https://www.repository.cam.ac.uk/items/66efc6dd-3f21-48f2-bebf-eff6aa3b4705/full
*Author* Daniel Warnes 2025 *Abstract* Geoengineering refers to deliberate and large scale interventions in the Earth’s climate, in this case, in pursuit of global warming mitigation. Stratospheric aerosol injection (SAI) and marine cloud brightening (MCB) are two methods of geoengineering that both aim to achieve solar radiation management, by reducing the net magnitude of radiation reaching the Earth’s surface. Solar radiation management via geoengineering could buy the world time in the face of climate change, but it will not preclude the requirement to meet global net zero emissions. In fact, solar geoengineering strategies such as SAI and MCB have many potential negative consequences, alongside their potential to limit or reverse global warming. Sulfates and titanium dioxide are amongst the candidates being considered for SAI. Whilst promising, they introduce a plethora of environmental risks. This thesis focusses on a new candidate for SAI: cellulose nanocrystals (CNCs) as a safe and possibly sustainable alternative. It will also investigate the potential for CNCs to act as cloud condensation nuclei, for deliberate or inadvertent MCB. CNCs are a bio-sourced nanomaterial, isolated from naturally occurring cellulose. A recent, specific, use has been cellulose as a sustainable alternative to light scattering enhancers such as titanium dioxide, as a “white pigment” in paints and cosmetics. It is hypothesised that cellulose could be effective as a scattering enhancer in the aerosol form too. This thesis strives to answer two research questions: First, can the aggregation of CNCs upon aerosolisation be controlled? It is widely understood that surface chemistry and mechanical treatment can impact aggregation in liquid suspensions of CNCs. A detailed analysis of the morphology of aerosolised CNCs was performed, and related to the behaviour of the initial CNC suspensions. These results indicate that the colloidal stability of CNC suspensions drives aggregation in CNC aerosols, unlocking a strategy to tune CNC aerosol morphology. Second, how do CNC aerosols perform as solar geoengineering candidates? The work in this thesis shows that, whilst suboptimal for marine cloud brightening due to possessing only a moderate hygroscopicity, CNCs are promising for stratospheric aerosol injection. Desirable properties for agents of stratospheric aerosol injection include an ability to scatter incident shortwave solar radiation from space and a low propensity to absorb emitted longwave radiation from Earth. Multiphase atmospheric simulation chamber experiments enabled the understanding of optical, physical and chemical responses of CNCs to atmospheric ageing, and compared favourably to an existing sulfate-based SAI candidate, and similarly to novel solid aerosol particles that have been proposed in literature. The single scattering albedo was found to be greater than 0.99 across the shortwave spectrum and the absorption of longwave radiation was minimal. These findings are the first step towards understanding the aerosolisation of CNCs and can be the foundation for detailed climate modelling of CNCs as solar geoengineering candidates. *Source: University of Cambridge* -- 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 geoengineering+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/geoengineering/CAHJsh9-MxmoaGtVh%2B2M%3Do3dwgmHCcckfWLmUg%3DLmLXuNOSDE7A%40mail.gmail.com.
