Strong light absorption by sp hybridized carbon impurities in diamond dust

Stratospheric aerosol injection (SAI) using diamond dust has been proposed as a solar radiation management (SRM) technique to mitigate global warming by scattering incoming solar radiation, offering advantages over sulfur-based aerosols such as reduced ozone depletion and acid rain risks. However, detonation synthesis—the most economical method for large-scale nanodiamond production—inevitably introduces sp 2 -hybridized carbonaceous impurities, often forming shells around diamond cores, which may enhance shortwave absorption and undermine SRM efficacy. This study employs density functional theory and ab-initio molecular dynamics to model these impurities across hydrogen-to-carbon (H/C) ratios from 0.0 to 1.0, revealing a continuum of optical properties in which decreasing sp 2 content reduces the imaginary refractive index ( k ). Particle-scale core-shell Mie scattering simulations at 550 nm for diamond cores of 300 nm diameter with carbonaceous impurity shells (1.95 + k i refractive index, shell thickness of ∼0.1–10 nm corresponding to 0.1–10% impurity mass fraction) show that these impurities elevate the effective mass absorption coefficient to up to ∼1 m 2 /g—nearly 15% that of black carbon (∼7.5 m 2 /g)—and decrease single-scattering albedo by up to 25% relative to pure diamond. These absorption enhancements, driven by the impurity shell’s k and mass fraction, could shift diamond dust's radiative forcing toward warming. Our findings highlight the critical need to revisit diamond’s efficacy as an SAI candidate material. • Strongly scattering diamond dust is proposed for Solar Radiation Management. • Economical detonation synthesis introduces > 5% sp 2 hybridized carbon impurities. • Density Functional Theory revealed a range of highly light-absorbing impurities. • Trace impurities on diamond particles introduce shortwave absorption. • Impurities decrease diamond’s scattering by up to 25%, questioning its efficacy.