Aircraft-based mass spectrometric measurements of biogenic precursors of aerosol nucleation in the upper troposphere above the Amazon rainforest
In the atmosphere, aerosol particles can be formed from gaseous precursor species, such as sulphuric acid and highly oxidised organic molecules with extremely low volatilities. The related processes are quite well studied within the continental boundary layer, nut not in the upper troposphere. In the tropics, deep convection causes fast upwards transport of chemical species emitted within the boundary layer. In the Amazon rainforest, biogenic precursor substances such as isoprene or terpenes are hence transported into the upper troposphere efficiently. In the outflow region of deep convective clouds, favourable conditions for nucleation can be found. It can be assumed that sulphuric acid and particles with small surfaces are scavenged by the cloud droplets. Thus, it is hypothesised that biogenic highly oxidised molecules account for the major part of nucleation in the upper tropical troposphere. If this is proven correct, this biogenic nucleation pattern can represent nucleation processes in the pre-industrial atmosphere. The hypothesis is going to be tested through aircraft-based measurements with a time-of-flight mass spectrometer coupled to a chemical ionisation source on-board the research aircraft HALO during CAFE-Brazil campaign. Knowledge about the biogenic nucleation processes in the tropical upper troposphere are crucial for a better understanding of climate processes today and in pre-industrial times, and to better project climate change, eventually.