干旱区生态环境知识资源中心

North Eastern Mediterranean is under the influence of sporadic dust transportation from desert sources in North Africa (The Great Sahara) and the Middle East (Arabian Peninsula) particularly during the spring and autumn. Mineral dust originated from these arid regions has characteristic reddish yellow-reddish brown color due to its high iron oxide content. Following atmospheric transport, mineral dust settles by either dry or wet (washout or rainout) deposition mechanisms. Precipitation samples collected it Mersin on the Eastern Mediterranean coast of Turkey during the period of December 2003-December 2004 have been investigated with respect to their red dust contents, Backward air mass trajectories corresponding to the rainy days were analyzed to determine potential source regions of red dust transported to the Northeastern Mediterranean. Approximately, 1/4 of the total precipitation samples can be evaluated as "red rain". The mean electrical conductivity arid the volume weighted mean Al concentration of red rain was found to be approximately seven times and five times higher than normal rain, respectively; while the dissolution of the calcite in dust has caused an order of magnitude decrease in the volume weighted mean hydrogen ion concentration of red rain, by neutralizing (buffering) the acidity of rainwater. Due to dissolution of atmospheric CO2 in rainwater, natural precipitation is slightly acidic (pH approximate to 5.6). In this study, the volume weighted mean pH values were calculated to be 6.09 for normal rain arid 7.27 for red rain. Using Al concentration of precipitation samples, wet deposition flux of mineral dust during 2004 was found to be 2.13 g m(-2) yr(-1). If dry deposition flux is added to this value, a total flux of 4.84 g m(-2) yr(-1) is found for atmospherically transported mineral dust.