Optical properties of Aluminum Oxide Aerosols: A Candidate for Stratospheric Aerosol Injection
TAVEEN KAPOOR, Prabhav Upadhyay, Benjamin Sumlin, Dhruv Mitroo, Guodong Ren, Rohan Mishra, Rajan K. Chakrabarty,
Washington University in St. Louis Abstract Number: 514
Working Group: Aerosol Physics
AbstractStratospheric aerosol injection (SAI) is a proposed geoengineering technique to counteract the rising global temperature by injecting sunlight-reflecting particles into the stratosphere. The ideal SAI particles should not absorb ultraviolet-visible-infrared radiation and should efficiently backscatter incoming solar near-UV-visible radiation. Recent studies have highlighted the advantages of solid aerosol particles (over sulfate aerosols) for SAI because of their theoretically high backscatter ratios and negligible absorption. However, crystal defects in the materials may lead to non-trivial absorption, hence, there is a need to study the optical properties of industrially generated candidate solid aerosol particles. This study presents the optical properties of aluminum oxide (Al
2O
3), a candidate SAI material potentially exhibiting the desired optical properties. We generated nanometer-size Al
2O
3 particles using a bench-scale powder dispersion system and measured their optical and morphological properties. We use custom-built single-pass single-wavelength (375, 405, 532, 721, and 1047 nm) Integrated-Photoacoustic-Nephelometers, a dual-cell multi-wavelength (405, 488, 561, and 637 nm) IPN (mIPN), and an integrating nephelometer with backscatter shutter to measure real-time, spectrally varying absorption, scattering, and backscattering coefficients. A scanning mobility particle sizer and an aerodynamic aerosol classifier were used to calculate the electrical mobility and aerodynamic diameters, respectively. Aerosol particles were collected on lacey carbon grids for transmission electron microscopy. Electron microscopy images showed irregularly shaped particles, which will be used to estimate shape factors determining their backscatter fractions. The collected particles will also be used to estimate particle-scale complex refractive indices using electron energy loss spectroscopy. The findings from the present study will provide fundamental information on the optical properties of aluminum oxide particles which will are necessary for radiative forcing calculations and climate model simulations to assess the viability of SAI using Al
2O
3.
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