PROBLEM TO BE SOLVED: To provide a method for artificially suppressing rainfall. SOLUTION: Cobalt oxide (II) nanoparticles are sprayed from an aircraft such as an airplane or a helicopter or a balloon on a cloud in which sunlight is shining toward the cloud. When cobalt (II) oxide nanoparticles and light come into contact with water, which is a component of clouds, the water almost immediately separates into hydrogen and oxygen at a ratio of 2: 1 so that the clouds can be extinguished. [Selection diagram] None
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