Abstract: Catalysts for warm cloud seeding have significant potential for applications in warm cloud catalytic precipitation and fog elimination. In recent years, numerous innovative materials have been developed, each with the potential to be used in warm cloud catalysis. However, a universally recognized ideal formulation has not yet been established. It is necessary to conduct a scientific analysis on the performance of various hygroscopic catalysts under consistent experimental conditions.
Therefore, 9 types of typical powdered hygroscopic catalysts are collected, and experiments involving fog chamber and static testing of catalysts are conducted at CMA Key Laboratory of Cloud-precipitation Physics and Weather Modification in May 2023. Fog elimination capabilities and hygroscopic characteristics of various catalysts are comprehensively evaluated and compared. Results indicate that, under the same fog conditions, salt type catalysts demonstrate the shortest time to eliminate fog, and porous composite materials (PCM-100 and PCM-10) are also effective, while fog elimination effects of modified starch, molecular sieves, organic bentonite and sodium bentonite are not obvious after seeding. In static detection, under normal temperature and humidity conditions, CaCl₂ exhibits the strongest static hygroscopicity, followed by porous composite materials such as PCM-100 and PCM-10. Composite salt catalysts exhibit strong hygroscopic absorption, whereas the static hygroscopic absorption capacity of other catalysts is not as pronounced. In high humidity conditions, bentonite and molecular sieve catalysts still do not exhibit moisture absorption characteristics. The hygroscopic abilities of CaCl₂, PCM-100, and PCM-10 are significantly higher than those of other catalysts. The performance of various catalysts in the fog chamber experiment and static detection is basically consistent.
Microstructures of various catalysts with strong hygroscopic properties do not show significant changes after 30 minutes. PCM-10 primarily exists in the form of liquid droplets after standing for 5 minutes and can continue to provide hydration. PCM-100 remains in irregular crystal form after 5 minutes and transforms into droplets after 30 minutes. CaCl₂ absorbs moisture rapidly under the microscope, initially existing as liquid droplets for 5 minutes. Subsequently, there are no significant changes, primarily small droplets. Complex salts always form crystals, while the size of liquid droplets formed is larger.
It should be noted that, although the hygroscopicity and the ability of fog elimination of various catalysts are important indicators, the dispersibility, corrosiveness and ease of preparation and storage of the catalyst are also important parameters of whether they can be used as efficient warm cloud catalysts. Follow-up research and evaluation of various catalysts will be conducted.