What are the catalysts for artificial rainfall? Will the use of these catalysts affect the environment?

Did you know that salt has many uses? In addition to being edible, it is also one of the main catalysts for artificial rainfall.

So, at this moment, do you have an idea: go to the kitchen, grab a handful of salt, and sprinkle it into the clouds in the sky, can it achieve the purpose of increasing rainfall?

Actually, no. Generally speaking, the diameter of a grain of table salt is about 0.1 mm, or about 100 microns. This size is very small for most foods. But for water vapor in the air, a grain of table salt is a huge guy, because in clouds where no rain forms, generally speaking, the size of water vapor molecules is only 5-10 microns. Throwing a handful of table salt grains into the clouds in the air is like throwing a shot put at cotton candy. Due to gravity, the salt grains have reached the falling standard and will pass through the clouds and fall straight down. So you can imagine that when the operator throws a handful of table salt into the clouds in the plane, the salt grains will fall down, and the cloud will still be the same cloud.

So, how does salt increase rainfall through clouds?

Salt is mainly used to increase rainfall in warm clouds. When warm clouds naturally precipitate, the diameter of cloud droplets generally needs to reach more than 100 microns before they can defeat the rising air currents and form raindrops that fall to the ground. When there is abundant water vapor in warm clouds, the diameter of water vapor particles is generally only 5 to 10 microns. These particles are freely suspended in the air because they are very light and will not fall down. If you seize the opportunity to spread salt powder in the clouds, the arrival of salt powder will unite the water vapor particles. When the diameter of the water vapor particles grows to tens of microns, they will continue to collide and merge with the surrounding small water droplets, and finally overcome the rising air currents and become raindrops that fall down.

Therefore, it is true that salt can be used as a hygroscopic agent to increase rainfall, and it has been used for many years. However, in order to increase rainfall, the salt particles must be "slimmed down" first. In the early days, the salt particles used to increase rainfall in warm clouds were ground by physical methods until their diameter was as small as about 30 microns. However, because they were still too large, when these salt powders were sprinkled into the clouds, the rainfall-increasing effect was not very good.

After repeated practice, the chemical method is now adopted, through the combustion reaction between substances, salt particles (potassium chloride, sodium chloride) less than 1 micron are produced. These salt particles are very suitable as playmates of water vapor in the clouds because of their small size. They are sent into the clouds and can be closely combined with water vapor molecules. In this process, they constantly absorb moisture, collide, and grow larger. Experiments have shown that when the same volume of salt powder is spread, the smaller the diameter of the salt particles, the more rain will be produced.

In actual operation, it is more common to use artificial methods to increase precipitation on cold clouds. In layman's terms, it is to use catalysts to make the ice crystals in the clouds more and larger, and finally settle and melt into rain. The catalysts for cold cloud precipitation increase include ice-forming agents (such as silver iodide) and refrigerants that can cause a sudden drop in temperature (such as dry ice, liquid carbon dioxide, liquid nitrogen, etc.).

In summary, weather modification catalysts are divided into three categories: ice-forming agents, refrigerants and desiccant agents.

Ice-forming agent : Mainly used for cold cloud catalysis operations at -6℃~-20℃. Silver iodide is one of the most commonly used ice-forming agents. Its crystal structure is similar to ice crystals, and it is a master at making ice crystals. Tiny silver iodide particles are mainly obtained by chemical methods. On the human shadow plane, the staff ignites a certain proportion of chemical components and combustion aids. When the temperature reaches above 2000℃, the generated silver iodide instantly vaporizes, and quickly condenses when it encounters cold air. The tiny silver iodide particles immediately enter the cloud layer and enter the working state to participate in ice formation. Generally speaking, 1013 to 1014 silver iodide particles can be differentiated from each gram of silver iodide.

Refrigerant : used for 0℃~-6℃ convective cloud or layered cloud catalysis operation, including dry ice, liquid nitrogen, propane and other members. Dry ice is solid carbon dioxide, its sublimation temperature is -78.5℃, after warming up, it directly sublimates from solid to gaseous state, 1 gram of dry ice can produce tens of billions of ice crystals, it is a refrigeration expert. The boiling point of liquid nitrogen is -195.8℃, and the boiling point of propane is -80℃, and its working principle is similar to that of dry ice.

Desiccant : used for warm cloud catalysis above 0℃. It includes sodium chloride (salt), calcium chloride, ammonium nitrate, urea and other members. One gram of salt can catalyze tens of millions of raindrop embryos.

In terms of weight, 1 gram of catalyst can produce 1,000 to 10 billion ice nuclei, raindrop embryos, and ice crystals, so only a small amount of catalyst is needed for each operation to complete the task efficiently.

In terms of composition, for example, refrigerants such as dry ice and liquid nitrogen, after participating in the rain-enhancing mission, vaporize into carbon dioxide and nitrogen - they are all components of air. Another example is desiccant salt, urea, etc., they originally come from nature and return to nature after the rain-enhancing is completed. Therefore, they are all ecologically safe catalysts and will certainly not pollute the environment.

Another example is silver iodide, which is used frequently, but its usage in aircraft rain-making operations and rocket operations is very small. Long-term data monitoring shows that the concentration of silver ions accumulated in the water and soil in the operation area is far lower than the concentration specified by the World Health Organization.

Therefore, the correct use of human shadow catalyst will not cause environmental pollution.