Das Projekt "Aerosole, Wolken in der polaren Stratosphaere und die Messung ihrer chemischen Zusammensetzung in der Arktis und Westskandinavien" wird vom Umweltbundesamt gefördert und von Universität Bonn, Physikalisches Institut durchgeführt. The main objective of this project is to perform field measurements of chemical species and aerosols at high latitudes yielding data which help to test the present understanding on how polar stratospheric clouds and (volcanic) aerosols affect the nitrogen and chlorine partitioning. Particulate measurements will be performed by lidar, one ground-based at Andoya (69.3 degree N, 16.0 degree E) and one airborne with the aircraft stationed at Kiruna (67.9 degree N, 21.1 degree E) during SESAME. The lidar measurements will show the presence of aerosols and the vertical distribution. In the case of LEANDRE lidar the horizontal scales can be determined, while the Andoya lidar measures the temporal evolution at a fixed location. Polarization and two colour measurements will delineate the particulate shape, i.e. its physical phase, and distribution changes, which can be used to identify spherical PSCs among sulfur acid droplets. Composition measurements will be performed by two ground-based spectrometers at Kiruna. One of the instruments is a differential absorption spectrometer (DOAS) using zenith scattering, off-axis solar scattering or direct moonlight observation geometries. The other instrument is a Fourier transform spectrometer (FTIR) operated in solar occultation geometry. The primary quantities derived will be zenith column amounts of various trace gases, among them NO2, NO3, CIONO2 and HNO3, which are involved in the nitrogen partitioning scheme. In addition other gases of relevance to the ozone depletion problem are measured. They include O3, HCl, BrO, OCIO, CFC12, CH4, H2O and HDO. For some of these gases, the tropospheric and stratospheric contributions can be separated or even an altitude profile derived. The techniques used are based on measurements at several zenith angles (DOAS) or exploit the high spectral resolution (FTIR). Also, it is possible for the DOAS to detect changes in the sky colour during twilight which may be attributed to polar stratospheric clouds above the station. Prime Contractor: Rheinische Friedrich-Wilhelms-Universität Bonn, Physikalisches Institut; Bonn; Germany.