© by PSP Volume 17 – No 10a. 2008 Fresenius Environmental Bulletin 1648 WET DEPOSITION IN TWO GREEK SITES: LARISSA AND ATHENS Panagiotis T. Nastos 1* , Agelos Papaioannou 2 , Athanasios G. Paliatsos 3 , Konstandinos Kakavas 2 , Panagiotis Plageras 2 and Eleni Dovriki 2 1 Laboratory of Climatology and Atmospheric Environment, Department of Geography and Climatology, Faculty of Geology and Geoenvironment, University of Athens, Panepistimiopolis, 157 84 Athens, Greece 2 Department of Medical Laboratories, Faculty of Health and Care, Technological and Education Institute of Larissa, 412 00 Larissa, Greece 3 General Department of Mathematics, Technological Education Institute of Piraeus, 122 44 Athens, Greece Presented at the 14 th International Symposium on Environmental Pollution and its Impact on Life in the Mediterranean Region (MESAEP), Sevilla, Spain, 10 – 14 Oct. 2007 ABSTRACT The determination of the chemical composition of rain- fall related to the origin of the air masses, in two urban sites in Greece during the year 2006, is investigated in this study. Two model automatic rain samplers were installed, the first in the city of Larissa, Thessaly, central Greece and the sec- ond in Heraklio, Attica, a northern suburb of Athens. The concentrations (ppm) of the major cations (H + , Na + , K + , Ca 2+ , NH 4 + and Mg 2+ ) and major anions (NO 3 - , NO 2 - , HCO 3 - , and SO 4 2- ), as well as total hardness (ppm CaCO 3 ), pH and electric conductivity in 25 o C (µS/cm) for 27 rainfall sam- ples -11 samples in Larissa and 16 samples in Heraklio (Athens)- were determined. In Larissa, the figures of pH range from 5.13 to 6.13 while in Heraklio (Athens), the pH within the range 5.62 to 7.88 indicates a shift of the rainfalls towards alkalinity. The electric conductivity in Larissa ranges from 16.30 µS/ cm to 110.60 µS/cm and in Heraklio (Athens) from 7.00 µS/ cm to 151.00 µS/cm. The analysis showed that Ca 2+ and Mg 2+ appear the highest concentrations out of the examined cations, while HCO 3 - and SO 4 2- present the highest concen- trations within the anions. Moreover, in order to find out the origin of the air masses, the air mass back trajectories were calculated using the HYSPLIT 4 model of Air Re- sources Laboratory of NOAA for two different levels: 1500 and 3000 m (a.m.s.l.). KEYWORDS: Wet deposition, air mass back trajectories, Athens, Larissa, Greece. INTRODUCTION Acid rain is responsible for many environmental prob- lems, such as impacts on the life in the water as well as the life on land. It is almost worse in water than on land because the fish that are in the water need the water to breathe. Trees are also harmed by acid rain. The atmosphere depos- its a lot of toxic metals into the forests because acid rain contains metal, such as lead, zinc, copper, chromium, and aluminium. The main components that produce acid rain are the sulphur dioxide (SO 2 ) and the nitrogen oxides (NO x ). These ambient air pollutants are emitted by natural and human activities. A lot of studies and analyses have been carried out concerning the emissions and deposition of air pollutants which cause acid rain [1-3]. In the central-eastern Mediterranean, acid episodes (pH<5), and a great percent- age of episodes with pH>6 appeared [4-9]. In Greece, the phenomenon of acid rain has been studied since approxi- mately 25 years ago in order that the reasons responsible for the observed deterioration of the marbles of Parthenon are revealed [10-12]. Later on, a lot of researchers studied systematically the phenomenon of acid rain during differ- ent time periods in Athens [5, 13-18], in Thessalonica [6], in Patras [4, 19], in Crete [20] and in central Greece [21]. This work presents the results of the chemical com- position of the wet deposition, with respect to the concen- trations of major anions and cations, in two Greek cities: the city of Larissa (LAR) and the city of Heraklio (HER), Attica, a northern suburb of Athens, during 2006. The ob- jective of the analysis is to find out the possible differen- tiations in the chemical composition of the rainfall in the two sites and make an effort to interpret these, using the air mass back trajectories analysis. DATA AND ANALYSIS The data analyzed concern the concentrations (ppm) of the major cations (H + , Na + , K + , Ca 2+ , NH 4 + and Mg 2+ ) and major anions (NO 3 - , NO 2 - , HCO 3 - , and SO 4 2- ), as well total