Arctic aerosols - from the boundary layer to the stratosphere

Climate models struggle with the parameterization of aerosols, because they strongly interact with radiation and clouds. This thesis provides a comprehensive overview of various aerosol measurements for the determination of aerosol properties in the Arctic and changes over the last two decades. For this purpose, the data sets of sun and star photometer were homogenized to analyze the entire course of a year. Compared to lower latitudes, the Arctic atmosphere is very pristine and has significantly fewer aerosol sources, but warms fastest globally. Therefore, the investigation and understanding of long-range transport are important. It is shown that observed aerosol events can generally not be traced back to a single aerosol source, but rather result from a superposition of several sources and sinks along the transport pathway into the Arctic. The aerosol budget in March and April is predominantly influenced by this long-range transport, while local sources contribute most in summer, as a multiple linear regression analysis has revealed. When the aerosol layers reach Svalbard, the orography of Kongsfjord plays an important role on their shape and arriving altitude. Due to the fjord and the mountain ridges, a turbulent wind shear zone is formed, which can mix aerosols from the free troposphere into the boundary layer. A clear annual cycle has been found in a homogenized 20 year long data set from sun and star photometer, with a large variability, high AOD and large particles in winter. On the other hand, summer is characterized by more homogeneous aerosol levels, a clearer atmosphere and smaller particles. Additionally, the period of the Arctic Haze in spring becomes clearer, while in autumn the AOD increases. The length of a single aerosol event is estimated to several hours by autocorrelation analysis. The stratosphere was analyzed with Raman Lidar observations. A clear annual cycle is also observed, with enhanced backscattering in summer and early autumn. This can be traced back to the Southeast Asian summer monsoon. Typically, these aerosols in the lower stratosphere are spherical and small (<100 nm). Additionally, an innovative validation procedure for the star photometer is presented. With this new method, only one good two-star measurement is needed to calibrate an unlimited number of stars. To achieve a height-resolved profile of aerosol properties, Raman Lidar observations are crucial. With the inversion of an applicable scattering theory, even microphysical properties, like particle volume size distribution or refractive index, can be retrieved from these profiles. A regularization of Lidar signals also improves the extinction profile significantly. With this result, the optical depth can be obtained by Raman Lidar in the troposphere and, in some cases, even for clouds in the lower stratosphere. Last but not least, remote sensing and in-situ observations are used together to achieve a better understanding of aerosol properties. With the knowledge gained, the understanding of Arctic aerosol has improved, and the results help to enhance climate models for better parameterization of aerosols from the boundary layer to the lower stratosphere in the Arctic.