Stratospheric transport and tropospheric sink of solar geoengineering aerosol: a Lagrangian analysis

Stratospheric aerosol injection (SAI) aims to reflect solar radiation by increasing the stratospheric aerosol burden. To understand how the background circulation influences stratospheric transport of injected particles, we use a Lagrangian trajectory model (lacking numerical diffusion) to quantify particles' number, flux, lifetime, and tropospheric sinks from a SAI injection strategy under present-day conditions. While particles are being injected, stratospheric particle number increases until reaching a steady-state. During the steady-state, the time series of particle number shows a dominant period of ~2 years (rather than a 1-year cycle), suggesting modulation by the quasi-biannual oscillation. More than half of particles, injected in the tropical lower stratosphere (15° S to 15° N, 65 hPa), undergo quasi-horizontal transport to the midlatitude. We find a zonal asymmetry of particles' tropospheric sinks that are co-located with tropopause folding beneath the midlatitude jet stream, which can help predict tropospheric impacts of SAI (e.g., cirrus cloud thinning).