"Relatively minuscule quantities of sulfur dioxide (SO2) in the stratosphere are extremely reflective, scattering some of the sun’s light before it hits the Earth, and in the process contributing to the atmospheric haze that gives sunsets their characteristic red color. "

Sounds idyllic of course, but we really don't fully understand what effects such an intervention would have, and unlike what is claimed, we can't turn it off if it goes wrong.

A much safer alternative IMHO is to spray seawater to enhance marine cloud formation.

Also a possible alternative to grinding up mountains is marine iron fertilization, but again, we don't fully understand the effects.