Combining Laboratory Studies and Radiative Transfer Modeling to Better Assess the Risks of Geoengineering Using Stratospheric Aerosols

Discussions of technological solutions that could complement essential emissions cuts to mitigate climate change in the coming decades have become significantly more prominent in the scientific discourse in recent years. One proposal that has received significant attention is to utilize sulfate aerosols in the stratosphere to scatter solar radiation back to space. It is known that this proposal carries multiple risks, including ozone loss, dynamical changes to the stratosphere, and changes in the ratio of diffuse to direct solar radiation. Other types of particles might plausibly reduce these negative impacts relative to sulfate aerosols. For example, there are studies analyzing the use of solid aerosol particles, such as alumina and titania. Furthermore, the optical properties of other materials may feature a reduced infrared heating rate, and a more favorable ratio of backwards scattering to forward scattering. Because volcanic eruptions can inject sulfate aerosols directly into the stratosphere, there is a substantial body of scientific knowledge to analyze how sulfate aerosol injection would affect the stratosphere. Any consideration of novel materials, such as solid aerosol particles, would require a rigorous assessment of chemical and optical properties as a starting point for further discussions.

Laboratory experiments would play a primary role in such assessments. Studies to quantify the rates of heterogeneous reactions, such as the activation of halogens, on solid aerosols require careful design to control the interaction of gas flows with chamber walls and to measure reaction products with adequate sensitivity. Ideally, these experiments would consider the impact of UV illumination to analyze photocatalytic effects on gas- and liquid-phase constituents when illuminated by a realistic spectral distribution relative to the sun. We will present a new flow tube system under development in our research group and radiative transfer modeling results that, when combined, will provide a quantitative framework for assessing the risks and efficacy of solid particles for geoengineering applications.