| Study of precipitation chemistry is always one of the highlight and the hotspot of atmospheric wet deposition in China. Based on chemical composition of precipitation, evaluating precipitation pollution, studying translation and transportation of atmospheric pollutants, and analyzing harm to environment were carried out. Affected by human excessive use and natural conditions, the rainwater acidification in Beijing-Tianjin region is rapidly deteriorating in recent years. It specifically shows on the expanding acidification area and acid increasing rain frequency. Tianjin, located in the Bohai Bay,2-5m above sea level, effect by warm temperate continental monsoon climate. And it is the largest industrial city and one of the oil producing of North China. So, analysis of wet deposition chemical composition and its characteristics are very important for the study on sources of air pollution and transportation of atmospheric pollutants in northern China, and even the East Asia.To understand the ionic composition characteristics of wet deposition and the source of pollutants at Tianjin, the sampling points is collected in Jixian, Tianjin Normal University and Dagang from September2011to October2012. Twelve indexes for134collected samples were measured including pH value, electrical conductivity, the major water-soluble cation (Ca2+、Mg2+、NH4+、K+、Na+) and anion (SO42-、NO3-、Cl-、F-) and sulfur isotopes of SO42-. The relationship between the indexes and their sources were analyzed. The air-masses of precipitation were simulated by Hybrid Mix Particle Lagrangian Integrated hysplit model and classified. Finally, the analysis on the different air-masses of precipitation from different directions and routes impacted on the ionic composition of wet deposition was conducted.The results showed that the wet deposition in Tianjin was acidic. pH values ranged from3.55to7.41with an average of4.63. The frequency of acid wet deposition (pH<5.6) was21.9percent. The average pH value at central city was5.9, below6.2and6.1at Jixian and Dagang, respectively. The frequency of acid wet deposition at central city is26percent, higher than23.1and19.5at Jixian and Dagang. The average of electrical conductivity in Tianjin was126.5μs·cm-1, and at the central city, Jixian and Dagang was165.8μs·cm-1,112.4μs·cm-1and109.4μs·cm-1, respectively.Ca2+and NH4+, as the major cations, accounted for18and20percent of the total ion content. SO42-, Cl-and NO3-, as the major anions, respectively accounted for26,13and11percent of total ion. Mg2、K+、Na+、F-respectively accounted for4、3、4and1percent.[SO42-]/[NO3-] was equal to2.34, the type for air pollution was the mixture type of vitriol and nitric acid.[Ca2++NH4+]/[SO42-+NO3-] was equal to1.03, acidification tend to be serious city in northern China. According to enrichment factor analysis, K+, Ca2+and Mg2+the main source for the earth, the marine contribution rate was about3.6,3.6and1percent, respectively. Na+main source for ocean, its soil contribution rate was about23percent. Cl-ocean contribution rate was about40percent, its anthropogenic contribution rate was about58percent and its soil contributed less than2percent. Both of SO42-and NO3-ocean contribution and soil contribution rate no more than3percent, more than97percent of all were the source anthropogenic contribution.Average of δ34S value for sulfate wa s+4.6%o, and it has no obvious correlation between concentration and sampling points. δ34S values in Tianjin Xiqing were slightly lower than in Jixian and Dagang, and winter and spring slightly higher than summer and autumn. Air flow backward trajectory analysis showed that formation of acid rain in Tianjin was mainly affected by the rising air mass by CA/C, and the impact of air mass from Northeast and Northwest China was less. |
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