天津市大气降水化学组分变化趋势及来源研究

Trend and sources of chemical composition of atmospheric precipitation in Tianjin

2001—2013年对天津市降水样品进行了采集,分析了p H、电导率(EC)、主要离子浓度(SO2-4、NO-3、Cl-、F-、NH+4、Ca2+、Mg2+、Na+、K+).结果表明:2001—2013年,降水的雨量加权平均p H、EC分别为5.48、87μS·cm-1.降雨的p H、EC及总离子当量浓度呈现上升趋势,酸雨频率呈现下降趋势.降水中各离子雨量加权平均当量浓度排列顺序为:SO2-4>Ca2+>NH+4>NO-3>Cl->Mg2+>Na+>F->K+,SO2-4、Ca2+、NH+4和NO-3是降水中的主要离子,占离子总量的84.8%.SO2-4雨量加权平均当量浓度表现为先轻微上升,后显著下降趋势.NO-3、Ca2+雨量加权平均当量浓度表现为明显上升趋势.NH+4雨量加权平均当量浓度显示为下降趋势.F-、Cl-、K+、Mg2+、Na+等雨量加权平均当量浓度变化趋势基本保持平稳.SO2-4对总阴离子的分担率、NH+4总阳离子的分担率均呈现下降趋势.NO-3对总阴离子的分担率、Ca2+对总阳离子的分担率均呈现明显上升趋势.[NO-3]/[SO2-4]、[Ca2+]/[NH+4]呈现出明显上升趋势.富集因子计算结果表明:Ca2+主要来自地壳.Mg2+和K+部分来自海源输入,但绝大部分来自地壳.大部分Cl-来自海源的输入,其余小部分来自地壳和人为排放.降水中SO2-4、NO-3主要来自人为活动.

Precipitation samples were collected from 2001 to 2013 in Tianjin ionic （ SO＋-, NO＋, CI-, F-, Ca2＋, NH＋, Mg2＋, Na＋ and K＋ ） concentrations All the samples were analyzed for pH, electrical conductivity（ EC ）and main Average annual volume-weighted mean pH and EC during 2001-2013 were 5.48 and 87 μS· cm-1 , respectively. Increasing trends were found for pH, EC and total ionic concentrations, while decreasing trend for frequency of acid in precipitation. The volume-weighted mean equivalent concentration of precipitation components followed the order SOl-〉Ca2＋ 〉NH＋ 〉NO＋ 〉C1-〉Mg2＋ 〉 Na＋〉F-〉K＋. SO24-, Ca2＋, NH] and NO＋ were the dominant compositions in percipitation, accounting for 84.8% of the total ions. A trend of SO24 increased slightly followed by significant decrease. Significant increasing trends for NO＋, Ca2＋ and decreasing trend for NH＋ were observed, while F-, CI-, K＋ , Mg2＋ and Na＋ levels remained relatively stable. Decreasing trend was found for contributions of [ SOl- ] to total anion mass and [ NH＋ ] to total cation mass. significant increasing trends were found for contributions of [ NO3 ] to total anion mass and [ Ca2＋ ] to total cation mass. The ratios of [ NO＋ ]/[ SOl- ] and [ Caz＋ 1/[ NH＋ ] showed i ing trends. Enrichment factor was used to assess sources of major ions. Ca2＋ was mainly originated from crust source. Mg2＋ and K＋ were partly from the marine source while the contribution of the soil source was considerable. CI- mainly came from marine source, with small parts from anthropogenic sources. SOl-and NO＋ were mostly attributable to anthropogenic sources.