CAFE-Brazil (Chemistry of the Atmosphere: Field Experiment in Brazil) is a HALO mission that takes place in winter 2022/23 above the Amazon rainforest. Researching the upper tropical troposphere is of high importance because elevated aerosol particle concentration have been observed in this area compared to the middle and lower troposphere. These particles can be transported into the stratosphere, where they contribute to the global radiation balance and thus, the global climate. Also, the particles can sink and contribute to the regional climate and water balance of the Amazon rainforest as cloud condensation nuclei.

With the CAFE-Brazil campaign, we want to test the hypothesis that gaseous substances such as terpenes and dimethyl sulfide (DMS), which are being emitted from the vegetation of the rainforest, are efficiently transported towards the upper troposphere through deep convective clouds. In the outflow of these clouds, there are ideal conditions for particle formation. We want to study if the oxidation products of organic compounds are mainly responsible for new particle formation without the influence of sulphuric acid.

To study this, physical parameters such as pressure and temperature, and chemical species such as trace gases and components of aerosol particles are measured during the flights. We participate with a CI-APi-TOF mass spectrometer. In 2020, it was successfully employed in the CAFE-EU/BLUESKY mission. We want to measure highly oxygenated molecules (HOMs) with it. In CLOUD experiments, we showed that HOMs strongly participate in particle formation and growth processes at atmospherically relevant conditions. It has been observed that new particles are formed at high altitudes above the Amazon. However, the processes and the involved substances are still unknown. We want to address these questions with our measurements.