Fea wg rakeal, perth Malad Sel c seat ad « , ae ein Figure 1 further shows that the French thermonuclear tests in mid-1968 abruptly ended the influence of the 6th Chinese test debris in the Southern Hemisphere, plunging the ratio to below 1%. The Chinese 8th test in December of 1968 apparently generated a ratio of Pu-239/Sr-90 of about 2% since the pattern in the Northern Hemisphere was not markedly affected in early 1969. The Pu-239/Sr-90 in the lower stratosphere, pause, just above the tropo- is illustrated in Figure 2, and exhibited a similar pattern with one striking difference. At this altitude the high ratios generated by small French tests in the Southern Hemisphere in mid-1967 are clearly seen. Most important to note, however, is that in the Northern Hemis- phere the highest ratios observed in the entire period shown were greater than 2.5% but less than 3%, and in early 1969 virtually all of the data were below 2.5%. This observation holds true not only for the lowest stratosphere but also for altitudes as high as 19.2 km (Fig. 1}. Surface Air Data The Pu-239/Sr-90 ratios in surface air for the period 1966 through mid~1969 are shown in Figure 3. This figure was derived from the data Obtained in the Health and Safety Laboratory (HASL) Surface Air Sampling Program (9). I - 16 we come STAg Rae 8 pene es sen peers ener SETSer pee spernme oy . ¥ “