Efficacy and cloud impacts of SO2 injections in the upper troposphere and lower stratosphere

Injection of sulfur dioxide (SO2) in the stratosphere to form reflective sulfate aerosols has been suggested as a leading solar radiation management idea to cool the planet. Studies with sectional aerosol models suggest limited efficacy due to aerosol growth; and studies with coupled models suggest possible impacts on stratospheric dynamics and chemistry. Modeling simulations to date have specified tropical SO2 injections at 18 km altitude or higher, which is above the flying ceiling of most existing aircraft. We simulate tropical SO2 injections at 13 km altitude (160 mb) and 20 km altitude (50 mb) and mid-latitude injections at 13 km altitude using the 60-level CAM5/CARMA model, which allows for detailed vertical resolution of the stratosphere, sectional aerosol bin representation, and interactions between aerosols, chemistry, radiation, and clouds. We quantify the resulting aerosol evolution, radiative effects, and surface temperature effects, as well as the impacts of SO2 injections on tropospheric clouds.