Resolving the SAI Trilemma with a Novel Core–Shell Mineral Aerosol: DoloSil-20, a Silica-Passivated Dolomite Architecture for Simultaneous Optical Efficiency, Thermal Neutrality, and Ozone Safety

ABDUL HASEEB TANOLI, Shams ul Arfeen

Conventional stratospheric aerosol injection (SAI) strategies based on liquid sulfate aerosols (H2SO4.H2O) introduce well-documented risks of catalytic ozone destruction and stratospheric near-infrared heating. From a materials-science perspective, the core challenge is one of multi-objective material selection: identifying a particle composition that simultaneously optimizes optical performance, chemical inertness, and thermal neutrality in the stratospheric environment.

We formalize these competing requirements as the SAI Trilemma: (1) radiative efficiency, maximizing shortwave backscattering per unit injected mass; (2) thermal neutrality, suppressing stratospheric heating; and (3) ozone safety, mitigating heterogeneous ozone chemistry. To screen candidates across this Trilemma, we propose and evaluate a novel materials-engineering solution: a novel core-shell mineral aerosol (DoloSil-20)—a dolomite (CaMg(CO3)2) core encapsulated by a 20 nm amorphous silica shell, synthesized via Stober-type wet chemistry and designed as a core-shell heterostructure that combines high refractive index contrast with chemical passivation. This architecture is evaluated against pristine calcite and a liquid sulfate reference using a 1D vertical sectional aerosol model integrated over a 1825-day (~5-year) horizon.

At lambda = 550 nm and D = 500 nm outer diameter, the mass-specific backscatter proxy beta_back of the DoloSil-20 reaches 0.3405 m2 g-1—a +45.17% advantage over the sulfate reference (0.2346 m2 g-1)—computed via the Aden-Kerker analytical solution for concentric spheres [Aden & Kerker, 1951; Bohren & Huffman, 1983]. This constitutes a wavelength-specific screening result at lambda = 550 nm; spectrally integrated radiative forcing requires a full broadband radiative transfer calculation not performed here. Both mineral proxies exhibit negligible imaginary refractive indices (k ~ 0 at 1500 nm), yielding temperature-anomaly proxy values at the numerical floating-point noise floor (< 10^-15 K). This result is mechanistically expected from the prescribed optical properties and functions as a model consistency check rather than an independent physical prediction. Using a first-order partial-column (10-40 km) ozone surrogate—not equivalent to three-dimensional photochemical model output, and initialized above typical observed partial columns—the silica-passivated core-shell constrains peak ozone depletion to 10.03% of the model domain column, compared to sulfate's 47.11% and calcite's 14.77%. The principal trade-off is atmospheric persistence: higher particle density yields a day-1825 mass retention of 53.98% versus sulfate's 69.46%, a direct consequence of gravitational sedimentation scaling with particle density.

Within the constraints of this reduced-order 1D screening framework, the DoloSil-20 architecture simultaneously addresses all three axes of the SAI Trilemma. These results motivate evaluation in three-dimensional chemistry-climate models, which constitute the necessary next step before deployment-relevant conclusions can be drawn.