Global Tropospheric Chemistry A Plan for Action (1984) / Chapter Skim
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3 A PROPOSED PROGRAM
3 A PROPOSED PROGRAM
Pages 19-49
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From page 19... ...
The long-term goals of this Global Troposphenc Chemist Program should be as follows: 1. To understand the basic chemical cycles In the troposphere through field investigations, theory aided by numerical modeling, and laboratory studies.
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The four basic processes that control chemical cycles and their interactions in the troposphere production, transport and distribution, chemical transformation, and removal provide a unifying framework for the development of the Global Tropospheric Chemistry Program. Attainment of the program goals will also require the development of three-dimensional models of tropospheric chemical processes linked to meteorological and climatic processes, i.e., tropospheric chemistry systems models (TCSMs)
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These considerations led to the field and laboratory investigations of biological sources of tropospheric chemicals that are proposed here. Much of the early field research in the Biological Sources of Atmospheric Chemicals Study must be exploratory in nature.
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. Biomass Burbling Some of the most easily recognized sources of tropospheric chemicals can be described as point sources.
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interact with episodic events such as severe weather to influence both production and exchange rates. Both exploratory and intensive field studies of trace gas fluxes are needed in coastal wetland and estuarine environments.
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In Part II, Chapter 5, in the section by Cicerone et al., we discuss the potential of emissions from rice paddies to exert a strong influence on regional and global tropospheric chemistry. Particular attention should be paid to volatile species containing nutrient elements in reduced valence states, e.g., CH4, N2O, NH3, NO, methylated metals, isoprene, and possibly CO.
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The direct emission of significant quantities of aerosol particles by trees has been suggested, but little quantitative information is available. To obtain the minimum necessary information on these emissions, sampling should be conducted at representative sites for the major forest types.
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Needs for Instruments and Verification of Methods In the discussion of the Biological Sources of Atmospheric Chemicals Study, we have emphasized selected blames and processes that are known or suspected to be important sources of key tropospheric chemicals. Although the proposed program is broad in scope, it is not complete nor are all means of investigation and an exact sequence of projects spelled out.
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From page 27... ...
to detect, quantify, and explain long-term trends in environmentally sensitive trace gases and aerosol particles, especially those that are radiatively important. It is not possible at this time to define precisely the structure of this network and its sampling protocol because there is insufficient knowledge of the global concentration fields for the chemical species of interest and of the large-scale transport processes that affect these distributions.
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From page 28... ...
Carbon dioxide measurements are included to provide data on the anthropogenic emissions of this substance, and information about meteorological alla oceanographic processes and interactions with the biosphere. Nitrous oxide Is also TABLE 3.2 Possible Species to be Measured in the Global Tropospheric Chemistry Sampling Network Medium Species Sourcea Used Lifetimes Networks Notes Gas Particles Precipitation CC13F CC12F2 CHC12F CHC1F2 CH3CC13 C2C14 C2HC13 CH4 Alkanes < Cs co2 CO COS CS2 N2O o3 H2O Na+,C1 ~ SO4 NOs NH4+ Soil Excess V 2lopb Total C Total Organic C ~ .
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From page 29... ...
Improved instruments for measuring the low-water-vapor concentrations characteristic of the upper troposphere should be developed, and this instrumentation should be used in the O3 sounding program. The concentration and composition of aerosol particles could be measured by using samples collected on filters.
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Global Distributions Network The Global Distributions Network would provide greater spatial resolution than that obtained from the-Long-Term Trends Network. This network would be needed for the relatively short-lived species, such as 03, H2O, CO, and for the reactive nitrogen and sulfur species when techniques are available for their measurement.
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From page 31... ...
The surface-level measurements provide information on the transport of dust and anthropogenic particles from major source regions. Measurements of the concentration and rates of deposition of mineral aerosol particles from major desert regions as a function of latitude, longitude, and season would provide significant tests for transport models and considerable information about long-range transport mechanisms.
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The modeling and measurement efforts should be sufficiently advanced that planning can begin for large-scale regional experiments that require a greater density of network stations and a higher sampling frequency. These experiments would coincide with one or more of the other major studies proposed as part ofthe Global Tropospheric Chemistry Program.
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In no case have the postulated basic mechanisms been validated by comprehensively measuring all relevant photochemical species in a well-defined atmospheric setting. Thus we recommend the initiation of a major research effort on photochemical transformations in the troposphere.
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In addition, knowledge of the history and trajectory of the air mass under study will provide information on the distributions of long-lived species that will be important for data interpretation. Table 3.3 summarizes the Level 1 and Level 2 critical measurement requirements for three of the elements in the proposed Theory Validation Experiments.
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Both types of platforms will be required. Instrument Readiness The objective of the proposed fast-photochemical Theory Validation Experiments is to take a chemical "snapshot" of the troposphere.
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For some key photochemical species, e.g., CH2O, concentrations have been measured even in remote areas. These measurements have primarily involved grab samples, and there .
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Instrumentation Unlike the Theory Validation Experiments, the instrumentation required to assess mean concentrations of key photochemical species will not have major time resolution restrictions. Thus both indirect and grab-sampling measurement systems could be seriously considered · .
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This model development should lead to a more accurate simulation of tropospheric chemical cycles. CONVERSION, REDISTRIBUTION, AND REMOVAL Understanding the basic chemical cycles in the troposphere requires a detailed knowledge of the processes by which gases and aerosol particles undergo chemical conversion and redistribution, both in clear air and by clouds and precipitation.
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Thus a general research strategy is to call for near-term field experiments to attack specific questions with available technology and, as knowledge grows from these experiments, and new instruments are developed, to broaden the scope of effort accordingly, both scientifically and geographically. As progress is made toward the attainment ofthese objectives, a framework can be developed for major future field experiments to quantify the complex physical and chemical processes linking clouds, precipitation, and both wet and dry deposition with the major chemical cycles.
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Further instrument development may be required in these areas. Field programs investigating conversion and removal processes in several tropospheric chemical cycles can be initiated with currently available instruments.
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The rising warm sector air cools until condensation occurs, effectively scavenging trace gases and aerosol particles from the warm air mass by in-cloud processes. Most of the precipitation occurs north of the surface front (in the northern hemisphere)
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PART I A PLAN FOR ACTION Dry Removal Experimental Program Dry deposition includes the turbulent and diffusive transfer of trace gases and aerosol particles from the air to the underlying surface, and the gravitational settling of large particles. The processes that control dry deposition are normally associated with the nature of the surface itself, or with characteristics of the neighboring media.
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We propose the following studies leading to experimental investigations of surface exchange at sea. Phase I Through the use of meteorological towers at appropriate land sites, evaluate surface fluxes for trace gases, including SO2, NO, NO2, HNO3, NH3, H2O, H2O2, 03, and measurable species in the halogen and carbon cycles, as well as species present on aerosol particles.
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From page 44... ...
However, to achieve the objectives of the proposed Global Tropospheric Chemists Program, it Will also be necessary to have a more ambitious long-term perspective toward model development. That is, for the successful application of the field program data and to advance scientific understanding, it will be necessary to develop comprehensive models of the overall tropospheric chemical system.
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From page 45... ...
These studies would compare model results with the data sets including measured variances obtained through the Global Tropospheric Chemists Sampling Network and, if necessary, would develop the model improvements required for satisfactory validation. Most of the modeling studies would be carried out in a climatological framework, but detailed event studies would also be performed in conjunction with intensive periods of field data collection.
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From page 46... ...
We anticipate a two-way interaction with the other components of the Global Tropospheric Chemistry Program (i.e., field programs and laboratory studies of kinetics, photochemical data, and heterogeneous equilibria and reaction rates)
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From page 47... ...
A strong, active program of laboratory measurements of chemical reaction kinetics will be required in the Global Tropospheric Chernist7~ Program. The program will require the continuing commitment of chemical kineticists and the further development of laboratory instrumentation systems for the investigation of the mechanisms and rates of the gas- and liquid-phase reactions critical to an understanding of tropospheric chemical cycles.
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Therefore, oceanographic sampling platforms will be a compromise between the needs of the atmospheric chemistry community and the missions for which the ships were designed. Sufficient ships are available to undertake the proposed field research at sea in the Global Tropospheric Chemistry Program.
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From page 49... ...
A third possible approach to the development of international cooperation in a Global Tropospheric Chemistry Program would be the formation of a special committee by the International Council of Scientific Unions with appropriate representation from the nations and scientific unions concerned with tropospheric chemistry research. The strength and ultimate success of any international Global Tropospheric Chemists Program win depend upon the quality of science and scientists involved.
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