Investigation of key aerosol nucleation mechanisms in the tropical troposphere above the Indo-Pacific during the HALO mission CAFE-Pacific

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This project aims at the investigation of aerosol formation in the tropical upper troposphere above the Indo-Pacific. The chemical species that are responsible for aerosol nucleation and growth of aerosol particles in the tropical upper troposphere have not yet been identified. A central goal of the CAFE-Pacific mission with the research aircraft HALO will be to investigate the nucleation processes that occur in the upper tropical troposphere and, in particular, to identify and quantify the substances responsible for nucleation for the first time. With the help of the chemical ionization mass spectrometer used in this project, substances of very low volatility such as sulfuric acid, methanesulfonic acid and highly oxidized organic compounds can be measured. The photochemkeyical oxidation processes that take place in the outflow of deep convection are investigated, for example the conversion of dimethyl sulfite into sulfur dioxide, sulfuric acid and methanesulfonic acid. The elucidation of the oxidation and nucleation processes makes it possible to assess the role of aerosol nucleation in the tropical upper troposphere as the source region for both the formation of cloud condensation nuclei that supply the tropical troposphere as well as the stratospheric aerosol layer.