| This paper was based on the chemical characteristic of atmospheric precipitation in Xi’an and Yan’an from September,2011to October,2012and July,2011to August,2012respectively. The variation characteristic of pH and conductivity were analyzed and the concentrations temporal distribution and of ions were studied by using Ion Chromatograph. The chemical characteristics of ions in atmospheric precipitation were analyzed and assessed through the value of ionic equilibrium, fractional acidity, neutralization factor and wet deposition fluxes. The main conclusion of this study were as follows:(1) The results of the value of pH in precipitation in Xi’an and Yan’an showed that the value of pH ranged from3.58to9.08and4.72to5.70, and the mean were5.65å'Œ5.33, respectively, which showed that the acidity of Yan’an was higher than Xi’an. The monthly variation of pH in Xi’an and Yan’an were that the highest value in October and September,2011were7.1and5.78, respectively and the lowest value in December and August,2011were3.79and4.72, respectively. The daily variation of pH in precipitation in Xi’an was in the shape of "W" in September,2011and the fluctuation was not so apparent in Yan’an in November,2011. The monthly variation of conductivity of precipitation in Xi’an were apparent and the mean value of conductivity was higher than its of Yan’an.(2) The monthly variation of concentrations of ions in precipitation in Xi’an and Yan’an showed that the variation trend of ions in Xi’an was similar to its in Yan’an. The concentrations of F-, CI-, Mg2+and Na+were very low and the variation trend was not significant. The variation range of was small of NO3-and large of SO42-in precipitation in Xi’an the highest values were in April,2012and the heating period, respectively. The highest value of K+, NH4+and Ca2+in Xi’an were all in April,2012. The concentrations of NO3-and SO42+were relatively high in Yan’an and the highest value were in November,2011. The variation of concentrations of K+and Ca2+in Yan’an were relative apparent and the highest value were in April,2012.(3) The seasonal variation of ions in precipitation in Xi’an showed that the variation of concentrations of F-, Cl-and SO4-were winter>autumn>spring>summer, and the NO3-was spring> autumn> winter> summer. The concentrations of cations in spring were higher than other seasons except NH4+. The seasonal variation of ions in precipitation in Yan’an showed that the concentrations of anions in summer were lower than other seasons except F". The variation trend of Na+was that the spring and autumn were higher than summer, which was consistent with NH4+. The variation of K+, Mg2+and Ca2+were in reduction gradually from spring and autumn.(4) The. correlation of NO3-and SO42+, Ca2+and Mg2+in precipitation in Xi’an and Yan’an were relative high, respectively which showed that the source of these ions was similar. The Ca(NO3)2, CaSO4and Ca(Cl)2mainly existed in precipitation in Xi’an because of the high correlations between NO3+and Ca2+, SO42+and Ca2+, Ca2+and Cl-. The Mg(Cl)2and CaSO4mainly existed in precipitation in Yan’an because of the high correlations between Cl-and Mg2+, Ca2+and SO42-.(5) The values of ionic equilibrium are all below1and the value in Xi’an was lower than its in Yan’an, which shows that some unknown ions were not be detected in samples. The annual mean values of SO42-/NO3-in precipitation in Xi’an and Yan’an were1.86and1.57, respectively and the types of acid rain were all mixed type. The neutralizing effect of Ca2+and NH4+to H+in precipitation in Xi’an was significant. The neutralization factors of cations in Yan’an were in a complicated and large variation except Mg2+(6) The wet deposition fluxes of SO42-was the highest and Ca2+was second in Yan’an, the mean value of them were233.91g/m2and109.12g/m2; The variation trend of wet deposition fluxes of NO3-was similar to SO42-, with the mean value98.26g/m2; The variation trend of wet deposition fluxes of NH4+-N and was the same to total N and they have a good correlation. The contribution of NH4+to total N was higher than in the wet deposition fluxes of nitrogen. |
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