Overview
Recent studies have shown that gaseous SO2 injection entails several drawbacks, such as stratospheric ozone depletion or stratospheric heating, which modify the Brewer-Dobson circulation and stratospheric humidity and can cause further adverse effects on surface climate5. Injection of solid particles, such as calcite (CaCO3), alumina (Al2O3) or diamond (C) might overcome several of these limitations, such as reducing stratospheric warming7 and reducing ozone depletion8, while simultaneously increasing the surface cooling efficiency per stratospheric aerosol burden. However, past studies relied on a limited experimental basis and used simplified modelling approaches, which for example did not fully consider transport, microphysical processes, dynamical feedbacks, or heterogeneous chemistry on solid particles4. Interactions between these processes affect the resulting size distribution, optical properties, stratospheric residence time, and thus the resulting cooling efficiency and the associated impacts on the stratospheric chemistry and dynamics. Detailed consideration of the processes occurring during the life cycle of SAI-relevant solid particles by using appropriate laboratory techniques and reliably incorporating the measurement results in global models, is an urgent need. We have developed a solid particle microphysics scheme and incorporated it into the global Earth System Model (ESM) SOCOL. The solid particle scheme is fully interactive with the model’s radiative transfer code, aerosol microphysics module, and the chemistry scheme (see Figure 1 for the description of processes). Therefore, the model allows, for the first time, to interactively simulate feed-backs between stratospheric microphysics, chemistry, dynamics, and climate of SAI scenarios with solid particles online in one model, which allows for a holistic assessment of their effects. Very recently, we integrated and analysed the still very limited existing experimental data on heterogeneous chemistry on alumina and calcite particles into SOCOL, combined with physically based parameterizations for extrapolating to stratospheric conditions with respect to temperature, trace gas concentrations (i.e., HCl and HNO3, H2SO4) and relative humidity (RH). We found substantial uncertainty in the resulting stratospheric ozone response, ranging from complete healing of the stratospheric ozone hole to ozone depletion significantly larger than the historical minimum in the 90s. The most relevant causes for these uncertainties are the amount and properties of adsorbed or condensed species on the alumina surface.
