We have natural experiments where sulfur aerosols were injected. The 1991 eruption of Mt. Pinatubo, for example. It injected 17 megatonnes of sulfur dioxide into the stratosphere, causing a global cooling of 0.4 C and a northern hemisphere cooling of 0.5-0.6 C. This also affected ozone, which suggests aerosols other than sulfuric acid droplets might be a better idea.
