They directly resolve the separate contributions by various aerosol components and forcing mechanisms. (ipcc.ch)
The relative importance of the various aerosol components is critical for the aerosol climatic effect, since atmospheric aerosols behave differently when their chemical composition changes. (pubs.giss.nasa.gov)
Sulphate is not typically the dominant anthropogenic aerosol component however, though many climate models treat it as such. (realclimate.org)