Unveiling the Shortwave Absorption Spectra of Alumina Aerosols: Radiative Implications for Solar Radiation Modification

Taveen Singh Kapoor; Prabhav Upadhyay; Jian Huang; Guodong Ren; John Cavin; Dhruv Mitroo; Sandro Vattioni; John Dykema; Jan Sedlacek; Joshin Kumar; Jordan A. Hachtel; Lu Xu; Rohan Mishra; Rajan K. Chakrabarty

doi:10.1029/2026GL121668

Unveiling the Shortwave Absorption Spectra of Alumina Aerosols: Radiative Implications for Solar Radiation Modification

Taveen Singh Kapoor
, Prabhav Upadhyay
, Jian Huang
, Guodong Ren
, John Cavin
, Dhruv Mitroo
, Sandro Vattioni
, John Dykema
, Jan Sedlacek
, Joshin Kumar
, Jordan A. Hachtel
, Lu Xu
, Rohan Mishra
, Rajan K. Chakrabarty

electron Microscopy and Microanalysis

Research output: Contribution to journal › Article › peer-review

1 Scopus citations

Abstract

Alumina is proposed for Stratospheric Aerosol Injection (SAI)-based solar radiation modification due to its presumed ability to scatter sunlight strongly while absorbing weakly. Alumina is assigned negligible solar shortwave absorption in climate models; this assumption is not validated owing to technological challenges in quantifying its weak absorption signals. We report alumina's shortwave imaginary refractive index (k), a determinant of its absorption strength, using sensitive in situ photoacoustic spectrometry, finding values ranging from 1.4 × 10⁻⁴ to 1.2 × 10⁻³. Particle-scale electron energy-loss spectroscopy provided independent validation and revealed that the non-ideal absorption arises from oxygen vacancy defects in the alumina. Aerosol chemistry climate model simulations of an established scenario reveal that shortwave absorption has negligible effects on radiative forcing and stratospheric warming. While these results suggest that alumina's shortwave absorption is unlikely to significantly increase model uncertainty, further holistic assessments are required to confirm these impacts.

Original language	English
Article number	e2026GL121668
Journal	Geophysical Research Letters
Volume	53
Issue number	16
DOIs	https://doi.org/10.1029/2026GL121668
State	Published - Aug 28 2026

Funding

We acknowledge the Simons Foundation (Grant SFI‐MPS‐SRM‐00005174, SFI‐MPS‐SRM‐00005217 and SFI‐MPS‐SRM‐00005208) for project funding. We thank Dr Huafang Li for helping acquire electron microscopy images at Washington University and the Institute of Material Science and Engineering, Washington University in St Louis for the use of the Scanning Transmission Electron Microscope. Scanning transmission electron microscopy at Oak Ridge National Lab was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy, Office of Science User Facility at Oak Ridge National Laboratory.

Keywords

aerosol radiation interaction
alumina
solar radiation modification
spacecraft emissions
stratosphere
stratospheric aerosol injection

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10.1029/2026GL121668

Cite this

Kapoor, T. S., Upadhyay, P., Huang, J., Ren, G., Cavin, J., Mitroo, D., Vattioni, S., Dykema, J., Sedlacek, J., Kumar, J., Hachtel, J. A., Xu, L., Mishra, R., & Chakrabarty, R. K. (2026). Unveiling the Shortwave Absorption Spectra of Alumina Aerosols: Radiative Implications for Solar Radiation Modification. Geophysical Research Letters, 53(16), Article e2026GL121668. https://doi.org/10.1029/2026GL121668

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title = "Unveiling the Shortwave Absorption Spectra of Alumina Aerosols: Radiative Implications for Solar Radiation Modification",

abstract = "Alumina is proposed for Stratospheric Aerosol Injection (SAI)-based solar radiation modification due to its presumed ability to scatter sunlight strongly while absorbing weakly. Alumina is assigned negligible solar shortwave absorption in climate models; this assumption is not validated owing to technological challenges in quantifying its weak absorption signals. We report alumina's shortwave imaginary refractive index (k), a determinant of its absorption strength, using sensitive in situ photoacoustic spectrometry, finding values ranging from 1.4 {\texttimes} 10−4 to 1.2 {\texttimes} 10−3. Particle-scale electron energy-loss spectroscopy provided independent validation and revealed that the non-ideal absorption arises from oxygen vacancy defects in the alumina. Aerosol chemistry climate model simulations of an established scenario reveal that shortwave absorption has negligible effects on radiative forcing and stratospheric warming. While these results suggest that alumina's shortwave absorption is unlikely to significantly increase model uncertainty, further holistic assessments are required to confirm these impacts.",

keywords = "aerosol radiation interaction, alumina, solar radiation modification, spacecraft emissions, stratosphere, stratospheric aerosol injection",

author = "Kapoor, \{Taveen Singh\} and Prabhav Upadhyay and Jian Huang and Guodong Ren and John Cavin and Dhruv Mitroo and Sandro Vattioni and John Dykema and Jan Sedlacek and Joshin Kumar and Hachtel, \{Jordan A.\} and Lu Xu and Rohan Mishra and Chakrabarty, \{Rajan K.\}",

note = "Publisher Copyright: {\textcopyright} 2026 The Author(s). Geophysical Research Letters published by Wiley Periodicals LLC on behalf of American Geophysical Union.",

year = "2026",

month = aug,

day = "28",

doi = "10.1029/2026GL121668",

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Kapoor, TS, Upadhyay, P, Huang, J, Ren, G, Cavin, J, Mitroo, D, Vattioni, S, Dykema, J, Sedlacek, J, Kumar, J, Hachtel, JA, Xu, L, Mishra, R & Chakrabarty, RK 2026, 'Unveiling the Shortwave Absorption Spectra of Alumina Aerosols: Radiative Implications for Solar Radiation Modification', Geophysical Research Letters, vol. 53, no. 16, e2026GL121668. https://doi.org/10.1029/2026GL121668

TY - JOUR

T1 - Unveiling the Shortwave Absorption Spectra of Alumina Aerosols

T2 - Radiative Implications for Solar Radiation Modification

AU - Kapoor, Taveen Singh

AU - Upadhyay, Prabhav

AU - Huang, Jian

AU - Ren, Guodong

AU - Cavin, John

AU - Mitroo, Dhruv

AU - Vattioni, Sandro

AU - Dykema, John

AU - Sedlacek, Jan

AU - Kumar, Joshin

AU - Hachtel, Jordan A.

AU - Xu, Lu

AU - Mishra, Rohan

AU - Chakrabarty, Rajan K.

PY - 2026/8/28

Y1 - 2026/8/28

N2 - Alumina is proposed for Stratospheric Aerosol Injection (SAI)-based solar radiation modification due to its presumed ability to scatter sunlight strongly while absorbing weakly. Alumina is assigned negligible solar shortwave absorption in climate models; this assumption is not validated owing to technological challenges in quantifying its weak absorption signals. We report alumina's shortwave imaginary refractive index (k), a determinant of its absorption strength, using sensitive in situ photoacoustic spectrometry, finding values ranging from 1.4 × 10−4 to 1.2 × 10−3. Particle-scale electron energy-loss spectroscopy provided independent validation and revealed that the non-ideal absorption arises from oxygen vacancy defects in the alumina. Aerosol chemistry climate model simulations of an established scenario reveal that shortwave absorption has negligible effects on radiative forcing and stratospheric warming. While these results suggest that alumina's shortwave absorption is unlikely to significantly increase model uncertainty, further holistic assessments are required to confirm these impacts.

AB - Alumina is proposed for Stratospheric Aerosol Injection (SAI)-based solar radiation modification due to its presumed ability to scatter sunlight strongly while absorbing weakly. Alumina is assigned negligible solar shortwave absorption in climate models; this assumption is not validated owing to technological challenges in quantifying its weak absorption signals. We report alumina's shortwave imaginary refractive index (k), a determinant of its absorption strength, using sensitive in situ photoacoustic spectrometry, finding values ranging from 1.4 × 10−4 to 1.2 × 10−3. Particle-scale electron energy-loss spectroscopy provided independent validation and revealed that the non-ideal absorption arises from oxygen vacancy defects in the alumina. Aerosol chemistry climate model simulations of an established scenario reveal that shortwave absorption has negligible effects on radiative forcing and stratospheric warming. While these results suggest that alumina's shortwave absorption is unlikely to significantly increase model uncertainty, further holistic assessments are required to confirm these impacts.

KW - aerosol radiation interaction

KW - alumina

KW - solar radiation modification

KW - spacecraft emissions

KW - stratosphere

KW - stratospheric aerosol injection

UR - https://www.scopus.com/pages/publications/105047529702

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DO - 10.1029/2026GL121668

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AN - SCOPUS:105047529702

SN - 0094-8276

VL - 53

JO - Geophysical Research Letters

JF - Geophysical Research Letters

IS - 16

M1 - e2026GL121668

ER -

Unveiling the Shortwave Absorption Spectra of Alumina Aerosols: Radiative Implications for Solar Radiation Modification

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Keywords

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