Abstract. In order to evaluate the observed high rural ozone levels in the eastern Mediterranean area during summertime, vertical profiles of ozone measured in the period [1994][1995][1996][1997][1998][1999][2000][2001][2002][2003][2004][2005][2006][2007][2008] in the framework of the MOZAIC project (Measurement of Ozone and Water Vapor by Airbus in Service Aircraft) over the eastern Mediterranean basin (Cairo, Tel Aviv, Heraklion, Rhodes, Antalya) were analyzed, focusing in the lower troposphere (1.5-5 km). At first, vertical profiles collected during extreme days with very high or very low tropospheric ozone mixing ratios have been examined together with the corresponding back-trajectories. Also, the average profiles of ozone, relative humidity, carbon monoxide, temperature gradient and wind speed corresponding to the 7 % highest and the 7 % lowest ozone mixing ratios for the 1500-5000 m height layer for Cairo and Tel Aviv have been examined and the corresponding composite maps of geopotential heights at 850 hPa have been plotted. Based on the above analysis, it turns out that the lower-tropospheric ozone variability over the eastern Mediterranean area is controlled mainly by the synoptic meteorological conditions, combined with local topographical and meteorological features. In particular, the highest ozone concentrations in the lower troposphere and subsequently in the boundary layer are associated with largescale subsidence of ozone-rich air masses from the upper troposphere under anticyclonic conditions while the lowest ozone concentrations are associated with low pressure conditions inducing uplifting of boundary-layer air, poor in ozone and rich in relative humidity, to the lower troposphere.

[1] The Photochemical Activity and Ultraviolet Radiation (PAUR) II project (a continuation of an earlier PAUR I project) had the purpose of studying the interrelationships between changes in total ozone, tropospheric aerosols, UV radiation and photochemical activity. As part of PAUR II project, a campaign took place in Greece and Italy during MayJune 1999, with the participation of 15 European and 3 American research institutions. A variety of radiation and gaseous and aerosol atmospheric composition and optical characteristics measurements were made during the campaign. Radiative transfer models and three-dimensional (3-D) regional chemistry transport models (CTM) were applied and compared to the available data set of PAUR II. The present overview paper gives an introduction to the project and to the meteorological and environmental conditions that prevailed and outlines some results that are extensively described in the subsequent papers which form this special section. The modulation of the UVB field in the presence of different types of aerosols, its transmittance and role in the photochemistry of the particular eastern Mediterranean environment is overviewed. Using a 3-D CTM, it is shown that even a 50% reduction in Greek anthropogenic emissions has only a small effect in reducing the ozone levels over the eastern Mediterranean in summer. The environmental conditions, which prevailed during the PAUR I and PAUR II campaigns, offered cases of background conditions over the Aegean Sea as well as conditions with Saharan dust episodes and extremes in total ozone.

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This study investigates the simulated changes in temperature and precipitation over Greece from nine Regional Climate Models (RCMs) for the period 2071-2100 under the A2 emission scenario and evaluates their performance during the control period 1961-1990 using Greek gridded datasets of temperature and precipitation. In winter, most RCMs show a bias towards warmer and dryer conditions and a bias towards higher inter-annual temperature variability and lower inter-annual variability of precipitation than the Greek gridded datasets during the control period . In summer, all RCMs show a cold bias for the maritime sub-regions and generally all sub-regions show very small biases in precipitation. Concerning the future projections of the RCMs for Greece the mean change of the nine RCMs for the mean air temperature, T 2mean, between the future period and the control period for the integrated Greek domain is 3.4°C for winter and 4.5°C for summer with the changes being larger in continental than in the marine sub-regions. The inter-annual temperature variability in the future simulations generally increases in summer and decreases in winter almost for all RCMs with these changes being larger in the continental sub-regions than in maritime sub-regions of Greece. Almost all RCMs simulate a decrease of the precipitation for the future climate for both winter and summer with the inter-annual variability of summer precipitation decreasing for the majority of RCMs. The reported future climatic changes will have important impacts for the region of Greece in vital sectors such as water resources, agriculture, tourism, forest fire risk and energy demand.