Chemical and isotopic interpretation of major ion compositions from precipitation: A one-year temporal monitoring study in Wrocław, SW Poland

Abstract

The chemical compositions (Na+, NH4+, K+, Mg2+, Ca2+, Cl−, NO2−, NO3−, SO42−, HCO3−) of wet precipitation and nitrogen isotope compositions δ15N(NH4+) were studied from January to December 2010 in Wrocław (SW Poland). Results of a principle component analysis show that 82% of the data variability can be explained by three main factors: 1) F1 (40%) observed during vegetative season (electrical conductivity, HCO3−, NO3−, NO2−, NH4+ and SO42−), mainly controlling rainwater mineralization; 2) F2 (26%) observed during vegetative and heating seasons (K+, Ca2+ and Mg2+), probably representing a combination of two processes: anthropogenic dusts and fertilizers application in agricultural fields, and 3) F3 (16%) reported mainly during heating season (Na+ and Cl−) probably indicating the influence of marine aerosols. Variations of δ15N(NH4+) from -11.5 to 18.5‰ identify three main pathways for the formation of NH4+: 1) equilibrium fractionation between NH3 and NH4+; 2) kinetic exchange between NH3 and NH4+; 3) NH4+ exchange between atmospheric salts particles and precipitation. The coupled chemical/statistical analysis and δ15N(NH4+) approach shows that while fossil fuels burning is the main source of NH4+ in precipitation during the heating season, during the vegetative season NH4+ originates from local sewage irrigation fields in Osobowice or agricultural fertilizers.