"Stratospheric aerosol injection would involve flying aircraft into the stratosphere, or between 10 miles and 30 miles skyward, and spraying a fine mist that would hang in the air, reflecting some of the sun’s radiation back into space."

https://web.archive.org/web/20221014041448/https://www.cnbc.com/2022/10/13/what-is-solar-geoengineering-sunlight-reflection-risks-and-benefits.html