Analysis of mid-tropospheric space shuttle exhausted aluminum oxide particles

Abstract

Aluminum oxide (Al 2O 3) particles from the exhaust of the space shuttle were collected from the shuttle column cloud immediately after the launch of STS-61A on 30 October 1985. The participates were collected on Teflon filters during a tight descending aircraft spiral maneuver over the altitude interval of 7.6-4.6 km. Scanning electron microscope (SEM) examination of the particles revealed that they were virtually all spherical and ranged in diameter from about 0.1 μm to 10 μm. Particles of < 0.1 μm in diameter were not readily visible in the SEM photomicrographs; however, such particles would not be captured efficiently on the Teflon filters used. Results from energy dispersive analysis by X-ray (EDAX) and electron spectroscopy for chemical analysis (ESCA) confirmed that the particles were predominantly composed of Al and O 2. A particle size distribution was determined from the Al 2O 3 samples. The distribution was bimodal, with one observed peak centered near 2.0 μm. The data indicated the existence of another mode centered at a diameter of < 0.3 μm, but could not be accurately located because our technique cut off at diameters of < 0.1 μm. A mass median diameter of slightly < 2 μm was determined. The collection was evaluated for ice nucleation activity, using the filter technique with a static vapor-diffusion chamber. Only a small fraction (about 1:10 6) of active ice nuclei were determined among the Al 2O 3 particulates.