Better certainly than trying to reignite old volcanoes to get them spewing light blocking material into the air.

Hard to say, though, what exactly the ultimate effects might be, long term, on doing something like this.

This also breaks the maxim that, if you want to dial an effect up, you better be able to dial it back down again, in reasonably practical time frames; and you need to be able to do that both because you can't be sure of the overall effects, given the nature of how unintended side effects can creep into a complex system that you start throwing changes at; but also because you might actually achieve your result, and then would certainly want to start cutting back on the whole reflecting thing; perhaps a lot sooner than you expected, for completely different reasons than you expected.

The chemical indicated here is sulfur dioxide. Not something normally thought of in connection with big chemical companies spewing poisons simply because it's quick, and will probably address the main problem, as well as make a tidy profit but, by the very fact that we have been given good reason to worry about such connections from past history, we ought to be at least concerned here.

So not only is the obvious question about how long term in the air, whatever chemical is used, might be, pertinent, but also what it might do, harm wise down stream, so to speak, as they undoubtedly will precipitate out in due course, and actually end up flowing through a number of various flow systems, each with their own sets of sensitivities.

The other part of this, for me, though, is why send big money, to whatever kind of company sells the chemical used, and not have something else, other than the hoped for effect, to show for it; not that the hoped for effect is any slouch mind you. But if you intend to spend some "infrastructure" type money, why not build infrastructure that will help you solve this problem, and other problems as well?

And that is where, certainly, I like going down the path of setting up the construction capability, as a non profit, public entity, to build very large scale, lighter than air constructs, in which I include now both Hybrid Dirigible Blimp trains, and the kinds of multi mile cubic structures that would be able to float flexible, reflective mats at whatever altitude, up to the limit of where weather balloons can get to. Floating, flexible mats that could also have solar collectors on them to created quite significant amounts of power with. And assuming you were using the right lift primitive (as in my Lift Doughnut design), you might also be able to pipe cold air back down to further your efforts at cooling.

And understand here, these will be installations that might make the difference between cities lying at, or near, the equator to remain habitable at all, going forward, as they might provide a perfect trifecta of shade, perhaps cooling air, and electrical power, not to mention helping to save some ice at the poles, and whatever other important glaciers need protecting, within either pole's arctic circle.