Inhaltszusammenfassung

The Amazon basin serves as one of the largest ecosystems, providing remote and mostly natural conditions. In this context, airborne measurements were conducted in the scope of a field campaign above the Amazon rainforest at altitudes up to 14 km. Quantitative chemical composition measurements of out-of-cloud aerosol particles as well as of cloud particle residuals (CPR) in the size range of 40 - 800nm were analysed in this thesis. The in-situ data were obtained using a compact time-of-flight ...The Amazon basin serves as one of the largest ecosystems, providing remote and mostly natural conditions. In this context, airborne measurements were conducted in the scope of a field campaign above the Amazon rainforest at altitudes up to 14 km. Quantitative chemical composition measurements of out-of-cloud aerosol particles as well as of cloud particle residuals (CPR) in the size range of 40 - 800nm were analysed in this thesis. The in-situ data were obtained using a compact time-of-flight aerosol mass spectrometer (C-ToF-AMS). Besides the chemical composition of submicron aerosol, the focus is on secondary organic aerosol (SOA) and different formation pathways of SOA occurring in the Amazonian atmosphere. The out-of-cloud aerosol consist at all altitudes predominantly of organics. The highest aerosol mass concentrations were found in the lower troposphere (0.1 - 4.5 km, LT) decreasing at higher altitudes. However, organic and nitrate mass concentrations show enhanced values in the upper troposphere (8 -14 km, UT). The organic aerosol was mainly oxidized in the LT, whereas a lower oxidation state was found for the organics measured in the UT. These findings are explained by SOA formation in the UT and supported by aerosol size distribution measurements. One significant contributor to the organic aerosol composition in the LT (10 %) as well as in the UT (20 %) was identified as isoprene epoxydiol secondary organic aerosol (IEPOX-SOA). A ubiquitous occurrence of IEPOX-SOA was found at all altitudes and can be explained with the abundance of isoprene, the precursor gas of this compound emitted by vegetation. The formation pathway of IEPOX-SOA depends on the aerosol acidity as the condensation of gaseous IEPOX is favoured on acidic surfaces. Indeed, the aerosol particles observed in the UT were acidic. The increased values of nitrate suggest that the acidic conditions can be provided not only by sulfate but also by nitrate resulting in the formation of organic nitrates. Taken together, the formation of SOA is an important process in the Amazonian atmosphere affecting the aerosol properties at low and high altitudes. For the first time, airborne measurements of a C-ToF-AMS coupled with the aircraft inlet system HALO counterflow virtual impactor (HALO-CVI) were conducted during the same field campaign at altitudes up to 14 km allowing the investigation of CPR especially in the UT. The measurements were obtained in liquid and ice clouds. The CPR sampled in liquid clouds consist mainly of organics (70 %), whereas the inorganics are dominated by sulfate. In contrast, organics contribute up to 95 % to the ice cloud residuals. Whereas the CPR of liquid clouds consist of oxidized, most likely secondary organic matter, the ice residuals consist of primarily emitted hydrocarbon-like organic aerosol (HOA). It seems that the HOA-containing CPR in the UT acted as ice nucleating particles (INP), while the CPR consisting of oxidized organic aerosol (OOA), sulfate and nitrate are activated in the LT as cloud condensation nuclei (CCN) and removed by wet deposition. The freezing process in the observed ice clouds appears to be dominated by heterogeneous freezing induced by vertically transported HOA-containing particles and thus affecting aerosol-cloud-interactions. This study offers valuable insights into formation processes of SOA in the pristine Amazonian atmosphere regarding IEPOX-SOA and organic nitrates, as well as provides new findings of the composition of CPR in the tropical upper troposphere.» weiterlesen» einklappen

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DDC Sachgruppe:
Naturwissenschaften