ES&T
OUTLOOK Global tropospheric chemistry An NAS report calls for a new sampling network and a comprehensive international study
The troposphere, the layer of the atmosphere nearest to the surface of the earth, contains the only air that people breathe. It contains myriad natural chemicals of biological origin as well as synthetic chemicals from industry, all at trace amounts. We breathe oxygen and use rain and nutrients from the troposphere to grow crops. And now we are able to change its composition on a global scale, and to see that change within this lifetime. In the more recent past, we as a nation have muddled through a disturbing, recurring sequence of identifying and responding to environmental problems. These include the effects of smog on health; of acid rain on lakes, forests, and agriculture; of carbon dioxide and other trace chemicals on climate; and of chemicals moving upward through the troposphere to the stratosphere. Understanding global tropospheric chemistry is no longer simply an intellectual challenge. The time has come for us to understand and safely maintain the atmospheric component of our life support system. A recent report of the National Academy of Sciences, perhaps the most timely report done by the NAS, calls for the establishment of a project to study tropospheric chemistry. Funding for the effort has been put at $10-$20 million a year. Requested by the National Science Foundation and the National Aeronautics and Space Administration, the NAS report calls for a comprehensive study of the subject in the form of a major international research program aimed at understanding our life support system. The need for better data One problem with atmospheric data today is that they are perhaps as much as 90% unreliable. For this reason, intercalibration of measurement techniques and development of standard measurement protocols are the project's 374A Environ. Sci. Technol., Vol. 18, No. 12, 1984
first priorities. Jack Calvert of the National Center for Atmospheric Research has said that we have outlived the time when individual scientists are responsible for their collections of data. To attain the objectives of the NAS program, sensitive instrumentation will be required for the measurement of chemicals in the remote troposphere. Significant breakthroughs in analytical methodology have enabled us to measure many substances at concentrations that were not possible only five years ago. The measurement of nitric oxide, for example, has improved by three orders of magnitude in sensitivity, from the parts-per-billion range years ago to 2-3 ppt now. In 1979 it was possible to measure hydroxyl radical (OH) with ppt sensitivity; techniques have now been devised for its measurement at the parts-per-quadrillion level. Photochemistry is a key Sunlight causes many reactions in the atmosphere. The reason OH measurements are so important is that the hydroxyl radical is believed to be the most critical ingredient in the photochemical reactions that occur in the troposphere. The OH radical is formed when ozone absorbs UV radiation from the sun, and the resulting photofragments (atomic oxygen) then react with atmospheric water vapor. Because of its high chemical reactivity, the OH radical can oxi-
dize most of the reduced gases injected into the troposphere. The atmospheric chemistry of the OH radical, as well as the many related hydrogen oxide species, such as the hydroperoxyl radical (0 2 H), is one of the major research frontiers of atmospheric chemistry. —Stanton Miller
The five objectives of the global program • To e v a l u a t e t h e b i o l o g i c a l sources of chemical substances in the troposphere. • To determine the global distribution of tropospheric trace gases and airborne particles and to assess their relevant physical properties. • To test photochemical theory through field and laboratory investigations of photochemically driven transformation processes. • To investigate wet and dry removal processes for trace gases and aerosol particles. • To develop models for global tropospheric chemistry systems. Copies of the report, "Global Tropospheric Chemistry: A Plan for Action," are available for $20.95 from the National Academy Press, 2100 C St. N.W., Washington, D.C. 20418
0013-936X/84/0916-0374A$01.50/0
© 1984 American Chemical Society
