Das Projekt "Photochemical activity and ultraviolet radiation modulation factors" wird vom Umweltbundesamt gefördert und von Technische Universität München, Forstwissenschaftliche Fakultät, Lehrstuhl für Bioklimatologie und Immissionsforschung durchgeführt. General Information: The proposed research aims in the first place at quantifying the hierarchy of UV-B modulating factors moving from stratospheric ozone to tropospheric ozone and other environmental factors such as aerosol, clouds and air quality. This project builds on recent results from EU campaigns which have shown that south-eastern Europe and particularly the Aegean sea, is experiencing enhanced background ozone up to the tropopause, with extreme gradients in the J(O1D) prevailing in the first 2 km above sea level in the region. Therefore the project in addition to quantifying with model results validated by calibrated observations the factors influencing UV transfer, it will next move on to unravel the mechanisms maintaining the high background ozone over South-eastern Europe and its interplay with UV transfer. 3-D model studies will be done in large regional and sub regional scales to understand the extend of enhanced background ozone and its sources. The tropospheric effect on UV transfer is not as large as the absorption in the stratosphere but can be important due to photon path enhancements in the presence of different types of aerosols. This synergistic effect of the aerosol burden will be separately studied, being at present an open question. The above objectives of the project will be achieved through extensive state-of-the-art campaign measurements and modelling studies. The sites selected (islands of Crete and Lampedousa)are both in central and eastern Mediterranean and provide unique environments to meet the objectives presented before. They are located in the sunniest part of Europe and are exposed to high background levels and to alternating types of aerosols (Sahara/maritime) for which the quantification of combined effects are targeted in the study. The campaign and modelling efforts include studies on the variability of aerosol in the region. The project is focusing mainly in two major objectives: (a) Quantification of UV modulating factors and validation of UV models with calibrated data sets from an extensive campaign in the Mediterranean and (b) Modelling and validation studies on the mechanisms maintaining the enhanced tropospheric ozone in the region of study and quantification of interrelationships with the UV radiation field. Prime Contractor: Aristotle University of Thessaloniki, Department of Physics, Laboratory of Atmospheric Physics; Thessalonki; Greece.