Absorption not Reflection.
Image Credit: Scientific Frontline
Scientific Frontline: Extended "At a Glance" Summary: Stratospheric Aerosol Injection with Diamond Dust
The Core Concept: Stratospheric aerosol injection (SAI) is a solar geoengineering strategy intended to cool the Earth by dispersing highly reflective aerosols into the stratosphere, mimicking the natural cooling effects of volcanic eruptions. Recent studies evaluated synthetic diamond dust as a potentially safer alternative to environmentally damaging sulfate aerosols.
Key Distinction/Mechanism: While previous large-scale climate models theorized that diamond dust would be an optimal reflective particle, new first-principles calculations demonstrate a critical flaw. The most economical method for mass-producing nanodiamonds (detonation synthesis) inevitably introduces sp2-hybridized carbon impurities. These impurities form a hard, dark carbon shell around the diamond core that absorbs heat rather than reflecting sunlight, decreasing the material's light-scattering efficacy by up to 25%.
Origin/History: The definitive research disproving the efficacy of diamond dust in SAI was published in the Journal of Aerosol Science (Volume 194, 2026) by researchers at Washington University in St. Louis, utilizing sophisticated simulations funded by a 2024 grant from the Simons Foundation International.
Major Frameworks/Components:
- Stratospheric Aerosol Injection (SAI): A theoretical climate intervention framework designed to increase planetary albedo by maintaining a continuous presence of reflective particles in the upper atmosphere.
- Detonation Synthesis: The thermodynamic process of producing nanodiamonds by detonating carbon-rich explosive mixtures in a metal chamber, which inherently yields light-absorbing carbonaceous "soot."
- \(sp^2\)-Hybridized Carbon Impurities: Residual contaminants comprising 1-5% of the synthetic dust mass that fundamentally alter the thermodynamic profile of the particles from reflective to absorptive.
- First-Principles Calculations: Advanced computational modeling techniques used to analyze the atomic and molecular interactions, composition, and physical constraints of synthetic aerosols.
Branch of Science: Aerosol Science, Materials Science, Environmental Engineering, and Atmospheric Chemistry.
Future Application: By disproving the viability of a massive "diamond shield," climate scientists can now efficiently redirect computational modeling resources, physical testing, and funding toward identifying safer, more effective aerosol candidates for solar radiation management.
Why It Matters: Eliminating chemically flawed candidates in solar geoengineering is critical to avoiding severe unintended consequences. Deploying compromised diamond dust would require immense logistical effort and financial expenditure (an estimated 5 million tons dropped annually via high-altitude aircraft) while paradoxically risking accelerated atmospheric warming, ozone destruction, and unforeseen atmospheric feedback loops.
The field of solar geoengineering revolves around the idea of cooling the globe via the injection of aerosols to reflect sunlight or to thin clouds. One such strategy, stratospheric aerosol injection (SAI), aims to mimic the effects of a volcanic eruption. Volcanoes spew sulfur dioxide into the stratosphere, which then reflects light back into space, cooling the Earth for potentially a year or longer, as documented in previous eruptions.
But sulfate aerosols are not ideal particles to deploy because of their effects contributing to acid rain, degrading the ozone layer and harming human health. Instead, researchers have used large-scale climate models to run virtual solar geoengineering experiments with different particles that could potentially reflect the sun while causing less harm to the environment. Previous such research pointed to a sparkling alternative: diamond dust.
However, researchers at Washington University in St. Louis using first-principles calculations that allow them to explore material properties at the atomic and molecular levels, have found it won't work. Diamond dust from detonation synthesis, the most economical method for large-scale nanodiamond production, could cause an expensive mess, they found. Such particles inevitably contain residual carbon impurities, typically ranging from 1-5% by mass. Even the most minute carbonaceous impurity in the dust causes further absorption, not reflection, of heat, their research found. It's now published online in the Journal of Aerosol Science.
WashU researchers provided this analysis using sophisticated simulations for analyzing the composition, size and chemical interactions of synthetic diamond dust aerosols formed using detonation synthesis, thanks to a 2024 grant from the Simons Foundation International.
The research details how the synthesis of diamond dust during the high-temperature detonation process introduces \(sp^2\)-hybridized impurities that can form a hard carbon shell around the diamond core, enhancing absorption of light rather than reflection. Rajan Chakrabarty, the Harold D. Jolley Professor of Engineering, and Associate Professor Rohan Mishra, along with postdoctoral scholars Joshin Kumar, Gwan-Yeong Jung, and Taveen Kapoor all at the McKelvey School of Engineering, are co-authors on the paper.
Mining diamonds for science would be prohibitively expensive. So scientists generate diamond particles, or nanodiamonds, by detonating an explosive mixture of carbon-containing compounds in a metal chamber, producing diamond “soot.”
And the soot exists on a brown-black continuum of light-absorbing carbonaceous aerosols, said Kumar, the study's lead author.
“The process of making the diamond dust inevitably introduces carbon impurities that end up absorbing light instead of reflecting it,” Chakrabarty said. This reduces the diamond’s light scattering affect by up to 25%, ultimately making the hypothesis of using a “diamond shield” to cool the Earth much less viable.
Previous research identifying diamond dust as a potential SAI candidate found that it would take 5 million tons of those particles those particles into the stratosphere yearly to cool the planet by 1.6 degrees Celsius, and that they would be deployed using high-altitude aircraft to dump the gem particles. What sounds like something out of a James Bond movie may ultimately not be worth the effort, expense and potential risks of it going sideways.
But it’s as important to eliminate candidates for solar geoengineering as it is to find new ones; thanks to this research, climate scientists now can devote limited time and resources to more promising particles for cooling the Earth.
“Investigating impurities in solar geoengineering particles is crucial,” Chakrabarty said. “Unintended chemical contaminants can alter particle reflectivity, catalyze ozone destruction or create unknown atmospheric feedback loops that reduce cooling efficiency and increase environmental risks.”
Funding: This work was supported by a grant from the Simons Foundation International (SFI-MPS-SRM-00005174, R.C.). This work used computational resources through allocation DMR160007 from the Advanced Cyberinfrastructure Coordination Ecosystem: Services & Support (ACCESS) program, which is supported by National Science Foundation grants #2138259, #2138286, #2138307, #2137603, and #2138296.
Published in journal: Journal of Aerosol Science
Title: Strong light absorption by \(sp^2\) hybridized carbon impurities in diamond dust
Authors: Joshin Kumar, Gwan-Yeong Jung, Taveen S. Kapoor, Rohan Mishra, and Rajan K. Chakrabarty
Source/Credit: Washington University in St. Louis | Leah Shaffer
Reference Number: as032126_01