Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 15397-15412, 2016
https://doi.org/10.5194/acp-16-15397-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
12 Dec 2016
Heterogeneous reaction of ClONO2 with TiO2 and SiO2 aerosol particles: implications for stratospheric particle injection for climate engineering
Mingjin Tang1,2,7, James Keeble1, Paul J. Telford1,3, Francis D. Pope4, Peter Braesicke5, Paul T. Griffiths1,3, N. Luke Abraham1,3, James McGregor6, I. Matt Watson2, R. Anthony Cox1, John A. Pyle1,3, and Markus Kalberer1 1Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, UK
2School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK
3National Centre for Atmospheric Science, NCAS, Cambridge, UK
4School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK
5IMK-ASF, Karlsruhe Institute of Technology, Karlsruhe, Germany
6Department of Chemical and Biological Engineering, University of Sheffield, Sheffield S1 3JD, UK
7State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Abstract. Deliberate injection of aerosol particles into the stratosphere is a potential climate engineering scheme. Particles injected into the stratosphere would scatter solar radiation back to space, thereby reducing the temperature at the Earth's surface and hence the impacts of global warming. Minerals such as TiO2 or SiO2 are among the potentially suitable aerosol materials for stratospheric particle injection due to their greater light-scattering ability than stratospheric sulfuric acid particles. However, the heterogeneous reactivity of mineral particles towards trace gases important for stratospheric chemistry largely remains unknown, precluding reliable assessment of their impacts on stratospheric ozone, which is of key environmental significance. In this work we have investigated for the first time the heterogeneous hydrolysis of ClONO2 on TiO2 and SiO2 aerosol particles at room temperature and at different relative humidities (RHs), using an aerosol flow tube. The uptake coefficient, γ(ClONO2), on TiO2 was ∼ 1.2 × 10−3 at 7 % RH and remained unchanged at 33 % RH, and increased for SiO2 from ∼ 2 × 10−4 at 7 % RH to  ∼ 5 × 10−4 at 35 % RH, reaching a value of  ∼ 6 × 10−4 at 59 % RH. We have also examined the impacts of a hypothetical TiO2 injection on stratospheric chemistry using the UKCA (United Kingdom Chemistry and Aerosol) chemistry–climate model, in which heterogeneous hydrolysis of N2O5 and ClONO2 on TiO2 particles is considered. A TiO2 injection scenario with a solar-radiation scattering effect very similar to the eruption of Mt Pinatubo was constructed. It is found that, compared to the eruption of Mt Pinatubo, TiO2 injection causes less ClOx activation and less ozone destruction in the lowermost stratosphere, while reduced depletion of N2O5 and NOx in the middle stratosphere results in decreased ozone levels. Overall, no significant difference in the vertically integrated ozone abundances is found between TiO2 injection and the eruption of Mt Pinatubo. Future work required to further assess the impacts of TiO2 injection on stratospheric chemistry is also discussed.

Citation: Tang, M., Keeble, J., Telford, P. J., Pope, F. D., Braesicke, P., Griffiths, P. T., Abraham, N. L., McGregor, J., Watson, I. M., Cox, R. A., Pyle, J. A., and Kalberer, M.: Heterogeneous reaction of ClONO2 with TiO2 and SiO2 aerosol particles: implications for stratospheric particle injection for climate engineering, Atmos. Chem. Phys., 16, 15397-15412, https://doi.org/10.5194/acp-16-15397-2016, 2016.
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Short summary
We have investigated for the first time the heterogeneous hydrolysis of ClONO2 on TiO2 and SiO2 aerosol particles at room temperature and at different relative humidities (RHs), using an aerosol flow tube. The kinetic data reported in our current and previous studies have been included in the UKCA chemistry–climate model to assess the impact of TiO2 injection on stratospheric chemistry and stratospheric ozone in particular.
We have investigated for the first time the heterogeneous hydrolysis of ClONO2 on TiO2 and SiO2...
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