Shading the earth via sulfate aerosols

One of the proposed techniques, suggested by Budyko (1977) and Crutzen (2006), follows the natural example of volcanic eruptions emitting large amounts of sulfur dioxide (SO2) into the stratosphere. Chemical and microphysical reactions cause the formation of sulfate aerosols, which reduce the incoming solar radiation. It is however unclear, to what extent this volcanic example can be used as analogue for the effect of geoengineered aerosol because of likely differences in aerosol size distributions and radiative properties resulting from different emission patterns.

The particle size is a crucial parameter for the effectiveness of stratospheric aerosols as it influences its absorption and scattering properties. For the temporal development of the aerosol size distribution, the injection strategy is likely of importance. Sulfur could be injected at different rates and different heights, continuously or pulsed, in a single small area or distributed along the equator.

Model simulations with a general circulation model including aerosol microphysics (Niemeier et al, 2010) show 

  • lifetime of sulfate aerosols depends on the emissions strength
  • effective radius of sulfate particle increases with increasing emissions
  • emission of H2SO4 gas instead of SO2 slightly enhances the lifetime of sulfate aerosol

Literature

Bodyko MI. 1977. Climatic Change. AGU. Washington, D.C : 261.

Crutzen PJ. 2006. Albedo enhancement by stratospheric sulfur injections: A contribution to resolve a policy dilemma?.  Clim Change 77: 211-219.

Niemeier U, Schmidt H, Timmreck C. 2010. The dependency of geoengineered sulfate aerosol on the emission strategy, Atmos. Sci. Let.,DOI: 10.1002/asl.304