STUDY OF THE AEROSOL EFFECT ON THE UV-B IRRADIANCE AT THE EARTH’S SURFACE. CASES STUDIES SELECTED FROM URBAN SITES IN THE FRAME OF THE EARLINET PROJECT

The effect of various types of aerosols on the UV-B radiation has been subject of various studies. These studies include simultaneous measurements of the UV irradiance and measurements of optical properties of the aerosols such as the aerosol optical depth and the angstrom exponent, as well as extensive modelling of the radiative transfer in this spectral region (e.g. Balis et al., 2001, Kylling et al., 1998, Papayannis et al., 1998). The variable aerosol conditions, alternating from urban/maritime to Sahara dust, which are observed over south-eastern Europe, and their effect on UV irradiance have been previously studied on a campaign basis, in the frame of the EU funded PAUR projects (Zerefos, 2001). In certain cases it was found that, under clear skies, the day-to-day variability of the aerosol loading can mask changes in the UV-B irradiance that correspond to changes in the total ozone column. The ground-based lidar network of the EARLINET project provides the unique opportunity to build a 3-year climatology of the different aerosol conditions over the European continent. This data set in addition to the routine UV measurements over various sites (e.g. Thessaloniki, Athens, Garmsich-Partenkirchen) will help to improve the use UV modelling tools and thus will help to quantify the aerosol effect on the levels of UV irradiance reaching the Earth's surface.