 40 60 80
LAYER 8
80
•80 -60 -40 -20 0
LATITUDE
1 INDIA
J JAPAN
20 40 60 80
N NORTH AMERICA
S SOUTH AMERICA
Ozone trend estimates for November 1978 to April 1982, as determined
by SBUV data, are indicated by solid line. Superimposed letters
indicate results from Umkehr stations .
Source: World Meteorological Organization, (1986).
-------
5-87
As the final element in this section we discuss the inclusion of a solar
flux variation within the trend analysis. For the umkehr data, Reinsel et al.,
(personal communication) have included the flO.7 cm solar radio flux as an
additional independent variable. (World Meteorological Organization, 1986).
For each umkehr layer, 5 to 9, and for a given Unkehr station, the nodel was
used:
ext
Where
Y = Monthly average for month t of a station's observations
at a given layer
S = seasonal component (annual and semi-annual)
xt = 0 to t < T (T denotes 12/1696)
= (t - T)/12 for t > T
e = annual rate of change parameter '(trend)
V_ = a smoothed version of the transmission data at Mauna Loa
nl = a parameter providing an empirical measure of the aerosol
effect on Umkehr data
V = monthly mean of 10.7 cm solar radio flux (2800 MHz)
n2 = a parameter for an empirical measure of the solar effect
on Dnkehr data
N = an autocorrelated noise term, modelled as an
autoregressive process to account for non-independence of data
m = intercept which is very close to the average value
A term to account for a shift in mean level due to instrument recalibration
was also included in the model for some stations, as described above. (World
Meteorological Organization, 1986).
The trend estimates including the solar flux series are shown in [Exhibit
5-61] as the solid triangles (Reinsel et al., personal communication). We see
that there is very little impact on the decadal trend with this term added. The
overall estimates for the regression coefficients of the solar flux series with
accompanying 95 percent confidence intervals are 0.81 + 2.56, 0.46 + 1.80, 2.04
+1.32, 1.53+0.78 and 1.18 + 0.86 percent, respectively, for layers 9 through
5. These coefficient estimates represent percentage change in ozone per 100
units change in solar flux. The solar effect is largest in layer 7, and
statistically significant in both layers 7 and 6. The estimates correspond to a
solar effect on ozone from solar cycle minimum to maximum of about 1.3, 0.8,
3.4, 2.5, and 2.0 percent respectively, for layers 9 through 5. (World
Meteorological Organization, 1986).
-------
5-88
EXHIBIT 5-61
Ozone Trend Estimates and 95% Confidence Intervals
95% Interval (%/yr.) 95% Interval (%/yr.)
Layer KM (Without Intervention) (With Intervention)
Above 6B 35+ -0.05 ± 0.38 0.22 + 0.56
6B
6A
5B
5A
4B
4A
3B
3A
2B
2A
ID
1C
IB
1A
30-35
25-30
20-25
15-20
10-15
5-10
0-5
0
0
0
0
-0
-0
-0
-0
-0
-0
0
1
1
1
.04
.22
.15
.05
.07
.21
.33
.56
.30
.17
.93
.44
.43
.72
± o
± o
± o
± o
± o
± o
+ 0
± o
+ 0
± o
+ 1
± 1
± o
± 1
.33
.31
.17
.18
.15
.22
.25
.31
.53
.67
.04
.23
.87
.17
0
0
0
-0
-0
-0
-0
-0
-0
-0
0
0
0
0
.27
.46
.18
.02
.16
.30
.48
.71
.48
.64
.08
.57
.66
.75
+
±
±
±
±
±
±
±
±
±
±
±
+
±
0
0
0
0
0
0
0
0
0
0
0
0
0
0
.54
.51
.21
.27
.22
.21
.26
.27
.49
.75
.88
.74
.53
.83
Combined ozone trend estimates in the various layers along with their 95%
confidence limits. We see that with and without the data intervention at
the 4 Canadian sites the negative trends in the lower stratosphere appear
statistically significant and of the same magnitude, about -5% per decade.
In the lower troposphere, however, the values are very different although
they remain positive.
Source: World Meteorological Organization (1986).
-------
5-89
It is not at all clear as to Why the solar flux tern should have a
significant regression coefficient in layers 7 and 6 and not in layers 9 and 8,
and rises serious questions on the effect of the solar flux variations. (World
Meteorological Organization, 1986).
Balloon Data for Ozone Trends at Different Altitudes
In a recent update of ozone variations determined from balloonsondes, Angell
and Korshover (183) determined that in the tropospheric layer of north temperate
latitudes, 2-8 km, the data suggest a 12% increase in ozone between 1970 and
1981. This is accompanied by a 1-3% decrease in the region 16-32 km. Since
then, several on-going studies have focused on the quality of the ozonesonde
data for trend detection (Tiao et al., personal communication; Logan, 1985) and
the discussion is presented here with the author's kind permission. Formal
publication is planned for the near future. From Tiao et al., Ozonesonde data
from 13 stations have been processed to obtain monthly averages of ozone in 14
fractional umkehr layers, (1A, IB, 1C, ID, 2A, 2B, 3A, 3B, 4A, 4B, 5A, 5B, 6A,
6B), (e.g. [Exhibit 5-61] and an additional layer above 6B. For each station,
the daily sonde data (in partial pressure) were first integrated into ozone
readings (in Dobson units), within each layer, and monthly averages for each
layer were then computed from the integrated readings. The data were screened
to meet the following criteria: (World Meteorological Organization, 1986).
The correction factor was between .8 to 1.3 for ECC and
.8 to 1.4 for Brewer.
The balloon reached a burse level of 15.8 mbar (top of
layer 5B).
There were no zero partial pressure readings recorded
in each daily sondes.
The total ozone reading for the daily sonde data had a
nonzero value.
The station locations, data span and methods of measurement are given in
[Exhibit 5-62] (Tiao et al., personal communication), where the Canadian
stations changed from the Brewer system to the ECC at the designated times.
(World Meteorological Organization, 1986) .
One of the first elements examined were the correction factors for the
various instruments and, as examples of this parameter, we present in [Exhibit
5-63] (Reinsel et al., personal communication), the results at Goose Bay, and
Hohenpeissenberg. At Goose Bay we see that the individual months show large
variations with a small tendency for decrease till 1980 where the change to ECC
was effected. The impact of this change will be discussed further below. For
Hohenpeissenberg the diagram also shows some interesting month-to-month
variations and we note, in particular, the tendency for the corrections to
increase during the first few years followed by the strong minimum in the late
'70's. (World Meteorological Organization, 1986).
The cause of these tendencies in the correction factors is unclear and may
be related to instrument manufacture, personnel changes or changes in the Dobson
-------
5-90
EXHIBIT 5-62
Ozone Balloonsonde Stations
Station
Data Span
Methods
Hohenpeissenberg
Biscarrosse
Lindenberg
Pay erne
Aspendale
Churchill
Edmonton
Goose Bay
Resolute
Wallops Island
Kagoshima
Sapporo
Tateno
1/70-2/83
3/76-1/83
1/75-2/83
9/68-12/81
6/65-5/81
10/73-1/83
10/70-12/82
6/69-12/82
1/66-1/83
5/70-4/82
1/70-12/82
12/68-12/82
3/68-12/82
Brewer
Brewer
Brewer
Brewer
Brewer
Brewer/ECC 9/79
Brewer/ECC 9/79
Brewer/ECC 12/80
Brewer/ECC 12/79
ECC
ECC
ECC
ECC
Source: World Meteorological Organization (1986).
-------
5-91
EXHIBIT 5-63
Correction Factors for Balloonsonde Measurements
GOOSE BAY
1.4
1.2
1.0
0.8
**••"" v. .*. .*- ..
• • • .*..•••
. .. •» . . f
65 70 75 80 85
HOHENPEtSSENBERG
1.4
1.2
1.0
08
65 70 75 80 85
Shown for Goose Bay and Hohenpeissenberg.
Source: World Meteorological Organization, (1986).
-------
5-92
system. The Major point Is that we can not expect the correction factors to be
random about some average value and that we will have to consider, in detail,
the possible impacts of these variations. As Hilsenrath et al., (1984) have
indicated, this brings into question whether or not the factors should be
applied as they are, as a percentage change to the profile, or in some height:
dependent manner. (World Meteorological Organization, 1986).
The above notwithstanding, trend estimates (1970) have been obtained from
the monthly averages using standard models reported previously with and without
an intervention at the 4 Canadian sites for the changes of measurement method.
As a cross-validation an overall trend estimate for each station was obtained by
calculating a weighted average of the individual estimates of the 15
layers.These estimates may then be compared with the corresponding trend
estimates obtained from the Dobson total ozone reading on the ozonesonde file.
The results are shown in [Exhibit 5-64] (Tias et al., personal communication).
For the nine non-Canadian stations, the trends from weighted averages are in
close agreement with those from Dobson total ozone readings on the sonde file.
For Churchill, Edmonton and Resolute, the agreement seems much better without
the intervention level adjustments. This is in direct contrast to what we would
expect and reflects, again, the question as to whether the correction factors
between the Brewer Mast and EGG sondes are applied in a consistent manner.
Finally, in [Exhibit 5-61 above] (Tias et al., personal communication) we
present the combined ozone trend estimates ([Exhibit 5-64]) in the various
layers along with their 95% confidence limits. We see that with and without the
data intervention at the 4 Canadian sites the negative trends in the lower
stratosphere appear statistically significant and of the same magnitude, about
-5% per decade. In the lower troposphere, however, the values are very
different although they remain positive. Thus, there is evidence to suggest the
existence of overall negative trends at layers 3A and 3B, and perhaps also at 2B
and 4A. (World Meteorological Organization, 1986).
The results for the troposphere have recently been examined by Logan (1985)
and her analysis indicates that the surface ozone at mid-latitudes displays two
modes of seasonal behavior: a broad summer i»aTriimn» within a few hundred
kilometers of populated and industrialized regions in Europe and the United
States; and a summer na-gimm in sparsely populated regions remote from
industrial activity, in Canada and Tasmania, for example. She argues, in
addition, that the current data base for different regions, in combination with
limited historical data indicates that summertime concentrations of ozone near
the surface in rural areas of Europe and the central and eastern U.S. may have
increased by approximately 10-20 ppb (30-100%) since the 1940's. The seasonal
cycle of ozone in the middle troposphere over Europe, the United States, and
northern Japan is very similar to that at the surface, with a summer maximum,
but it is quite different from that at 300 mb, which is characterized by a
iBa-gTimim in spring. There is good evidence for an increase in ozone in the
middle troposphere over Europe during the past 15 years, and weaker evidence for
a similar increase over Northern America and Japan. From this she argues that
the summer ma-sriimim in ozone and the observed trends are due to photochemical
production associated with anthropogenic emissions of NOx hydrocarbons and CO
-------
5-93
EXHIBIT 5-64
Ozone Trend Estimates (% Per Year) As Determined from Balloon
Ozonesondes Versus Those Determined from Dobson Measurements
(Tiao, et al., personal communication)
Station
Ozonesonde
Total Ozone
Readings
on Sonde File
Aspendale
(6/65-5/82, Brewer)
Biscarrosse
(3/76-1/83, Brewer)
Hohenpeissenberg
(1/70-2/83, Brewer)
Lindenberg
(1/75-2/83, Brewer)
Payerne
(9/68-12/81, Brewer)
Kagoshima
(1/70-12/82, ECC)
Tateno
(3/68-12/82, ECC
Sapporo
(12/68-12/82, ECC)
Wallops, Isl.
(5/70-4/82, ECC)
Churchill
(10/73-1/83, Brewer/ECC 9/79)
Edmonton
(10/70-12/82, Brewer/ECC 9/79)
-.115
(.055)
-.416
(-1U)
-.174
(.052)
-.287
(.128)
-.149
(.045)
.136
(.090)
.085
(.082)
.148
(.103)
.034
(.075)
.473*
(.118)
.405*
(.095)
-.162
(-075)
-.587
(.185)
-.220
(.088)
-.269
(.266)
-.181
(-074)
.215
(.155)
-.055
(.094)
.203
(.138)
.037
(.122)
-.310** .282
(.197) (.234)
.027** .360
(.152) (.149)
-------
5-94
EXHIBIT 5-64 (Continued)
Ozone Trend Estimates (% Per Year) As Determined from Balloon
Ozonesondes Versus Those Determined from Dobson Measurements
(Tiao, et al., personal communication)
Station
Ozonesonde
* Without inteirvention adjustment.
** With intervention adjustment.
Source: World Meteorological Organization (1986).
Total Ozone
Readings
on Sonde File
Goose Bay
(6/69-12/82
Resolute
(1/66-1/83,
, Brewer/ECC 12/80)
Brewer/ECC 12/79)
.029*
(.060)
- . 194*
(.045)
-.095**
(.077)
- . 240**
(.070)
-.123
(.099)
-1.64
(.074)
-------
5-95
from combustion of fossil fuels. A strong seasonal variation in ozone observed
at Natal, Brazil (6°S) may also result from emissions of NOx and hydrocarbons,
in this case from agricultural burning. Maximum concentrations at Natal are
similar to values found at mid-latitudes in summer. (World Meteorological
Organization, 1986).
With the limited network of ozonesonde stations, however, the question
remains as to whether the tropospheric ozone increase is due to local pollution
effects or is symptomatic of a more general atmospheric behavior. (World
Meteorological Organization, 1986).
Ground-Based and Satellite Data for Antarctica
Recently, Farman et al. (1985) have published the data, displayed in
[Exhibit 5-65] , showing a large secular decrease in total ozone for the month of
October over their station at Halley Bay, Antarctica [76 degrees south]. Since
1957 the mean total ozone for the month of October over Halley Bay has decreased
by about 40 percent with most of the decrease occurring since the mid-1970's.
Since 1978, satellite data from the Nimbus & TOMS and SBUV instruments confirm
these findings. Along with data in the early 1970's from the Nimbus 4 BUV
instrument, the satellites show that in the southern hemisphere total ozone is
generally at minimum during the springtime over the Antarctic continent (or
generally poleward of about 70 degrees south). This minimum is surrounded by a
range of maximum total ozone values centered at about 55 degrees south. The
surrounding maximum region displays significant wave structure. The minimum
often becomes distorted into an oblong shape and rotates along with the maximum.
Exhibit 5-66 shows a twelve day sequence for October of 1984 which displays a 7
day rotation period. There is a marked tendency for the minimum to be displaced
off the pole towards the direction of Halley Bay -(World Meteorological
Organization 1986).
Since 1979, the Nimbus 7 data show decreases in both the maximum and minimum
region. The largest decreases (of order 40 percent) are in the minimum region
leading to the lowest total ozone values ever recorded (less than 150
milli-atmosphere-centimeters -- Dobson units). Exhibit 5-67 (taken from
Stolarski, et al., 1986) shows a map of the mean total ozone for each of the 7
Octobers measured by the TOMS instrument. The map is a polar projection with
the outer edge at 30 degrees south latitude (Stolarski et al. 1986).
The other major feature of the data is the seasonal variation of the ozone
minimum. The minimum values of total ozone appear in the spring, after the long
polar night, at approximately the values entering the polar night. The rapid
decline then takes place during September with the minimum being reached in
October and a. rapid recovery in November when the polar vortex breaks down
(Stolarski, et al., 1986). These data indicate that some mechanisms or
mechanisms are at work in the cold southern polar night or twilight that are not
generally included in models. This clearly warrants further investigation
(World Meteorological Organization, 1986).
Alternate Hypotheses of Antarctic Depletion
Explanation of the Antarctic ozone phenomenon still remain in the category
of hypotheses. Many interesting ideas have been put forward which are, in
principle, capable of explaining parts of the observed phenomena. Further data
-------
5-96
EXHIBIT 5-65
Monthly Means of Total Ozone at Halley Bay
300
N
o
o
200
T 1 T
1 T
— OCTOBER
I - 1 - 1 - 1 - 1
I _ I I
1960
J L
1970
1980
Total Ozone above Halley Bay in October for the years 1957 to 1984.
Source: World Meteorological Organization, (1986).
-------
5-97
EXHIBIT 5-66
Nudws 7 Antarctic Ozone Measurements: 12 Day Sequence
11 October 1984 12 October 1984 13 October 1984 14 October 1984
15 October 1984
16 October 1984
17 October 1984
18 October 1984
19 October 1984
20 October 1984
21 October 1984
22 October 1984
"Twelve-day sequence (11-22 October 1984) of TOMS measurements of
total ozone content. The data are shown in south polar projections,
with the pole indicated by a cross (SP) and Halley Bay shown by an
asterisk. Contours are every 30 Dobson units (1 DU = 10 atm cm).
The region shown extends to "45° latitude and the Greenwich meridian
is towards the top of each diagram. Shaded regions indicate total
ozone values <180 and 210 DU and >390 and 420 DU."
Source: Stolarski et al. (1986)
-------
5-98
EXHIBIT 5-67
Antarctic Ozone Measurements: Mean Total Ozone in October
1M1
1982
1983
1984
1985
"Six-year sequence of October monthly means of total ozone. South polar
projections, with the pole indicated by a cross and 30°S latitude by a dashed
circle. The Greenwich meridian is towards the tope of each panel. Contours are
every 30 DU. The shaded regions indicate monthly mean total ozone amounts of
<240 and >390 DU."
Source: Stolarski et al. (1986).
-------
5-99
are clearly necessary to differentiate among competing ideas before a scientific
consensus can be reached on the cause of the changes. The first concept put
forward was that the decrease was caused chemically by the action of chlorine
which is known to have increased due to chlorofluorocarbon release (Farman et
al. 1985; Solomon et al. 1986; McElroy et al. 1986). For this explanation to
work, the cold polar night and the polar stratospheric clouds must be invoked to
modify the previously known chemistry in a major way. The rate limiting
radical, CIO, must be present in the part per billion range (almost 100 times
what would have been assumed based on previously known chemistry) in the lower
stratosphere during September and October. Bromine has also been introduced as
a possible enhancement for the chlorine theory. The chlorine theory is
susceptible to test by the microwave instrument which is in place at McMurdo in
the spring of 1986. The primary aspect of this hypothesis is that the driving
force, chlorine chemistry, has a known secular variation.
Another primarily chemical hypothesis is that the depletion is due to
nitrogen oxide (NOx) chemistry which is varying due to solar cycle variations in
the production of Nox in the thermosphere. This idea requires the transport of
this excess NOx downward such that polar night and twilight values are
increasing to show a maximum a number of years after solar maximum. For this
idea to work, NOx would have to be high, CIO normal, and the effect should show
an 11 year cycle. Thus the major problem is the lack of an apparent cyclic
behavior in the Halley Bay data.
A third class of hypotheses is that the depletion is caused primarily by a
modification of the climatological pattern of the wind fields in the southern
hemisphere. One suggestion is that increased aerosols from the El Chichon
eruption and their associated stratospheric heating lead to lifting of the
atmosphere and low total ozone values (Tung et al., 1986). Analysis of the data
indicates that there are variations that exist that are superimposed on the
secular decrease. These year-to-year differences may be due to variations in
atmospheric dynamics. Furthermore, secular decrease in Antarctic stratospheric
temperature has accompanied the ozone decrease. Present understanding would
seem to indicate that these are not a result of the ozone decrease. Thus, it is
possible that a secular change in the climatology of the south polar region is
taking place. A test of these ideas would be that the chemistry would be
relatively normal but analyses of temperature and constituent data should
clearly show effects of modifications in transport properties. The primary
problem with this hypothesis is to trace such modifications back to a cause that
shows an apparent secular variation of the time period under consideration.
Several satellite systems, Firos, Nimbus 7, and NOAA9, exist for measuring
column ozone at different latitudes and global ozone. The TOVS system on Tiros,
and TOMS and SBUV-2 on Nimbus 7 and SBUV on the NOAA series. SBUV-2 can also
measure ozone at various altitudes.
All satellite systems rely on interpreting irradiances as ozone and require
corrections for aerosols and instrument drift. Thus, the major problem in
determining ozone trends from these instruments is maintaining the calibration
of the systems.
Exhibit 5-68 shows global ozone measurements for the TOVS.
-------
5-100
EXHIBIT 5-68
Global (60-N-60-S) Monthly Total Ozone
Determined from NOAA TOYS System
310
300
290
280
270
MAY OCT MAR AUG JAN JUN NOV APR SEP FEB JUL DEC MAY
1979 1980 1981 1982 1983 1984
Ozone trend estimates shown for global scale.
Source: World Meteorological Organization (1986).
-------
5-101
The main problem in this system is that the TOYS system requires regression
against the ground-based Dobson network. These data seem to indicate a drop in
ozone, perhaps attributable to El Chichon. The data record is too short to
determine if the trend is a short-term fluctuation or part of a longer trend.
Nimbus 7 Results
Results from Heath's analysis of Nimbus 7 have not yet been published, but
results have been mentioned by NASA at Senate hearings and shown at several
meetings.
Heath shows a .56+19 percent per year global ozone decline from 1978 to
1984 (Heath, personal communication). Heath's interpretation of this trend is
qualitatively consistent with seasonal and latitudinal predictions in Isaksen's
two-dimensional time-dependent runs, although of greater magnitude. Exhibit
5-69 shows the 1978 to 1984 estimates of depletion from Isaksen's model and
according to Heath's interpretation of the Nimbus 7 data. Clearly the pattern
is similar, although Heath's interpretation of the satellite data suggests
depletion eight times greater at 80°N than Isaksen's model. Isaksen's estimates
of Antarctic ozone (without special chemistry), however, are smaller than Arctic
estimates, contrary to Heath's data.
One problem with interpreting data is the shortness of the satellite data.
It is not clear whether these "trends" are long-term in nature, or short-term
fluctuations. Additional analysis is needed and 1985 and 1986 is needed
quickly.
Use of Antarctic and Satellite Measurements in Risk Assessments
The published Antarctic and yet unpublished satellite data present a
difficult challenge to us in this risk assessment. Clearly, if the Antarctic
trends are chemical in origin and extrapolatable to the world, or if the Nimbus
7 data have been correctly interpreted and portend a chemically induced trend,
the risks of depletion are significantly greater than predicted in models being
used in this assessment. Given the disequilibrium between current emission and
concentrations of CFCs, if these results portend the future, depletion can be
expected to increase with a large cutback in depleting chemicals.
In our judgment, however, it is premature to reach the conclusion that these
observations can be used for assessing global trends. The scientific analysis
to support such a judgment is incomplete. Until the analysis reaches the stage
where the Antarctic situation can be extrapolated to the rest of the world or
until the Nimbus 7 data is shown to be real and representative of the rates of
depletion in the future, these data should be treated with caution. Thus, for
decisionmaking purposes we propose that current models be considered the
appropriate tools for assessing future risks.
The satellite and ground-based Antarctic data do, however, raise a "blinking
yellow alert," which may require reassessment of risks. Because both sets of
data present sufficiently stark pictures of a possible future efforts need to be
made on an expedited basis to better resolve our understanding of these data
sets. The Nimbus 7 data, already global in character, need the earliest
analysis so that resolution of its implications can be reached. In particular,
-------
5-102
EXHIBIT 5-69
Preliminary Ozone Trend Data (Heath
versus 2-D Model Results) (Isaksen)
zu-
18
16
14
Ozone 12
Depletion 10
W 8
6
4
2
0
17.4
\
,'-
', •.
-/
*'/
..;
„"'
6.0
rv
J;
">
//eo//i
2.4
2.4
ret
°^ o.o 1^1 fM |
Latitude: South -80 -60 -40
Pole
.0-
Ozone
Depletion 9.5-
0
-20
Equator +20
1.8
^1
+40
Isaksen
A *•
u.:
>
0.4
'%
'-
7.2
3.0
['•- 1
— 1—
'$
%>
+60 +80 Non)
Pole
0.7
0.4 0.4
0.3
V1
.,''
Latitude: South -80 -60 -40
Pole
0.3
.,'• ,
, \
-20
0.2
t
&
'•'.,
\ '':
'':\
Equator +20 +40
/•^'
"•":""
'',
'-,',_'
\ '';
0.9
s
"?\
$
•$
'\'*
".,"'
+60 +80 Nort
Pole
Predicted ozone changes from Isaksen's 2-D model are qualitatively
consistent with preliminary data from Heath.
Source: Heath (personal communication); and Isaksen and Stordal
(1986).
-------
5-103
a very strong effort must be made to expedite the flow of data from satellites
to analysis to peer review. The flow of data must be as close to "real time" as
possible, not a year or two behind.
-------
5-104
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