🚨How much does the shape of particles matter for #SolarGeoengineering?
A new study tests whether non-spherical particles could improve the cooling efficiency of #SAI.
The result: shape can help slightly, but particle size & refractive index dominate the cooling effect.🧵1/11
2/ SAI aims to cool Earth by injecting particles into the lower stratosphere that scatter incoming sunlight back to space, increasing planetary reflectivity (albedo).
The effectiveness of these particles depends on their optical properties, how they scatter and absorb sunlight.
3/ Most previous studies optimized SAI particles assuming they're perfect spheres, focusing on 2 parameters: particle radius & refractive index.
But real particles in the atm are often irregular or elongated, raising an imp Q: could particle shape improve solar reflection?
4/ To investigate this, researchers examined a wide range of non-spherical particles, including elongated spheroids and more complex superspheroids, and tested how these shapes influence shortwave radiative cooling across the solar spectrum.
5/ They evaluated several potential SAI materials, including rutile, anatase, silicon carbide, diamond, zirconia, alumina, calcite, and sulfate, comparing how particle shape affects their ability to scatter sunlight and increase planetary reflectivity.
6/ The results show a clear pattern: changes in Earth’s Bond albedo (ΔA), a measure of planetary reflectivity, are largely controlled by particle size and refractive index, not particle morphology.
7/ When particles are compared at the same volume-equivalent radius, differences in shape produce only negligible changes in cooling performance.
In other words, whether particles are spherical, elongated, or slightly box-like makes little difference to overall radiative effect.
8/ Even though some non-spherical shapes can slightly increase sunlight backscattering, the improvement in cooling per unit mass is small.
The potential gains from shape optimization are therefore modest at best.
9/ This leads to an important design implication: particle shape should not be a primary focus when designing SAI aerosols.
Instead, optimizing material properties and particle size remains the most effective way to enhance solar reflection.
10/ The study suggests that targeting particles with high refractive index, minimal visible-light absorption, and a radius around ~0.1 μm offers the best optical performance for reflecting sunlight in SAI scenarios.
📝For more details, read the study entitled "The effect of particle shape on shortwave radiative forcing in stratospheric aerosol injection" here:
🧵11/11 #SolarGeoengineering #SRM #SAIsciencedirect.com/science/articl…
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