The effect of particle shape on shortwave radiative forcing in stratospheric aerosol injection

[Geoengineering News]

https://www.sciencedirect.com/science/article/pii/S0022407326000828

Authors: Benjamin Vennes, Thomas C. Preston 

26 February 2026

https://doi.org/10.1016/j.jqsrt.2026.109888

Highlights

•Develops a T-matrix–based method to compute the isotropic upscatter fraction.

•Quantifies shortwave cooling from non-spherical stratospheric aerosols.

•Uses spheroid and superspheroid shape families in full T-matrix calculations.

•Shows Bond albedo depends mainly on particle size and refractive index.

•Finds particle shape only weakly alters cooling per mass.

Abstract

Stratospheric aerosol injection (SAI) seeks to increase Earth’s planetary albedo by introducing particles into the lower stratosphere that efficiently backscatter solar radiation. Most optical optimization studies have focused on spherical particles, leaving the potential benefits of non-spherical morphologies largely unexplored. Here, we develop an analytical Legendre-moment method that uses closed-form expansion coefficients within the T-matrix framework to efficiently and accurately evaluate the isotropic upscatter fraction for randomly oriented non-spherical particles. This is used to quantify how particle shape and aspect ratio influences the change in Bond albedo, ΔA, within a single-scattering framework. Orientation-averaged extinction and scattering cross-sections and phase function moments are computed over the solar spectrum to obtain ΔA and global-mean radiative forcing per unit mass for candidate SAI materials (rutile, anatase, α-SiC, diamond, cubic ZrO2, α-Al2O3, calcite, and sulphate). We systematically explore spheroids with varying aspect ratio and superspheroids spanning a wide range of roundness/boxiness. Overall, once volume-equivalent radius and refractive index are optimized, ΔA is only weakly sensitive to particle morphology. Therefore, while non-spherical particles can improve ΔA, the resulting gains are modest at best, and ΔA remains controlled primarily by volume-equivalent radius and refractive index.

Source: ScienceDirect