Chemical Composition And Air Trajectory Analysis Of Atmospheric Pollutants From Precipitation Samples In Addis Ababa

Atmospheric deposition has been recognized as a serious environmental problem in many parts of the world. Countries are striving for corrective measures based on research outputs to minimize human health and ecological problems related to atmospheric deposition. This study tries to present the chemical composition of 22 precipitation samples collected between March and June 2007 at AAU Science campus.rnThe major cations and anions of the rainwater samples were analyzed using DX-600 Ion Chromatography and Buck scientific 210 VGP Flame Atomic Absorption Spectrophotometer. Conductivity and pH measurements carried out immediately after sample collection have showed ranges of variation between 14.00 μScm-1and 58.43 μScm-1, and 6.28 and 7.44 with mean values of 27.36 μScm-1 and 6.99 for the respective parameters. 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 μeqL-1 have been detected for the ionic species of N-NH4+, HCO3-, S-SO42-, Ca2, N-NO3-, Na +, Cl-, Mg2+, and K+ respectively. Analytical results of the flame atomic absorption spectrophotometer for lead concentrations have also revealed the presence of lead in 5 samples above the detection limit of the instrument (>0.1 mg/L).rnThe dominant abundance of NH4+, and Ca2+ from agricultural activities including livestock breeding and soil dust dictate the neutral to alkaline character of the rain water samples. Hence, the majority of the hydrogen ions (acids) generated in the atmosphere from the oxidation of SO2 and nitrogen oxides (NOx) are primarily neutralized by ammonia (NFNH4+=0.78) followed by calcium (NF Ca2+ = 0.60). 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. From the trajectory analysis, calm weather conditions over the city are also observed to stagnate and favour the accumulation of SO2 which in turn proves the presence of significant SO2 emissions from vehicles and industries in the city. Finally, the need for ecological impact assessment regarding the excessive ammonium and calcium deposition has become evident from the analytical results.rnKey words:rnWet deposition, ionic species, precipitation, Trajectory, Addis Ababa

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