Early in 1975, as preliminary results of the Climatic Impact Assessment Program (CIAP) conducted in the U.S.A. were beginning to appear, there occurred a surge of public concern about possible partial destruction of the earth's stratospheric ozone layer by anthropogenic pollutants such as nitrogen oxides (NOx) emitted from supersonic jet aircraft, NOx released photochemically from nitrous oxide (N2O) derived from bacterial denitrificotion of fertilizers, and the industrially produced chlorofluoromethanes CCl2F2 and CCl3F. A reduction of stratospheric ozone, which strongly absorbs solar ultraviolet radiation, would increase the amount of biologically active (UV-B) radiation received at the ground, with possibly harmful effects to humans, animals, and crops. Also, because the temperature of the stratosphere is largely maintained by a balance between absorption of solar ultraviolet radiation by ozone and emission of atmospheric infrared radiation by ozone, carbon dioxide and water vapor, a reduction in stratospheric ozone would cause changes in heating rates leading to changes in the temperature distribution within the stratosphere and possibly the troposphere. Such temperature changes would probably have an effect on the pattern of atmospheric circulation, and hence on weather and climate.

          In recognition of a pressing need for a coordinated international program under the leadership of the WMO to monitor and study all aspects of the stratospheric environment relevant to ozone, the Secretary-General arranged a meeting of the CAS Working Group on Stratospheric and Mesospheric Problems in September 1975. In addition to drafting a statement, entitled "Modification of the ozone layer due to human activities and some possible geological consequences" (Annex I to Report EC-XXVIII), the Group prepared an outline of a proposed coordinated international monitoring and research program on the composition of the stratosphere. After further elaboration by an ad hoc group of experts in January 1976, this proposal was approved in Resolution 8 (EC-XXVIII) as the Global Ozone Research and Monitoring Project.

          Recognizing the important environmental aspects of the problem, UNEP sponsored a meeting of experts in March 1977, and agreed to provide some support for WMO activities. The outcome of the meeting was an agreed World Plan of Action on the Ozone Layer in which WMO was designated as the lead agency in work connected with the monitoring of ozone, relevant atmospheric trace gas species, and UV-B radiation, and in research into the overall problem of inadvertent modification of the ozone layer by man.

          Within the WMO Global Ozone Research and Monitoring Project, high priority was given to the furtherance of global total ozone monitoring with Dobson ozone spectrophotometers for the purpose of determining hemispheric and world ozone trends as well as to provide "ground truth" for satellite ozone observations. While an operational, global Dobson instrument station network was already in existence, largely because of the pioneering work of G. M. B. Dobson of Oxford, England, and the promotional activities and guidance provided by the WMO and the International Ozone Commission since the International Geophysical Year (1957-1959), improvements were needed in geographical coverage as well as standardization and uniform calibration of instruments. With the collaboration of experts from the U S.A. and Canada, action was taken to improve the network of Dobson spectrophotometer stations. A World Standard Dobson Ozone Spectrophotometer was established at the NOAA Laboratories in Boulder, Colorado, and a number of instruments at key network locations were modernized and recalibrated. A number of Dobson comparisons have been carried out during the past few years. The first in Belsk (Poland) in 1974; a comparison of Dobson spectrophotometers from eight countries in Boulder in August 1977, a two-phase intercomparison for instruments from RA VI, Arosa, Switzerland in August 1978 and in Potsdam, German Democratic Republic in June 1979. In association with these efforts, preparation of this manual was undertaken so that operations at the global total ozone station network might be updated, improved and standardized.

  W. D. Komhyr
NOAA/ERL, Boulder
Colorado, U. S. A.

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