Stratospheric Data The Pu-239/Sr-90 ratios at 19.2 km and just above the tropopause are illustrated in Figures 1 and 2 April 1969. for the period August 1967 through These figures were constructed from data obtained in Pro- ject Airstream (5,6,7,8) and represent the minimum and maximum alti- tudes routinely sampled in this program. varies with latitude, Since the tropopause height the altitudes in Figure 2 also vary as follows: Latitude Altitude 75°N-65°N 12.2 km 6 5°N-36°N 13.7 km 36°N-3 49s 15.2 km 34°s-51°s 13.7 km Figure 1 shows that at the higher altitude, the Pu-239/Sr-90 was uniformly less than 2% in both hemispheres, until the debris from the 6th Chinese test of June 1967 was intercepted in the last quarter of the year. At this point the ratio rose to greater than 2 but less than 3% and essentially remained within this range through all of 1968. The contours suggest that this debris at 19.2 km crossed the equator into the Southern Hemisphere in the spring of 1968 and influenced the ratio to as far south as the Airstream sampling network extends, I - 15 51°s,