Stratospheric Aerosol Injection: An Engineering Review
MIRANDA HACK, Gernot Wagner, Dan Steingart, V. Faye McNeill, Columbia University
Abstract Number: 169
Working Group: Aerosol Physics
Abstract
Stratospheric aerosol injection (SAI) has been proposed for purposes of climate mitigation via solar radiation management. We recently reviewed potential environmental and climate impacts of SAI (Huynh and McNeill 2024). A variety of materials and injection strategies have been proposed, but these studies mainly rely on climate models with minimal consideration of technical, logistical, or economic feasibility. Those that do have focused primarily on sulfate aerosol, but solid aerosol candidates have also been proposed due to their desirable optical properties and heterogeneous reactivity relative to sulfate. Here, we take an engineering approach to analyze the feasibility of several SAI strategies, organized by particle type and injection pattern.
Along with optical properties, the efficacy of an SAI material is strongly linked to particle number size distribution (PNSD). We address several technical challenges in producing and dispersing aerosol candidates in the desired sub-micron PNSDs. The logistical and financial feasibility of using solid aerosol materials, liquid H2SO4, or sulfate formed via SO2 (g) is assessed using both the current state of achievable PNSDs and the optimal scenario.
Injection strategy is another key driver of SAI outcomes. Reynolds and Wagner (2019) described a decentralized SAI model executed with many SO2-filled balloons, an approach which has been pursued commercially. However, timing, latitude and altitude of injections play key roles in PNSDs and SAI’s impact on climate feedback mechanisms like the quasi-biennial oscillation and intertropical convergence zone. This decentralized scenario has not been simulated in global climate models, but compiling the results of several studies on injection strategy allows us to infer that decentralized action may result in suboptimal SAI outcomes, particularly when considering geopolitical factors that may limit these climate actors to the Global North. Practical considerations, including lifting gas availability and plastic waste generation, may also limit the feasibility of this decentralized model.