| Abstract |
In order to clarify the mechanism of ice-fog formation, various atmospheric factors in ice fogs such as size and concentration of ice-fog crystals, condensation nuclei and ice nuclei, amount of water vapor, temperature profile near the sources of ice fog, etc. were measured. Nuclei of the ice-fog crystals were studied by use of an electron microscope and electron-diffraction. Most nuclei of ice-fog crystals were combustion by-products and many individual crystals collected near open water did not have a nucleus, especially at emperatures below -40C. Dust particles or particles from air pollution are not essential for formation of ice fog; they merely stimulate freezing of water droplets at higher temperatures than the spontaneous freezing temperature. The essential factor is to first form many water droplets in the atmosphere through condensation of water vapor. Based on these measurements and calculations of time required for water droplets to freeze, a physical mechanism of ice fog formation is proposed as follows: (1) Water vapor coming from open water which is exposed to a low temperature atmosphere, plus water vapor from various exhausts of combustion processes is released into the almost ice-saturated atmosphere and condenses into water droplets, (2) The droplets freeze very shortly after their formation and before entirely evaporating, (3) Such ice particles do not evaporate or grow much and stay in the atmosphere with insignificant fall out, and (4) These processes operate more efficiently in colder environments. (Author) |
