Secondary organic aerosol formation and particle growth in the tropical upper troposphere: Particle composition measurements by aerosol mass spectrometry

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The upper troposphere, especially in the tropics, is an important source region for atmospheric new particle formation. On one hand, the newly formed particles can be transported downwards into the middle and lower atmosphere where they can act as cloud condensation nuclei, on the other hand the particles can also be transported upwards into the stratosphere, thereby supplying the stratospheric aerosol layer (Junge layer). The precursor gases for this particle formation, which are transported into the upper troposphere by convection, can be sulfur-containing species (SO2, H2SO4), but also organic compounds, like isoprene and its degradation products. The exact mechanisms of the formation and growth of these particles, as well as the chemical composition and the sources of the precursor gases, are not clarified yet. Therefore, the proposed project deals with chemical composition measurements of the precursor gases and the newly formed and growing particles in the tropical upper troposphere over Brazil, in the frame of the HALO mission CAFE-Brazil. Focus of the current proposal okis the mass spectrometric analysis of the grown particles using an aircraft-based aerosol mass spectrometer. In a precursor project (ACRIDICON-CHUVA 2014), we could show that about 20% of the organic aerosol mass in the tropical upper troposphere is due to a certain isoprene degradation product (IEPOX). The objective of the proposal is therefore the identification of the precursors and the formation mechanisms of the remaining 80%. Observations of organic nitrate in the upper troposphere suggest that nitrate as well plays a role in upper tropospheric secondary aerosol formation, but this process is also not clarified yet.