Impact of iodine injections from the suface and the small satellites using iodine propulsion system in the upper atmosphere on ozone depletion

Iodine has the potential to cause stratospheric ozone depletion.  However, there is still significant uncertainty concerning the magnitude of its effect, ranging from a few percent to 10% based on the literature studies. Moreover, these studies have only considered that up to  0.77±0.10 per trillion by volume (pptv) total inorganic iodine is entrained into the stratosphere from the surface emissions. Recently the first 12U CubeSat using the iodine electric propulsion was launched in November 2021 into an orbit at ~480 km. The system produces iodine ions after vaporizing solid iodine. Thus the launch of nanosatellites using iodine propulsion will inject gas-phase iodine species into the thermosphere, which upon re-entering the atmosphere could potentially cause depletion of the ozone layer and consequently impact climate. 

Here we use the 3-D Whole Atmospheric Community Climate Model (WACCM) to investigate stratospheric ozone depletion due to the launch of small satellites (e.g., CubeSats) with an iodine propulsion system and understand the potential risks caused to stratospheric ozone . We have separted the contribution to the stratospheric ozone depletion from the surface emissions of Iodine and its injection from the upper atmosphere. We have performed a number of model sensitivity runs with different additional scenarios of iodine injection at 120-140 km to explore the potential  stratospheric ozone depletion from small satellites powered in this way. For the base case scenario in the current condition (for example year 2014), a steady-state nanosatellite launch rate of 20,000/year (e.g., 8 tons of I+ injected), the perturbation to the total column ozone is negligible. However, a 10 or 100-fold increase in the mass of iodine launched into near-Earth orbit will cause significant ozone depletion. This study quantifies the extent to which the injection of iodine into the thermosphere can deplete stratospheric ozone, which will be a useful guide for limiting the population of satellites with iodine propulsions systems in low Earth orbit. The impact of iodine for the extreme large ozone depletion years (for example, 2020)  and future scenarios of the results will be also discussed.