Frank Keutsch – laboratory studies of stratospheric aerosol: a critical gap for reducing uncertainties of radiative and chemical impact of geoengineering and non-geoengineering aerosol under UT/LS conditions

Solar radiation management (SRM) via stratospheric aerosol injection could in principle have a faster response than emissions cuts and even aggressive carbon capture in order to achieve the IPCC 1.5°C target, although fast changes would have significant associated risks. Some of the risks of SRM using sulfate aerosol, the aerosol until recently believed to be the only naturally occurring aerosol in the stratosphere, carries significant risks. Besides the risk of ozone loss, stratospheric heating is a leading risk, as it results in adjustments of large-scale stratospheric circulation with models suggesting that strong heating of this type may lead to fundamental changes in stratospheric dynamics.

This project proposes a series of laboratory studies to improve (i) understanding of radiative and chemical properties of organic/sulfate aerosol critical to the understanding of the unperturbed stratosphere, and (ii) understanding how organics impact the radiative and chemical properties of alternative SRM materials. The first goal is important as observations have now shown that stratospheric aerosol can have a significant organic fraction. The direct implications for our understanding of the chemistry and radiative properties of the stratosphere have not been studied. Models have assumed all aerosol is sulfate and the observation of organics questions our fundamental understanding, or at least the model representation, of stratospheric chemistry and composition. The second goal is important as alternate solar radiation management materials need to be explored due to the inherent risk of sulfate aerosol, in particular with respect to dynamics. Alternate materials promise to greatly reduce risk, but their chemical and radiative properties remain largely explored under stratospheric conditions.