From measurements made in the stratosphere and upper troposphere, atmospheric inventories of CCl3F, CCl4, and SF6 are calculated for April and July 1975. Mean Northern Hemispheric altitude profiles Of CCl3F and CCl4 in April 1975 show reasonable agreement with predictions of one‐dimensional diffusion models. From the distribution of these trace gases in the stratosphere, including comparisons with a few 85Kr and tritium measurements, we deduce a stratospheric circulation pattern consistent with patterns of a number of radioactive substances which have been injected into the stratosphere. The observed stratospheric and tropospheric inventories Of CCl3F and SF6 are consistent with an atmospheric residence time of 26 years and discount the existence of an important tropospheric sink.

In 1976 the annual rate of deposition of 90Sr from atmospheric tests of nuclear weapons reached its lowest value since the systematic measurement of radioactive fallout began in the 1950's. The late 1976 Chinese tests may have contributed about 9 kCi to the total of about 49 kCi deposited during 1976.The past few years have seen a renewed public and scientific interest in the fallout of the radioactive debris produced by atmospheric tests of nuclear weapons. This interest has mainly concerned environmental levels of the fission product, 131I, which has an 8.04-day half-life. This nuclide was studied less intensely during the early years of fallout measurements, however, than was the long-lived fission product, 90Sr, which has a half-life of 28.6 years. Consequently, there is some merit in considering the more complete historical record of deposition of 90Sr in evaluating the relative significance of the contribution by recent nuclear weapons tests to levels of environmental radioactivity.The Environmental Measurements Laboratory (EML), which prior to October 1977 was named the Health and Safety Laboratory (HASL), has maintained a worldwide network of samplers since 1957 to collect fallout to be measured for 90Sr.Based upon data from this network, an estimate has been made each year (1) since 1958 of the annual worldwide deposition and of the cumulative deposit of 90Sr. The EML network of samplers of 90Sr fallout grew during 1957-1964, and included 142 sites in 1964, 99 in the Northern and 43 in the Southern Hemisphere. During 1964-1975 the network gradually decreased in size, and in mid-1976 it was cut back to 72 sites, 47 in the Northern and 25 in the Southern Hemisphere. The samples are collected at these sites by exposing either a steep-walled, stainless steel pot or a plastic funnel which drains through a column containing Dowex-50 ionexchange resin. At the end of each month, the total material collected in each pot and each exposed column of ion-exchange resin is analyzed radiochemically for 90Sr. Starting with the July 1976 sample, analyses have been made on quarterly composites. The analyses are performed at contractor laboratories using procedures similar to those used at EML (2). ResultsAll of the detailed monthly precipitation and radiochemical data accumulated since the inception of the EML pot and column network have recently been tabulated (3).Various methods for calculating the total fallout of 90Sr on the surface of the earth from limited data were discussed by Volchok (4). Some of these methods involve the analysis of soil samples, while others involve the analysis of precipitation samples. In some of these methods, the values of 90Sr per unit area of the surface of the earth are averaged over each latitude band, while in others the concentrations of 90Sr per unit volume of rainfall are averaged over each latitude band and this average is multiplied by an assumed value of average annual

During the years 1974‐1979 the CCl3F concentration in the Northern Hemisphere stratosphere increased by a factor of 2. The annual rates of increase were directly related to annual rates of emissions at the surface of the earth. The production data for fluorocarbons, published by the Chemical Manufacturers Association, show a decline in the yearly rate of emission of CCl3F during the last decade. The yearly percent increase in the mean stratospheric concentration in the Northern Hemisphere has shown a similar decline. Data for CCl4, CCl2F2 and SF6 also show a slowing in the annual rate of increase in the stratospheric mean concentration. The calculated globally averaged concentration of N2O in the Northern Hemisphere remained constant at 249±7 n1/1 during the years 1976‐1979.

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there is a typographical error in equation (3). The right-hand side of (3) should be 'le-rift% ' not 'e-rffr•-. '