Chemical composition, transformation, and cloud activation properties of submicron aerosol particles in the outflow of large major population centers

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Major population centers (MPC) represent large concentrated sources of anthropogenic gaseous and particulate pollutants. The HALO mission EMeRGe focuses on the investigation of the atmospheric transport and transformation processes of these emissions in the outflow of MPCs in the free and upper troposphere. Here we propose to use aerosol mass spectrometry in combination with cloud condensation nuclei (CCN) measurements and other aerosol instrumentation for a detailed characterization of the aerosol-related processes in the outflow of MPCs. A Compact Time-of-Flight Aerosol Mass Spectrometer (C-ToF-AMS) together with a Single Particle Soot Photometer (SP2) allows for a complete chemical characterization of the submicrometer aerosol composition and the detection of photochemical transformation processes. Microphysical properties like size distribution and number concentrations in different size ranges will contribute to the characterization. Size selective CCN measurements will be linked to the observed changes in composition and oxidation state, allowing for an assessment of the influence of MPC emissions on cloud formation. Additionally, transport of the aerosol particles by deep convection into the Tropical Transition Layer (TTL) acting as a "gateway" to the lower stratosphere will be investigated.