Modeling the atmospheric transport and possible radiative impact of alumina aerosols emitted from the projected increase in annual satellite reentry emissions.

The recent uptick in rocket launch rates, as well as the proposal of large low earth orbit satellite constellations (LLC’s) has renewed interest into how space traffic might impact Earth’s climate. One issue, the potential atmospheric response to a significant increase in aerosols released into the lower mesosphere/upper stratosphere during satellite reentry, remains under studied. It is predicted that if all proposed LLC’s are implemented, the total number of satellites in low earth orbit (LEO) will balloon from ~5,000 to over 60,000 individual satellites by as early as 2040. The corresponding annual emissions of metallic aerosol from satellite reentry is also expected to increase and approach 10 Gg/year. This reentry emission source would be on the same scale as the naturally occurring meteoric mass flux which is estimated to fall between 8 Gg and 20 Gg per year. Little is currently known about what type of exotic aerosols may be released during satellite ablation, but a significant portion of the aerosol population may be aluminum. Reentering LEO satellites are expected to completely vaporize in the mesosphere, and the subsequent vapor cloud will cool and coalesce into metallic aerosol roughly between 60km and 70km. As a result, aluminum aerosol could be rapidly transported into the stratosphere by atmospheric circulation and oxidize into aluminum oxide (Al₂O₃). Past studies have shown how Al₂O₃ released by solid rocket motors in the stratosphere can impact heterogeneous chemistry and thus ozone. Additionally, not much work looking at the radiative impact from Al₂O₃ aerosols in the stratosphere has been conducted. Here we present results from a study which focuses on the radiative impacts and atmospheric transport of hypothetical Al₂O₃ emissions from satellite reentry. The WACCM6 global model coupled with the CARMA sectional model was run with a 10 Gg/year mass flux of Al₂O₃ between 60 km and 70 km. We simulate multiple reentry patterns and aerosol size distributions. Our results show that reentry Al₂O₃ begins to accumulate in the polar region of both hemispheres on a time frame of months to two years, depending on the reentry location and aerosol size. Additionally, anomalous longwave cooling near the stratopause may lead to as large as 1.5 K temperature anomalies in the high latitude stratosphere and perturb the strength of the stratospheric polar vortex by as much as 10%. Due to modeling limitations, the work presented here does not consider important interactions between metallic reentry aerosol and stratospheric chemistry, but our results provide a first order approximation of the potential atmospheric response to an increased influx of satellite reentry aerosol.