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The existence of a spring maximum in fallout deposition due to the disruption of the tropopause in middle latitudes has been debated for the past several years. Evidence obtained from air filters indicates elevated levels of radioactivity from nuclear tests in surface air during April through July 1960.

Samples of surface air collected at Argonne National Laboratory since early 1952 have been analyzed for specific fission products by NaI scintillation spectrometry. The W181 and Rh102 produced in the Hardtack series (1958) have been used to assign nuclear debris to the low‐ and high‐altitude phases of this series, respectively. Activity ratios between appropriate radionuclides have been used to determine the portion of total debris arising from the Soviet October 1958 series. The differences in mean stratospheric residence time as a function of latitude and altitude of injection, as deduced from these data, are discussed in detail.

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