Over the past several years we have collected 2µm to 30µm particles from the stratosphere using high volume air sampling techniques. In 1970 and 1971 we flew balloon experiments to 34 km, sampling particles from 1.1 × 104 m3 of ambient air. Beginning in March 1974 we have flown 100 hours of sampling time on a NASA U-2 aircraft yielding a sampling volume of 9.3 × 104 m3. In both programs particles are collected by inertial deposition from a 200 ms−1 airstream on to clean surfaces coated with thick films of 500,000 centistokes silicone oil.
2.3.4 Extraterrestrial Particles in the Stratosphere