人工影响天气碘化银催化剂研究进展

Advances of Silver Iodide Seeding Agents for Weather Modification

碘化银(AgI)类催化剂是人工影响天气外场试验和业务作业中使用最广泛的催化剂,其核化效率和核化机制在很大程度上影响催化效果。在总结美国、中国和欧洲多个国家利用云室和风洞研究AgI类催化剂的核化机制、核化阈温及成核率的室内实验成果的基础上,梳理利用室内实验成果发展的AgI数值催化模式,旨在为下一步优选新型高效AgI类催化剂和改进数值催化模式提供借鉴。AgI类催化剂核化机制包括凝华核化、接触冻结核化、凝结冻结核化和浸没冻结核化,其核化过程受大气温湿条件、催化剂粒子大小、成分等多种因素影响,并与催化剂粒子的燃烧溶液法、燃烧焰剂法和爆炸法等发生方式有关。目前国内外使用的AgI类催化剂含有不同成分,有多种催化剂粒子产生方式,催化剂粒子的核化机制和成核率有很大差异。将来应重点基于高性能云室和风洞,分析不同催化剂配方的核化机制和成核率,优选新型高效催化剂,改进AgI数值催化模式。

Silver iodide(AgI)is the most widely-used seeding agent in field experiment and operations of weather modification.There are several nucleation modes for AgI seeding agents,and the nucleation process is affected by many factors including atmospheric temperature,humidity,particle size,composition of seeding agent and its particle generation method.The nucleation efficiency,nucleation modes affect the number of nucleated crystals,and thus affect the seeding effect.Through laboratory research of cloud chamber and theoretical calculation,the critical embryo sizes required for different nucleation mechanisms,nucleation threshold temperature,nucleation mechanisms,factors effecting nucleation for AgI and with some other added materials are analyzed.It is currently accepted that there are four nucleation mechanisms,including deposition,condensation freezing,contact freezing and immersion freezing nucleation.And it is recognized that nucleation processes depend on the varied temperature,humidity,and cloud conditions that can be encountered in the atmosphere.Immersion nucleation refers to nucleation of freezing by a particle immersed in water,and deposition nucleation refers to nucleation of the ice phase from the vapor,contact nucleation refers to the nucleation of the freezing induced by a particle during first contact with supercooled water,and condensation freezing is the nucleation of the freezing from the condensation of vapor to liquid droplet.The ice-nucleating properties and nucleation effectiveness of cloud seeding materials produced by burning acetone solutions or pyrotechnics of AgI and other materials are tested in a wind-tunnel cloud chamber test facility along with isothermal cloud chamber and dynamic cloud chamber.Through laboratory test,different formulations are compared,and high nucleation efficiency of seeding materials are selected,and nucleation features for four nucleation modes separately are obtained.Silver iodide seeding cloud model are based on a combination of theory and laboratory results.The ice nucleation schemes employed in cloud models vary widely.Hsie’s seeding scheme simulated both contactfreezing and deposition nucleation on the laboratory measured effectiveness spectra of nucleus.Meyers seeding scheme considers all the four processes on cloud chamber results of ice-forming processes by AgI.In China,AgI seeding models are developed since the 1990 s,either similar with Hsie’s seeding scheme on three nucleation mechanisms,or similar with Meyers seeding scheme on four nucleation mechanisms.