SCoPEx: Stratospheric Controlled Perturbation Experiment

SCoPEx is a scientific experiment to advance understanding of stratospheric aerosols that could be relevant to solar geoengineering. It aims to improve the fidelity of simulations (computer models) of solar geoengineering by providing modelers with experimental results vital to addressing specific science questions. Such simulations are the primary tool for estimating the risks and benefits of solar geoengineering, but current limitations may make the simulations look too good. SCoPEx will make quantitative measurements of aspects of the aerosol microphysics and atmospheric chemistry that are currently highly uncertain in the simulations. It is not a test of solar geoengineering per se. Instead, it will observe 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, without increasing other physical risks?

At the heart of SCoPEx is a scientific balloon, fitted with repurposed off-the-shelf airboat propellers. The repurposed propellers serve two functions. First, the propeller wake forms a well mixed volume (roughly 1 km long and 100 meters in diameter) that serves as an experimental ‘beaker’ in which we can add gasses or particles. Second, the propellers allow us to reposition the gondola to different locations within the volume to measure the properties of the perturbed air. The payload can achieve speeds of a few meters per second (walking speed) relative to the surrounding air, generally for about ten minutes at a time.

The advantage of the SCoPEx propelled balloon is that it allows us to create a small controlled volume of stratospheric air and observe its evolution for (we hope) over 24 hours. Hence the acronym, Stratospheric Controlled Perturbation Experiment. If we used an aircraft instead of a balloon, we would not be able to use such a small perturbed volume nor would we be able to observe it for such long durations.

SCoPEx builds on four decades of research on the environmental chemistry of the ozone layer in the Anderson/Keith/Keutsch groups. SCoPEx will use or adapt many of the high-performance sensors and flight-system engineering experience developed for this ozone research. Analyzing these experiments will improve our knowledge beyond what is currently available within computer models or is measurable with confidence under laboratory conditions.