The role of gravitophotophoresis for stratospheric and mesospheric particulates |
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| Authors: | Hans rohatschek |
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| Institution: | (1) Institute of Experimental Physics, Johannes Kepler University, Linz, Austria |
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| Abstract: | Gravitophotophoresis, a type of photophoresis related to the direction of gravity, is examined in view of its possible importance to some aerosols in stratosphere and mesosphere. particles of various materials from about 1 to 100  m in size show levitation by photophoretic forces under laboratory simulation of irradiation by the sun at air densities of the middle atmosphere. Minimum air densities for levitation are about 2–3 g m–3 with mineral and metallic powders, about 0.08 g m–3 with carbonaceous powders. The fraction of rising particles can be about 0.01 to 1%. Velocities of ascent are in the range of 0.001 to 0.01 m s–1 at a pressure of several mbar. The magnitude and the mechanical character of the force of gravitophotophoresis can be explained if it is identified with a radiometer force caused by a difference of the accommodation coefficient on the surface. It is suggested that gravitophotophoresis can be important to the residence time and the maximum altitude of carbonaceous and mineral particles, such as volcanic ash or products of meteorite impact, and to the presence of microorgnisms in the middle atmosphere. |
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| Keywords: | aerosols middle atmosphere vertical transport residence time photophoresis |
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