Production of Sulfates Onboard an Aircraft: Implications for the Cost and Feasibility of Stratospheric Solar Geoengineering

Abstract

Injection of sulfate aerosols into the stratosphere, a form of solar geoengineering, has been proposed as a means to reduce some climatic changes by decreasing net anthropogenic radiative forcing. The cost and technical feasibility of forming aerosols with the appropriate size distribution are uncertain. We examine the possibility of producing the relevant sulfur species, SO2 or SO3, by in situ conversion from elemental sulfur onboard an aircraft. We provide a first‐order engineering analysis of an open cycle chemical plant for in situ sulfur to sulfate conversion using a Brayton cycle combustor and a catalytic converter. We find that such a plant could have sufficiently low mass that the overall requirement for mass transport to the lower stratosphere may be reduced by roughly a factor of 2. All else equal, this suggests that—for a given radiative forcing—the cost of delivering sulfate aerosols may be nearly halved. Beyond reducing cost, the use of elemental sulfur reduces operational health and safety risks and should therefore reduce environmental side effects associated with delivery. Reduction in cost is not necessarily beneficial as it reduces practical barriers to deployment, increasing the urgency of questions concerning the efficacy, risks, and governance of solar geoengineering.

Exploring accumulation-mode-H<sub>2</sub>SO<sub>4</sub> versus SO<sub>2</sub> stratospheric sulfate geoengineering in a sectional aerosol-chemistry-climate model

“…We assume that AM-H2SO4 is produced in situ in the plumes behind planes which generate SO3 or H2SO4 from burning elemental sulfur. As a 100 % conversion rate is unlikely to be achieved (Smith et al, 2018), we also performed two runs emitting mixtures of SO2 and AM-H2SO4 with only 30 % or 70 % in the form of AM-H2SO4 and the rest in the form of SO2 (runs 17 and 18, respectively).…”

Exploring accumulation-mode H<sub>2</sub>SO<sub>4</sub> versus SO<sub>2</sub> stratospheric sulfate geoengineering in a sectional aerosol–chemistry–climate model

“…In that case, the AER-2D model (Weisenstein et al, 1997(Weisenstein et al, , 2007 was used to calculate global aerosol properties, which were prescribed in the SOCOLv2 3-D chemistry-climate model. The SOCOL-AER (Sheng et al, 2015;Sukhodolov et al, 2018) model is based on SOCOLv3 (Stenke et al, 2013) and improves on the earlier versions of SOCOL by incorporating a sectional aerosol module based on the AER-2D model. In a recent study SOCOL-AER was successfully applied to simulate the S. Vattioni et al: Exploring sulfate-aerosol versus SO 2 stratospheric geoengineering magnitude and the decline of the resulting aerosol plume after the 1991 Mt.…”

The Reaction of Sulfur Dioxide Radical Cation with Hydrogen and Its Relevance in Solar Geoengineering Models

“…[19] Solar geoengineering schemes require SO 2 to be at a pressure of 1 bar when injected by balloons or aircrafts. [70] This implies that the SO þ 2 density could locally reach a maximum value of about 10 7 ions/cm 3 , which is a relevant concentration for the chemistry in the stratosphere. On the basis of the discussion above, the ion-neutral reactions involving SO þ 2 and leading to OH may be considered as a relevant source of OH which can oxide SO 2 during the night, when OH can not be produced via neutral-neutral reactions triggered by sunlight.…”