Photophoretic Effects in the Stratosphere

Abstract

Photophoresis, the movement of small particles under the influence of light, may exert a significant effect on stratospheric processes. The photophoretic behavior of salt and metallic particles from 0.1 to 2.0 microns in radius under pressures of from 4 to 50 mm Hg with artificial light of known intensity was investigated. The velocities expected to be imparted to particles by sunlight at altitudes of from 22 to 40 km were then calculated from typical measured force values. It is concluded that, in the absence of wind and other effects, some particles may actually be caused to rise against the force of gravity while others are induced to fall considerably more rapidly than they would under gravity alone.