title: Chemical composition, sources, and deposition fluxes of water-soluble inorganic ions obtained from precipitation chemistry measurements collected at an urban site in northwest China.
abstract: Precipitation samples were collected at an urban site in Xi'an, northwest China during March to November in 2009 and were then analyzed to determine the pH and concentrations of water-soluble inorganic ions (Na(+), NH(4)(+), K(+), Mg(2+), Ca(2+), SO(4)(2-), NO(3)(-), Cl(-), and F(-)) in precipitation. The pH of precipitation ranged from 4.1 to 7.6 for all of the samples with an annual volume-weighted mean of 6.4. While a large portion of the precipitation events were weakly acidic or alkaline, around 30% of the precipitation events in the autumn were strongly acidic. Precipitation events with air masses from the northeast and the southeast were weakly acidic while those with air masses from the northwest and the southwest were alkaline. SO(4)(2-), Ca(2+), NH(4)(+), and NO(3)(-) were dominant ions in the precipitation, accounting for 37%, 25%, 18%, and 9%, respectively, of the total analyzed ions. Ca(2+) and NH(4)(+) were found to be the major neutralizers of precipitation acidity; however, the contribution of Mg(2+), although much lower than those of Ca(2+) and NH(4)(+), was important, in many cases, in changing the precipitation from weakly acidic to weakly alkaline. Enrichment factor analysis confirmed that SO(4)(2-) and NO(3)(-) were produced from anthropogenic sources, Ca(2+), K(+), and 80% Mg(2+) were from crustal sources, and Na(+), Cl(-), and ∼20% of Mg(2+) were from marine sources. The annual wet depositions were estimated to be 3.5 t km(-2) per year for sulfur; 2.3 t km(-2) per year for nitrogen, of which 0.8 t km(-2) per year was oxidized nitrogen and 1.5 t km(-2) per year was reduced nitrogen; and 3.0 t km(-2) per year for Ca(2+).
authors.affiliation: Department of Environmental Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China. zxshen@mail.xjtu.edu.cn
authors.forename: Zhenxing
authors.initials: Z
authors.lastname: Shen
authors.forename: Leiming
authors.initials: L
authors.lastname: Zhang
authors.forename: Junji
authors.initials: J
authors.lastname: Cao
authors.forename: Jing
authors.initials: J
authors.lastname: Tian
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.forename: Geihui
authors.initials: G
authors.lastname: Wang
authors.forename: Zhuzi
authors.initials: Z
authors.lastname: Zhao
authors.forename: Xin
authors.initials: X
authors.lastname: Wang
authors.forename: Renjian
authors.initials: R
authors.lastname: Zhang
authors.forename: Suixin
authors.initials: S
authors.lastname: Liu
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D000397:Air Pollution / Q000706:statistics & numerical data; D002681:China; D002947:Cities; D004784:Environmental Monitoring; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000032:analysis; D011891:Rain / Q000737:chemistry*; D012621:Seasons; D012995:Solubility
chemical_list: D000393:Air Pollutants; D007477:Ions