This study which is conducted on “Chemical Composition and Air trajectory Analysis of Atmospheric pollutants from precipitation Samples in Addis Ababa –Ethiopia” attempts to provide preliminary facts on the status of air pollution and the possible sources of the major pollutants in Addis - the capital city of Ethiopia. Modern scientific equipments DX-600 - Ion Chromatography and Buck Scientific 210 VGP Flame Atomic Absorption Spectrophotometer were used for the analysis of the precipitation samples. Volume weighted mean concentrations of 65.55, 57.04, 54.58, 50.50, 29.16, 11.66, 9.94, 5.53, 1.41, and 0.15 ?eqL-1 have been detected for the ionic species of N-NH4+, HCO3-, S-SO42-, Ca2, N-NO3-, Na +, Cl-, Mg2+, and K+ respectively. Forty eight hours back trajectory analysis performed for the rain events corresponding to peak sulphate and ammonium concentrations have revealed the advection of SO2 from the active volcanic center at Erta'' Ale (13.60° N, 40.67°E; summit elev. 613 m) in the rift valley of Northern Ethiopia. This book can therefore serve researchers working on environmental pollution, industrialists, environmental protection and monitoring activists.