| Summary: | Launch vehicles are a significant anthropogenic atmospheric emissions vector, and in the past have been shown to cause up to 50% as much global heating as aviation CO2. Despite this high magnitude of emissions impact, few studies quantify the variation in launch vehicle emissions beyond exploring launch number or propellant type, and as such there are few proposed avenues for reducing industry impact. Here, we present two new factors which may be relevant for reducing emissions impact; launch location (hemisphere) and launch season. I perform five two-year GEOS-Chem High Performance simulations, modeling the impact of 3000 Falcon-Heavy launches respectively across the months of January and July from Cape Canaveral in Florida and Rocket Lab Launch Complex in New Zealand. By examining zonal mean ozone and stratospheric water vapor accumulation, we find significant evidence for seasonal and hemispheric variation of launch vehicle emissions impact, leading to between 2 and 5 times as much ozone accumulation in summer versus winter launches for the same hemisphere, and 1.2-1.5x greater accumulation for southern hemisphere launches across the same launch season. The extent of these impacts provides substantial motivation for regulating and reducing summer-season and southern-hemisphere launches.
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