Solar geoengineering using solid aerosol in the stratosphere

Abstract

Abstract. Solid aerosol particles have long been proposed as an alternative to sulfate aerosols for solar geoengineering. Any solid aerosol introduced into the stratosphere would be subject to coagulation with itself, producing fractal aggregates, and with the natural sulfate aerosol, producing liquidcoated solids. Solid aerosols that are coated with sulfate and/or have formed aggregates may have very different scattering properties and chemical behavior than uncoated nonaggregated monomers do. We use a two-dimensional (2-D) chemistry-transport-aerosol model to capture the dynamics of interacting solid and liquid aerosols in the stratosphere. As an example, we apply the model to the possible use of alumina and diamond particles for solar geoengineering. For 240 nm radius alumina particles, for example, an injection rate of 4 Tg yr −1 produces a global-average shortwave radiative forcing of −1.2 W m −2 and minimal self-coagulation of alumina although almost all alumina outside the tropics is coated with sulfate. For the same radiative forcing, these solid aerosols can produce less ozone loss, less stratospheric heating, and less forward scattering than sulfate aerosols do. Our results suggest that appropriately sized alumina, diamond or similar high-index particles may have less severe technology-specific risks than sulfate aerosols do. These results, particularly the ozone response, are subject to large uncertainties due to the limited data on the rate constants of reactions on the dry surfaces.

Stratospheric ozone changes under solar geoengineering: implications for UV exposure and air quality

“…Ozone, nitrous oxide, and methane are fully interactive in the model so that any changes in these species are seen by the radiation module and thus affect the modelled climate. Changes in photolysis rates in the troposphere and the stratosphere are calculated interactively using the Fast-JX photolysis scheme (Bian and Prather, 2002;Neu et al, 2007;Telford et al, 2013;Wild et al, 2000). Photolysis in FastJX responds, inter alia, to ozone and solar flux as well as to multiple layers of clouds of varying degrees of thickness.…”

“…Heckendorn et al, 2011;Pitari et al, 2014;Pope et al, 2012;Rasch et al, 2008;Tilmes et al, 2008Tilmes et al, , 2009Tilmes et al, , 2012Weisenstein and Keith, 2015). This would have important implications for human health since stratospheric ozone is the major absorber of solar UV-B radiation.…”

Climate engineering and the ocean: effects on biogeochemistry and primary production

“…Here we have performed model experiments with stratospheric sulfur aerosol injections (Crutzen, 2006;Weisenstein et al, 2015), marine sky brightening (Latham, 1990), and cirrus cloud thinning (Mitchell and Finnegan, 2009) applied individually. Stratospheric aerosol injections (SAIs) would involve creating a layer of reflective particles in the stratosphere to reduce the amount of solar radiation reaching the surface.…”

Heterogeneous reaction of ClONO<sub>2</sub> with TiO<sub>2</sub> and SiO<sub>2</sub> aerosol particles: implications for stratospheric particle injection for climate engineering

“…In the previous work (Tang et al, 2014c), we used the UKCA model to construct a case study in which TiO 2 aerosols were distributed in the stratosphere in a similar way to the volcanic sulfuric acid particles after the eruption of Mt Pinatubo so that the solar-radiation scattering effect was similar for the two scenarios; however, the only heterogeneous reaction on TiO 2 particles considered was the uptake of N 2 O 5 (Reaction R1a). Injection of solid aerosols into the stratosphere can have a significant impact on ozone mixing ratios when heterogeneous reactions involving chlorine are considered (Weisenstein et al, 2015). Several previous studies (Jackman et al, 1998;Danilin et al, 2001;Weisenstein et al, 2015) have considered the effects of solid alumina particles on stratospheric chemistry; however, there is only very limited assessment of other potential solid aerosol compositions (e.g.…”

“…Injection of solid aerosols into the stratosphere can have a significant impact on ozone mixing ratios when heterogeneous reactions involving chlorine are considered (Weisenstein et al, 2015). Several previous studies (Jackman et al, 1998;Danilin et al, 2001;Weisenstein et al, 2015) have considered the effects of solid alumina particles on stratospheric chemistry; however, there is only very limited assessment of other potential solid aerosol compositions (e.g. TiO 2 and diamond) (Tang et al, 2014c).…”