Ionic composition of six-year daily precipitation samples collected at JRC-Ispra (Italy) in relation to synoptic patterns and air mass origin

Abstract

A six-year dataset of daily precipitation samples collected and analyzed at the rural background station of Joint Research Center (JRC) at Ispra (Italy), was studied in conjunction with synoptic patterns and Concentration Weighted Trajectory (CWT) model in order to identify atmospheric mechanisms and transport pathways affecting the concentrations of eight major inorganic ions: NO3−, Cl−, Na+, Mg2+, Ca2+, SO42−, NH4+ and K+. A Principal Component Analysis (PCA) distributed the studied constituents to three categories reflecting major emission sources: a) Anthropogenic b) Sea salt and c) Crustal. The concentrations of all ions in precipitation samples were negatively correlated with precipitation amounts, however the negative correlations were more enhanced for species having a mainly anthropogenic origin (NO3−, SO42−, NH4+ and K+). The anthropogenic constituents were transported mainly from continental Europe, while the primary role of emissions in the industrialized Po Valley was highlighted from the impact of Eastern airflows on NO3−, SO42−, NH4+ and K+ levels. In addition, a secondary Saharan dust source for SO42− was verified. Sea salt species (Cl−, Na+ and Mg2+) were originated from the Mediterranean Sea, the North Sea, the Baltic Sea, and possibly from the Atlantic through France, while Saharan dust intrusions clearly enhanced the levels of crustal constituents (Ca2+ and Mg2+). The elaboration of a multi-year precipitation dataset for the first time with CWT model, provided new insights regarding the emission sources and transport mechanisms affecting the ionic composition of precipitation samples collected at JRC-Ispra.