Vertical transport of absorbing aerosol in radiation field at the middle atmosphere altitudes

摘要

The observed existence of soot particles at 20-25 km altitudes from aviation transport engines requires the analysis of vertical transport mechanisms against gravity in thermally stable stratosphere. One of possible regular mechanisms can be the radiometric photophoresis. The presented theory forecasts that for some types of soot aerosols the negative "solar" photophoresis can result in levitation and in vertical lifting of particles against gravity in the upper troposphere - lower stratosphere. Similar are the capabilities of "thermal" photophoresis (motion of particles in the field of outgoing thermal radiation). The further development of theory requires the analysis of photophoretic motion for fractal aggregates. The results of laboratory experiments demonstrating intensive photophoretic motion of soot aggregates in the field of laser radiation are discussed. For the check of alternative hypothesis of gravito-photophoresis the gas-kinetic theory in the free-molecular regime was developed. The analysis of results has shown that the given mechanism hardly is significant for vertical particles transport on high altitudes, but its investigation is possible in model laboratory experiment. Among regular and effective mechanisms it is necessary to note the vertical stratospheric wind. The direction and magnitude of vertical wind from the UKMO model demonstrate the distinct latitude and seasonal dependences.