Dependence of Atmospheric and Climate Impacts on Launch Latitude and Seasonal Variation in Rocket Emissions

Abstract. Rocket launch emissions, including black carbon (BC), water vapor, and nitrogen oxides, can perturb atmospheric composition and climate, with impacts expected to increase under future growth in launch activity. Previous studies have shown that rocket-emitted BC can warm the stratosphere and alter ozone (O₃), but the dependence of these impacts on launch latitude and seasonal timing remains poorly understood. We investigate how launch latitude and seasonality influence the steady-state distribution of BC and the resulting climate responses. We use the Whole Atmosphere Community Climate Model version 6 to simulate emissions from a medium-lift kerosene launch vehicle at six launch latitudes: 55° S, 29° S, 0° N, 29° N, 55° N, and 70° N. Year-round emissions are applied at all latitudes, while boreal summer-only and boreal winter-only scenarios are applied at selected latitudes using the same annual emission rate, corresponding to 30 Gg yr^-1 of BC over approximately 11–70 km. The results show that Southern Hemisphere (SH) launches produce larger global BC burdens and stronger stratospheric warming, whereas O₃ depletion is stronger for Northern Hemisphere launches. Launch seasonality modifies BC transport. Low-latitude boreal summer launches transport more BC into the SH, leading to greater stratospheric warming but less O₃ depletion. At higher launch latitudes, launch season controls the altitude of the steady-state BC. These findings indicate that the climate impacts of launch activity depend not only on emission magnitude but also on the latitude and timing of launches.