Investigation of key aerosol nucleation mechanisms in the tropical troposphere with a CI-APiTOF-Mass Spectrometer above Amazonia during the HALO mission CAFE-Brazil

新粒子形成(NPF)在热带对流层高层频繁发生，但其形成机制和引发核化的化学物质至今仍未被观测到。在亚马逊地区，边界层和对流层下部不存在NPF，因此对流层上层的NPF可能是整个对流层云凝结核的主要来源。它也被认为是平流层气溶胶层的一个重要源区。我们发现，即使没有众所周知的无机成核剂如硫酸的参与，从单萜氧化形成的高含氧分子(HOMS)中提取的NPF也是非常有效的。亚马逊雨林中的树木大量排放单萜烯，单萜烯几乎不溶于水，因此通过深对流进入对流层上层。我们认为，亚马逊上空对流层上层的NPF主要由HOMS主导。为了证明这一机制，我们计划于22/23冬季在巴西马瑙斯执行CAFE-巴西任务(大气化学：巴西实地实验)期间，在德国研究飞机Halo上操作硝酸盐-化学电离大气压力飞行质谱仪(Nitrate-CI-APiTOF)。CI-APiTOF能够定量测量微量的关键成核物种，如HOMS和硫酸。结合对超细气溶胶浓度的测量，我们将能够得出气溶胶的成核率，并描述新形成的粒子的初始凝聚增长。

New particle formation (NPF) occurs frequently in the upper tropical troposphere but the formation mechanisms and the chemical species that initiate the nucleation have not been measured so far. In Amazonia NPF is absent in the Boundary Layer and in the lower parts of the troposphere, therefore NPF in the upper troposphere is probably a main source for Cloud Condensation Nuclei in the entire troposphere. It is also assumed to be an important source region for the stratospheric aerosol layer. We discovered that NPF from the highly oxygenated molecules (HOMs) that form from the oxdation of monoterpenes is very efficient even without participation of well-known inorganic nucleators such as sulfuric acid. Monoterpenes are emitted in large quantities by trees in the Amazon rain forest, and the monoterpenes are hardly water soluble and therefore survive transport into the upper troposphere by deep convection. We propose that the NPF in the upper troposphere above Amazonia is dominated by HOMs. To prove this mechanism we plan to operate a nitrate- Chemical Ionization Atmospheric Pressure interface Time of Flight mass spectrometer (nitrate-CI-APiTOF) onboard the German research aircraft HALO during the CAFE-Brazil mission (Chemistry of the Atmosphere: Field Experiment in Brazil) in Manaus, Brazil, in winter 22/23. The CI-APiTOF is able to measure quantitatively minute quantities of the key nucleating species such as HOMs and sulfuric acid. In combination with measurements of the ultrafine aerosol concentration we will be able to derive aerosol nucleation rates and describe the initial condensational growth of the newly formed particles.