Chemical characteristics of spring rainwater of Xi’an city, NW China

A comprehensive study on the chemical composition of spring rainwater was carried out in Xi’an, northwestern China. All samples were analyzed for pH, electrical conductivity and main ions (SO42−, NO3−, Cl−, F−, Ca2+, Mg2+, K+, Na+ and NH4+). The pH varied from 5.14 to 7.45, with a volume-weighted mean pH of 6.64. The volume-weighted mean equivalent concentration of rainwater components followed the order SO42− > Ca2+ > NH4+ > NO3− > Cl− > Mg2+ > Na+ > F− > K+. The dominant ions, SO42−, Ca2+, NH4+ and NO3−, accounted for 88% of the total ions. Significant positive correlation of SO42−, NO3− with Ca2+ and NH4+ and the calculated neutralization factors show that Ca2+ and NH4+ are the main neutralizing constituents. Sources of major ions were assessed based on the enrichment factor. Ca2+, K+ and Mg2+ mainly originated from crust, whereas SO42− and NO3− are mostly attributable to anthropogenic sources. The major likely source of NH4+ was agricultural activities.