Frank Keutsch — Stratospheric Controlled Perturbation Experiment (SCoPEx)

SCoPEx is a scientific experiment to advance understanding of stratospheric aerosols that could be relevant to solar geoengineering. It aims to reduce the uncertainty around specific science questions by making quantitative measurements of some of the aerosol microphysics and atmospheric chemistry required for estimating the risks and benefits of solar geoengineering in large atmospheric models. SCoPEx will address questions about how particles interact with one another, with the background stratospheric air, and with solar and infrared radiation. Improved understanding of these processes will help answer applied questions such as, is it possible to find aerosols that can reduce or eliminate ozone loss or stratospheric heating, without increasing other physical risks? 

In order to pursue these questions, a propelled balloon platform is proposed that is capable of injecting a small amount of aerosol (<1kg) at about 20km altitude preparing a plume with kilometer lengthscale and diameter of a few hundred meters. The propelled balloon will then be flown back through the plume to measure the temporal evolution of the perturbation resulting from the plume and study how the aerosol in the plume is developing.

Learn more via Frank Keutsch's SCoPEx FAQ.

Frank Keutsch

Frank Keutsch

Stonington Professor of Engineering and Atmospheric Science
Professor of Chemistry and Chemical Biology

Publications

Golja, C. M., L. W. Chew, J. A. Dykema, and D. W. Keith. “Aerosol Dynamics in the Near Field of the SCoPEx Stratospheric Balloon Experiment.” Journal of Geophysical Research (2021). Publisher's VersionAbstract
Stratospheric aerosol injection (SAI) might alleviate some climate risks associated with accumulating greenhouse gases. Reduction of specific process uncertainties relevant to the distribution of aerosol in a turbulent stratospheric wake is necessary to support informed decisions about aircraft deployment of this technology. To predict aerosol size distributions we apply microphysical parameterizations of nucleation, condensation and coagulation to simulate an aerosol plume generated via injection of calcite powder or sulphate into a stratospheric wake with velocity and turbulence simulated by a three‐dimensional (3D) fluid dynamic calculation. We apply the model to predict the aerosol distribution that would be generated by a propeller wake in the Stratospheric Controlled Perturbation Experiment (SCoPEx). We find that injecting 0.1 g s‐1 calcite aerosol produces a nearly monodisperse plume and that at the same injection rate, condensable sulphate aerosol forms particles with average radii of 0.1 µm at 3 km downstream. We test the sensitivity of plume aerosol composition, size, and optical depth to the mass injection rate and injection location. Aerosol size distribution depends more strongly on injection rate than injection configuration. Comparing plume properties with specifications of a typical photometer, we find that plumes could be detected optically as the payload flies under the plume. These findings test the relevance of in situ sampling of aerosol properties by the SCoPEx outdoor experiment to enable quantitative tests of microphysics in a stratospheric plume. Our findings provide a basis for developing predictive models of SAI using aerosols formed in stratospheric aircraft wakes.