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ACID
DEPOSITION
Atmospheric Processes en
Eastern North America
A Review of Current
Scientific Understanding
Committee on Atmospheric Transport and
Chemical Transformation in Acic Precipitation
Environmental Stuc~ies Boarc
Commission on Physical Sciences,
Mathematics, anc Resources
National Research Council
NATIONAL ACADEMY PRESS
Washington, D.C. 1983
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-NOTICE: The project that is the subject of this report
was approved by the Governing Board of the National
Research Council, whose members are drawn from the
councils of the National Academy of Sciences, the
National Academy of Engineering, and the Institute of
Medicine. The members of the committee responsible for
the report were chosen for their special competences and
with regard for appropriate balance.
This report has been reviewed by a group other than
the authors according to procedures approved by a Report
Review Committee consisting of members of the National
Academy of Sciences, the National Academy of Engineering,
and the Institute of Medicine.
The National Research Council was established by the
National Academy of Sciences in 1916 to associate the
broad community of science and technology with the
Academy's purposes of furthering knowledge and of
advising the federal government. The Council operates in
accordance with general policies determined by the
Academy under the authority of its congressional charter
of 1863, which establishes the Academy as a private,
nonprofit, self-governing membership corporation. The
Council has become the principal operating agency of both
the National Academy of Sciences and the National Academy
of Engineering in the conduct of their services to the
government, the public, and the scientific and
engineering communities. It is administered jointly by
both Academies and the Institute of Medicine. The
National Academy of Engineering and the Institute of
Medicine were established in 1964 and 1970, respectively,
under the charter of the National Academy of Sciences.
Library of Congress Catalog Card Number 83-61851
International Standard Book Number 0-309-03389-6
Available from
_ .
NATIONAL ACADEMY PRESS
2101 Constitution Avenue, N.W.
Washington, D.C. 20418
Printed in the United States of America
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N AT I O N A L
RESEARCH COUNCI L
2101 CONSTITUTION AVENUE WASHINGTON, D. C. 20418
OFFICE OF THE CHAIRMAN
This report was undertaken by the National Academies, funded in part
by a consortium of foundations*, because of the importance that we
attach to i lluminating the critical issues concerning acid rain.
The report summarizes current scientific understanding about what is
known and what is not known about relations between emissions of
acid f onning precursor gases and acid deposition. It should be of
considerable interest to policy makers involved in regulatory deci-
sion making and in setting research priorities.
Those charged with private and public policy decisions will be par-
ticularly interested in the study Committee' s evaluation of
currently available scientific evidence as it affects the issue of
linearity or non-linearity in relations between emissions and depo-
sition. The public policy implications of this relationship are of
major economic and political significance.
The Committee devotes a great deal of attention to discussion of
areas of uncertainty that are often the result of incomplete data.
But despite the uncertainties, and even though there is as yet no
complete understanding of the multiplicity of complex chemical
reactions and transport mechanisms, the Committee cone ludes that
there is no evidence that the relationship between emissions and
deposition in northeastern North America is substantially non-linear
when are rage d over a period of a year and over dimensions of the
order of a million square kilometers. It is the Committee's judg-
ment that if the emissions of sulfur dioxide f rom all sources in
thi s re gion were reduced }fly the same f raction, the re suit would be a
corresponding f Factional reduction in deposition. The data reviewed
by the Committee support this conclusion only in northeastern North
America. The judgment is based on several pieces of evidence.
*Carnegie Corporation of New York
Charles 13. Culpeper Foundation, Inc.
The Wi lliarn and Flora Hewlett Foundation
The John D. and Catherine T. MacArthur Foundation
The Andrew W. Mellon Foundation
The Rockef eller Foundation
The Alf red P. Sloan Foundation
THE NATIONAL RESEARCH COUNCIL IS THE PRINCIPAL OPERAllNG AGENCY OF THE NATIONAL ACADEMY OF SCIENCES AND THE NATIONAL ACADEMY OF ENGINEERING
TO SE RVE GOVERNMENT AND OrH ER ORGANIZATIONS .
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One is the well documented observation that the molar ratios of
sulfates to nitrates deposited at many observation points in this
region are nearly constant, and are similar to the molar ratios of
the integrated emissions. The Committee believes that the simplest
and most direct interpretation of this observation is the one they
have given. A second observation that supports the Committee' s
judgment comes from a 13-year run of observations at a single
location in North America that shows the linear relationship between
deposition at this one site and overall emissions. Although these
observations were made at a single geographic point, they represent
the result of well designed and carefully taken measurements.
Finally, the j udgment draws upon the results of recent laboratory
studies that are di scussed in the report.
The Academies' process of selecting a di~rersif led, expert study
Committee and subjecting the Conunittee's report to a substantive
review was carefully followed in the preparation of this document.
In fact, because of the importance of this particular question, the
review procedure took a longer time than usual and involved a larger
number of critical readers than is customary.
I believe that we could not have found a more expert panel or have
subjected this report to a more searching review. I hope that this
report will help inf arm t'ne public policy decision making process
and will also permit the design of research programs that will
result in more complete scientific data leading to more definitive
conclusions and recommendations in the future.
Sincere ly,
Frank Pres s
Chairman
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Committee on Atmospheric Transport and
Chemical Transformation in Acic Precipitation
JACK CALVERT, National Center for Atmospheric Research,
Chairman
JAMES N. GALLOWAY, University of Virginia
JEREMY M. HALES, Battelle Pacific Northwest Laboratories
GEORGE M. HIDY, Environmental Research & Technology, Inc.
JAY JACOBSON, Boyce Thompson Institute
ALLAN LAZRUS, National Center for Atmospheric Research
JOHN MILLER, National Oceanic and Atmospheric
Administration
VOLKER MOHNEN, State University of New York, Albany
MYRON F. OMAN, Staff Officer
v
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Environmental Studies Board
DANIEL OKUN, University of North Carolina, Vice Chairman
ALVIN ALM, John F. Kennedy School of Government, Harvard
University
JOHN CAIRNS, JR., Virginia Polytechnic Institute
J. CLARENCE DAVIES, The Conservation Foundation
JOHN FARRINGTON, Woods Hole Oceanographic Institution
JAMES A. FAY, Massachusetts Institute of Technology
GEORGE M. HIDY, Environmental Research & Technology, Inc.
MARGARET HITCHCOCK, Yale University School of Medicine
JULIUS JOHNSON, Dow Chemical U.S.A, retired
CHARLES H. KRUGER, JR., Stanford University
CLIFFORD RUSSELL, Resources for the Future
EDITH BROWN WEISS, Georgetown University Law Center
MYRON F. UMAN, Executive Secretary
vi
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Commission on Physical Sciences,
Mathematics, and Resources
HERBERT FRIEDMAN, National Research Council, Cochairman
ROBERT M. WHITE, University Corporation for Atmospheric
Research, Cochairman
STANLEY I. AUERBACH, Oak Ridge National Laboratory
ELKAN R. BLOUT, Harvard Medical School
WILLIAM BROWDER, Princeton University
BERNARD F. BURKE, Massachusetts Institute of Technology
HERMAN CHERNOFF, Massachusetts Institute of Technology
WALTER R. ECKELMANN, Sohio Petroleum Company
JOSEPH L. FISHER, Office of the Governor, Commonwealth of
Virginia
JAMES C. FLETCHER, University of Pittsburgh
WILLIAM A. FOWLER, California Institute of Technology
GERHART FRIEDLANDER, Brookhaven National Laboratory
EDWARD A. FRIEMAN, Science Applications, Inc.
EDWARD D. GOLDBERG, Scripps Institution of Oceanography
KONRAD B. KRAUSKOPF, Stanford University
CHARLES J. MANKIN, Oklahoma Geological Survey
WALTER H. MUCK, University of California, San Diego
NORTON NELSON, New York University Medical Center
DANIEL A. OKUN, University of North Carolina
GEORGE E. PAKE, Xerox Research Center
CHARLES K. REED, National Research Council
HOWARD E. SIMMONS, JR., E.I. du Pont de Nemours & Co.,
Inc.
HATTEN S. YODER, JR., Carnegie Institution of Washington
RAPHAEL G. KASPER, Executive Director
vii
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Preface
In 1981 the National Research Council issued a report
titled Atmosphere-Biosphere Interactions: Toward a
Better Understanding of the Consequences of Fossil Fuel
Combustion. The report focused on the effects on living
systems of atmospheric pollutants associated with energy
production. One chapter in the report described in
detail the state of knowledge concerning the effects of
acid precipitation on the biosphere. Based on its survey
of field data in sensitive areas and the results of
experiments, the report concluded that with respect to
sensitive freshwater ecosystems, "It is desirable to have
precipitation with pH values no lower than 4.6 to 4.7
throughout such areas, the value at which rates of degra-
dation are detectable by current survey methods. . . . In
the most seriously affected areas (average precipitation
pH of 4.1 to 4.2), this would mean a reduction of 50
percent in deposited hydrogen ions." ~However, a change
in pH, which is measured on a logarithmic scale, from 4.1
to 4.6 corresponds to a threefold decrease in deposited
hydrogen ions rather than a twofold decrease.
The conclusion was misinterpreted in the press and by
others (see, for example, Science 214:38 October 2, 1981,
and page A26 of The Washington Post for October 16, 1981)
as a recommendation for a 50 percent reduction in emis-
sions of the pollutant gases, sulfur dioxide and the
oxides of nitrogen, that are precursors to acid precipi-
tation. While the report concluded that the desired
reduction in the deposition of hydrogen ions implies a
reduction in emissions, it did not indicate how much
additional control of emissions would be required to meet
the goal.
As a consequence, the Chairman of the National
Research Council asked the Environmental Studies Board to
1X
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review the current state of knowledge about atmospheric
processes that link emissions to deposition with the
purpose of describing to the extent possible the
consequences of the goal of reduced deposition for
emissions. By how much would emissions have to be
reduced to reduce the deposition of hydrogen ions by 50
percent in sensitive areas? Conversely, by how much
would depositions be reduced if there were specific
reductions in emissions?
Our committee was organized in January 1982 under the
auspices of the board to address this question. The work
of the commitee was supported by funds provided by the
National Academy of Sciences.
We conducted the study by reviewing the current
literature and consulting with a number of colleagues who
are knowledgeable in one aspect or another of atmospheric
science related to acid precipitation. To assure an
up-to-date assessment, we did not restrict our review to
the literature that had already been published but
included where appropriate materials that had been
accepted for publication in the peer-reviewed literature
although not yet actually published. Although initial
drafts of various sections of our report were prepared by
individuals, the document was extensively reviewed and
revised by the entire committee. The report represents
the collective views of the members. The appendixes were
prepared by individuals to provide more detailed tech-
nical discussions than seemed warranted in the report.
We are grateful to our colleagues for their enthusi-
astic cooperation when we asked for their data, analyses,
and views. In particular, we want to express our thanks
to Perry Sampson, who modified his computer model of
deposition chemistry at our request. The results are
described in Chapter 3. We are also grateful to Paul
Altschuller and Rick Linthurst for allowing us to
incorporate material into Appendix C that originally was
prepared at their request for a Critical Assessment
Document on Acidic Deposition (being prepared by them
under contract to the U.S. Environmental Protection
Agency) and to Bruce Hicks and Jake Hales, who wrote that
material. Noor Gillania and D.E. Patterson also
graciously permitted John Miller to prepare Appendix B
based on work they originally prepared for the Critical
Assessment Document. William Stockwell carried out
numerous simulations of the complex chemistry of the
atmosphere, and Brian Heikes assisted with our analysis
x
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of observational data. Ginger Caldwell helped in our
review of statistical methods of analysis.
We also want to thank the members of the NRC staff who
assisted in our work. Myron F. Oman, Janis Friedman,
Kate Nesbet, and Janet Stoll provided staff support.
Editorial assistance was provided by Robert C. Rooney,
Jacqueline Boraks, Christine McShane, and Roseanne
Price. The manuscript was processed under the capable
and patient leadership of Estelle Miller, and the
graphics were prepared by the Design and Production
Department of the National Academy Press under the
direction of James Gormley.
Finally, it is a pleasure to acknowledge the
enthusiasm, dedication, and cooperation of my colleagues
on the committee. They assumed responsibility for a
difficult analysis in a highly charged political
atmosphere, and they carried out that responsibility with
distinction.
Jack Calvert, Chairman
Committee on Atmospheric
Transport and Chemical
Transformation in Acid
Precipitation
xi
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Contents
SUMMARY
1
12
1. INTRODUCTION
Deposition Acidity, 12
Environmental Effects, 16
Physical and Chemical States of Deposited
Materials, 18
Reversibility and Irreversibility, 20
Other Related Regional Air Pollution Phenomena, 21
Purpose of the Study, 23
Organization of the Report, 25
Notes, 25
References, 26
2. ATMOSPHERIC PROCESSES
Transport and Mixing, 30
Chemical Transformation, 35
Homogeneous Gas-Phase Reactions, 38
Homogeneous Aqueous-Phase Reactions, 40
Relative Roles of Gaseous- and Aqueous-Phase
Chemistry, 43
Deposition, 44
Dry Deposition, 44
Wet Deposition, 48
Attachment Processes, 48
References, 53
3. THEORETICAL MODELS OF REGIONAL AIR QUALITY
Material Balance, 56
Deterministic Models, 58
Treatment of Transport and Mixing, 59
Treatment of Transformation Chemistry, 69
Treatment of Dry and Wet Deposition, 70
. . ~
x~,
29
55
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Linearity or Nonlinearity in Theoretical
Models, 72
Findings and Conclusions, 83
References, 84
4. EMPIRICAL OBSERVATIONS AND SOURCE-RECEPTOR
RELATIONSHIPS
87
Aerometric Data and Their Limitations, 89
Relationships among Aerometric Parameters, 90
The Influence of Meteorological Conditions, 95
Classification of Meteorological Conditions, 96
Air-Mass Trajectories, 102
Statistical Methods of Analysis, 108
Regression on Principal Components, 109
Empirical Orthogonal-Function Analysis, 111
Elemental-Tracer Analysis, 113
Analysis of Historical Trends, 116
Analysis of Relative Behavior of Sulfur and
Nitrogen Emissions, 127
Findings and Conclusions, 138
Nonlinearity, 139
Influence of Local and Distant Sources, 140
References, 141
5. RESEARCH NEEDS
Field Studies, 149
Cloud Processes, 149
Studies of Chemical Mechanisms, 150
Dry Deposition, 151
Tracers, 151
Meteorological Studies, 153
Laboratory Studies, 153
Development of Theoretical Models, 154
Appendix A: THE CHEMISTRY OF ACID FORMATION
148
155
Appendix B: TRANSPORT AND DISPERSION PROCESSES 202
Appendix C: ATMOSPHERIC DEPOSITION PROCESSES
Appendix D:
BIOGRAPHICAL SKETCHES OF COMMITTEE
MEMBERS
XIV
213
374
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ACID
DEPOSITION
A~cmospherec Processes en
Eastern North America
A Review of Current
Scientific Understanding
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