The impact of rocket-emitted chlorine on stratospheric ozone

Although stratospheric ozone is recovering under the Montreal Protocol, the rapidly expanding space industry may influence the pace of this recovery. We assess the potential for rocket-emitted chlorine, under various launch growth scenarios, to offset the decline in chlorine from regulated Ozone Depleting Substances (ODSs). We use the Whole Atmosphere Community Climate Model (WACCM6) nudged to meteorological reanalyses to simulate realistic atmospheric variability. A modest (times ten) increase in chlorine emissions from rocket launches relative to 2019 causes a near-global column ozone loss of less than 0.1 Dobson Unit (DU) (0.04 %), while a large (times 52) increase leads to 0.6 DU (0.23 %) depletion. Local ozone decreases reach 0.4 % and 2 %, respectively, in the upper stratosphere for these scenarios. Column losses peak at high latitudes, with strong seasonality and meteorology-driven variability in the Arctic. The impact peaks in October in the Antarctic (0.5 and 3 DU depletion for × 10 and × 52 cases), and in April in the Arctic (generally up to 2 DU for the × 52 case, or greater than 8 DU in cold years with meteorology such as 2010/11). Ozone depletion throughout the stratosphere scales linearly with chlorine enhancement. Overall, while the effects of rocket-emitted chlorine under plausible growth scenarios are small, they could partially offset the gains achieved by the Montreal Protocol and should be considered in future assessments of rocket propulsion systems and ozone layer recovery projections.