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OCR for page 7
1 The Need for a Program
:,
The recent history of atmospheric chemistry research
(i.e., since 1970) is characterized by a multitude of sur-
prising discoveries. The perception ofthe atmosphere as
a chemical system has changed dramatically. It is now
known that the atmosphere is a dynamic system where
many chemical reactions, physical transformations, and
types of transport occur. There are intense inputs of raw
materials from natural processes (often biological) and
from human activities. The movement and reactions of
chemicals in the atmosphere are now clearly seen as
components and links in global biogeochemical cycles of
the chemical elements. It is not a trivial task to appreci-
ate the significance of these current concepts and the
opportunities they present, largely because so many
new ideas and facts have emerged so quickly.
When one reviews the knowledge of atmospheric
chemical composition as it existed two or three decades
ago, one is struck by the primitive state of the science.
Quantitatively, only the atmospheric concentrations of
nitrogen (N2), oxygen (02), the noble gases, carbon
dioxide (CO2), water below the tropopause, and ozone
(03) in the stratosphere were then known. By 1950,
methane (CH4), nitrous oxide (N2O), carbon monoxide
(CO), and hydrogen (H2) had been detected, but mea-
sured only to about 50 percent accuracy. The existence
of airborne particles was known, but little information,
even on their bulk properties, was available. On the
basis of extant data on the visible and ultraviolet light
spectrum of the sun, one could speculate that strato-
spheric O3 was important as an ultraviolet shield, but
other possible absorbers were unexplored. Tropospheric
03, although known to be a product of photochemical
reactions in urban smog, was little more than a curiosity
when detected in clean background air. The roles of
CO2, water, and O3 in climate and atmospheric dy-
namics were identified qualitatively, but they were not
well understood.
The atmosphere near the earth was viewed as a fluid
in motion, transporting moisture and heat. It also trans-
ported pollutants arising from cities, factories, and fires.
The chemical species in the air were regarded as essen-
tially inert and for good reason- most of the compo-
nents that were known were inert gases. A fair amount
was known about radionuclides in the atmosphere from
studies related to nuclear weapons testing. Indeed, the
use of radiochemical techniques in atmospheric studies
was more prevalent in 1960 than in 1980. Because of
these studies, a great deal has been learned about strato-
spheric transport processes; this knowledge has been
extremely valuable in the efforts to assess the global
impact of anthropogenic chlorofluorocarbons and the
exhaust from high-flying aircraft.
Since those early days, progress has been rapid and it
is still accelerating. It is now understood that the tropo-
sphere is a reactive environment. Because of the com-
plexity inherent in such an environment, new programs
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8
in which a broad spectrum of studies are coordinated,
are needed. Indeed, much of the current understanding
of tropospheric chemistry is the result of the coupling of
new chemical data with new theoretical insights and
models.
It has also become clear, both to atmospheric chemists
and to laymen, that humans are increasingly capable of
PART I A PLAN FOR ACTION
perturbing the atmosphere. Often inadvertent and un-
foreseen, these perturbations are sometimes direct and
sometimes subtle, and they can extend to the earth's
soils, waters, biota, and climate. Thus, perturbations to
tropospheric processes can affect earth's biogeochemical
cycles and the total life support system of the planet.
PUBLIC POLICY PROBLEMS AND ATMOSPHERIC CHEMISTRY
Over the past decade or so, human perturbations and
influences on the chemistry of the atmosphere have been
identified at a rate that exceeds the ability of scientists to
predict the behavior of the perturbed system, even
though knowledge has grown explosively. The array and
scope of these perturbations are impressive, as are the
related research and policy questions they raise. Notable
examples are (1) the acid rain phenomenons 2 with its
regional and hemispheric scale manifestations and its
contributions from gas-phase, liquid-phase and solid-
phase species, reactions, and deposition; (2) distur-
bances to the stratospheric O3 layer and its photo-
chemistry:3 4 5 6 7 caused by ground-level emissions of
chlorofluorocarbons, chlorocarbons, N2O, and direct
stratospheric injections of nitric oxide (NO) by high-
altitude nuclear weapons testing and, potentially, from
stratospheric aviation; and (3) the potential effects of the
growing concentrations of carbon dioxides and several
radiatively active trace gases (whose sources are largely
either directly or indirectly under human control) on the
entire background tropospheric chemical system and
the earth's climate. Indeed, the combined effects of
CH4, nitrogen oxides, chlorofluoromethanes, and other
Acid Deposition: Atmospheric Processes in Eastern North Amer-
ica, A Review of Current Scientific Understanding, Committee on
Atmospheric Transport and Chemical Transformation in Acid Pre-
cipitation, National Academy Press, Washington, D.C., 1983, 375
PP
2Atmosphere-Biosphere Interactions: Toward a Better Understand-
ing of the Ecological Consequences of Fossil Fuel Combustion, Com-
mittee on the Atmosphere and the Biosphere, National Academy
Press, Washington, D.C., 1981, 263 pp.
Stratospheric Ozone Depletion by Halocarbons: Chemistry and
Transport, Panel on Stratospheric Chemistry and Transport of the
Committee on Impacts of Stratospheric Change, National Acad-
emyofSciences, Washington, D.C., 1979, 238 pp.
4Halocarbons: Effects on Stratospheric Ozone, Panel on Atmo-
spheric Chemistry of the Committee on Impacts of Stratospheric
radiatively active trace gases could be equivalent to the
doubling of CO2 during the next 30 to 40 years. Further
examples include (4) perturbations to global r~utrient-
element cycles that have significant atmospheric compo-
nents and consequences, e. g., the carbon, nitrogen, and
sulfur cycles; and (5) modification of the radiative prop-
erties of the atmosphere by aerosol particles.
These problems are real, and the areas of the world
affected by pollution are large and they are growing;
indeed, some of the problems are demonstrably and
inherently global and are of concern to atmospheric
chemists and public policymakers. Further, the recent
history of technology is one of exponential growth, for
example, in the variety arid rates of production of manu-
factured chemicals and of their application to agricul-
tural soils and their release to water supplies. A1SO7 ever-
increasing allergy production leads to increased releases
of combustion products to the atmosphere. The in-
creased use of technology and the introduction of new
technological processes will have further impacts on the
atmosphere and thus more questions concerning pollu-
tion control and resource management will inevitably
arise.
Change, NationalAcademyofSciences, Washington, D.C., 1976,
352 pp.
Environmental Impact of Stratospheric Flight: Biological and Cli-
matic Effects of Aircraft Emissions in the Stratosphere, National
Academy ofSciences, Washington, D.C., 1975, 348 pp.
6Ca uses and Effects of Stratospheric Ozone Reduction: An Update,
Committee on Chemistry and Physics of Ozone Depletion, aIld
Committee on Biological Effects of Increased Solar Ultraviolet Ra-
diation, National Academy Press, 1982, 339 pp.
7Causes and Effects of Stratospheric Ozone Reduction: Update
1983, Committee on Causes and Effects of Changes in Strato-
spheric Ozone: Update 1983, National Academy Press, Washing-
ton, D.C., 1983, 254 pp.
Changing Climate, Carbon Dioxide Assessment Committee,
National Academy Press, 1983, 496 pp.
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THE NEED FOR A PROGRAM
ATMOSPHERIC CHEMISTRY: TOOL, SCIENCE, OR BOTH?
A detailed examination of the activities and achieve-
ments in the field of atmospheric chemistry over the past
15 to 20 years reveals a recurring pattern in which a
potentially serious problem is identified and a crisis re-
sponse is evoked from the scientific community. Re
. . . . .
searc ~ carried out In a cr~s~s-response mode attempts to
obtain, as quickly as possible, the minimum amount of
information needed for policy formulation. In this man-
ner, considerable progress was made in quantifying the
atmospheric effects of many human activities. However,
there has been too little time and insufficient support to
carry out the systematic and exploratory research
needed to go beyond the confines of the immediate prob-
lem, i.e., to achieve a more complete understanding of
the global troposphere so as to be able to anticipate
pollution problems and to establish a more reliable base
from which to formulate a response.
The identification of an anthropogenic effect on the
atmosphere is in itselfprogress. However, it is difficult, if
not impossible, to assess accurately the extent and impli-
cations of human impacts on natural processes if their
workings are not understood. Thus, it is necessary to
~.
. .
Obtain a more quantitative understanding of the dy-
namics of the perturbations and of the background state
and dynamics of the unperturbed natural atmosphere
and biogeochemical system. The formulation of effec-
tive strategies for pollution control and resource man-
agement require this. Because of the rapid increase in
human population, technology, and consumption of re-
sources and because of the limited knowledge available
even in 1970, the relatively small community of atmo-
spheric chemists could not foresee or keep pace with the
need for more and more quantitative information on air
chemistry. A further proliferation of problems has oc-
curred since then.
One can draw upon the experiences of atmospheric
chemists over the last 10 to 15 years to devise more
effective research strategies. For example, major discov-
eries have arisen from isolated, undirected research,
often conducted by individuals. Indeed, major prob-
lems in environmental chemistry have been so discov-
ered. Examples are Lovelock's early detection of the
chlorofluorocarbons CC13F and CC12F2 in the atmo-
sphere and the theoretical investigation of their atmo
9
spheric chemistry by Molina and Rowland. At the out-
set of this research, no specific goal demanded that it be
conducted. Similarly, when Keeling began his high-pre-
cision CO2 monitoring in 1957, only a few farsighted
individuals recognized that such data would ever be of
such practical relevance or scientific value. One con-
cludes from these and other such important examples
that there must always be a place for the undirected
research of individuals, research that does not always
offer immediate applied results. One suspects that the
field of atmospheric chemistry supports too little of this
research largely because of the more pressing demands
for problem- or mission-oriented research that is often
directed at specific, identified pollution problems.
The science of atmospheric chemistry has reached a
much more robust state in the last few years. The
present state can now permit more progress to be made
from more systematic research. For example, the poten-
tial effects of human activities on the atmosphere can be
better quantified and future problems can be antici-
pated on the basis of a growing understanding of the
pathways of atmospheric chemical transformations and
dynamics and from a growing data base on atmospheric
chemical composition. With increased knowledge of the
chemical composition of the atmosphere and of the
chemical pathways in it, one can draw from relevant
knowledge of chemistry, physics, and biology and per-
form laboratory experiments; in this way one can de-
duce what other chemical substances might be found in
the air and how they might behave. General principles
have been sought and applied with increasing success. A
prominent example involves the mapping out of chain
reaction schemes that achieve chemical transformations
through chemical catalysis. Thereby, it has become clear
that certain reactive species can have importance far
beyond that suggested by their extremely small concen-
"rations. For example, NO is apparently important
even at levels of one part in loll, and the hydroxyl
radical (OH) is important at much lower concentrations
still. It is important to note that the very existence of
odd-electron or radical species like the hydroxyl radical
has been proposed and explored only in the last 20 years
. . ., . .
Or so; to near s~gn~cance In atmosp~ Uric processes was
firmly established only a decade ago.
TROPOSPHERIC CHEMISTRY: THE PROSPECTUS
Atmospheric chemistry is confronted by an array of
identified environmental problems for which public pol-
icymakers are demanding research solutions. We sus-
pect that even more problems that derive from human
activities are on the horizon. Although dramatic prog-
ress has been made toward understanding the basic sys-
tems and implementing solutions to applied problems, it
is clear that future environmental issues and policy deci
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lo
signs will require a deeper understanding of the entire
global atmospheric chemical system and of biogeochem-
ical cycles. A major research effort in tropospheric
chemistry should be made with this objective in mind.
In Chapters 1 through 4 (Part A, we propose and justify
a coordinated program of tropospheric chemistry re-
search whose scope extends to global scales. In Chapters
5 through 9 (Part II) of this report, the current status of
the science is described in more detail.
The program described here is realistic and feasible.
It is soundly based on the results of a decade of intensive
investigation of the earth's stratosphere and climate and
about two decades of research on urban air pollution.
Instrumentation is available now for many of the pro-
posed investigations, and it is at an advanced stage of
development for others. The development of instru-
mentation and advanced numerical models is being
conducted in a number of laboratories that have demon-
strated excellence. Highly skilled individuals are avail-
able to perform the research, and many of these individ
PART I A PLAN FOR ACTION
uals are already mounting research activities very
relevant to the proposed research. A number of U.S.
and European universities are expanding their graduate
programs in atmospheric chemistry. Several U. S. scien-
tific institutions and agencies have begun to accept re-
sponsibilities and propose initiatives; similar activity is
evident in Europe, Australia, and Canada and may
reasonably be anticipated elsewhere. Further, the need
to perform research that effectively couples chemistry
and meteorology is now well recognized. Moreover, be-
cause of the inherent heterogeneity of the troposphere,
the plethora of sources, and the complexity of biological
processes and of surface effects, there will be tremendous
challenges to be faced. Great care must be exercised in
formulating scientific concepts and in implementing a
coordinated program. Given these, society will reap the
rewards of more effective and efficient management of
resources, maintenance of human health, and a safer
global environment.
Representative terms from entire chapter:
atmospheric chemical
