50 O i ~ Samples from 30,000 to 35,000 feet Trend in the tropical stratosphere x 40 _ Samples from 60,000 to 70,000 feet Samples from 40,000 to 55,000 feet ® _. — O 7’”.l™ / ® oO e o.|0|UO ~. SA ~ ~ O oN O @ ~ o~. n @O7 WO O e @ - — xXx SO ~ mn dpm Ce 1a4 /dpm Sr 5 SL @ 90 20 — fos, e ~ O ~ e x oO a~_ 8 bd T O - ~ 7 °°. *e.8 Oo ~Q. @ oe) ~ — ~ ~ T O al 5 e —_ ~ 4 4 P miailmiujujalsjo[n{o vf [mjalm] vy vJA}S]O]N [0 vfFim{ajm{u I958 1960 4 9 Fig. 3 -- Variation with time of the monthly average for Ce! 4 sr 0 in samples collected in the northern polar stratosphere (30°N-90°N) a9