Stratospheric aerosol particles and solar-radiation management

Pope, Francis D.; Braesicke, Peter; Grainger, R. G.; Kalberer, Markus; Watson, I. Matthew; Davidson, Peter; Cox, R. A.

doi:10.1038/nclimate1528

Cited by 81 publications

(109 citation statements)

References 44 publications

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“…At RH relevant to the lower stratosphere (<40%) the measurements showed that γ (HO 2 ) is in the range 0.020-0.028 at 295 K. An inverse temperature dependence of γ (HO 2 ) onto dry seasalt aerosols has previously been observed (Remorov et al, 2002); although there have been no systematic experimental studies of the temperature dependence of γ (HO 2 ), parameterisations have developed (Thornton et al, 2008;Macintyre and Evans, 2011). At stratospherically relevant temperatures (T = 200-220 K), γ (HO 2 ) is likely to be considerably larger than observed at 295 K; however it is not possible to cool the aerosol flow tube/SMPS system to verify this experimentally.…”

Section: Comparison Of γ (Ho 2 ) With Literature Valuesmentioning

confidence: 78%

“…The refractive index of TiO 2 at 550 nm is 2.5 compared to a value of 1.5 for naturally occurring sulfate aerosols (Tang et al, 2014). Assuming that the size of TiO 2 particles can be optimised, it has been reported that, to achieve the same cooling effect that sulfate aerosols had during the Mt Pinatubo event, significantly less TiO 2 than sulfuric acid would be required: approximately 3 times less in mass and 7 times less in volume (Pope et al, 2012). However, the impacts of the presence of TiO 2 particles on stratospheric chemistry have to be determined before this kind of geoengineering solution can be considered.…”

Section: Introductionmentioning

confidence: 99%

“…The impact of sulfate geoengineering to stratospheric ozone concentrations is projected to decrease in time as concentrations of Br-and Cl-containing atmospheric species are expected fall, so much so that beyond 2050 the additional available surface area provided by sulfate geoengineering is predicted to enhance conversion of NO x (NO x = NO + NO 2 ) to HNO 3 , resulting in an increase of stratospheric ozone (Visioni et al,328 D. R. Moon et al: Heterogeneous reaction of HO 2 with airborne TiO 2 particles 2017). Other candidates for particle types, such as TiO 2 , have been put forward due to their large refractive indices (Pope et al, 2012), meaning that less stratospheric aerosol loading would be necessary to achieve the same level of cooling. The refractive index of TiO 2 at 550 nm is 2.5 compared to a value of 1.5 for naturally occurring sulfate aerosols (Tang et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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Heterogeneous reaction of HO2 with airborne TiO2 particles and its implication for climate change mitigation strategies

Moon¹,

Taverna²,

Anduix‐Canto³

et al. 2018

Atmos. Chem. Phys.

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Abstract. One geoengineering mitigation strategy for global temperature rises resulting from the increased concentrations of greenhouse gases is to inject particles into the stratosphere to scatter solar radiation back to space, with TiO 2 particles emerging as a possible candidate. Uptake coefficients of HO 2 , γ (HO 2 ), onto sub-micrometre TiO 2 particles were measured at room temperature and different relative humidities (RHs) using an atmospheric pressure aerosol flow tube coupled to a sensitive HO 2 detector. Values of γ (HO 2 ) increased from 0.021 ± 0.001 to 0.036 ± 0.007 as the RH was increased from 11 to 66 %, and the increase in γ (HO 2 ) correlated with the number of monolayers of water surrounding the TiO 2 particles. The impact of the uptake of HO 2 onto TiO 2 particles on stratospheric concentrations of HO 2 and O 3 was simulated using the TOMCAT three-dimensional chemical transport model. The model showed that, when injecting the amount of TiO 2 required to achieve the same cooling effect as the Mt Pinatubo eruption, heterogeneous reactions between HO 2 and TiO 2 would have a negligible effect on stratospheric concentrations of HO 2 and O 3 .

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Section: Comparison Of γ (Ho 2 ) With Literature Valuesmentioning

confidence: 78%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Heterogeneous reaction of HO2 with airborne TiO2 particles and its implication for climate change mitigation strategies

Moon¹,

Taverna²,

Anduix‐Canto³

et al. 2018

Atmos. Chem. Phys.

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“…Heating of the lower stratosphere is therefore a significant contributor to the risks of sulfate aerosol SRM. Calcite may reduce these risks because it causes less warming than either sulfates or solids such as titania or alumina that have been analyzed elsewhere (12)(13)(14)(15)(16)(17). A high-accuracy radiative calculation using a column model with fixed dynamical heating shows that for a −2-W·m −2 radiative forcing using optimally sized particles, sulfate warms the lower stratosphere by 2.4 K, whereas warming is only 0.2 K for calcite (18).…”

Section: Resultsmentioning

confidence: 99%

“…That work and most subsequent analyses focused on the mass-specific scattering efficiency, with the implication that solid aerosol might be able to reduce the total mass required for SRM (9)(10)(11)(12). In prior work (2), we explored the possibility that solid aerosol might reduce important environmental risks of SRM including (i) heating of the lower stratosphere, (ii) diffuse scattering of incident sunlight, and (iii) ozone loss.…”

mentioning

confidence: 99%

Stratospheric solar geoengineering without ozone loss

Keith

Weisenstein

Dykema

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

120

121

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Injecting sulfate aerosol into the stratosphere, the most frequently analyzed proposal for solar geoengineering, may reduce some climate risks, but it would also entail new risks, including ozone loss and heating of the lower tropical stratosphere, which, in turn, would increase water vapor concentration causing additional ozone loss and surface warming. We propose a method for stratospheric aerosol climate modification that uses a solid aerosol composed of alkaline metal salts that will convert hydrogen halides and nitric and sulfuric acids into stable salts to enable stratospheric geoengineering while reducing or reversing ozone depletion. Rather than minimizing reactive effects by reducing surface area using high refractive index materials, this method tailors the chemical reactivity. Specifically, we calculate that injection of calcite (CaCO3) aerosol particles might reduce net radiative forcing while simultaneously increasing column ozone toward its preanthropogenic baseline. A radiative forcing of −1 W⋅m−2, for example, might be achieved with a simultaneous 3.8% increase in column ozone using 2.1 Tg⋅y−1 of 275-nm radius calcite aerosol. Moreover, the radiative heating of the lower stratosphere would be roughly 10-fold less than if that same radiative forcing had been produced using sulfate aerosol. Although solar geoengineering cannot substitute for emissions cuts, it may supplement them by reducing some of the risks of climate change. Further research on this and similar methods could lead to reductions in risks and improved efficacy of solar geoengineering methods.

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Stratospheric dynamics and midlatitude jets under geoengineering with space mirrors and sulfate and titania aerosols

2015

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The impact on the dynamics of the stratosphere of three approaches to geoengineering by solar radiation management is investigated using idealized simulations of a global climate model. The approaches are geoengineering with sulfate aerosols, titania aerosols, and reduction in total solar irradiance (representing mirrors placed in space). If it were possible to use stratospheric aerosols to counterbalance the surface warming produced by a quadrupling of atmospheric carbon dioxide concentrations, tropical lower stratospheric radiative heating would drive a thermal wind response which would intensify the stratospheric polar vortices. In the Northern Hemisphere this intensification results in strong dynamical cooling of the polar stratosphere. Northern Hemisphere stratospheric sudden warming events become rare (one and two in 65 years for sulfate and titania, respectively). The intensification of the polar vortices results in a poleward shift of the tropospheric midlatitude jets in winter. The aerosol radiative heating enhances the tropical upwelling in the lower stratosphere, influencing the strength of the Brewer-Dobson circulation. In contrast, solar dimming does not produce heating of the tropical lower stratosphere, and so there is little intensification of the polar vortex and no enhanced tropical upwelling. The dynamical response to titania aerosol is qualitatively similar to the response to sulfate.

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Stratospheric aerosol particles and solar-radiation management

Cited by 81 publications

References 44 publications

Heterogeneous reaction of HO<sub>2</sub> with airborne TiO<sub>2</sub> particles and its implication for climate change mitigation strategies

Heterogeneous reaction of HO<sub>2</sub> with airborne TiO<sub>2</sub> particles and its implication for climate change mitigation strategies

Stratospheric solar geoengineering without ozone loss

Stratospheric dynamics and midlatitude jets under geoengineering with space mirrors and sulfate and titania aerosols

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Stratospheric aerosol particles and solar-radiation management

Cited by 81 publications

References 44 publications

Heterogeneous reaction of HO&lt;sub&gt;2&lt;/sub&gt; with airborne TiO&lt;sub&gt;2&lt;/sub&gt; particles and its implication for climate change mitigation strategies

Heterogeneous reaction of HO&lt;sub&gt;2&lt;/sub&gt; with airborne TiO&lt;sub&gt;2&lt;/sub&gt; particles and its implication for climate change mitigation strategies

Stratospheric solar geoengineering without ozone loss

Stratospheric dynamics and midlatitude jets under geoengineering with space mirrors and sulfate and titania aerosols

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Product

Resources

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Heterogeneous reaction of HO<sub>2</sub> with airborne TiO<sub>2</sub> particles and its implication for climate change mitigation strategies

Heterogeneous reaction of HO<sub>2</sub> with airborne TiO<sub>2</sub> particles and its implication for climate change mitigation strategies