The chemical compositions (Na + , NH 4 −) of wet precipitation and nitrogen isotope compositions δ 15 N(NH 4 +) 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, HCO 3 − , NO 3 − , NO 2 − , NH 4 + and SO 4 2−), mainly controlling rainwater mineralization; 2) F2 (26 %) observed during vegetative and heating seasons (K + , Ca 2+ and Mg 2+), 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 δ 15 N(NH 4 +) from −11.5 to 18.5‰ identify three main pathways for the formation of NH 4 + : 1) equilibrium fractionation between NH 3 and NH 4 + ; 2) kinetic exchange between NH 3 and NH 4 + ; 3) NH 4 + exchange between atmospheric salts particles and precipitation. The coupled chemical/statistical analysis and δ 15 N(NH 4 +) approach shows that while fossil fuels burning is the main source of NH 4 + in precipitation during the heating season, during the vegetative season NH 4 + originates from local sewage irrigation fields in Osobowice or agricultural fertilizers.