A Need For In Situ Observations to Inform Nearfield Plume Transport and Aerosol Dynamics as well as Chemistry of Alternate Geoengineering Materials in the Stratosphere

Studies of the impacts of stratospheric geoengineering depend, perhaps implicitly, on processes that would take
place in the near field of an aircraft injection plume. All models ultimately depend on observations, yet we lack experimental data to assess some of the critical transport, microphysical, and chemical processes that directly control aerosol dynamics in the nearfield. Models can utilize existing measurements of solid rocket motor plumes, wake sampling of high altitude aircraft, convective overshooting events, and volcanic eruptions as observational analogs to compare some important stratospheric impacts with these model results. Although these bodies of literature are quite robust, they are inadequate for geoengineering because they exclude (a) relevant scales of atmospheric transport, (b) particle microphysics, and (c) chemistry of alternate geoengineering materials specific to stratospheric solar radiation management (SRM). In this document we review existing in situ data sets and describe their utility for SRM as well as areas where they are unable to shed light on the issues described above. We then suggest how new measurements could reduce uncertainty by injecting these materials into the stratosphere and comparing the results of in-situ observations with results obtained by models based on laboratory studies of both their chemical and optical properties.