Atmospheric Environment Vol. 26B, No, 3, pp. 359-367, 1992. 0957-1272/92 $5.00+0.00 Printed in Great Britain. (() 1992 Pergamon Press Ltd CHEMICAL COMPOSITION OF RAIN IN THESSALONIKI, GREECE, IN RELATION TO METEOROLOGICAL CONDITIONS C. SAMARA,* R. TSITOURIDOU~" a n d CI4. BALAFOUTIS~ *Environmental Pollution Control Laboratory, Department of Chemistry, tLaboratory of Analytical Chemistry, Department of Chemical Engineering and ~Laboratory of Meteorology and Climatology, Department of Geology, Aristotelian University of Thessaloniki, 540 06 Thessaloniki, Greece (First received 1 June 1991 and in final form 21 October 1991) Abstract--Wet precipitation was collected in Thessaloniki, Greece, during the period March 1989-December 1990 by using an automatic wet-only precipitation sampler. Rainwater samples were analysed for major cations (H +, NH2, Na +, K +, Ca 2÷, Mg2* ) and anions (CI-, NO~, SO~-), in addition to acidity and conductivity measurements. The majority of rain had a neutral or alkaline character as a result of neutralization, primarily caused by calcareous soil dust and secondarily by atmospheric ammonia. In all rain, SO2- concentration exceeded NO~ concentration. The contribution of maritime sources to the total SOn 2- concentration was very low (< 2%). The chemical composition of precipitation was analysed in conjunction with meteorological variables (season of the year, precipitation type, airflow patterns) to evaluate temporal variations and chemical source influence. Rain caused by weak, localized flows showed the highest acidity and the minimum influence of neutralization processes. Key word index: Wet precipitation chemistry, acid rain, air trajectories. INTRODUCTION Research in precipitation chemistry has been intensi- fied in recent years because of increased awareness of the potential ecological deterioration caused by acid rain (forest decline, lake and soil acidification, marble sulfation and deterioration of ancient monuments; Edney et al., 1988; Cheng et al., 1987; Mosello, 1986; Binns, 1985; Skoulikidis, 1983). For about 20 years, acid precipitation has been the subject of research projects conducted in western Europe, the north- eastern U.S., Canada, etc. (Hansen and Hidy, 1982; CEC, 1985; Chan et al., 1985). However, acid rain cannot be regarded solely as a local phenomenon of areas with important emission sources, because in- dustrial and urban pollution may affect larger regions by long-distance transport of pollutants (Ontario Ministry of the Environment, 1980; Manes and Segal, 1976; Raynor and Hayes, 1982a). The processes controlling the composition of rain are complex and influenced by both natural and anthropogenic sources. These processes that result in the incorporation of air pollutants into cloud droplets or the incorporation of the particles below the cloud in falling droplets are poorly understood and difficult to study experimentally. The relation of the chemical composition of rain to the associated meteorological conditions can improve the understanding of the causes of acid rain. In Greece, acid rain has been investigated for the last 15 years in several places, particularly in large cities, such as Athens (Dikaiakos et al., 1990), Thessal- oniki (Samara et al., 1988) and Patras (Glavas, 1988). Special attention has been drawn to the deterioration of the marbles of the Acropolis in Athens (Skoulikidis, 1983; Vocom, 1979; Skiotis et al., 1981). Thessaloniki is the second largest city in Greece in terms of population (Fig. 1). The city has grown rapidly since 1960 as a consequence of the increased industrialization of the area. Atmospheric pollution is a serious problem which has drawn special attention over recent years. The main urban sources of air pollution are central heating and vehicle traffic, al- though there are numerous emission sources in the industrial area (oil refinery, mineral acid-producing plants, fertilizer and cement industries, iron and steel manufacturers, smelters, etc.). A big complex of coal- burning power plants is located in Ptolemais, about 100 km southwest of Thessaloniki. Previous investigation of pH and specific conduct- ance of rain in Thessaloniki showed that about 25% of precipitation events are characterized by relatively high acidity (pH 4.5-5.1), which was attributed to the fast movement of air masses originating in northern and central Europe (Samara et al., 1988). This paper presents the chemical composition of the rain that occurred in Thessaloniki during the period March 1989-December 1990. Samples were analysed for SO 2-, NO 3, CI-, Ca 2+, Mg 2+, K +, Na ÷ and NH2 in addition to pH and specific conductance. Rain events were classified regarding the predominant meteorological conditions in order to investigate the 359