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

对流层上层，特别是热带地区，是大气新粒子形成的重要源区。新形成的粒子一方面可以向下输送到中低层大气中，在那里它们可以作为云凝结核，另一方面也可以向上输送到平流层中，从而提供平流层气溶胶层（Junge层）。这种颗粒形成的前体气体通过对流输送到对流层上部，可以是含硫物质（SO2，H2SO 4），也可以是有机化合物，如异戊二烯及其降解产物。这些颗粒的形成和生长的确切机制，以及前体气体的化学成分和来源，尚未澄清。因此，拟议的项目涉及在HALO使命CAFE-巴西的框架内，对巴西上空热带对流层上层的前体气体以及新形成和增长的粒子进行化学成分测量。目前建议的重点是使用基于飞机的气溶胶质谱仪对生长的颗粒进行质谱分析。在一个前体项目（ACRIDICON-CHUVA 2014）中，我们可以证明热带对流层上部约20%的有机气溶胶质量是由于某种异戊二烯降解产物（IEPOX）。因此，该提案的目标是确定剩余80%的前体和形成机制。对流层上层有机硝酸盐的观测结果表明，硝酸盐在对流层上层二次气溶胶形成中也起作用，但这一过程还不清楚。

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.