Grains shade Earth most effectively when they are within the LLagrange point. There, every photon they absorb or deflect is one that would have struck Earth. Serendipitously, grains at Lare almost as effective; about 80% of the photons they intercept would have been Earth-bound. Further from Earth, this effectiveness is diminished.
The details of shading depend on grain size, shape, and composition, all of which determines the extinction efficiency . Typically, micron-size grains have higherthan nanoparticles. Breaking up micron-size grains into more numerous smaller particles increases the physical surface area of a cloud, but generally reduces the amount of shade it can provide because of the loss of extinction efficiency.
from a given cloud mass, grains with high porosity are promising, as are particles with large aspect ratios, including cylindrical tubes. The effectiveness of a dust cloud as a sun shield depends on how long it can persist between Earth and the Sun before non-gravitational forces disperse it. Persistence of grains at Lis low for sizes below 100 microns as a result of radiation pressure and drag from the solar wind. Micron-size grains, if released at L, drift away within in a week or so. The persistence time increases with particle mass, as well as the degree to which a grain forward scatters light.
Variations on the choice of materials, launch method, and orbit types may lead to strategies with advantages over the ones considered here. For example, if designer glass grains were manufactured from raw materials on the lunar surface, they may be delivered to an L-like orbit more efficiently, or tuned to have mass and scattering properties that enable them to follow Earth-Sun-intercept orbits for longer periods of time than raw lunar dust.
PLOSClimate The cooling after WWII is what happened when large amounts of dust and smoke were blown up in the air.