Sort of. One could release sulfur dioxide (or burn sulfur to form sulfur dioxide) at high altitude, or release slower-reacting sulfur species like carbonyl sulf

Sort of. One could release sulfur dioxide (or burn sulfur to form sulfur dioxide) at high altitude, or release slower-reacting sulfur species like carbonyl sulfide from surface locations. In any of these cases what will happen is that reactions with nitrogen oxides, ozone, light, atmospheric moisture, and other particles will ultimately convert the sulfur to sulfuric acid, which will then form additional particles of high reflectivity. It would somewhat increase the surface precipitation acid burden, similar to the acid rain that was a byproduct of 20th century industrialization, but most sulfur oxides that come from power plants or metal refining are flushed out of the lower atmosphere by precipitation. By directly or indirectly adding SO2 to the stratosphere instead of the troposphere, the ratio of reflection:acid content would be higher than that of incidentally produced waste-product SO2. (That's why we can't start cooling the planet just by removing sulfur controls from existing coal plants; most of that SO2 would produce acid rain accompanied by little additional sunlight reflection.)