Modelling impacts of ablated space debris on atmospheric aerosols

Around 10% of Junge layer sulphuric acid droplets have been measured to contain metals from ablated space debris. Some metals – Al, Li, Cu, Ni, Mn etc. – already exceed natural background levels from cosmic dust that has ablated in the mesopause region. The effect of these metals on the stratosphere is not yet known, and space debris input has been projected to increase by more than an order of magnitude in the next 15 years. It is therefore vitally important to determine the level of re-entering space debris that will cause significant changes to atmospheric aerosols and stratospheric chemistry, in particular to the ozone layer.  Our calculations predict that the primary component of space debris particles (SDPs) will be aluminium hydroxide (Al(OH)₃), which is expected to polymerise rapidly to form nano-particles and react with atmospheric HCl. The resulting complex is predicted to have a photolysis rate ~10 000 times faster than that of gas-phase HCl, and so Cl concentrations and therefore destruction of ozone by chlorine radicals are expected to increase. 

Here we present preliminary results of a modelling study using a sectional aerosol model within an Earth system model (Whole Atmosphere Community Climate Model with the Community Aerosol and Radiation Model for Atmospheres, WACCM-CARMA).  We simulate the transport of SDPs and meteoric smoke particles (MSPs) produced by condensation of Fe and Mg silicates from ablated cosmic dust. The particles grow by coagulation and deposition of sulphuric acid through 28 size bins (0.34 nm to 1.6 µm radius). The SDPs and MSPs are initially injected in concentrations consistent with current models and observations (7.9 t d^-1 MSPs and 0.96 t d^-1 SDPs) to assess the transport and lifetimes of the particles in the atmosphere. The effect of increasing the mass of SDPs in line with future increases in space travel is also simulated. The maximum possible impact of SDPs on stratospheric chemistry is then estimated from the available SDP surface area and assuming upper limits for unmeasured physico-chemical parameters.