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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.