The Impact of Rocket-Emitted Chlorine on Stratospheric Ozone

Although stratospheric ozone is showing signs of healing following the implementation of the Montreal Protocol, the impact of the rapidly developing space industry may affect the rate and extent of this recovery. We assess the potential for rocket-emitted chlorine, under different scenarios of launch rates, to offset the decrease in chlorine from controlled long lived Ozone Depleting Substances (ODSs). We use the Whole Atmosphere Community Climate Model Version 6 (WACCM6) nudged to meteorological reanalyses in order to simulate realistic atmospheric conditions and variability. Chlorine emissions from modest (×10) increase in launch rates relative to 2019 causes near-global column ozone depletion of less than 0.1 DU (0.04%), while large (×52) growth causes depletion of 0.59 DU (0.23%). These two scenarios respectively cause local ozone decreases of up to 0.4% and 2% in the upper stratosphere. Lower stratospheric loss and column ozone depletion are largest at high latitudes with a pronounced annual cycle and, in the Arctic, large meteorology-driven variability. The impact on Antarctic ozone peaks in October (additional depletion of 0.5 DU (modest growth) and 3 DU (large growth)), while the impact in the Arctic peaks in April (2 DU for large growth). Although the mean impact in the Arctic is much smaller than for the Antarctic, the ozone loss shows large variability. In very cold years (exemplified by 2010/11 meteorology), the column loss in the Arctic exceeds the Antarctic for all launch scenarios and can exceed 8 DU for large growth. Ozone depletion in both the polar lower stratosphere and upper stratosphere shows a linear dependence on the level of chlorine enhancement. Overall, the estimated impact of rocket-emitted chlorine for reasonable growth scenarios is small but does have the potential to offset some of the gains of the Montreal Protocol. This impact needs to be considered when deciding on propulsion systems for future launches and in projections of ozone layer recovery.