Which chemical is commonly used as an ice-forming agent in cloud seeding?

Silver iodide is commonly used as an ice-forming agent in cloud seeding.

Its crystal structure resembles that of ice, so tiny silver iodide particles can help supercooled cloud droplets freeze. Aircraft or ground-based generators release the particles into suitable clouds, where the resulting ice crystals may grow and fall as snow or melt into rain.

Cloud seeding cannot create clouds from clear air. It requires existing clouds with appropriate temperature, moisture, and airflow conditions. Results also vary, making the extra precipitation difficult to separate from what would have happened naturally.

Other materials, including dry ice and hygroscopic salts, have also been used for different cloud-seeding goals. Silver iodide is especially associated with glaciogenic seeding, which promotes ice formation in cold clouds. Environmental monitoring is used because silver is a metal, although reported concentrations from many operations are generally low.