Das Projekt "Hochalpen-Aerosolforschungsprogramm" wird vom Umweltbundesamt gefördert und von Paul Scherrer Institut durchgeführt. Leading Questions: - To assess the direct and indirect effect of aerosol on climate. - To determine the relative contribution of natural and man-made sources to the physical and chemical properties of the aerosol. Abstract: Aerosols may influence the atmosphere in two important ways, through direct and indirect effects. The resulting climate forcing may be of the same magnitude, but opposite in sign to the combined effect of all greenhouse gases. It is therefore the objective of GAW to determine the spatio-temporal distribution of aerosol properties related to climate forcing and air quality up to multi-decadal time scales. To achieve this objective, a large number of aerosol parameters need to be measured, including the multiwavelength scattering and backscattering coefficients, the absorption coefficient, aerosol number concentration, cloud condensation nuclei (CNN) concentration, and chemical composition. Most of these parameters have been measured since 1995 or will be measured shortly at the high alpine research station Jungfraujoch, Switzerland (3454 m). The station is part of the combined Global Atmosphere Watch (GAW) baseline station of Europe, also comprising the Zugspitze (2962 m, Germany) and Sonnblick (3106 m, Austria). The continuous measurement programme is complemented by a number of specific research projects and specially tailored field campaigns.