450R84505
REPORT OF THE
ACID RAIN PEER REVIEW PANEL
JULY 1984
WILLIAM A. NIERENBERG, CHAIRMAN
FOR
DR. GEORGE A. KEYWORTH, II
SCIENCE ADVISOR TO THE PRESIDENT
AND
DIRECTOR
OFFICE OF SCIENCE AND TECHNOLOGY POLICY
WASHINGTON, D.C. 20500
U.$. Environmental Protection Agency
fleeioii V. Library
230 South Dearborn Stroet
Chicago, Illinois 60604
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U'S' Env'ronmenta( Protection Agency
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ACID RAIN PANEL REPORT
TABLE OF CONTENTS
Executive Summary ii
Acknowledgments vi
I - Introduction 1-1
II - General Comments on the MO I Reports II-l
III - General Comments on Acid Rain III-l
IV - Research Recommendations IV-1
V - Review of Work Group 1 Report - Impact Assessment . . . V-l
VI - Review of Work Group 2 Reports - Atmospheric
Sciences and Analysis VI-1
VII - Review of Work Group 3B Report - Emissions,
Costs and Engineering Assessment VII-1
Appendix 1 - Panelists' Institutional Affiliations and
Scientific Disciplines Al-1
Appendix 2 - Charges of the Panel Charter A2-1
Appendix 3 - Work Group Structure for Negotiation of a
Transboundary Air Pollution Agreement A3-1
Appendix 4 - Materials Provided to the Panel A4-1
Appendix 5 - Benefit-Cost Analysis Applied to the Acid Rain
Problem A5-1
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ACID RAIN PANEL REPORT
EXECUTIVE SUMMARY
In January 1982, the Office of Science and Technology Policy asked
Professor William A. Nierenberg, the Director of Scripps Institution of
Oceanography, to assemble and chair a scientific panel on acid rain. He
agreed and a panel of nine scientists was formed shortly thereafter. They
were chartered to perform three tasks.
The first was to complete a peer review of the scientific basis
relating to acid deposition in Eastern North America performed by three
U.S.-Canadian scientific work groups. These bi-lateral studies were
called for by the August 1980 Memorandum of Intent between the U.S.
and Canada on transboundary air pollution. The peer review of each of
these three studies is the subject of a separate chapter in this report.
The peer review finds the bilateral reports to be basically sound
and thorough. The scientists reviewed a large amount of material, both
published and unpublished, but there is a tendency toward recitation
rather than synthesis and integration. The reports often depend too
much on unpublished data, but this may reflect the growing but still
incomplete state of knowledge.
Work Group I reviewed a huge amount of data, which was often in-
complete or conflicting, in its long report. But its message was weakened
considerably because it did not comply with its fundamental charge to
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examine squarely the strength of the link between acid deposition and
chemical and biological ecological changes. Work Group 2 produced a
comprehensive series of reports but greatly overemphasized the present
role of computer models for understanding long-range transport. Work
Group 3B presented & large amount of data on emissions, control techniques
and costs, but enclosed it in a report which is difficult to read and
harder still to interpret.
The biggest failing of these reports was that the two parties of
Work Group 1 were unable to agree on a preliminary acceptable deposition
rate. In view of the importance of this subject and the feasibility
of establishing a value (deductible from the MOI reports themselves), we
recommend that Work Group 1 reconvene for this express purpose.
The second task the Panel was asked to perform was to provide further
research and monitoring recommendations to reduce uncertainties in the
scientific and technical knowledge regarding acid deposition. The panel
finds that current scientific understanding of acid deposition is still
highly incomplete. In order to begin to eliminate the major gaps most
efficiently, it is recommended that highest priority be given to research
on quantifying the effects of acid deposition (both wet and dry) on the
total ecological system, distinguishing between the ecological effects of
dry and wet deposition of sulfur and nitrogen, differentiating the en-
vironmental effects of acid deposition from those of natural stresses,
measuring dry deposition ac selected representative sites in eastern North
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America, and applying tracer techniques on a broad scale to improve our
knowledge of the source-receptor relationship. At lower-priority, research
should include determining quantitatively the detailed mechanisms for the
atmospheric oxidation of SC^ and the oxides of nitrogen (NOX), improved
refinement of computer models of long-range transport, better data on
emission of SC^ and NOX, evaluating new or improved control technologies
for SC>2 and NO , and economic analyses of costs and benefits.
Up to 1984, the way in which the Federal Government conducted its
research program on acid rain was disappointing. A greater portion of the
funds should be allocated outside the Federal laboratories to attract new
research groups, disciplines and approaches. Particular emphasis needs
to be placed upon supportive research to understand the ecological con-
sequences of both wet and dry acid deposition.
Finally, the panel was asked to provide an independent assessment of
the uncertainties in available scientific and technical information on
which recommendations of the U.S.-Canadian Work Groups are based. In
response to this charge, general comments, findings, and recommendations
concerning acid deposition that encompass policy matters as well as science
were developed. Chapter III of this report contains these general comments.
In summary, the panel views the acid rain problem as follows:
Acid deposition belongs to a socially very important class of problems
that only appear to be precisely soluble by a straightforward sum of ex-
isting technological and legislative fixes. This is deceptive. Rather,
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this class of problems is not permanently solved in a closed fashion, but
must be treated progressively. As knowledge steadily increases, actions
are taken which appear most effective and economical in the light of in-
creasing understanding.
Large portions of eastern North America are currently being stressed
by wet deposition of acids, by dry deposition of acid-forming substances,
and by other air pollutants such as ozone, metals, and organics. Annual
wet deposition of acidity in the northeastern United States and portions of
Canada is at lease 10 times that of remote areas. Acid deposition has
altered the chemistry and biology of aquatic and terrestrial ecosystems of
eastern North America. The principal agent altering the biosphere acidity
is traceable to man-made sulfur dioxide (802) emission. The Clean Air Act
of 1970 has reduced the emission of SO? considerably, and may continue to
do so. Nevertheless, the ecological problems that clearly result from
man-made acid emissions are sufficiently well substantiated that ad-
ditional reductions are required to prevent even more consequential
environmental effects. The panel recommends that cost effective steps
to reduce emissions begin now even though the resulting ecological
benefits cannot yet be quantified.
There exist large uncertainties in every aspect of acid deposition —
emission, transport, transformation, and eventual deposition, interaction
with the biosphere, and economic consequences. Nevertheless, when all
the converging partial indicators are considered, it becomes clear that
acid deposition is a problem for which solutions should be sought now,
and further remedial steps taken.
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ACID RAIN PANEL REPORT
ACKNOWLEDGMENTS
The panel wishes to express its appreciation to Mrs. Julie Rahn, a
consultant to the panel, for her efforts in improving the readability and
clarity of this document. Her many hours of work have made this report a
cohesive whole, rather than the many separate pieces she started with.
Typing of the report and its many drafts, as well as logistics support
for the October 1983 meeting, was provided by Mrs. Shirley Bonsell and her
staff—Mrs. Judi Dubaldi, Mrs. Gail Rainey and Ms. Susan Romano—of the
Science Research Laboratory at West Point.
Lastly, we thank Major John K. Robertson, Executive Secretary, for his
time and work on behalf of the panel. His efforts in supervising
production of drafts of this report, collating comments, proofreading,
negotiating word changes, and attempting in vain to enforce deadlines are
appreciated.
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ACID RAIN PANEL REPORT
I - INTRODUCTION
In January 1982, in anticipation of the March 1982 publication of the
Work Group reports produced under the United States-Canadian Memorandum of
Intent (MOI) on Transboundary Air Pollution, Dr. George A. Keyworth, II,
Science Advisor to the President, asked Dr. William A. Nierenberg, Director
of Che Scripps Institution of Oceanography, to chair a panel to review the
final MOI reports. After consulting members of the National Academy of
Science and the National Academy of Engineering, Dr. Nierenberg nominated a
panel of scientists and engineers to the task. In May 1982, Dr. Nierenberg
approached the nominees and asked them to serve. The panelists, their
institutional affiliations, and scientific disciplines are listed in
Appendix 1.
In August 1982, formation of the Acid Rain Peer Review Panel was
announced in the Federal Register. The charges in the charter given to the
panel by the Office of Science and Technology Policy in that announcement
are reproduced in Appendix 2.
Prior to its first meeting, the panel received the only MOI report in
final form, that of Work Group 33; the table of contents for each of Che
draft Work Group reports (1, 2 and 3B); the table of contents for any
supplementary materials produced by the Work Groups; and the United SCates
and Canadian membership lists for the Work Groups. (The organization and
terms of reference of the MOI Work Groups are given in Appendix 3.)
The panel's first meeting in Washington, D.C. on 7 and 8 October 1982
consisted of background briefings by the United States co-chairmen and some
American members of the three Work Groups. Dr. Keyworth addressed the
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ACID RAIN PANEL REPORT
panel, reaffirming its Charter. Officials from EPA and the State
Department also addressed the panel regarding coordination of the United
States Work Groups and negotiation of the transboundary treaty. The
Executive Director of the Interagency Task Force on Acid Precipitation
briefed the panel on the task force's organization and mission. Because
agreement seemed imminent on the Work Group 1 and 2 reports, the panel
agreed to start reviewing the current draft reports of these groups.
Between the October meeting and a second meeting scheduled for 1 and 2
December 1982, draft final documents were obtained from the American
co-chairmen of the Work Groups, copied and disseminated. The Work Group 1
report was marked by the Work Group to indicate which sections were still
in question. A list of materials provided to panelists for review and
background reading is furnished in Appendix 4.
Further meetings of the panel were held on 1 and 2 December 1982 in
Washington, D.C., 27-29 January 1983 in La Jolla, California, and 2-4 June
1983 in Washington, B.C. These meetings were held to discuss the MOI
reports, to plan the structure and content of the panel's report, and to
begin writing drafts. In March 1983 the panel was provided with the final
versions of the Work Group 1 and 2 reports, along with a list of
differences between the final versions and the drafts they had been working
with since November 1982. A final meeting was held in West Point, New York
on 26-28 October 1983 to complete the rough draft of the panel's report.
Successive drafts were mailed to panel members for revision from November
1983 to March 1984.
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ACID RAIN PANEL REPORT
II - GENERAL COMMENTS ON THE MOI REPORTS
The panel is impressed with the efforts of the United States-Canadian
Work Groups. They faced a monumental task in reviewing and integrating the
vast amount of written material available on acid rain. Much of this
material has not yet been published in the scientific literature and is
available only as unreviewed monographs and technical reports by agencies
of both federal governments and by industrial special-interest groups.
Generally, the Work Groups have reviewed the material well, but in some
areas we feel there has been overdependence on "soft" literature (writings
which are not formally published, not peer-reviewed and not available to
the general public, such as in-house reports, personal communications, and
preprints).
We are disappointed that the two parties of Work Group 1 were unable
_ 2
to agree on a preliminary target loading for sulfate (804 ). The Work
Group agreed that no ecological or chemical effects in sensitive
fresh-water lakes and streams are observed when the sulfate loading
(deposition) is less than 17 kilograms per hectare per year (kg/ha/yr).
They also agreed that chemical and biological effects begin to be observed
in these bodies at loadings of 20 and 30 kg/ha/yr respectively.
We know that it is not possible at this time to establish a precise
loading below which the average sensitive aquatic system will be protected.
The present loading, however, is at least 10 times greater in the Northeast
than in remote areas of the world. We believe that this present loading is
too high and that a target loading should be set.
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ACID RAIN PANEL REPORT
If the figures Chat Work Group I agreed on are used, it would follow
that a decrease to 30 kg/ha/yr would serve to eliminate damage to all but
the most delicate of the fresh-water biological ecosystems. This is
equivalent to a 25% reduction in deposition. We recommend that, given the
degree of agreement to date, the two sides reconvene to develop an agreed
preliminary target loading which can be used until better target loading
values are available. We expect that the reassessment will recognize the
large annual variability of the loadings as a normal effect.
The panel feels there was an overdependence on modeling, particularly
by Work Group 2. This dependence on modeling is questionable in that the
science behind the models is still not definitive, and proper data for
verifying the models are not yet available. The extensive use of models
may not be the responsibility of the Work Groups, but of those who defined
the terms of reference for the Work Groups in the MOI.
The reports say little of dry deposition or of pollutants other than
S02« The reports describe sulfur pollution in wet deposition as the
predominant factor in acid deposition and acidification of our ecosystems.
Little mention is given to co-pollutants, or the combined effects of
multiple pollutants. Natural pollutants are ignored or mentioned in
passing (granted, little is known about their amount or role). The reports
are not well-rounded scientific documents (e.g., they do not assess
conflicting data, gaps in knowledge, strengths or weaknesses in their
conclusions, or alternate theories or explanations). Again, this may
stem from the terms of reference given to the MOI Work Groups.
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ACID RAIN PANEL REPORT
In the assessment of control strategies, material is presented which
will allow workers to begin to assess the costs of controlling emissions
and their effects (unit costs are presented, but no attempt is made at
integration). On the other hand, the panel notes a complete lack of
framework or any attempt at assessing the benefits of emission control,
perhaps because of problems in assessing the value of natural ecosystems.
The models for benefit-cost analysis presented in the MOI reports require
data for both costs and benefits.
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ACID RAIN PANEL REPORT
III - GENERAL COMMENTS ON ACID RAIN
The United States and Canada together annually emit approximately
25,000,000 tons of sulfur dioxide and a comparable amount of nitrogen
oxides. These oxides can be converted by atmospheric chemical processes
into sulfuric and nitric acids (112804 and HN03, respectively). The
emissions are large enough to increase appreciably the acidity of natural
rainfall. Rain in most of eastern North America is considerably more acid
than expected from natural processes alone. The Clean Air Act of 1970
marked the formal recognition by the United States government of the
importance of reducing emissions of sulfur and nitrogen oxides to the
atmosphere. New power plants constructed since 1970 do control such
emissions to lower levels. Such controls were a prudent first step, but
have not accomplished all that was initially intended. We recommend that
additional steps should be taken now which will result in meaningful
reductions in the emissions of sulfur and nitrogen compounds into the
atmosphere, beginning with those _steps_ which are most cost-effective
in reducing total deposition. Emission reductions are meaningful when they
produce a detectable decrease in both acidic deposition and degradation of
the biosphere.
An incomplete data base and sometimes contradictory interpretation of
these data prevent the kinds of certainty which scientists would prefer.
There are, however, many indicators which, taken collectively, lead us
to conclude that acid deposition is a problem for which solutions should be
sought. These indicators are as follows:
(1) In eastern North America, emissions of S02 and NOX from human
activities appear to be at least ten times larger than emissions from
natural processes.
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(2) A substantial fraction of such emissions returns as sulfate and
nitrate (NC>3~) in rainfall; a comparable amount returns as "dry" deposition
through surface-interaction processes which are more difficult to monitor
than "wet" deposition.
(3) In eastern North America the areas receiving the most-acid rain
are found within and close to the major source regions.
(4) Acidity (sulfate and nitrate) in wet deposition is substantially
greater in eastern North America than in areas without industrial
activity.
(5) Acid precipitation contributes to the greater-than-natural
hydrogen-ion levels in some lakes and streams in eastern North America.
(6) Although some kinds of lakes have been acid throughout their known
history, others in areas subjected to acid deposition have become
appreciably more acid during the past few decades.
(7) These changes in lake acidity have been accompanied by major
changes in the biological activity within them, often including the
disappearance of various aquatic biota, most visibly fish.
(8) The largest of such aquatic effects have occurred in "sensitive"
regions, in which acidity is not "buffered" by the presence of alkaline
minerals.
(9) Large areas of eastern North America have been identified whose
geologic composition is characterized by the absence of any important
buffering capacity.
(10) Forest damage has been increasing in eastern North America during
the past few decades; acid deposition may be a contributor.
The overall scientific understanding of the various aspects of acidic
precipitation is incomplete at the present time, and will continue to
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have major uncertainties well into the future. Some of these gaps in our
knowledge are permanent because the necessary measurements were not made
ten, twenty, or fifty years ago; the potential future utility of such
information was not yet recognized. Other gaps exist because the needed
scientific techniques have not yet been perfected or have not been adapted
to the scale required for measurements covering much of the entire Western
Hemisphere. Some of the important information will require at least ten or
twenty years of additional data collection to take full cognizance of
atmospheric variability and atmospheric cycles. Biological systems are
extremely complex and variable. Response and recovery of many of these
systems to external stress will require long-term (decades) detailed study
for full evaluation. For these reasons, any current scientifically derived
recommendations must be based on an imperfect, but always increasing, body
of pertinent data whose quality and completeness can be expected to improve
for decades. Recommendations based on imperfect data run the risk of
being in error; recommendations for inaction pending collection of all the
desirable data entail the even greater risk of ecological damage.
The chemical processing of SC>2 and NOX into acids in the atmosphere
potentially involves a very large number of chemical reactions, whose
relative importances change drastically with time and location, often in
response to varying meteorological conditions. Sulfur and nitrogen can be
removed from the atmosphere in various chemical forms, and by both dry
processes at the surface and wet processes in rainfall. Measurements of
804" and NC>3~ in rainfall are now widespread, but do not have a long
historical base. Measurements of dry deposition are so scattered (and of
questionable validity) that quantitative assessment is essentially not
possible even now.
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Modeling of atmospheric emissions, transport and deposition has been
confined almost entirely to the sulfur cycle, leaving nitrogen and other
pollutants to the future. The existing models do not agree with one
another, and cannot be verified by good field data because such data are
scarce. The models do not even reproduce well the observations on gaseous
SC>2 that are available. Models cannot be relied on to estimate how much
material emitted at one place will be deposited in another, or how much SC>2
will be'converted to H2S04 before deposition,,
There exists now no acceptable method for determining source-receptor
relationships on a scale much smaller than "eastern North America". With a
very large effort in laboratory atmospheric chemistry, field measurements,
and atmospheric modeling, it might be possible within ten years (but
certainly more than five years) to produce a verified source-receptor model
for eastern North America. We have great hope that methodology based on
natural tracers in fossil fuels may bypass some of these difficulties and
perhaps reduce the time needed to elucidate this complex of problems. Even
if a verified model is developed in the future, the source-receptor
relationship may be found to be sufficiently complex and variable that
emission controls would still need to be assigned over large areas rather
than locally.
Reducing present SC>2 emissions would reduce deposition of total
sulfur, and, consequently, both reduce the probability of major degradation
of additional acid-sensitive lakes or forests and allow anthropogenically
acidified areas to begin to return to their original biological condition.
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The effects of acid deposition on biological systems in North America
range from certain to speculative. There is no question that fresh water
bodies in sensitive areas have been altered. At high concentrations,
acidity can release, or "mobilize", aluminum from solid minerals; this may
lead to toxic effects on biota in both lakes and forest soils. While there
is strong evidence for damage to limestone monuments, bridges, buildings,
and other structures from SC>2 anc* other corrosive gases, there is no good
estimate of the economic magnitude of these effects or of the contribution
from acid deposition. The effects of air pollutants and acid deposition on
agriculture may be important but quantitative evidence is scanty.
Lakes and streams may require years or decades to recover from
anthropogenic acidification once the acidic inputs are removed, with the
recovery time depending on local geochemical factors, flushing rates, rates
of species colonization, extent of alteration of trace-element composition,
and other factors. In contrast, recovery times for stressed terrestrial
ecosystems are decades to centuries. At its simplest level, this
difference in recovery times arises because the major photosynthetic
organisms in aquatic environments are relatively short-lived compared to
trees. There are, however, many other complex differences between the two
types of systems.
We are especially concerned about real and potential changes in the
chemistry and biology of soils in nonagricultural areas (i.e., unmanaged
soils). Because soils need hundreds to thousands of years to develop, they
will recover very slowly from anthropogenically induced changes unless
artificial amendments such as lime are used.
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Soil microorganisms may be particularly sensitive to changes in
acidity; this fundamental part of the biological cycle is responsible for
cycling nitrogen, carbon, phosphorus and other essential nutrients through
the food web. For example, the entire biosphere depends on proper
functioning of denitrifying microbes. Although evidence that increased
acidity is perturbing populations of microorganisms is scanty, the prospect
of such an occurrence is grave. Biogeochemical changes in soils appear to
be particularly long-term. It may take years or even decades of
accumulation of acidity and other toxic airborne pollutants before
consequences can be observed. It may take at least that long for the soils
to revert to their original condition. It is this aspect which gives us
the greatest concern.
Acid deposition belongs to a socially very important class of problems
that appear to be precisely soluble by a straightforward sum of existing
technological and legislative fixes. This is deceptive. Rather, this
class of problems is not permanently solved in a closed fashion, but is
treated progressively. As knowledge and understanding steadily increase,
actions are taken which appear most effective and economical at each
stage.
Actions to reduce acid deposition will have to be taken despite
incomplete knowledge. We have earlier estimated how long it may take to
understand "wet" atmospheric chemistry or the biological response to
acidity. Reasonably accurate models incorporating relevant meteorology,
chemistry, mineralogy and biology will take even longer. Yet, if we wait
until scientific knowledge is definitive, recovery times may have increased
to decades or a century or more (for mature forests and soils).
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We feel that the proper initial approach is to begin immediately with
the most economically effective steps for reducing acid deposition.
Control costs appear to range widely, especially for sulfur removal; some
steps can be much more cost-effective than others. Some of the most
economically efficient means for lessening sulfur emissions in eastern
North America and other sensitive areas are intensifying coal washing and
placing initial controls on nonferrous smelters; switching to fuel of lower
sulfur content during summer (when most sulfuric acid is deposited) might
lessen the overall deposition in distant regions without necessarily
changing annual emissions. Other control technologies are often more
expensive, but research is steadily decreasing their cost.
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IV - RESEARCH RECOMMENDATIONS
It is critical that new funds be made available both to initiate
additional studies and to continue and expand present studies.
There are four general areas of uncertainty for quantitatively
understanding how and to what extent anthropogenic emissions of S02 (and
NOX) may damage ecosystems:
A. Magnitude of anthropogenic emissions and their relation to natural
emissions.
B. Chemistry of conversion of S02 (NOX) to sulfuric (nitric) acid in
the atmosphere, in precipitation, and after dry deposition.
C. Transport of acid and its precursors from sources to points of
deposition.
D. Present and potential ecological consequences of the deposition.
By far the largest quantitative and even qualitative uncertainties
exist in the fourth category, (D), which is the most complex because of the
large number of components and their variabilities. It also has been the
least adequately supported with research funds, especially in the area of
effects on unmanaged soils, wetlands, and forests. This fourth category is
the most important to the acid rain problem, because ecological
consequences are the raison d'etre of the problem. At present, the need
for quantitative description or precision in the other three areas is much
less urgent. Unfortunately, acquiring quantitative and decisive
information in this fourth category will take at least a decade of careful
field and laboratory study.
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For these reasons, we suggest the following order of priorities for
research support:
1. We give highest priority to quantifying the effects of acid
deposition, both wet and dry, on the total ecological system, including
natural and managed vegetation, soil, and ground water. Of special
importance may be effects on microbial activity in soil and wetlands and,
through that, on the nitrogen cycle.
These investigations should include laboratory and field studies as
appropriate on:
1) Detailed ecosystem analyses on a variety of terrestrial
watersheds, including associated lakes and streams. These studies
should determine the relative inputs of H+, 804" , and N03~ from
direct deposition and from biological and chemical activities
within soils, lakes and lake sediments. The studies should
include landscapes containing clear-water lakes, brown-water
lakes, and streams. Although the studies should concentrate on
eastern and north central states, they should include sensitive
areas in other parts of the country. These ecosystem studies
should also emphasize:
a) Effects on vegetation and soils. Detailed studies are
urgently needed on direct and indirect effects of acid precipi-
tation on vegetation and soils of managed (i.e., agricultural) and
unmanaged (i.e., forest) systems. These studies should be
long-term, so they can include the natural variability in climate
and biological response.
b) Biogeochemical processes, including effects of acidity and
metals released by acidity on microorganisms which process
nutrients and organic material in soils, lake sediments, rivers
and, most importantly, fresh—water wetlands; the effects of
acidity on geochemistry of the soil; and mechanisms controlling
the chemistry of drainage waters.
c) The relative effects of natural and anthropogenic sources of
acidity.
2) Physiological bases of toxicity from acid and dissolved
aluminum. We are approaching an understanding of the mechanisms
of acid toxicity on fish, but relatively little is known about the
physiology of acid toxicity on other aquatic and terrestrial
organisms, plants in particular. Moreover, at least in field
studies, it is clear that acid and aluminum may act
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synergistically. Their individual physiological effects should be
distinguished by laboratory studies. Effects of calcium, humate
and fulvates on the uptake of metals should be an important part
of such research. Liming may actually increase the toxicity of
aluminum dissolved by the acidified water and then complexed by
dissolved organic carbon. Liming precipitates the dissolved
organic carbon and leaves the aluminum in a more toxic ionic form.
The generality of this occurrence should be investigated because
it affects the utility of liming as a countermeasure to lake
acidification.
3) Study of historical trends in lakes and bogs. To evaluate the
temporal trends of acidity in lakes from various parts of the
country, cores taken from the bottom of lakes should be analyzed
for shifts in species in the watershed (by pollen analysis),
shifts in chemistry of the water and sediments, and shifts in
organisms in the lake (diatoms, desmids, chironomids, cladocerans,
fish). Bogs and lakes should be selected from the entire East,
the upper Midwest, and various parts of Canada. As part of these
studies, the identities of the species must be verified and
voucher specimens must be kept. Long-term experimental studies in
natural ecosystems should be initiated to provide a basis for
interpreting existing sediment profiles.
4) Extended data bases. Lakes and streams in the northeastern
United States are clearly being affected by acid rain. Before
such effects become severe in other parts of the country (e.g.,
southeastern United States), the extent and severity of the
problem should be surveyed. Teams of scientists should examine the
condition of sensitive surface waters throughout the United
States, including clear, poorly buffered waters at relatively high
altitudes. These studies should include analyses for pH, Ca+ ,
Mg+ , 304" , NC>3~, dissolved metals and alkalinity, and should
continue for at least a decade.
5) The effects of reduced emissions should be quantified by
carefully designed ecological studies and monitoring programs.
2. Quantifying the relative effects of dry deposition of acid
precursors (SO?, NOV) vs. wet deposition of acid onto a given ecological
system. Because dry deposition should dominate over wet deposition in many
regions, it is important to know how relevant the form of deposition is to
ecological systems. For example, how much difference does it make whether
sulfur is adsorbed as 862 by a soil (whose surface is often wet) or
deposited as sulfuric acid in precipitation? This question can probably be
answered before the full effects of acidification are understood.
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3. Natural vegetation is stressed by a variety of agents acting
separately or together. Some, such as droughts, are independent of S02 and
NOX emissions. Others are associated with these emissions and acid
deposition. It is important to have laboratory data and particularly field
observations directed toward disentangling the effects of acid deposition
from those of other anthropogenic atmospheric insults (especially 0^,
SO? and toxic trace elements), drought, pests, and plant diseases.
4. Next, but much less important, would be a reliable relation
between emission of S02 and NOX in one region and deposition of these gases
or the acids derived from them in another region. Models do not yet give
such information and are unlikely to do so before a sufficient data base is
acquired with respect to which models can be tested. For dry deposition,
which may be as important as wet deposition (only one-fifth of the S02
emitted in eastern North America comes down "wet"), there is not even a
full year's data for any natural ecosystem. Therefore, developing and
implementing methods for carefully measuring dry deposition at a limited
number of regionally representative sites in eastern North America is
particularly important for verifying models and predicting ecological
effects. As a complement, more monitoring data on SO? and NOX in rural
areas are needed. These data should also lead to improved sulfur and
nitrogen budgets for eastern North America.
5. Understanding of transport also may profit greatly from network
measurements of tracers (elements, compounds, stable isotopes) presently
emitted continuously (or perhaps artificially inserted tracers), because
relative abundances of certain tracers can uniquely characterize area and
point sources of S09 and NOX. Both of the above measurement programs
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(4 and 5) appear to us more urgent at this time than expanded efforts in
constructing mathematical models, which can be verified only by comparing
them with data which do not yet exist.
6. Next in importance is understanding the atmospheric chemistry by
which SO? and M0y are acidified before they are deposited by precipitation.
The importance of such information depends upon the answers to priorities 2
and 4. Thus, if the ecological consequences and transport ranges were
shown to be insensitive to degree of conversion to acid, it would not be
particularly important to determine the details of atmospheric oxidation.
But if, for example, sulfuric acid deposited in precipitation were found to
be potentially harmful, the atmospheric chemistry of SC>2 conversion would
become very important for verifying models and (more significantly) for
selecting the best control strategies. (For example, would it be easier to
control oxidants or S02 to reduce wet deposition of sulfuric acid?)
Necessary to understand quantitatively the atmospheric transformation to
acid would be field programs in cloud chemistry (especially on the surface
of and within droplets) and oxidant measurement (especially R2®2> an<^
probably 03 and oxidant precursors) at droplet altitudes. Laboratory
experiments should include mechanisms of oxidizing SC>2 and NOX, as well as
isotopic f ractionation of *°0 in sulfate as a function of S02 oxidation
mechanisms and isotopic composition of reactants (for comparison with field
data on *°0 in rainwater, sulfate, and cloud-droplet oxidizers such as
7. The information resulting from priorities 4 through 6 should then
be incorporated into improved computer models. (One purpose will be to
decide whether the improved models perform significantly better than the
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original ones did.) A key question involving both chemistry and
meteorology is the degree of linearity between SC>2 emission and eventual
wet and dry deposition, but a precise answer is not achievable now because
of insufficient data.
8. Although emission data for SO? and N0y can be improved, their
accuracy is already much better than for deposition; however, better
emission data on alkaline particles and oxidant precursors may be useful.
Natural sources of many species still need to be characterized more
thoroughly.
9. Engineering research on ways to remove sulfur at the source should
still be supported by federal and industrial agencies.
10. The main applied purpose of the scientific understanding which
could be advanced by these programs is to inform those who decide upon
control strategies. To a great extent, optimal strategies must await
such understanding. Some important relevant information, however, may be
obtained now from improved economic analyses on:
a) Cost of material damage from 302 emission.
b) Cost of altered yields of agricultural crops from S02 and 03.
c) Future S02 and NOX emissions with more realistic projections of
electric-power use, retirement of old generators, steel
production, coal vs. oil, etc.
d) Costs of using low-sulfur fuels when season (e.g. , summer) or
frequency of precipitation favors wet deposition of acid.
e) For each S02 source, one should determine the lowest-cost
approach for removing increasing amounts of sulfur.
f) What kind of legislation would result in least cost
to society for a given total emission reduction? For example,
if one assumes that sulfur emitted from one source is
ecologically equal to that from any other, what would be
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the consequence of allowing a free-market sale of limited
pollution rights for SC>2?
We are disappointed at the way in which the Federal Government has
been conducting its research program on acid rain. A much larger share of
the research should be given to non-Federal laboratories. In addition, we
feel strongly that highest priority be given to the most creative ideas
and innovative approaches.
We realize that the Federal Government and other agencies are
supporting important ongoing research on acid deposition. At the same
time, however, imbalances exist, with some areas seriously underfunded.
One example is ecological effects, where a relatively modest increase in
support (several million dollars annually) would have disproportionately
great results. Although current funding of acid rain studies is much
higher than in the past and increasing, carefully chosen priorities in
fields and investigators can markedly accelerate progress in this difficult
field.
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V - REVIEW OF WORK GROUP 1 REPORT - IMPACT ASSESSMENT
Introduction
Large areas of eastern North America are currently being stressed by
wet deposition of acids, by dry deposition of acid-forming substances, and
by various other air pollutants such as ozone. The panel has concluded
that acid deposition has altered aquatic and terrestrial ecosystems of
eastern North America both qualitatively and quantitatively. Perhaps the
best known of these changes is that numerous recently acidified lakes in
the northeastern United States and southeastern Canada no longer contain
viable populations of some species of fish.
Work Group 1 was charged with reviewing the past, present, and
projected impacts of transboundary transport of air pollutants into
sensitive receptor areas in the United States and Canada. In addition,
Work Group 1 was to estimate the number of years remaining until the
sensitive areas were affected significantly, and to propose the amount of
reductions in deposition of the pollutants on various time scales that
would be required to protect these areas.
Work Group 1 produced a final report which was very long—626 pages
of text. Most of this length was due to the large amount of evidence
reviewed. But part of the length came about because the Canadians and
Americans could not agree on certain sections and issued them separately,
and because the Work Group went well beyond its charter by including extra
chapters on damage to man-made structures, methods to estimate benefits
from controlling transboundary transport, an inventory of natural
resources, and liming.
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In the seccions below, we first offer general remarks on the
report as a whole, and then deal with each chapter individually.
General Remarks
Perhaps the greatest strength of this report is the amount of evidence
presented for relatively recent chemical and biological changes in natural
ecosystems in parts of North America remote from urban or industrial
centers. The evidence is convincing—something is happening. Some of
these changes may be natural, because ecosystems are not always static.
But the report offers massive evidence that air pollutants are associated
with many of these changes. The report documents clearly that high levels
of acidic deposition are linked with ecological changes in parts of eastern
North America. In areas with less deposition, similar changes are weaker
or absent altogether.
But is the link to air pollution causal or coincidental? In some
cases, such as ozone and vegetation or sulfur dioxide and man-made
structures, it is definitely causal, and the report says so. In the case
of acid deposition and ecosystems (the major concern of the entire
Memorandum of Intent), however, the degree of causality is drawn much less
clearly. To be sure, whole-lake and stream acidification experiments in
Canada and the United States have shown that systematic, widespread, and
reproducible chemical and biological changes occur as pH drops below about
5.5. Similar changes are observed in numerous lakes and streams which have
been acidified recently.
This is not direct evidence of causality, however; it is only
circumstantial evidence. In our view, the crux of the acid precipitation
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debate is the strength of the link between acid deposition in a given
region and ecological changes in that region. The fundamental charge of
Work Group 1 was to address this point in detail, by documenting the past,
present, and future adverse effects of transported and deposited air
pollutants.
Work Group 1 did not meet this charge fully. Commendable as its
Final Report is, it dwells too much on data rather than on ideas, and on
individual relations rather than on the big picture. Too much of the
material is not digested; critical issues are hedged or obfuscated rather
than met squarely. The terras of reference demand clear statements; the
Work Group often neither offered them nor noted their absence. This
failure to deal directly with some of the most important questions is the
greatest weakness of the Final Report.
We recognize fully that the environmental effects of acid deposition
(and of ozone and other transported pollutants) are exceedingly complicated
and not amenable to any simple description. Nevertheless, brief statements
of the current understanding are required by decision-makers, and are
extremely important to the concerned public as well. We feel that Work
Group 1 could and should have summarized its findings much more succinctly
than it did.
Consider aquatic effects, for example. Although it is presently not
possible to prove that acid deposition has changed the chemistry or biology
of aquatic systems in eastern North America (absolute proof of causality is
usually impossible in science), an extremely convincing argument can be
made. Recently acidified lakes and streams are found only where there is
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acid rain (not in the Sierra or Cascade Mountains, the Boundary Lakes Area
of northern Minnesota, or northern Scandinavia, for example, even though
these areas are environmentally sensitive). In recently acidified lakes,
the dominant anion is sulfate, as it is in acid raia. Elevated sulfate is
found in most surface waters throughout eastern North America and southern
Scandanavia, even in those not yet acidified. In non-acidified lakes the
dominate anion is usually bicarbonate. In lakes near very strong sources of
sulfur dioxide, such as the smelters of Sudbury, Ontario, ecological effects
have been severe. Thus, there can be no doubt that high loadings of acid
can destroy the normal biology of a lake.
But what about the majority of the lakes, which are subject to more
typical rates of acid deposition? At present, the percentage of these
lakes affected chemically or biologically is not known. (In fact, the
total number of lakes in eastern North America is not known.) Of the known
lakes, only a tiny percentage has ever been studied, and only a tiny
percentage of these studies has systematically surveyed the ecological
changes. Thus, we are dealing with an enormous deficit of data relative to
the potential importance of the problem.
One point is certain—it is very difficult to generalize about lakes
and their response to acid deposition because the response of a lake depends
on factors such as its underlying geology, nearby vegetation, size and depth
of the lake, nature and depth of surrounding soils, relative area of lake
and watershed, and other factors, all of which vary over large ranges.
Thus, a population of lakes should respond in a great variety of ways to a
given amount of acid deposition, and that is exactly what is seen in eastern
North America.
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At high elevations in the Adirondack Mountains, where soils are thin,
minerals are resistant to weathering, and lakes are poorly buffered and
receive heavy loadings of acid, a large fraction of the lakes is already
acidified. At lower altitudes, some lakes are acidified, some are being
titrated, and others show no effects of acidification. Some large lakes,
such as Erie and Cayuga, are basic and will remain so indefinitely because
of their size and buffering. Other large lakes, however, such as Honnedaga
in the Adirondacks, are already quite acidic (pH < 5.0) because of the
small size of the watershed relative to the lake (only 4:1); thus, the
water in the lake is largely rainfall, with minimal alteration by soils in
the watershed. A "typical" nonacidified New England lake may have a pH
above 6 because it contains small amounts of bicarbonate, but sulfate has
become the dominant anion. And so it goes throughout the spectrum of lake
response to acid deposition.
As a lake receives acidity, its alkalinity first decreases (the
titration phase), then disappears altogether, after which the lake
acidifies rapidly. It is now known that biological effects occur
throughout the titration phase, not solely after the lake is acidified.
(By acidified, we mean having reached a pH of lower than about 5.5).
In summary, then, lakes do not have to be acidified to be acidifying,
and may show biological effects well before they are acidified. For the
reasons given above, lakes in a given area will follow highly
individualized pathways toward acidification. Some may never become
acidified, some may already be acidified, and many will be somewhere in
between. Others, the so-called "brown-water" lakes, are naturally acid
from organic acids, and hence are not as directly affected by contemporary
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acid deposition. (All lakes in the eastern United States have some amount
of humate.) With such variety available in the lakes of a given region,
exceptions can be found for any statement. These exceptions are expected,
however, and should not be overemphasized in developing the total picture.
Our last general remark on the Final Report of Work Group 1 concerns
our mixed feelings regarding the extra chapters on additional topics. On
the one hand, the effort and concern behind them were commendable. On the
other hand, we regret any time they took away from dealing with the central
issues.
Remarks on individual chapters
Aouatic Impacts
The chapter on aquatic impacts takes up nearly half the Final Report,
and rightly so, because this aspect of acid deposition is one of the most
important and complex. In our view, the huge mass of material on aquatic
effects was covered well by Work Group 1. As noted above, there was a
certain lack of synthesis throughout, which greatly weakened the force of
their message.
One very important aspect of aquatic effects which could have been
treated more fully in this chapter is the general confusion between the
various types of naturally acid surface waters. There are three distinct
types. The first type has high concentrations of organic acids, is often
yellow or brown in color, usually contains growths of Sphagnum, and normally
has a pH below 5. The second type results from volcanic activity: these
waters are high in mineral acids and can have pHs below 4. (This second
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type does not occur in eastern North Airerica and will not he discussed
further.) The third type contains clear water and is found over granite or
sand; these waters have very low conductivity, poor buffering, and pHs of
5 .6 to 7.0 .
The first type, the brown-water lakes and streams, have been naturally
acid for thousands of years, yet much of the literature on these lakes and
streams was not considered. In these waters, dissolved aluminum and other
toxic metals are low in concentration and are conplexed hy the dissolved
organic matter and thereby rendered nontoxic to organisms. As a result,
brown-water lakes and streams may support thriving communities of plants,
animals, and microbes. In contrast, the recently acidified waters are
normally derived from the third type listed above. Their major acids are
mineral (e.g., J^SC^ and UNO}), and their concentrations of dissolved
organic matter are low. At low pH, dissolved metals such as aluninun exist
in inorganic forms which may be quite toxic to organisms. These acidified
lakes and streams have depleted populations of plants, animals, and
microbes. It is these acidified waters and aquatic effects that are of
concern relative to acid rain.
Much of this aquatic chapter was devoted to reviewing effects of acid
deposition under controlled or laboratory conditions. A clearer
demarcation between laboratory results and symptoms noted in real
ecosystems would have been desirable. It is easy for the reader to confuse
potential effects with actual ones.
The different fates of hydrogen and sulfate ions in watersheds was
properly stressed in this chapter. While more than 80% of the acidity is
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absorbed, even by the less-buffered granitic soils, this is not the case
with sulfate which reaches the lakes and streams in much higher proportion.
Perhaps the most important aspect of the aquatic chapter needing
comment is the failure of the American and Canadian members to agree on a
value for target loading, or rate of deposition of sulfate necessary to
protect sensitive ecosystems in eastern North America. Separate summaries
issued by the United States and Canada for the aquatic chapter represented
the only area of the entire MOI process in which the two countries
officially disagreed. Careful reading of these summaries convinces us,
however, that the the American and Canadian delegates were actually quite
close on target loadings, but had many other differences of opinion about
aquatic effects. The American summary consistently stressed the gaps and
uncertainties in the data and the consequent difficulties in drawing
conclusions from them, whereas the Canadian summary consistently stressed
that much of importance could be concluded from the available data. The
present data document large-scale chemical and biological effects of acid
deposition on non-brown-water lakes in eastern North America. These
effects are numerous and severe enough to warrant mitigation of SC>2 and NOX
from anthropogenic sources.
Terrestrial Impacts
This chapter is not as comprehensive as the one on aquatic impacts.
The literature is not covered as well, especially in the sections on
forests and soils. This is unfortunate, because terrestrial effects of
acid precipitation may be extremely important, and may rival or exceed
those in surface waters. Laboratory experiments have shown that acid
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deposition adversely affects both plant growth and foliage. In the natural
environment, however, the effects are not so clear because acid rain is
only one of several stresses on plants, some others being ozone, SC>2,
metals, and droughts. Also, it is often difficult or impossible to
distinguish effects of direct deposition to the exposed plant from effects
of increased ground-water acidity or leaching of essential micronutrients
on root systems.
Another important terrestrial effect of acid deposition may be on
cycling of nutrients by bacteria, blue-green algae, and fungi. For
instance, pHs of 3.2 inhibit mineralization of glucose in soils, pHs of 3.0
to 4.0 reduce decomposition of plant litter, and pHs below 6.5 decrease
sulfur reduction in soils. Because cycling of nutrients is such a critical
function of the biosphere, any adverse effect could be significant. More
research in this area is needed, particularly in wetlands, lake and river
sediments, and terrestrial soils.
Lichens are apparently quite sensitive to S02« In some areas, they
have merely been depleted; in others, the species have changed.
Agricultural plants are sensitive to acid deposition in the laboratory, but
effects on actual crops are much less clear, possibly because most crops
are annuals and are fertilized routinely. Some recent field experiments,
however, have shown large decreases in yield. Forests might be expected to
show more clear-cut effects of acid deposition, because trees are
perennials, are usually not fertilized, and often grow in soils whose
levels of nutrients are low. Although forests in numerous areas receiving
heavy loadings of acid are growing less rapidly now than earlier, it is
very difficult to ascribe these changes uniquely to acid deposition. More
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recent data from Germany (not reviewed in the Final Report) have suggested
that acid deposition affects forest growth significantly and support the
conclusion that the major effect is on roots, not foliage.
Acid deposition probably does not affect terrestrial wildlife
directly, but may influence it indirectly via decreased plant growth or
contamination by metals. Soil bacteria and fungal microrhizae may also be
affected by acidified soils; because both are important in cycling
nutrients through terrestrial ecosystems, affecting them would affect the
entire ecosystem.
It is still difficult to estimate economic effects of acid deposition
on the terrestrial biosphere. It is also not yet possible to map forest
sensitivity to acid deposition. Nevertheless, it appears that acid
deposition has increased rates of podzolization in forests of eastern North
America. Such changes are extremely rapid in the context of historic soil
development and thus represent an important alteration of the biosphere.
Human health and visibility
In general, this chapter is done well. We accept the assertion that
acidic deposition does not directly affect human health. Even indirect
effects such as increases in aluminum or lead in water supplies appear to
have no immediate health effect, although they should be monitored.
On the other hand, degradation of visibility by fine-particle acidic
aerosol is real and widespread. While it is true that its effects show up
most clearly in the West, where virtually unlimited visibility surrounding
scenic vistas is expected, we differ from Work Group 1 on the relative
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importance of visibility there. Preoccupation with the West is largely
cultural. Eastern North America has many regions with great vistas which
are widely valued when seen. When weighted for the larger number of people
in the East, we believe that maintaining visibility there is at least as
important as in the West. Once one becomes attuned to atmospheric optics,
reduced visibility can be just as annoying over distances of 5 miles as
over 150 miles.
Man-made structures
In our view, this chapter is not required by the terms of reference
of Work Group 1. It is interesting, however, and possibly important,
because cultural relics as well as modern structures are being corroded by
atmospheric chemicals. This chapter points out, however, that most of the
damage to materials is probably caused by corrosive gases generated locally
rather than by regional pollutants or deposited acidity. S02 (in
combination with adsorbed water) is the most important corroding agent,
followed by NOX and ozone.
Methodologies for estimating economic benefits of controls
We consider this chapter to be of limited value. Its basic problem
lies in the first sentence of the summary: "Traditionally, the
decision-making process has required an appreciation of the costs and
benefits associated with following a prescribed set of actions." The
benefits of a properly functioning ecosystem are much more than matters of
dollars and cents, and are often not appreciated by people unfamiliar with
ecology. To a large extent, our clean air and clean water depend on
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ecological cycles. Unfortunately, the inherent worth of an ecosystem, its
components, or the benefits associated with their maintenance can not
yet be expressed in terms of pure economics, nor are they liable to be in
the foreseeable future.
Thus, we feel that this chapter is not helpful at the present time.
We also feel that its statement that current benefit-cost analyses must
"either omit real but intangible benefits or include a wide uncertainty
range" is overly bland and fails to deal with the real point of the
relevance of economics to ecological protection.
Resource inventory
In our view, the major result of this chapter is that it is presently
impossible to evaluate our natural resources accurately. In the words of
Section 1.7.1, "The completion of this inventory has served to underline
the considerable weakness which exists in our ability to adequately
quantify the extent of the resource at risk." We agree.
Liming
We share with Work Group 1's mixed feelings about liming. It is a
temporary solution which should be applied as sparingly as possible in as
few locations as possible. Before wholesale liming is undertaken, careful
field studies of its aquatic effects are needed.
Did Work Group 1 meet its terms of reference?
Work Group 1 was given eight specific terras of reference. We now
review each of them.
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"identify and assess physical and biological consequences possibly
related to transboundary air pollution" This was met well, for both
pollutants such as ozone and deposition of acidity.
"determine the present status of physical and biological indicators
which characterize the ecological stability of each sensitive area
identified" We are not sure whether the intent of this term of reference
was to evaluate the inherent stability of sensitive areas of eastern North
America (ecological stability is currently a controversial topic) or the
actual extent of changes in the various areas. Work Group 1 seems to have
addressed the latter reasonably, but not the former. Sensitive organisms
and their disappearance were treated in some detail.
"review available data bases to establish more accurately historic
adverse environmental impacts" Work Group 1 evaluated historic trends in
ecosystems at least as well as had been done previously, if not better.
Brown-water, hutnate-rich lakes and streams, however, which would have
rounded out their analysis, were ignored.
"determine the current adverse environmental impact within identified
sensitive areas-annual, seasonal, and episodic" This represents an
enormous undertaking. This term of reference embodies the ultimate goal of
all studies about effects of acidic deposition. Were the answer known, a
precise program of controls could be begun with full confidence. Work
Group 1 tried, but the two countries diverged concerning the dose-response
curve for deposited acidity. In actuality, there are as many dose-response
curves as there are water bodies and ecosystems. Some cases are known
accurately, but many more cases are completely unknown, and will remain so
for many years.
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"determine the release of residues potentially related to
transboundary air pollution, including possible episodic release from
snowpack melt in sensitive areas" Work Group 1 dealt satisfactorily with
melting of snowpacks, but did not consider any other residues in detail.
"assess the years remaining before significant ecological changes are
sustained within identified sensitive areas" Work Group 1 did this only
poorly, but it is exceedingly difficult to do at all. It demands the
history of every ecosystem of interest from which to develop models for
testing. Considering that every lake in eastern North America responds
individually to acid deposition, and even though helpful groupings can be
made, to perform this task quantitatively presents a formidable challenge
even for the next hundred years.
"propose redactions in the air pollutant deposition rates-annual,
seasonal, and episodic-which would be necessary to protect identified
sensitive areas" Work Group 1 tried this only for annual rates, and could
not agree on the value.
"prepare proposals for the "Research, Modelling and Monitoring"
element of an agreement" This was done satisfactorily.
In summary, Work Group 1 met three of the eight terms of reference
well, two partially, and three poorly. It seems to us, though, that the
failure to meet certain terms of reference was mostly a consequence of the
difficulty of the terms of reference.
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VI - REVIEW OF WORK GROUP 2 REPORTS - ATMOSPHERIC SCIENCES AND ANALYSIS
Work Group 2 produced a Final Report (2F) and four supporting
technical papers:
2F-A Atmospheric Sciences Subgroup Report
2F-M Regional Modeling Subgroup Report
2F-I Monitoring and Interpretation Subgroup Report
2F-L Local and Mesoscale Analysis Subgroup Report
The first section below discusses some of the major topics dealt with
in these reports. The next section offers remarks on the individual
reports themselves. The last section considers whether Work Group 2 met
its terms of reference.
Remarks on Specific Topics
Items of Concern
In general, the reports of Work Group 2 are carefully done and
credible, and give a fair and balanced account of the state of current
knowledge of many meteorological and chemical aspects of acid deposition as
of 1982. A great deal of effort was obviously put into them.
Nevertheless, we have reservations about certain portions of these
reports. The specific topics in question are the emphasis on modeling, the
modeling of sulfur only, the lack of data on dry deposition, and the
treatment of the linearity question.
Our greatest concern is the emphasis placed on modeling—at the
expense of traditional scientific approaches—to deduce the relative
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importances of local and distant sources of sulfur in air and in
deposition. When Work Group 2 was formed, it was widely expected that
transport models could be developed to derive such source-receptor
relationships. The reports make it abundantly clear, however, that the
models failed to furnish reliable source-receptor relationships. The
creation of the Subgroup on Monitoring and Interpretation partway through
the work was an attempt to restore a balance between models and the more
traditional approaches, but it seems to have been too little and too late.
We feel that Work Group 2 concentrated too heavily on sulfur.
According to the MOI terms of reference, Work Group 2 was to deal with "the
transport of air pollutants between source regions and sensitive areas" and
calculate how to "achieve proposed reductions in air pollutant
concentration and deposition rates which would be necessary in order to
protect sensitive areas." The terms of reference do not mention any
specific pollutant. But Work Group 2 modeled the transport and deposition
of sulfur only. The nitrogen system, the other major contributor to
acidity in deposition, was not included. Other gaseous and particulate
pollutants which are proven to be or are potentially injurious (ozone,
organics, metals, etc.) were relegated to a single chapter in the Final
Report. In so doing, any relations between these pollutants and sulfate or
acidity were never clarified. By delving deeply into the transport of
these other substances, much could have been learned about transport of
acidic materials. Instead, the "other pollutants" were used merely as
additional examples of materials which can be transported across political
borders. An interesting class of problems not considered by Work Group 2
is how pollutants interact to produce a given effect.
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In great contrast to wet deposition of sulfur and nitrogen, which is
now being measured routinely and accurately at many sites in North America,
dry deposition is far behind. Reliable techniques are still being
developed; very little quantitative information is available. From
quantitative measurements in a few calibrated watersheds (Hubbard Brook in
New Hampshire, for example), it is clear that dry deposition of sulfur is
important, because more sulfur arrives at the surface than can be accounted
for by precipitation alone. But measurements of this type are
time-consuming, and hence too scattered to have provided any general
picture of dry deposition. Without accurate dry-deposition velocities,
transport models are hardly more than educated guesses.
Confusion about the definition of "linearity" is common in discussions
of acid deposition. To its credit, Work Group 2 adopted a strict
definition and used it consistently. Unfortunately, though, the difference
between this definition and the more common colloquial use of "linearity"
was not given. As a result, Work Group 2's discussion on linearity can be
quite hard to follow.
Long-range transport models
Earlier in this chapter we stated that Work Group 2 placed far too
much emphasis on long-range transport models as the primary source of
information on transboundary transport of acidity. To a large extent, the
terms of reference of Work Group 2 forced this emphasis upon its members.
The terms of reference of Work Group 2 (reproduced in Appendix 3 of this
report) indicate clearly that in August 1980 it was widely held that
transport models would soon be the most reliable way to understand
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long-range transport. The very first sentence of the Work Group's specific
terms of reference shows how central the models were to be: "The Group
will provide information based on cooperative atmospheric modeling
activities leading to an understanding of the transport of air pollutants
between source regions and sensitive areas . . ." Work Group 2 was also to
"provide initial guidance on suitable atmospheric transport models to be
used in preliminary assessment activities." Only near the end of the terms
of reference were traditional scientific methods mentioned, and then in a
subordinate way: "assess historic trends of emissions, ambient
concentrations and atmospheric deposition to gain further insights into
source-receptor relationships for air quality, including deposition." Not
only do these terms of reference assign the responsibility strongly to
models, they also indicate no doubts that models would succeed. This
orientation was even incorporated into the original title of Work Group 2,
"Atmospheric Modeling Work Group."
The fraraers of Work Group 2 were not alone in their optimistic view of
models. A similar opinion was elaborated somewhat in the recent OTA
(Office of Technology Assessment) report, "The Regional Implications of
Transported Air Pollutants: An Assessment of Acidic Deposition and Ozone",
Interim Draft, July 1982: "Transport models are the only practical
procedure available to estimate the relationship between areas of origin
and areas of deposition of long-range transport pollutants. Large-scale
regional transport cannot now be measured directly for the large number of
sources of emissions and deposition regions of interest, and under the
variety of meteorological conditions needed to perform the analysis.
Models describing long-range transport of sulfur oxides have been available
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for several years; preliminary models of nitrogen oxides transport are just
now being developed."
The dominance of transport models was built into the structure of Work
Group 2. Although meteorologists and measurement specialists were
originally included in the Group, their presence was intended primarily to
provide data for the modelers and only secondarily to allow independent
assessments of the source-receptor relationship. Subsequently, Work Group
2 was restructured to give a larger role to scientific approaches other
than modeling. It was then given a new title, "Atmospheric Sciences and
Analysis", which better reflected its new composition. Separate reports on
atmospheric sciences and monitoring were issued.
Work Group 2 treated its long-range transport models thoroughly and
fairly. Assumptions of the models are well articulated, characteristics of
the models are displayed in detail in an extensive table and elaborated in
the text, and results are presented both as raw output and in partially
digested form. We would have preferred, hoxrever, to see the results of the
models summarized more fully than they were, and their implications
explored more deeply. The Final Reports of Work Group 2 spent too much
time comparing the models and not enough time evaluating the meaning of
their results.
Final Report 2F comments on the diversity of approaches and parameters
in the eight models. We wish to stress again just how different the models
can be; the differences have significant consequences. For example,
consider the transformation rate of S02 to sulfate. While values in all
the models average about 1% per hour, some models assume a constant 1% per
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hour, others have different rates for winter and summer, and others have
diurnally varying rates which can range from 0.1 to 5.5% per hour. Winds
are also handled very differently by the models. Some use long-term means
or statistics, others calculate them every 3-6 hours; some average through
a mixed layer, others use discrete levels. Mean trajectories from Sudbury,
Ontario and St. Louis, Missouri during January and July 1978 (Report 2F-M)
reflect these differences by showing surprisingly wide divergence between
the models. Even the monthly-mean trajectories spread over angles of
30-60°. In one case, the angle was well over 90°, as the trajectory of one
model went westward while the others went eastward.
The strengths of transport models are well known and need no further
comment here. The important result to be recognized by all who seek to use
models as an aid in understanding or as part of decision-making is that
their overall performance is still marginal and their value is still
limited. In most discussions of models to date, this point has not been
stressed. To its great credit, Work Group 2 pointed this out clearly (with
the one exception discussed below). The more dominant the role given to
models, the more important it is to be fully cognizant of their
limitations.
The following limitations of the long-range transport models used by
Work Group 2 need to be kept in mind:
(1) With one exception, they consider only sulfur. The roles of
nitrogen, ozone and the hydrocarbons, all of which are intimately involved
in the atmospheric processing of sulfur compounds, are not considered
explicitly.
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(2) Only linear chemistry is included. In the real atmosphere,
rates of chemical reactions may be highly nonlinear, at least on the small
scale. On larger scales of distance and time, however, fluctuations in
rate may average to a pseudo-linear behavior. In Chapter 4 of Report 2F,
the performance of the transport models relative to the nonlinear ambient
system is acknowledged as follows: "The reaction rates are nonlinear with
regard to S02 because the free radical concentrations are not constant over
time and space. The LRT models, therefore, may not correctly predict the
quantity and the deposition patterns of H2S04 formed through the gas-phase
reactions."
(3) Cloud chemistry, which is now emerging as an extremely important
part of the sulfur cycle, is not considered by any of the eight transport
models. Work Group 2 has, though, attempted to assess the implications of
this new information (the most important of which is that the majority of
the oxidation of S02 fflay take place in the aqueous phase in clouds) to
control strategies in Chapter 4 of Report 2F. Among other things, they
concluded that, "Since the LRT models do not employ the 1^02 and Oj
concentration fields, which have important spatial-temporal variations, it
is unlikely that they can correctly predict the present quantity and
deposition patterns of H2S04 formed through aqueous-phase reactions."
Thus, the models cannot handle either gas-phase or aqueous-phase oxidation
properly.
(4) Because dry deposition of S02 and sulfate cannot be measured at
present, their simulation by the transport models cannot be verified. The
absence of dry deposition of S02 and sulfate, which is now considered
comparable to wet deposition of sulfate, is particularly important.
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Ultimately, variable dry-deposition velocities will probably be required to
simulate long trajectories in eastern North America which pass over areas
with different surface characteristics. Only one MOI model incorporated
surface-dependent rates of dry deposition (UMACID), and that model was not
among the most "successful" ones.
(5) Background deposition is not handled adequately. According to
the Executive Summary of Final Report 2F (Chapter II), "The role of natural
or very distant anthropogenic sources of acidity in eastern North America,
although likely to be small, remains to be clarified in order to determine
what 'background' deposition to use in constructing atmospheric models of
source-receptor relationships."
(6) There are meteorological limitations as well. For example,
the Executive Summary recognizes one of the well-known problems with
air-mass trajectories: "Back air-trajectories analyses are unable to
distinguish between near and more distant sources within the same
directional sector and cannot be used to trace an air-inass trajectory
during periods of weak, variable air flows or over very long distances."
Another meteorological problem is concerned with simulation of air
movement at the top of the mixed layer. The eight transport models
evaluated by Work Group 2 assumed that emissions were dispersed into the
mixed layer, whose top is typically one kilometer, and remained there. In
summer, when wet deposition of sulfate is greatest in the Northeast,
cumulus clouds commonly draw air out of the turbulent mixed layer and into
the more laminar air above. The time required to process a given parcel of
air in this way is typically 0.5 to 1 day. Thus, there can be a sink for
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SC>2 at the top of the mixed layer which is comparable to or greater than
dry deposition at the surface. This upper sink is not included in any of
the eight transport models.
Linearity and nonlinearity
The question of "linearity" was given a somewhat confused treatment by
Work Group 2. This is unfortunate, because the concept of linearity is
extremely important to formulating a strategy to reduce deposition of
sulfate. Linearity is used and understood differently in different
branches of science, and has colloquial usages which differ from the
scientific definitions. To its credit, Work Group 2 chose a single usage
and stuck to it. They could have eliminated a great deal of confusion,
however, by stressing their definition more and explicitly describing how
it differed from other current usages.
Work Group 2 never defined linearity directly. The closest they came
was in Appendix 3 of Final Report 2F, where a linear model is defined as
one "where all the interrelationships among the quantities involved are
expressed by linear equations which may be algebraic, differential, or
integral." This is essentially the definition of a linear system as one
whose variables are related only by linear equations. To this should have
been added the definitions of the three types of linear equations, for
there are differences among them. For example, a linear algebraic
equation is one whose variables appear to the first power only and have
constant coefficients, i.e., cannot involve other variables. In linear
differential equations, however, the coefficients of the dependent variable
and its derivatives may be functions of the independent variable.
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Work Group 2 used linearity in a restrictive fashion. While they
allowed the coefficients in a rate equation to contain other variables (see
pages 4-1 and 4-2 of Final Report 2F, for example), they required these
variables to reaain constant. If they did not, the systea was considered
nonlinear. According to Work Group 2's definition, the sulfur system in
the atmosphere will be linear when the rates of its reactions and
depositions are first-order in SC>2 or sulfate and have constant
coefficients. If, for example, the rate of oxidation of SC>2 is found to
involve any other atmospheric species whose concentration can vary (such as
the hydroxyl radical) or any meteorological variable such as sunlight or
humidity, the sulfur system must be considered nonlinear. By this
definition, it is in fact nonlinear, because the oxidation of S02 is known
to be a complex function of sunlight, moisture and co-pollutants.
Alternatively, if the concentration of any sulfur species, in either the
atmosphere or deposition, is found to depend on the abundance of any
chemical variable, the sulfur system in the atmosphere is nonlinear.
(Again, it is clearly nonlinear.)
The problem with this use of linearity is that it corresponds to
neither the standard algebraic nor differential definitions given above.
It is rather like the algebraic form applied to a differential equation.
Work Group 2 should have pointed this out.
Work Group 2's definition of linearity for atmospheric sulfur
corresponds to the common, or colloquial, use in which a given change
in S02 emissions produces the same percentage change in sulfate or sulfate
deposition. The recent National Research Council (NRC) report on acidic
deposition in eastern North America examined whether the sulfur system
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there was linear in this sense. Linearity in the colloquial sense is a
critical issue in deciding whether to bear the heavy expense of reducing
sulfur emissions nationally. Everybody agrees that the sulfur system is
nonlinear in Work Group 2's sense. 'The important sense is to determine how
much one can reduce deposition by reducing emission, i.e., how nearly
linear the sulfur system is on the temporal and spatial scales of eastern
North America.
An expanded discussion of the effect of scale on (colloquial)
linearity would have been useful at this point. On the global scale, the
sulfur system is clearly linear, for all the sulfur emitted is deposited
(sulfur does not accumulate in the atmosphere the way longer-lived
constituents such as carbon dioxide and the Freons do). On the smallest
scale, sulfur is highly nonlinear (again colloquially), for it is easily
transported away from the point of emission. On intermediate scales, such
as the size of eastern North America, the degree of linearity must be
intermediate. In this sense, we find the report of the NRG committee most
interesting, for it judged the most probable value in the northeast to be
80% linearity, with the range of possible values being 50 to 100%.
The source-receptor relationship
The source-receptor relationship (discussed explicitly in the Regional
Modeling Subgroup Report 2F-M) is implicit throughout all the material on
modeling. Work Group 2 recognized that this relationship forms the basis
of all control strategies for acid deposition, and that the present
uncertainties in our knowledge of this relationship may strongly affect
recommended courses of action. Thus, Work Group 2's conclusion that the
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source-receptor relationship is poorly known beyond the simple
demonstration of long-range transport is potent and must be reckoned with.
Essentially all the MOI modeling was an attempt to define the
source-receptor relationship as well as possible with current tools.
Local vs. distant sources
This important topic is treated fairly in both the Local and Mesoscale
Analysis Subgroup Report (2F-L) and the Final Report (2F). The potential
importance of local and regional sources, as well as distant sources, is
clearly recognized and stated. At the same time, the relative scarcity of
data on nearer sources is noted, and more research is called for.
More could have been done, however. Inspection of the transfer
matrices of the eight models shows clearly that six of them predict broadly
equal contributions from regional and distant sources to suspended and
deposited sulfate in the sensitive regions of New York and New England.
Even though it is presently impossible to verify these predictions, the
similarities from such different models when entire source regions are
considered is an important property. This is an example of the kind of
result from models which will eventually guide policy.
Effect of uncertainties in emissions on transport models
Chapter 2 of Final Report 2F summarizes the emission data used by Work
Group 2 in its regional transport models. The treatment for this topic is
brief and straightforward, presumably because emission data for S02 is the
least controversial aspect of transport modeling. We agree.
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Nevertheless, we find the passing reference to uncertainties in
emissions — a single sentence near the end of Chapter 2 — a bit too casual.
Work Group 2 took Work Group 3B's emission uncertainties at face value.
We feel that they should have at least commented on them.
In the Final Report of Work Group 33, the uncertainties in total
United States emissions of S02 and NOX are claimed to be less than 3%. For
Canada, the figures are estimated at 6 and 10%, respectively. Relative
uncertainties in S02 emissions from single states range from 10% for the
larger emitters to 20% for the smaller emitters. Within a state or
province, the uncertainty in emission of S02 from a given class of source
varies from roughly 15 to 100%, with the largest sources generally having
the smallest percentage uncertainties. Uncertainties of individual sources
appear to be in the same range. Uncertainties in NOX emission are
generally larger than those for
While it is difficult to find any particular flaw in the method used
by Work Group 3B to evaluate uncertainties, we feel that the results are
generally optimistic. For example, we are extremely reluctant to believe
that total United States emission of SC>2 is known to 3%. We also feel that
very few point-source emissions are known to 15%.
Nevertheless, uncertainties in emissions are surely much lower than
those in other aspects of acid deposition and associated transport models.
For example, the best natural emission estimates for S02 in eastern North
America are at least an order of magnitude smaller than currently estimated
anthropogenic emissions. Dry deposition of SC>2 , which is commonly believed
to be comparable to wet deposition of sulfate, is hardly more than guessed
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at for natural ecosystems. Thus, outflow of sulfur to the Atlantic Ocean,
which is the difference between total emission in eastern North America and
total deposition there, is also not well known. Limitations like this led
Work Group 2 to state in its Executive Summary (Chapter 11 of Final Report
2F) that wet deposition, dry deposition, and outflow of sulfur to the
Atlantic are all "roughly equal." Considering the large differences in
assumptions and parameters of the various transport models, the differences
in their results, and the unknown absolute accuracy of any of them, we
conclude that uncertainties in regional emissions are not likely to be the
limiting factor in developing and evaluating transport models for many
years to come.
Remarks on individual reports
Final Report (2F)
The Final Report (2F) of Work Group 2 is a fair and accurate summary
of the several supporting documents. It is written well. Many of the
remarks of the previous section refer to this report.
The Final Report discusses the various transport models evenhandedly.
Their limitations are stated directly. The strengths and weaknesses of
transfer matrices are discussed clearly at the outset. Where the report is
not intended to justify exhaustively certain aspects of the models (e.g.,
the discussion of deposition in Chapter 5), it says so.
We recommend that serious evaluation of the results of Work Group 2 be
based on its entire product, i.e., the four subgroup reports as well as
the Final Report.
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Final Report - Atmospheric Sciences Subgroup (2F-A)
The report of the Atmospheric Sciences Subgroup does not pretend to be
comprehensive, and should not be judged as such. Rather, it was intended
to provide "some information to Memorandum of Intent modelers in areas of
particular concern." It consists of four articles. The first two are
detailed, thorough and accurate, and were written expressly for the MOI
work. The last two, on dry deposition and precipitation scavenging, are
executive summaries from the EPA Critical Assessment Review Papers, and
were added later. Brief summaries of each are given below.
Paper 1 -"Sulfur and Nitrogen Chemistry in Long-range Transport
Models" by J. L. Durham et al.
This paper contains a detailed and accurate summary of homogeneous
(gas-phase) and heterogeneous (in water or on solid particles) chemistry of
nitrogen and sulfur. Nitrogen chemistry in the presence of hydrocarbons is
summarized as follows: "the major observed phenomenon in the system is
conversion of NO to N02 • • • accompanied by accumulation of 03." This
section contains considerable discussion of various reaction rates, but
with no conclusion that any particular values can be applied generally.
The complexities of oxidation of S02 are also covered in detail.
After concluding that gas-phase oxidation of 302 maY ^e dominated by the OH
radical in both the clean and polluted troposphere, the writers note that
the maximum rates of oxidation of S02 observed repeatedly in polluted
atmospheres cannot be accounted for even by summed gas-phase reaction
rates. Except for organics, the rates of oxidation of S02 in droplets are
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fairly well understood. Oxidation by 1^2 is the only reaction fast enough
to produce potentially important amounts of H2S04 in the troposphere. The
role of metallic catalysts in aqueous oxidation is still poorly understood.
The only important heterogeneous reaction on the surfaces of solid aerosol
particles involves soot.
Do field and laboratory studies agree? The paper states that
"uncritical acceptance of all of the rates (in a sample calculation) . . .
would lead to the S02 conversion rate exceeding 40% per hour. However, if
only the well-established rates are considered, the S02 conversion rate
becomes < 1.1% hour"*-." The uncertainty in this calculation can be
contrasted with other statements from this paper: "Field measurements on
the rates of S02 oxidation indicate that maximum S02 oxidation rates of the
order of 10% per hour are typical of many atmospheric pollution scenarios,"
and "the average diurnal rate is 1% per hour." In other words, this paper
amply confirms that great uncertainties still exist in the measurements and
even in the mechanisms for oxidizing S02 to H2S04 , and implies that it will
be a long time before these uncertainties are removed.
Paper 2 -"The Seasonal Dependence of Atmospheric Deposition and
Chemical Transformation Rates for Sulfur and Nitrogen Compounds"
by M. Lusis and L. Shenfeld.
A one-sentence summary of this comprehensive collection of seasonal
data is given on their page 2-31: "It must be concluded that at present
the available plume data is too conflicting to draw any firm conclusions
about the seasonal dependence of the 302 oxidation rate in plumes."
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Paper 3 -"Dry Deposition of Acid Substances" by B. Hicks.
Its opening sentence describes the situation succinctly: "Recent
workshops and committee deliberations have agreed that is is not possible
to monitor the dry deposition of acidic atmospheric materials directly."
The paper also outlines the difficulties and problems in any other
technique.
Paper 4 -"Precipitation Scavenging Processes" by J. Hales.
This paper is not actually a product of the United States-Canadian
Work Groups, but rather the Executive Summary from the EPA Critical
Assessment Review Paper on Acid Deposition.
We note that this review of atmospheric science material (2F-A) was
"prepared and compiled for the purposes of providing some background and
support for the modeling work" (emphasis added).
Final Report - Regional Modeling Subgroup (2F-M)
This report is well-written and makes its points clearly. Assumptions
in techniques and limitations of results are given adequately. The
performance of each of the eight models is reviewed in detail. The
conclusions drawn are reasonable. The writers were wise to include as much
raw data as they did, particularly in light of the critical role that
models were expected to play at the outset of the MOI process.
More specific remarks on modeling are given above.
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Final Report - Monitoring and Interpretation Subgroup (2F-I)
This is a very good treatise, which generally meets its terms of
reference. It is an excellent introduction to the deposition program and
its interpretation.
In spite of its length, we have the distinct impression that much of
the literature surveyed here is still under-interpreted. (We have the same
feeling about much of the other MOI material, as well.) Apparently, the
field of acid precipitation is growing so rapidly and its practitioners ara
so active that it is difficult to find qualified people who have enough
time to synthesize it into a coherent whole. This is one of the great
needs at present.
The section on "Preliminary data interpretation" seems a bit forced.
We would have preferred a briefer treatment of the ways to interpret data,
followed by a deeper interpretation of available data. The Monitoring and
Interpretation Subgroup had a golden opportunity to illustrate the role
that innovative scientific thought can play in the acid-deposition question
and should have been given more resources to do so. Considering that this
subgroup almost did not exist, though, the product is quite acceptable.
Proper interpretation of monitoring data, however, requires critical
attention at each step. For example, the use of single-station sector
analysis as an independent way to derive source-receptor relationships has
several limitations which may temper one's conclusions: (1) Because many
air-mass trajectories are curvilinear, they may originate in a different
sector than indicated by their final direction. (2) The method is
inherently episodic—conclusions may be influenced greatly by the
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selection of incidents. (3) Wet deposition is a function of volume of
precipitation, as well as trajectory. (4) Local and distant sources cannot
be distinguished by sector analysis alone. It is not clear that the
Monitoring and Interpretation Subgroup considered these factors fully.
The section on temporal trends of deposition and its relation to
trends in emission could have been expanded and refined. This critical
topic needs a great deal more attention and more data. The record is very
short.
The treatment of "other substances" was superficial, as it was in the
Summary Report. Organic materials were treated better than ozone and
metals.
The report offers seven recommendations concerning deposition
monitoring. Because a solid data base is so important to understanding
deposition, we endorse these recommendations strongly.
Final Report - Local and Mesoscale Subgroup (2F-L)
This report is excellent. Its literature review is thorough and
digested. The relevant models and their characteristics are documented in
detail. Scientific knowledge and models derived from this evidence are
presented in a balanced fashion. The potential weight of local and
uiesoscale effects relative to long-range effects is shown carefully. The
present limitations of local and mesoscale analysis are given, together
with recommendations for future work. This fine report should serve as the
basis for renewed interest in local and mesoscale effects.
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Did Work Group 2 satisfy its terms of reference?
The seven (six originally plus one added later) terms of reference for
Work Group 2 are given in Appendix 3 of this report. Three were related
directly to transport models. Ironically, we believe that Work Group 2
satisfied the other terras of reference, but not those associated with
transport models. In the paragraphs below, we discuss each term of
reference.
"identify source regions and applicable emission, data bases" This was
done satisfactorily, with data supplied by Work Group 3B.
"evaluate and employ available field measurements, monitoring data and
other information" This term of reference was met, both by using field
studies to help understand transport (Monitoring and Interpretation
Subgroup Px.eport) and by using the monitoring data to help evaluate the
transport models.
"assess historic trends of emissions, ambient concentrations and
atmospheric deposition trends to gain further insights into source-
receptor relationships for quality, including deposition" This was done,
primarily by the Monitoring and Interpretation Subgroup; however, much
more could have been done.
"prepare proposals for the "Research, Modelling and Monitoring"
element of an agreement" Thirteen proposals appear in Chapter 11 of Final
Report 2F.
"evaluate and select atmospheric transport models and data bases to be
used" This term of reference was met in the sense that eight available
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transport models were selected for further consideration. To the extent
that the performances of the eight models were to be evaluated and at least
one selected with confidence for further use, this goal was not met. As
stated in the preface to the Regional Modeling Subgroup Report (2F-J1), "In
view of significant uncertainties in the model input and validation data,
which could not be quantified within the time allotted for preparation of
this report, no recommendations on the absolute performance of the regional
models can be made at this time." In other words, all eight models were
considered unverified and unverifiable.
"relate emissions from the source regions to loadings in each
identified sensitive area" This task was fulfilled in the narrow sense
that calculations were run with each model. Work Group 2 made it quite
clear, however, that the results of this exercise were not considered
reliable. Thus, this term of reference was not met. For example, the
Executive Summary (Chapter 11 of Final Report 2F) states: "The transfer
matrices of the different models exhibit variations among the magnitudes of
the transfer matrix elements. This variability could lead to substantial
differences in the selection of optimum emission reduction scenarios
depending upon the particular model applied and the level of detail
required. ... It has not been possible to date to choose a 'best model1
among the eight or to produce with confidence a 'best estimate' single
transfer matrix for each variable based upon a valid statistical analysis
of all model results."
"calculate emission reductions required from source regions to achieve
proposed reductions in air pollutant concentration and deposition rates
which would be necessary in order to protect sensitive areas" Work Group 2
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stated that it had not met this term of reference. According to Chapter 4
of Final Report 2F, "it is unlikely that they (the models) will correctly
predict the resulting changes in dry and wet deposition patterns due to
reductions in concentrations of SC>2, H-2^2» or both." From the Executive
Summary: "The adequacy of available models to predict the results of
alternative emission patterns is uncertain."
In this context, we are puzzled by a statement in the Executive
Summary which is both self-contradictory and in opposition to other
conclusions of Work Group 2: "Work Group 2 has provided the kind of
'operational tools' required for calculating emission reductions required
to achieve concentrations and deposition rates necessary to protect
sensitive areas; however, the Work Group has not been able to provide
definitive guidance concerning a preferred model or the quantitative degree
of confidence that can be placed in any of the individual models." How can
a model be an "operational tool" if its accuracy is unknown? Work Group 2
has not provided the kind of operational tools which can be used to select
control strategies for 862• Work Group 2 has evaluated eight preliminary
models, some of which may, with considerable refinement, someday become
true operational tools.
Similar conclusions about models have been drawn by others. The OTA.
report cited above quotes a report by the Utility Air Regulatory Group
(UARG) on five transport models to the effect that they "cannot, at the
present time, provide adequate information that would assist in
distinguishing between policy options." On the other hand, the UARG review
also concluded that "the best available methodology currently available for
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investigating the transport, transformation, and deposition of atmospheric
pollutants on a regional scale involves the use of long-range transport
models."
In our opinion, the inadequate performance of the eight transport
models should not be considered the fault of the modelers or of the models.
The models were the state-of-the-art for that time. Their failure meant
merely that they were asked to do too much too soon in their development.
This result supported those members of Work Group 2 who maintained from the
beginning that decisions for reducing acidic deposition should not be based
solely on information which had been processed through models. It now
appears that it will be a good many years before transport models will be
ready to assume the responsibility accorded them in August 1980 in the MOI
terras of reference.
Information from tracers
The outlook for understanding the source-receptor relationship, even
when distant sources are involved, may not be as bleak as it would appear
from transport models alone. Tracers may provide an independent way to
derive such information. To date, the accuracy of transport models has
been impossible to verify because sulfate from one region cannot be
discriminated from sulfate from another region. But additional substances
which can be linked with one or another region offer ways to deduce the
regional origins of sulfate in air or in deposition.
Tracers may be pollutants already present (referred to as "natural"
tracers in Chapter 8 of Final Report 2F) or substances introduced
deliberately. Both types of tracers may be of great value, as acknowledged
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in Chapter 8, and are being developed intensively at present. Deliberate
tracers, such as SFg, heavy methanes, or perfluorocarbons, have been
exploited longer than the other type, but may be more limited in the long
term because they are usually long-lived gases whose atmospheric behavior
does not mimic that of the sulfur system. The principal usefulness of
these tracers is to study large-scale trajectories and diffusion.
Pre-existing tracers, especially those involving minor elements in the
aerosol, may offer more direct information on sources and transport of
atmospheric sulfur. Trace elements have been used successfully to
determine the relative importances of various sources of urban aerosol.
This approach is generally referred to as "urban receptor modeling" or the
"chemical element balance" method. Curiously, receptor modeling was not
mentioned by Work Group 2. One possible reason is that urban receptor
modeling is not directly applicable to acid precipitation, whose scale is
hundreds or thousands of kilometers and where regions rather than
individual stacks are the relevant sources.
Regional-scale source apportionment for aerosols is developing
rapidly. It is now known that aerosols from several source regions in
eastern North America have characteristic elemental signatures that can be
followed and discriminated hundreds of kilometers downwind. With proper
care, the major source areas for secondary constituents such as sulfate can
also be determined with reasonable confidence.
It would thus appear that tracer techniques, singly or in combination,
offer an alternative way to deduce the source-receptor relationship, and
that transport models need no longer be relied upon exclusively.
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VII - REVIEW OF WORK GROUP 3B REPORT - EMISSIONS, COSTS
AND ENGINEERING ASSESSMENT
Organization of report
Work Group 3B was given three major charges: to identify control
technologies (pollutants unspecified) and determine their costs, to
evaluate emissions (present emissions, better estimates of past trends, and
most probable future emissions), and to prepare proposals for research and
development projects aimed at improved control of emissions. Accordingly,
the report is built around these three principal topics. Emissions receive
nearly 200 pages of text, control technologies just over 100 pages, and
research and development nearly 50 pages. Most attention goes to S02, with
NOX second, and all other pollutants a distant third. "Other pollutants"
as a group are given less than 30 pages.
General remarks
This report contains a huge amount of information. Clearly, a great
deal of work has gone into preparing it. It will be of much use to many
persons and agencies.
Unfortunately, however, it contains major flaws which limit its value
significantly. The quality of writing and organization is very poor,
certainly the worst of the three reports this panel reviewed. This is not
just an academic matter, for the report is very difficult to read,
understand, and deal with.
For example, the Table of Contents is very difficult to use. The
headings are often insufficiently descriptive, if not misleading or wrong.
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The organization and titling of the chapters and sections make the report
very difficult to use. For example, as Chapter A is currently
organized, it is nearly impossible for the reader to sense the true
organization of the report as a whole. Chapcer 3 is nisleadingly entitled
"Trends in Emissions", when its most important section, current emissions,
is not a trend. Chapter C, on control technology and costs, should have
been so labeled instead of the inappropriate "Emission Source Sectors."
The report has not been carefully edited; it is full of misspellings,
poor grammar, and cumbersome expressions. In Appendix A, the reader is
referred to Chapter C for the 1980 emissions, when they are actually in
Chapter B. A problem with incorrect word-processing technique following
subscripts occurs throughout. Again we stress that the net effect of all
these errors is to make Report 3B much less readable than it should be.
The report is more a compendium of facts than a digestion of them.
Perhaps this resulted from the size of the task relative to the
resources and deadlines. If so, it would be regrettable. We note that
this report appeared several months before those of Work Groups 1 and 2
(June 1982 vs. January 1983 and November 1982, respectively).
It is true that matters of emission and control tend to be more
cut-and-dried than those of atmospheric transport, transformation,
deposition, and interaction with the biosphere, but this is no reason to
subjugate critical thought and reasoning to the extent that the writers of
report 3B have. For example, we are offered the emission inventory for
1980, together with a detailed discussion on how it and its uncertainties
were calculated. For the United States, the probable errors in both S02
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and NOX are given as about 3%. These figures are not discussed further,
even though they are almost certainly far too low. The projected emissions
are not seriously questioned, as they should be. The recommendations for
research and development are merely listed, without any attempt to rank
them in terms of inherent value, promise, etc. It is widely assumed that
emissions are the best-known component of the entire acid-rain phenomenon.
The writers of report 3B had an opportunity to comment on this topic, but
missed it.
Most importantly, the writers have offered us no statement on what
their report means. Decision-makers in both the United States and Canadian
governments, who often do not have technical backgrounds, need such a
section. As a result of its absence, intermediaries less familiar with the
original data will have to try to determine the meaning of this report for
them.
Remarks on specific topics
Identifying control technologies and costs
In our view, report 3B identifies all relevant control technologies
and assesses their costs reasonably. In this sense, the report is a very
useful handbook, although perhaps unduly pessimistic about prospects for
improvements in control technologies. Unit control costs (per kilogram of
sulfur) vary by nearly a factor of 100, but the report does not develop the
implications of this important finding.
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Emissions
Methods of calculating past emissions appear to be reasonable,
although little detail is given. We note that the report does not say
whether its historical trends are considered superior to other published
trends, or even different from them. Recall that one of the terms of
reference was to generate "improved" historical trends.
The estimates of current emissions also seem reasonable, as do' the
methods used to arrive at them. As noted above, the uncertainties seen
quite low, especially for the United States as a whole. Here the
methodology may be questionable. The technique used for combining
uncertainties requires errors to be random and nonsystematic; probably
neither condition is satisfied in practice. Consequently, we believe that
the actual uncertainties may be several times greater than those given in
the report.
Concerning projected emissions of S0£ and NOX, we note that report 3B
offers a single way of calculating each, without documenting that this
scenario is indeed the most probable, as specified in the terras of
reference. We fully realize the large effort involved in making
projections, but feel that their results are insufficiently supported.
Reasons for choosing one scenario or model over another should be given.
In addition, the effect of variations of several key parameters should be
considered, such as the rate of increase in generating electricity, the
degree of switching from oil to coal, the extent of replacing older power
plants by newer ones with tighter emission controls, and the mix of NOX
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emission characteristics for new vehicles. To the extent that projections
are intended to help plan for the future, the effects of reasonable
variations in these parameters would be useful.
Concerning research and development, we found it interesting that Work
Group 33 spent considerably more effort in identifying and tabulating
current projects than it did in proposing new ones or areas of
concentration for the future. The list of areas for future research cited
here is too long to be regarded neutrally; the projects must be ranked or
rated in some way.
The report indicates that per capita emissions of S02 are twice as
large in Canada as in the U.S., but the implications are not developed.
Did Work Group 3B meet its terms of reference?
Work Group 3B was given six terms of reference, on three topics; one
was deleted by the Work Group. We feel that three of the five remaining
terms of reference were met. We now list each term of reference and
whether it was met:
"identify control technologies, which are available presently or in
the near future, and their associated costs" This was met partially. The
report lists unit costs, but does not project costs for any abatement
scenarios.
"review available data bases in order to establish improved jiistorical
emission trends for defined source regions" Some data bases were reviewed;
the report does not say whether all were. Historical emission trends
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for source regions were produced, but the report does not specify whether
they are considered better than earlier trends. Consequently, this term of
reference was not met.
"determine current emission rates fron defined source regions" This
was met satisfactorily.
"project future emission rates from defined source regions for most
probable economic growth and pollution control conditions" Emissions were
projected from specific source regions under a certain growth pattern and
for the present degree of pollution controls. It was not stated whether
the conditions for economic growth or pollution control were the most
probable ones. Therefore, this term of reference has not been met.
"prepare proposals for the "Applied Research and Development"
element of an agreement" This was met satisfactorily, but without any
ranking of proposals.
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APPENDIX 1
PANELISTS' INSTITUTIONAL AFFILIATIONS
AND SCIENTIFIC DISCIPLINES
OFFICE OF SCIENCE AND TECHNOLOGY POLICY
ACID RAIN PEER REVIEW PANEL
Chairman
William A. Nierenberg Physicist-
Director Oceanographer
Scripps Institution of Oceanography
La Jolla, California
Vice Chairman
William C. Ackermann Civil Engineer
Department of Civil Engineering
University of Illinois
Urbana, Illinois
Members
David H. Evans Fish Physiologist
Department of Zoology
University of Florida
Gainesville, Florida
Gene E. Likens Ecologist
Section of Ecology and Systematics
Cornell University
Ithaca, New York
Ruth Patrick Limnologist
Department of Limnology
Academy of Natural Sciences
Philadelphia, Pennsylvania
Kenneth A. Rahn Atmospheric Chemist
Center for Atmospheric Chemistry Studies
Graduate School of Oceanography
University of Rhode Island
Narragansett, Rhode Island
F. Sherwood Rowland Atmospheric Chemist
Department of Chemistry
University of California
Irvine, California
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APPENDIX 1. CONTINUED
Members, continued
Malvin A. Ruderraan Physicist
Department of Physics
Columbia University
New York, New York
S. Fred Singer Environmental
Department of Environmental Sciences Scientist
University of Virginia
Charlottesville, Virginia
Executive Secretary
John K. Robertson Geochemist
Science Research Laboratory
U. S. Military Academy
West Point, New York
Office of Science and Technology Policy
Tom Pestorius Mechanical Engineer
Senior Policy Analyst
Office of Science and Technology Policy
Washington, DC
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APPENDIX 2
CHARGES OF THE PANEL CHARTER
OFFICE OF SCI.-:KCE A?;D TECHNOLOGY POLICY
ACIO PAIN' PEER REVI,-:w PA:.:EL
1 . Conmittee's Official Designation:
Acid Rain Peer Review Panel
2. Objectives and Scope of Activities and Duties:
0 Review the reports of the Working Groups directed hy the 5 August
1980 f'er.orandun of Intent (MOI) on Transboundary Air Pollution
between the U.S. and Canada talcing into account currently available
scientific and technical knowledge on the production, transport,
transformation, and deposition of pollutants; the effect of these
pollutants on our surroundings, and the economics and engineering
estimates of control technology performance.
0 Provide an assessnent of:
(a) whether the Working Groups have fulfilled their charters under
the Menorandun of Intent;
(b) whether the Working Groups have utilized all significant
research and data impacting on their topics in for^.ulatinp
their reports;
(c) whether the Working Groups' reports:
(1) clearly identify their assunptions,
(2) present and discuss alternate theories and explanations,
(3) provide support of conclusions and recommendations by the
data and other evidence considered, and
(4) address the uncertainties in the available knowledge and
its impact on their recommendations.
0 Provide an independent assessment of the uncertainties in available
scientific and technical information on which recommendations of the
working groups are based.
0 Recommend further research and monitoring tasks which will reduce
uncertainties in the scientific and technical knowledge.
0 Provide a written report, with executive surnary addressing the
above charter.
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APPENDIX 3
WORK GROUP STRUCTURE FOR NEGOTIATION OF
A TRANSBOUNDARY AIR POLLUTION AGREEMENT
I. Purpose
To establish technical and scientific work groups to assist in preparations
for and the conduct of negotiations on a bilateral transboundary air
pollution agreement. These groups shall include:
1. Impact Assessment Work Group
2. Atmospheric Modelling Work Group
3A. Strategies Development and Implementation Work Group
33. Emissions, Costs and Engineering Assessment Subgroup
4. Legal, Institutional Arrangements and Drafting Work Group
II. Terras of Reference
A. General
1. The Work Groups shall function under the general direction and policy
guidance of a Canada/United States Coordinating Committee co-chaired by the
Department of External Affairs and the Department of State.
2. The Work Groups shall provide reports assembling and analyzing
information and identifying measures as outlined in Part B below, which
will provide the basis of proposals for inclusion in a transboundary air
pollution agreement. These reports shall be provided by January 1982 and
shall be based on available information.
3. Within one month of the establishment of the Work Groups, they shall
submit to the Canada/United States Coordinating Committee a work plan to
accomplish the specific tasks outlined in Part 8, below. Additionally,
each Work Group shall submit an interim report by January 15, 1981.
4. During the course of negotiations and under the general direction and
policy guidance of the Coordinating Committee, the Work Groups shall assist
the Coordinating Committee as required.
5. Nothing in the foregoing shall preclude subsequent alteration of the
tasks of the Work Groups or the establishment of additional Work Groups as
may be agreed upon by the Governments.
This is the Annex of the "Memorandum of Intent between the Government of
Canada and the Government of the United States of America concerning
Transboundary Air Pollution."
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APPENDIX 3, CONTINUED
B. Specific
The specific tasks of the Work Groups are set forth below.
1. Impact Assessment Work Group
The Group will provide information on the current and projected impact of
air pollutants on sensitive receptor areas, and prepare proposals for the
"Research, Modelling and Monitoring" element of an agreement.
In carrying out this work, the Group will:
-identify and assess physical and biological consequences possibly related
to transboundary air pollution;
-determine the present status of physical and biological indicators which
characterize the ecological stability of each sensitive area identified;
-review available data bases to establish more accurately historic adverse
environmental impacts;
-determine the current adverse environmental impact within identified
sensitive areas-annual, seasonal and episodic;
-determine the release of residues potentially related to transboundary air
pollution, including possible episodic release from snowpack melt in
sensitive areas;
-assess the years remaining before significant ecological changes are
sustained within identified sensitive areas;
-propose reductions in the air pollutant deposition rates-annual, seasonal
and episodic-which would be necessary to protect identified sensitive
areas; and
-prepare proposals for the "Research, Modelling and Monitoring" element of
an agreement.
2. Atmospheric Modelling Work Group
The Group will provide information based on cooperative atmospheric
modelling activities leading to an understanding of the transport of air
pollutants between source regions and sensitive areas, and prepare
proposals for the "Research, Modelling and Monitoring" element of an
agreement. As a first priority the Group will by October 1, 1980 provide
initial guidance on suitable atmospheric transport models to be used in
preliminary assessment activities.
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APPENDIX 3, CONTINUED
2
In carrying out its work, the Group will :
-identify source regions and applicable emission data bases;
-evaluate and select atmospheric transport models and data bases to be used;
-relate emissions from the source regions to loadings in each identified
sensitive area;
-calculate emission reductions required from source regions to achieve
proposed reductions in air pollutant concentration and deposition rates
which would be necessary in order to protect sensitive areas;
-assess historic trends of emissions, ambient concentrations and atmospheric
deposition trends to gain further insights into source receptor
relationships for air quality, including deposition; and
-prepare proposals for the "Research, Modelling and Monitoring" element of an
agreement.
3A. Strategies Development and Implementation Work Group
The Group will identify, assess and propose options for the "Control" element
of an agreement. Subject to the overall direction of the Coordinating
Committee, it will be responsible also for coordination of the activities of
Work Groups I and II. It will have one subgroup.
In carrying out its work, the Group will:
- prepare various strategy packages for the Coordinating Committee designed
to achieve proposed emission reductions;
-coordinate with other Work Groups to increase the effectiveness of these
packages;
-identify monitoring requirements for the implementation of any tentatively
agreed-upon emission-reduction strategy for each country;
-propose additional means to further coordinate the air quality programs of
the two countries; and
-prepare proposals relating to the actions each Government would need to
take to implement the various strategy options.
work Group 2 added another specific term of reference to its work and
inserted it between the fourth and fifth terms of reference given here. It
reads (Work Group 2 Final Report, Appendix 1, pg. Al-2): "evaluate and
employ available field measurements, monitoring data and other
information."
3
Work Group 3A did not publish a final report.
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APPENDIX 3. CONTINUED
3B. Emissions, Costs and Engineering Assessment Subgroup
This Subgroup will provide support to the development of the "Control"
element of an agreement. It will also prepare proposals for the "Applied
Research and Development" element of an agreement.
In carrying out its work, the Subgroup will:
-identify control technologies, which are available presently or in the near
future, and their associated costs;
-review available data bases in order to establish improved historical
emission trends for defined source regions;
-determine current emission rates from defined source regions;
-project future emission rates from defined source regions for most probable
economic growth and pollution control conditions;
ti
-project future emission rates resulting from the implementation of
proposed strategy packages, and associated costs of implementing the
proposed strategy packages; and
-prepare proposals for the "Applied Research and Development" element of an
agreement.
4. Legal, Institutional and Drafting Uork Group
The Group will:
-develop the legal elements of an agreement such as notification and
consultation, equal access, non-discrimination, liability and
compensation;
-propose institutional arrangements needed to give effect to an agreement
and monitor its implementation; and
-review proposals of the Work Groups and refine language of draft
provisions of an agreement.
+
Work Group 3B deleted this specific term of reference from its work (Work
Group 3B Final Report, Appendix 1, pg. A-2).
Work Group 4 did not publish a final report.
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APPENDIX 4
MATERIALS PROVIDED TO THE PANEL
September 1982 - Work Group 3B Final Report, dated June 1982.
- Outlines of each Work Group's report and lists of the United
States and Canadian members in each Work Group. Prepared
by the Executive Secretary.
October - - Interim Draft of "The Regional Implications of Transported
November 1982 Air Pollutants: An Assessment of Acidic Deposition and
Ozone", Office of Technology Assessment, dated July 1982.
- Work Group Reports as follows:
Work Group 1
• Phase I Interim Report, dated February 1981.
o Phase II Interim Working Paper, dated October 1981.
« Phase III Draft Report, marked by the United States
Co-chairman to indicate sections not yet agreed to by
the Work Group, not dated.
Work Group 2
9 Phase I Interim Report, dated January 1981.
« Addendum to Appendix 8 - transfer matrices of the
Phase I Report on Atmospheric Modeling, dated
6 February 1981, revised 10 July 1981.
» Atmospheric Transport and Deposition Modeling:
Inventory, Analysis and Recommendations, dated
December 1980, revised June 1981.
•» Phase II Working Report (2-15), dated 10 July 1981.
•» Atmospheric Sciences Review (2-14), dated 10 July
1981.
3 Modeling Subgroup Report (2-13), dated 10 July 1981.
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APPENDIX 4, CONTINUED
« Model Profiles
o Documentation of the Atmospheric Environment
Service Long-Range Transport of Air Pollutants
Model AES-LRT (2-5), dated 15 May 1981.
o Documentation of the Advanced Statistical
Trajectory Regional Air Pollution Model ASTRAP
(2-6), dated 12 May 1981.
o Documentation of the Eastern North American
Model for Air Pollution ENAMAP (2-7), dated
30 June 1981.
o Documentation of the Ontario Ministry of the
Environment Statistical LRT Model OME-LRT (2-8),
dated 31 March 1981.
« Documentation of the University of Michigan
Atmospheric Contribution to Inter-Regional
Deposition Model UMACID (2-10), dated
24 June 1981.
o Documentation of the Transport of Regional
Anthropogenic Nitrogen and Sulfur Model MEP-TRANS
(2-11), dated 30 June 1981.
o Documentation of The Capita Monte Carlo Model
MCARLO (2-12), dated 30 June 1981.
9 Phase III Draft Report 2F, dated 15 October 1982.
» Atmospheric Science Review Sub-group Report, 2F-A,
dated 15 October 1982.
• Local and Mesoscale Analysis Subgroup Report, 2F-L,
dated 15 October 1982.
« Monitoring and Interpretation Subgroup Report, 2F-I,
dated 15 October 1982.
» Regional Modeling Subgroup Report, 2F-M, dated
15 October 1982.
» Replacement pages for the four subgroup reports,
dated 11 November 1982.
Work Group 3A
9 Interim Report, dated January 1981.
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ACID RAIN PANEL REPORT
APPENDIX 4, CONTINUED
Work Group 3B
9 Interim Report, dated 15 January 1981.
- Draft copy of "High-Leverage Investment in the
Atmospheric Sciences and Related Disciplines", paper by
the Committee on Science, Engineering and Public
Policy, National Academy of Science, dated 22 October
1982.
- Draft of EPA Critical Assessment Document, Volumes 1 and
2, dated October 1982.
2 February 1983 - Drafts of "Modeling Uncertainty About Carbon
Dioxide" and "A Review of Estimates of Future
Carbon Dioxide Emissions", papers for review by the
Carbon Dioxide Assessment Committee, National Academy
of Science.
2 March 1983 - Work Group 2 Final Report, dated 15 November 1982.
- List of differences between the above report and the
draft given to the panel in November 1982. Prepared
by the Executive Secretary.
- Model Profile
9 Documentation of the Regional Clitnatological
Dispersion Model RCDM-2 (2-9), dated September 1982.
29 March 1983 - Work Group 1 Final Report, dated January 1983.
- List of differences between the above report and the
draft given to the panel in November 1982. Prepared
by the Executive Secretary.
April 1983 - Executive Summaries - Work Group Reports, dated
February 1983.
May 1983 - Public Comments:
9 American Petroleum Institute: "Role of Organic Litter
in Lake Acidification and Buffering"; "Using
Historical Data to Ascertain Lake Water pH Trends";
"Comments on the MOI Emission Inventory"; "Total
Primary Sulfate Emissions"; "Emissions Projections for
Industrial Boilers"; "Comments on the MOI Emission
Inventory Uncertainty Estimates".
» Everett and Associates: "Comments on Section 3, Aquatic
Impacts".
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APPENDIX 4, CONTINUED
9 Hunton and Williams, on behalf of the Utility Air
Regulatory Group: "Review and Critique of the Work
Group 1 Phase II and Phase III Impact Assessment of the
U.S.-Canadian Transboundary Treaty Negotiations";
"Review and Critique of the Work Group 2 Phase II and
Phase III Modeling Activities of the U.S.-Canadian
Transboundary Treaty Negotiations"; "Comments on the
Final Report of Workgroup 33".
July 1983 - "Acid Deposition in North America - A Review of the
Documents Prepared under the Memorandum of Intent
between Canada and the United States of America, 1980,
on Transboundary Air Pollution - II Technical
Report", prepared by the Royal Society of Canada for
the Government of Canada, dated May 1983.
October 1983 - "The Ups and Downs of Acid Rain". Preprint by
Fred Singer.
- "Observations in German Forests during the Late
Summer of 1983", memorandum from Dr. Ellis Cowling,
dated 7 October 1983.
- The following papers, most translated from German,
were offered to the panel:
« "Devastating effect of acid rain on forests described."
Stern, 28 October 1982, pp. 35, 36, 38.
* "The Disease Picture—Different Species of Trees, but
Identical Symptoms," by Peter Schuett. Bild der
Wissenschaft 12: 86-101, 1982.
» "Air Pollution—A Danger to Trees for over 100 years
now," by Karl Friedrich Wentzel. Bild der Wissenschaft
^2: 103-106, 1982.
• "Die Versauerung - Giftstoffe Reichern Sich An," by
Bernhard Ulrich. Bild der Wissenschaft 12: 108-119,
1982.
« "Production and Consumption of Hydrogen Ions in the
Ecosphere," by B. Ulrich. In Effects of Acid
Precipitation on Terrestrial Ecosystems, pp. 255-281.
Edited by T. C. Hutchinson and M. Havas. New York:
Plenum Press, 1978.
• "Theoretical Consideration of the Ion Cycle in Forest
Ecosystems," by B. Ulrich. Z. Pflanzenernaehr. Bodnek.
144 (6): 647-659, 1981.
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APPENDIX 4, CONTINUED
a The Destabilization of Forest Ecosystems by the
Accumulation of Air Contaminants," by B. Ulrich. Per
Forst und Holzwirt 36 (21): 525-532, 1981.
3 "Balances of Annual Element Fluxes Within Forest
Ecosystems in the Soiling Region," by E. Matzner and
B. Ulrich. Z. Pflanzenernaehr. Bodenk. 144 (6):
660-681, 1981.
* "Dangers for the Forest Ecosystem Due to Acid
Precipitation - Necessary Countermeasures: Soil Liming
and Exhaust Gas Purification," by B. Ulrich. Preprint.
* "Appendix 3 - Explanations for Filling Out the Form
'Recording Forest Damage1." Preprint.
» "Chemical Changes Due to Acid Precipitation in a
Loess-Derived Soil in Central Europe," by B. Ulrich, R.
Mayer, and P. K. Khanna. Soil Science 130 (4): 193-
199, 1980.
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APPENDIX 5
BENEFIT-COST ANALYSIS APPLIED TO THE ACID RAIN PROBLEM
S. FRED SINGER
Before making any decisions or taking actions, it is natural to inquire
about the benefits following from these actions and the cost involved. This
kind of reasoning applies to both public and private decision-making. But
public decision-making, in addition, involves the concept of equity, the
consideration of whether those who are paying the cost of certain actions
are also receiving all or most of the benefits.
Equity considerations aside, one needs some estimate of costs and
benefits, expressed in similar units, so that one can make a comparison. It
is most convenient, but not always easy, to express the benefits and costs
in monetary units. Much progress is being made in quantifying benefits in
areas which are usually considered to be unquantifiable—not only health
effects but also improvement in visibility, aesthetic effects, and the
When weighing benefits against costs, it is not sufficient to have the
benefits large enough to be commensurate with the costs, i.e., to have the
benefits approximately equal to the costs. All this means is that the net
benefits, that is, the difference between benefits and costs, are zero. But
that same result can always be obtained by doing nothing, in which case
assuredly the benefits as well as the costs would be zero; hence, the net
benefits would also be zero.
What we would like to do, in principle at least, is to make the net
benefits as large as possible. A simple theoretical discussion tells us
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APPENDIX 5, CONTINUED
that this is equivalent to a situation where the incremental benefits
resulting from a particular action are equal to the incremental cost. This
can be seen as follows. If incremental benefits were greater than
incremental costs, then it would pay to continue with our actions and
thereby increase the net benefits. On the other hand, if incremental
benefits are less than incremental costs, then we have gone too far. Figure
1 demonstrates this principle of marginal benefit-cost analysis.
Most of the costs are usually incurred as capital coses in the initial
period, while the benefits may extend over a longer period of time. It is
necessary, therefore, to "discount" both the costs and benefits to the same
year, say to the present, with the use of an appropriate interest rate, in
order to carry out our analysis. This is a detail perhaps, but it can be
important.
More generally, "dynamic" benefit-cost analysis deals with the problem
of optimization in the presence of many sources of pollution, with only some
of them—usually the new ones—subject to stringent controls. Under those
conditions, large sums can be invested without any immediate benefits.
(See, e.g., Fig. 2). The classic example is automobile pollution where
great pollution control costs may be incurred for new cars initially, but ^
where there can be no substantial improvements in air quality until almost
•*
all of the old cars have disappeared from the fleet. This is a general -/
problem where one has facilities that are "grandfathered," for example,
grandfathered electric utilities and grandfathered industries, which are not
required to control their pollution to the same degree as new plants. Thus,
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APPENDIX 5, CONTINUED
25 50 75 100
PERCENTAGE REDUCTION IN EMISSIONS
FIGURE 1. Typical costs and benefits associated with increasing reductions
in emissions. Note that zero net benefits , i.e. E-C occur both if nothing
is done (i.e., zero reduction) and for large reductions (where the
benefit-cost ratio B/C is 1). Maximum net benefits occur somewhere between
these two cases.
1970
2000
YEAR
FIGURE 2. Emissions of S02 as a function of time. Curve A: without
emission controls. Curve B: with controls, emissions gradually declining.
However, the imposition of extreme new source performance standards (NSPS)
can produce a perverse effect (Curve C) by encouraging the continued
operation of older power plants that do not have to comply with NSPS. Curve
D shows the effects of the 1977 Clean Air Act Amendments which actually
encouraged the use o£ higher sulfur coal. (All curves are drawn
schematically.)
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APPENDIX 5, CONTINUED
there is an incentive to make old plants last longer, because if they are
not required to have pollution control equipment they are cheaper to
operate. Dynamic benefit-cost analysis also takes into account that
there may be other sources of emissions, including natural sources, so that
working on only one industrial pollution source, like electric utilities,
may not be optimal.
Benefits
When we apply this analysis to the acid rain problem, we can identify a
number of benefits which would result if acid deposition were to diminish.
Many of these benefits have been described in the Work Group 3B Report, but
they have not been evaluated or even estimated. They could include
recreational fisheries, commercial fisheries, the aquatic ecosystem
generally, agriculture, forestry, the general preservation of the ecosystem,
x^ater supply for various human uses, effects on buildings and structures,
atmospheric visibility, and, finally, human health (morbidity and
mortality).
Benefit analysis proceeds in two steps: (1) one estimates how much
reduction in damage would result if acid deposition were to be decreased by
a certain percentage, say ten percent; and (2) one judges what an emission
reduction of, say, one million tons of sulfur dioxide per year implies in
terms of reduced acid deposition—at a particular S02 emission level.
Step 1 is within the province of Work Group 1. Step 2 belongs to Work Group
2, and involves the well-known scientific complications having to do with
(a) the degree of mixing as opposed to advection; (b) the degree of
conversion of S02 into sulfuric acid, including questions of nonlinearity
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ACID RAIN PANEL REPORT
APPENDIX 5. CONTINUED
and saturation effects; and (c) the presence of other pollutants, whether
man-made or natural, which produce similar final effects.
r
It is important to make some rough, even order-of-magnitude estimates.
* One should at least be able to decide which effects (or benefits) are more
important and which are of lesser importance. The methodologies for making
such determinations are available but the work has not been done. For
example, one methodology which is useful in many situations is to estimate
benefits by measuring "willingness to pay." Into this category falls the
topic of "liming," whereby lime is applied to lakes or water supplies in
order to reduce the acidity of the water. From the cost of the liming
effort, one can at least derive a lower limit to the benefits which come
about with reduced acidity.
Costs
Estimating the control costs of emissions which are thought to be the
precursors of acid deposition is also a difficult subject, but perhaps not
as difficult as estimating benefits. Cost estimates require knowledge in
areas of technology and atmospheric science.
*" First of all, it is important to know what technologies can be brought
. to bear for the removal of, say, sulfur at different stages in the
•^
combustion process, ranging from cleaning coal and removing sulfur during
burning, to removing S02 from flue gases. Because of the rapid evolution in
technology and because of uncertainties about reliability and costs of
different technologies, such knowledge is often hard to come by.
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APPENDIX 5, CONTINUED
The Work Group 3B Report addresses this matter, but Is not altogether
hopeful about the efficacy and reliability of control devices. It is our
view, after reviewing research in progress and consulting industry experts,
that the technical problems can and will be solved. According to this view,
the unit cost of pollution control should stabilize or even decrease in the
future.
The other quantitative input relates to dispersion of emissions, their
conversion into acids, and eventual deposition. Here, however, one may
proceed in steps, starting with the simplest model and proceeding to more
complicated ones. Certainly the simplest model is that of a "single box" in
which emissions from the eastern United States and Canada are received. In
this box nodel, reduction of emissions from a source anywhere has the same
value as reduction of emissions from another source. The problem then
simply becomes that of reducing S02 emissions from all present sources and
future sources as well.
A more realistic approximation, yet still quite simple, could divide
the transport problem into two parts: (1) local, i.e., less than 300 miles
from the source; and (2) distant, i.e., greater than 300 miles. One would
then argue that all sources in one "box" contribute a certain fraction of
their emissions to distant pollution, with the fraction being the same for
all sources.
There may, however, exist a serious pollution problem in the disposal of
the slurry-like waste material from flue gas desulfurization.
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APPENDIX 5, CONTINUED
Least-Cost Approach
Borrowing the concept of the "bubble," which is now widely used to
allow emissions trading within any given plant, it may be possible to apply
emissions trading to the whole region so that a least-cost approach to the
reduction of emissions can be put into effect. It is interesting that many
2
people are coming to this conclusion. Setting aside for a moment the
question of who pays for the control of pollution—ultimately always, of
course, the consumer—pollution control can then be achieved by the
least-cost method. This means that, initially, sulfur will be removed by
simple washing of coal (thereby removing the inorganic sulfur in pyrites)
and by pollution control in presently uncontrolled smelters. As noted by
Work Group 3B, these techniques cost (per kilogram of sulfur removed) only a
few percent of the cost of flue-gas scrubbing in a power plant burning
low-sulfur coal, yet a kilogram of sulfur removed by any method should have
an equivalent effect on air quality, according to the simple box model.
The approach just described is in strong contrast to the following
scenario which is economically quite inefficient. The argument is often
made that since pollution control is expensive, it is best to apply it to
industries that can afford it or that can easily pass along the costs. It
is argued that pollution control on smelters would make them noncompetitive
2
For example, David Hawkins, former EPA Assistant Administrator for Air
Quality in the Carter Administration, writing in AMICUS, proposes a wider
bubble approach.
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ACID RAIN PANEL REPORT
APPENDIX 5, CONTINUED
and put them out of business, but that control on utilities might add only a
few percent to the electricity bill of their customers. But if it costs the
utility 100 times more to remove a kilogram of sulfur as it does the
smelter, wouldn't it make more sense to ask the utility customers to pay the
smelters to remove the sulfur?
A practical way of achieving the least-cost approach to pollution
control is to introduce what are called transferable emission rights. This
would guarantee that the market will work in such a way as to achieve the
lowest-cost methods of removing pollution. A central authority,
presumably the government, would have to decide how much sulfur may be
admitted into the atmosphere, based on some benefit-cost considerations. By
limiting the number of rights sold or made available by other means, one can
control exactly the amount of sulfur emitted. The rights can either be
given away, for example to existing polluters who would be grandfathered, or
they could be auctioned off so as to create greater equity as well as a
source of money for the Treasury. The only important matter for the
least-cost approach is that rights be issued and that they be transferable.
The present approach of prescribing ultrastrict performance standards for
new sources is extremely costly and wasteful to society. A recent report by
the Congressional Budget Office shows that emission trading would lower
considerably the cost of S02 abatement (The Clean Air Act, The Electric
Utilities, and The Coal Market, April 1982).
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APPENDIX 5, CONTINUED
KILOGRAMS OF SULFUR REMOVED
FIGURE 3. Control costs vs. increasing reduction in SC>2 emissions. The
slope of the curves gives the cost per pound of sulfur removed. Curve A
illustrates the approach mandated by present legislation, focussing on BACT
(best available control technology), such as flue gas desulfurization.
Curve B illustrates schematically a "least-cost" approach which starts with
lowest-cost methods, such as low-sulfur coal or coal washing, before
proceeding to higher-cost approaches.
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ACID RAIN PANEL REPORT
APPENDIX 5, CONTINUED
To take an actual example, smelters would be inclined to sell their
rights to the utilities and use the money to control their pollution.
Smelters might even make some money because they can remove their pollution
at very little cost and they can sell their rights at a higher price. The
overall result would be to achieve the desired reduction of emissions at the
lowest cost to society as a whole or a much higher degree of pollution
control with no more money spent overall.
Conclusion
In the absence of even order-of-magnitude estimates of economic damage
attributable to acid deposition, and with emission control costs certainly
in the multibillion dollar range, one must question whether we are attacking
a million-dollar problem with a billion-dollar solution.
An additional caveat derives from the present scientific uncertainties:
Will a reduction in emissions produce proportionate reductions in deposition
and in the environmental impacts believed to be associated with acid
deposition?
U.S. Environmental Protection Agency
Region V. Library
230 South Dearborn Street
Chicago, Illinois 60604
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