08 100 90; ~ FLIGHT 2488 (Il OCTOBER I960) BOF 70 T ALTITUDE (THOUSANDS OF FEET) FLIGHT 2468 ( 7JUNE 1960) 60 50 40: TROPOPAUSE 30 20 lO 20 1 L 30 40 1 50 L =~ 60 PB ACTIVITY (yc /10° FT, AMBIENT) 4 -70 al. -60 i -50 4 -40 | -30 TEMPERATURE(°C) Fig, 1 -- Impactor-filter flights, Minneapolis, Minn. -20