Global aerosol distributions and composition from the Earth's surface to the stratosphere

Atmospheric aerosols play a key role in Earth’s climate system, yet their vertical distribution, particularly in the free and upper troposphere, remains poorly constrained, strongly contributing to uncertainties in direct and indirect aerosol radiative forcing. We present an improved version of the EMAC (ECHAM5/MESSy for Atmospheric Chemistry) chemistry-climate model, evaluated against a comprehensive dataset from ground-based, remote-sensing, and aircraft observations, showing good agreement across the troposphere and lower stratosphere. Simulations reveal a global minimum in aerosol mass between 400 and 200 hPa, marking the transition from the free to the upper troposphere/lowermost stratosphere (UTLS), a region characterized by frequent new particle formation. Contrary to earlier model studies, boundary layer primary particles are rarely transported into the upper troposphere and stratosphere in our simulations, consistent with recent observational evidence. Finally, we outline specific aerosol process studies enabled by this improved model setup, in support of recent aircraft campaigns. The improved EMAC setup will provide the basis for detailed numerical studies of aerosol-(cloud-)radiation interactions across the lower and middle atmosphere.