Relationship between acidity and ionic composition of wet precipitation: A two years study at an urban site, Thessaloniki, Greece

Abstract

Wet precipitation samples were collected in the city center of Thessaloniki, northern Greece, for two years with different rainfall amount (April 2002–March 2004). All samples were analyzed for major anions and cations (Cl −, NO 3 −, SO 4 2−, NH 4 +, Na +, K +, Ca 2+ and Mg 2+). HCO 3 − concentrations were calculated through pH measurements. Arithmetic mean pH values of 6.06 and 6.57 were found for the two periods. 10.5% of the first year rain events (April 2002–March 2003) and 2.5% of the second (April 2003–March 2004) exhibited pH ≤ 4.5. The quite typical, for Mediterranean areas, trend Ca 2+ > SO 4 2− > NH 4 + > Cl − > NO 3 − was observed in the majority of the samples. The study of the relationship between the ionic concentrations and the precipitation amount gave information about the scavenging mechanism of ions (below or in-cloud). 67% of the rain acidity was found to be due to sulfuric acid and the rest 33% to nitric acid. The calculation of Neutralization Factors (NF) and the application of Multiple Linear Regression Analysis (MLR), showed the higher Ca 2+ contribution to the neutralization process. The impact of maritime sources was extracted from the SSF of Cl − and Mg 2+, while the anthropogenic origin of SO 4 2− was supported by the high NSSF (~ 98%). The local calcareous soil dust and possible long-range transport are the main sources of Ca 2+ in the area. A case study by using trajectory analysis to predict a long-range transport of pollutants from Etnean volcano, Italy, to the study area, is described.