My guess this is the "other" chemicals they need that when combined with the first series of spraying this stuff is sure to do the most damage.
Its like shooting someone TWICE in the head. One for the road.

Stratospheric Welsbach seeding for reduction of global warming United States Patent 5003186
Siemens Energy Solutions
Energy solutions for the US: The world leader in Green Technology.
www.usa.siemens.com/answersAbstract:A method is described for reducing atmospheric or global warming resulting from the presence of heat-trapping gases in the atmosphere, i.e., from the greenhouse effect. Such gases are relatively transparent to sunshine, but absorb strongly the long-wavelength infrared radiation released by the earth. The method incudes the step of seeding the layer of heat-trapping gases in the atmosphere with particles of materials characterized by wavelength-dependent emissivity. Such materials include Welsbach materials and the oxides of metals which have high emissivity (and thus low reflectivities) in the visible and 8-12 micron infrared wavelength regions