Hi All, A new paper of potential interest:
Mie scattering from optically levitated mixed sulfuric acid–silica core–shell aerosols: observation of core–shell morphology for atmospheric science https://pubs.rsc.org/en/content/articlelanding/2022/CP/D1CP04068E *Potential Stratospheric Aerosol Injection (SAI) implications* There's been various papers (my own included) that have suggested that materials other than sulphate would be optimal for light scattering and weight lifting considerations for SAI, e.g. alumina, titania, diamond etc... This paper suggests that the collision and coating of sulphuric acid on solid aerosol particles would cause the benefits of the solid particle scattering to diminish rapidly, with the scattering properties being driven by sulphuric acid coating. So you might as well use sulphuric acid / sulphate aerosols in the first place. Note - useful further work would repeat the experiments at stratospheric temperatures (this lab work was conducted at room temperature) and the coagulation dynamics needs to be explored to see how long it would take for a sufficient sulphuric acid coating to be generated upon the injected particles. Abstract Sulfuric acid is shown to form a core–shell particle on a micron-sized, optically-trapped spherical silica bead. The refractive indices of the silica and sulfuric acid, along with the shell thickness and bead radius were determined by reproducing Mie scattered optical white light as a function of wavelength in Mie spectroscopy. Micron-sized silica aerosols (silica beads were used as a proxy for atmospheric silica minerals) were levitated in a mist of sulfuric acid particles; continuous collection of Mie spectra throughout the collision of sulfuric acid aerosols with the optically trapped silica aerosol demonstrated that the resulting aerosol particle had a core–shell morphology. Contrastingly, the collision of aqueous sulfuric acid aerosols with optically trapped polystyrene aerosol resulted in a partially coated system. The light scattering from the optically levitated aerosols was successfully modelled to determine the diameter of the core aerosol (±0.003 μm), the shell thickness (±0.0003 μm) and the refractive index (±0.007). The experiment demonstrated that the presence of a thin film rapidly changed the light scattering of the original aerosol. When a 1.964 μm diameter silica aerosol was covered with a film of sulfuric acid 0.287 μm thick, the wavelength dependent Mie peak positions resembled sulfuric acid. Thus mineral aerosol advected into the stratosphere would likely be coated with sulfuric acid, with a core–shell morphology, and its light scattering properties would be effectively indistinguishable from a homogenous sulfuric acid aerosol if the film thickness was greater than a few 100 s of nm for UV-visible wavelengths. 4 Conclusions The study presented here demonstrates that sulfuric acid successfully forms a core–shell geometry aerosol upon collision with silica. Through application of optical trapping techniques alongside Mie spectroscopy, it was observed that when a sulfuric acid aerosol collides with a silica aerosol, the system would begin to resemble a sulfuric acid aerosol of similar diameter to the combined aerosol. Secondly, the study experimentally demonstrates that mineral aerosol emitted to the stratosphere will soon adopt the light scattering patterns associated with a pure sulfuric acid aerosol. The implication of the study to stratospheric science is that hydrophilic stratospheric mineral aerosol will rapidly resemble the optical properties of sulfuric acid through natural collision processes and the formation of core–shell morphology. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/geoengineering/7e9931c6-c62e-463a-96b0-3e48a7647143n%40googlegroups.com.
