In the troposphere in the three years since the 1954 Castle test at the 10 per cent per year figure used for fallout, about 3 x 10°’ C'* atoms should have descended, or about 1 x 1077 c'4 atoms per year. The average ci4 inventory in the troposphere is 3.3 x 1078 without including the ocean or biosphere, so the observed c'4 rise might be as high as 3 per cent per year as appears to have been observed. If mixing with the biosphere and top ocean above the thermocline occurred immediately, according to Arnold and Anderson® who gave 0.2 g/cm? in the top 100 m of the ocean,the total tropospheric reservoir would be 7.5 x 1078 giving an expected rate of increase due to the bombs of 1.3 per cent per year which is in fair agreement with the observations if we assume the mixing with the ocean and the biosphere, particularly the former, is not quite instantaneous. The main points are that the ratio of the Northern to Southern Hemisphere effect here is not enormousandfits fairly well with the notion that stratospheric gases have a residence time not too different from that of the ultra fine world-wide fallout particles. “Top bh 00 vy CASTLE U.S.S.R. REDWING — 2 600 2 ” 2 q e e S 400 LL - e — ee e ®. :° ° °® 6 of 1952 1953 Ree — oe e & e 0 ee e e 200 ‘to ® ® eet. 3 e ee * vsa.—Cti«dEsCsttgSStiédLCtstéitgSG—C‘��‘L'SCS*é«SQ'S Fig. 11—Tritium in rain and snow. In addition, Fergusson*! has recently found in studying fossil CO, and its effect on reducing the C‘4 content of the biosphere that the mean life of a CO, molecule before being absorbed from the tropospheric air into the oceans and biospheres is perhaps two years andthat north to south mixing of the fossil CO, occurs in less than two years. Consequently, it seems clear that the ten year residence time for stratospheric gases be- fore descent into the troposphere seemsto fit data for C!4 from bombs as well as the Sr? and Cs'3" fallout data. Figure 11 gives up-to-date data on the occurrence of tritium in rain water in the Chicago area.?!,46.47 Tt is clear that whereas Sr*” and probably C!4 remain in the stratosphere for years, the tritium from high yield thermonuclear detonations does not, but descends in a matter of 1 or 2 months. This most probably is due to the enormous mass of water carried into the stratosphere by the fireballs of detonations in the moist tropospheric air. The characteristic white mushroom cloud is evidence of the formation of ice crystals in the cold stratospheric air, which if large enough to be seen in this way must certainly be large enoughto fall into the troposphere where they melt and join in the ordinary phenomena;i.e., fall out as rain or snow. 265