An update on engineering issues concerning stratospheric aerosol injection for geoengineering

Lockley, Andrew; MacMartin, Douglas G.; Hunt, Hem

doi:10.1088/2515-7620/aba944

Cited by 7 publications

(5 citation statements)

References 16 publications

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“…Past research has increasingly focused on atmospheric albedo modification as a primary means to reflect solar radiation, either through stratospheric aerosols [66] or marine cloud brightening [39]. While the atmosphere presents a larger opportunity to reflect incoming radiation, our results show that the opportunity at the surface is nontrivial.…”

Section: Discussionmentioning

confidence: 74%

Mapping potential surface contributions to reflected solar radiation

Smoliak¹,

Gelobter²,

Haley³

2022

Environ. Res. Commun.

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Modifying Earth’s albedo is one of the strategies considered to reduce its energy imbalance and slow global warming by reflecting solar energy. Atmospheric contributions to reflected solar radiation through stratospheric aerosols or cloud brightening have received considerable attention; however, the efficacy of surface interventions is less understood. We address this gap by estimating the potential for surface contributions to reflected solar radiation at approximately 30 km resolution using a simple radiative transfer model. Long-term average annual-mean incoming and outgoing top-of-atmosphere and surface solar fluxes are input to determine atmospheric shortwave optical properties (i.e., transmittance, absorptance, and reflectance), which can be used with surface albedo to estimate surface-reflected outgoing solar radiation. A comparison of reanalysis- and satellite-based input datasets shows good agreement. The results indicate global annual-mean surface-reflected outgoing solar radiation potential of 109 Wm-2, nearly a factor of five larger than the actual value, and local areas where it could be increased above 200 Wm-2 with surface albedo enhancement. Regions with particularly strong potential include Andean South America, the Middle East, southwestern North America, southwestern Africa, Australia, and the sub-equatorial tropical oceans. Future research could extend the methods to account for seasonal variations and the potential to mitigate extreme heat events in particular.

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Section: Discussionmentioning

confidence: 74%

Mapping potential surface contributions to reflected solar radiation

Smoliak¹,

Gelobter²,

Haley³

2022

Environ. Res. Commun.

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“…We estimate particle dispersal costs of $760/ton, calculated using industry figures from aerial pesticide application (supplementary note 6) [53]. This value is about half the projected cost per ton of launching aerosols at higher altitudes of ∼20 km with jet aircraft [54,55].…”

Section: Aerosol-based Solar Photocatalysismentioning

confidence: 99%

“…A variety of other dispersion methods might be possible with modest engineering improvements, including guyed masts (up to ∼500 m), tethered balloons, and kites like those used for airborne wind power generation [55][56][57][58]. Aerosols could also be lofted in the heated gases from existing smokestacks [59].…”

Section: Aerosol-based Solar Photocatalysismentioning

confidence: 99%

Cost modeling of photocatalytic decomposition of atmospheric methane and nitrous oxide

Randall,

Jackson,

Majumdar

2024

Environ. Res. Lett.

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The photocatalytic decomposition of atmospheric methane (CH4) and nitrous oxide (N2O) could be valuable tools for mitigating climate change; however, to date, few photocatalyst deployment strategies have had their costs modeled. Here, we construct basic cost models of three photocatalytic CH4 and N2O decomposition systems: 1) a ground-based solar system with natural airflow over photocatalyst-painted rooftops, 2) a ground-based LED-lit system with fan-driven airflow, and 3) an aerosol-based solar system on solid particles dispersed in the atmosphere. Each model takes as inputs the photocatalyst’s apparent quantum yield (AQY; a measure of how efficiently photons drive a desired chemical reaction) and the local CH4 or N2O concentration. Each model calculates an overall rate of greenhouse gas drawdown and returns a levelized cost of greenhouse gas removal per equivalent ton of carbon dioxide (tCO2e). Based on prior studies of atmospheric carbon dioxide removal, we adopt $100/tCO2e as a target cost.We estimate that painting rooftops with photocatalysts might meet the target cost for decomposition of >10ppm CH4 with catalyst AQYs >4%. If painting and cleaning costs were reduced by a factor of ~3 from our scenario, removal of ambient CH4 could meet the cost target with AQYs >1% and removal of ambient N2O could do so with AQYs >0.1%. Fan-driven systems with LED illumination appear to be very challenging, achieving removal costs <$100/tCO2e only for AQYs of >10% for CH4 and >1% for N2O. Dispersing photocatalytic aerosols in the troposphere could be cost-effective with AQYs of >0.4% for ambient CH4 or >0.04% for ambient N2O. However, the mass of aerosols required is large and their side effects and social acceptability are uncertain. We note that, for any system, AQYs on the order of 1% will likely be extremely challenging to achieve with such dilute reagents.

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“…Irvine et al, 2016;Parker and Irvine, 2018;Pitari et al, 2014;Robock et al, 2009), a significant hitch is posed by the technological and economic challenge of transporting the necessary amount of material to the altitude regions where the scattering particles would actually have an effect (e.g. Lawrence et al, 2018;Robock et al, 2009;Lockley et al, 2020). To this end, it is only natural to think of carbonyl sulfide (OCS or COS), which is the most important natural non-volcanic precursor of sulfate aerosol in the stratosphere (Kremser et al, 2016, and references therein).…”

Section: Introductionmentioning

confidence: 99%

Comment on “An approach to sulfate geoengineering with surface emissions of carbonyl sulfide” by Quaglia et al. (2022)

Hobe¹,

Brühl

Lennartz

et al. 2023

Atmos. Chem. Phys.

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Abstract. Solar radiation management through artificially increasing the amount of stratospheric sulfate aerosol is being considered as a possible climate engineering method. To overcome the challenge of transporting the necessary amount of sulfur to the stratosphere, Quaglia and co-workers suggest deliberate emissions of carbonyl sulfide (OCS), a long-lived precursor of atmospheric sulfate. In their paper, published in Atmospheric Chemistry and Physics in 2022, they outline two scenarios with OCS emissions either at the Earth's surface or in the tropical upper troposphere and calculate the expected radiative forcing using a climate model. In our opinion, the study (i) neglects a significantly higher surface uptake that will inevitably be induced by the elevated atmospheric OCS concentrations and (ii) overestimates the net cooling effect of this OCS geoengineering approach due to some questionable parameterizations and assumptions in the radiative forcing calculations. In this commentary, we use state-of-the-art models to show that at the mean atmospheric OCS mixing ratios of the two emissions scenarios, the terrestrial biosphere and the oceans are expected to take up more OCS than is being released to reach these levels. Using chemistry climate models with a long-standing record for estimating the climate forcing of OCS and stratospheric aerosols, we also show that the net radiative forcing of the emission scenarios suggested by Quaglia and co-workers is smaller than suggested and insufficient to offset any significant portion of anthropogenically induced climate change. Our conclusion is that a geoengineering approach using OCS will not work under any circumstances and should not be considered further.

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An update on engineering issues concerning stratospheric aerosol injection for geoengineering

Cited by 7 publications

References 16 publications

Mapping potential surface contributions to reflected solar radiation

Mapping potential surface contributions to reflected solar radiation

Cost modeling of photocatalytic decomposition of atmospheric methane and nitrous oxide

Comment on “An approach to sulfate geoengineering with surface emissions of carbonyl sulfide” by Quaglia et al. (2022)

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