The proposals seem to be injecting less SO2 than we do now but mindfully making it very tiny particulates. It'll be just as reflective as the larger ones from diesel but less polluting in terms of acid rain, and it'll have a better resident time due to small size.
No one seems to want to talk about arctic geoengineering with wind driven ammonia as being a viable alternative. It's the only one that makes fuel as part of the remediation effort.
http://strandedwind.org/node/41
On the SO2, it is currently tropospheric and more localised (the concentrations are mainly on a sub-continental scale, I think). The proposal of Crutzen et al is to have stratospheric SO2, which will probably have negative effects on the ozone layer, for one.
