Das Projekt "STEP/ESMOS/ALPS: Europaeische Stratosphaerenueberwachungsstationen in den Alpen: Ein europaeischer Beitrag zum Netzwerk fuer den Nachweis von Veraenderungen der Stratosphaere (NDSC)" wird vom Umweltbundesamt gefördert und von Universität Bern, Institut für Angewandte Physik durchgeführt. This proposal is based on ground-based observations performed at mid-latitude in Europe, in order to study the chemical and physical processes determining the stratospheric composition and its variations and changes. The measurements are made by means of number spectroscopic methods: Lidar (ozone, temperature, aerosols); Microwave radiometry (ozone, NO2); IR high resolution spectroscopy (HC1, HF, HNO3, C1ONO2, NO2, NO, N2O, CH4). This study relies on the 'Alpine Station' selected for the Network for the Detection of Stratosphere Change (NDSC) as the mid-latitude, Northern hemisphere site. The objectives are to make intensive coordinated ground-based observations to provide climatological measurements of ozone total amounts and vertical profiles, aerosol vertical distributions, C1O vertical profiles, NO2, NO reservoirs and long-lived tracers total amounts; to provide validated ground-based measurements at mid-latitudes to meet the SESAME scientific objectives in 1994 and 1995; to study the seasonal and interannual variability of the measured trace species; to study the aeronomic processes involved in atmospheric composition changes at mid-latitude; to study the role of volcanic aerosols on ozone and NO2 reduction observed after the Mt Pinatubo eruption, by expanding the observations during the decay of volcanic aerosols during the next two years and by the development of aerosol modelling; to provide measurement to test and improve stratospheric models including heterogeneous processes and to validate the current and planned satellite observations of the stratosphere (eg UARS and ERS2/GOME). The validated data will be archived in the data center of NILU.