30 o 25 -— oO — ° 20 -—- 4 x o - Q 2 Ww = O x 15 --— x Eo x “ —_ x oO q x 40 -— 9 oO x x _4 o x x 5 _X ° x x x se _ x porasassste?. oO Lt ° D J F M A M J J A S 0 N D Fig. 6 — Beryllium measurements: ©, Station 1: x, Station 2. best available, suggests that the rate at which the Sr®° is leaving the stratosphere is about 20 per cent per year, if the amount of Sr*’ added to the stratosphere is correct. Figure 7 also shows that, if the rate were 20 per cent per year, then there should be about 20 Mt left in the stratosphere during the winter of 1956-1957 when a check of the stratospheric content was possible, Figure 8 provides this evidence of the amount of Sr®® in the stratosphere in the winter of 1956-1957. The crosses represent the stratospheric air content for stations at the indicated latitudes. The heavy line is the best estimate of the average world-wide content in the same units as the measurements if there were 20 Mt in the stratosphere. The observed stratospheric content is less than found by this prediction. If 10 per cent per year were the removal rate, then there should be about 24 Mt at the same date. This would make the discrepancy worse. Thus, if the data can be trusted, the average rate of removal is greater than about 20 per cent per year. This evidence is admittedly very weak. As yet, the results of the stratospheric sampling program make, in our view, very little sense in either the spatial and temporal distribution or inthe fission-product ratios from sample to sample. In addition, estimates of the stratospheric storage time or removal rate can also be found from the study of C'4 made by nuclear tests. The evidence supports the thesis that the stratospheric residence time is of the order of years. However, while this study may become a future powerful tool in the study of stratosphere-troposphere exchange, it is difficult to use it quantitatively to determine the removal rate at this time. It is our view, however, that the c'4 data are, if anything, more consistent with a 20 per cent per year removal rate than a slower rate of, say, 10 per cent per year. 334 ‘