Main water-soluble ions in precipitation of the central mediterranean region

Abstract

The chemical content of atmospheric deposition is the signature of several interacting physical and chemical mechanisms: i.e., emission and source amplitude; transport processes and dynamics of the atmosphere; atmospheric chemical reactions; and removal processes, among others. Studying deposition processes and amounts thus allow for tracing the spatio-temporal evolution of atmospheric chemistry. It is also an important way for distinguishing between natural and anthropogenic influences. Sulfate, nitrate and ammonium ions are formed in the atmosphere in gas-particle conversion processes. Sulfates represent one of the main components of atmospheric aerosols. In southern Europe, rainwater has similar concentrations of acidic anions to those of other parts of Europe, but the average precipitation is not acid due to neutralizing role of basic cations. The Mediterranean Sea is enclosed basin, which is susceptible to dust transport from desert sources in North Africa (Sahara) and the Middle East (the Arabian Peninsula and Syria), lying on its periphery. The climatic conditions are favorable for the transport of dust from North Africa into the eastern Mediterranean atmosphere during the spring, while other conditions favor transport into the western Mediterranean atmosphere during the summertime. An investigation of wet deposition of water soluble Na+, K+, Mg2+, Ca2+, Cl-, SO42-, NO3- and NH4+ were done in south-eastern Adriatic coast in the period from January 1995 until December 2000. The highest precipitation and the highest frequencies of air masses coming from the western Mediterranean cause the highest Wet Deposition (WD) of the main water soluble ions. The most abundant WD of SO42- in investigated region was caused by air masses coming from the western Mediterranean and western and central Europe. The sea salt components (Na+, Cl-, Mg2+) are significantly correlated. The correlations between Ca2+ and Mg2+, Ca2+ and SO42- and Ca2+ and K+ indicate that the main terrigeneous ions were associated with formation of eolian particles which include gypsum (CaSO4), calcite (CaCO3) and dolomite (CaMg(CO3)2). Although the Volume Weighted Mean (VWM) of Na+, K+, Mg2+, Ca2+, Cl-, SO42-, NO3- and NH4+ that are coming in air masses from the continental parts of Europe are significant, the total Wet Deposition (WD) is dominated by precipitation coming over Mediterranean due to abundances of precipitation from this segment.