甘肃省武威市大气降水特征及水汽来源

对2013年4月至2014年7月甘肃省武威市降水事件中常量离子进行测定，运用相关分析、富集因子分析、因子分析和HYSPLIT后向轨迹分析对常量离子的化学特征进行分析。结果表明：武威市降水pH值的变化范围为6.69～8.84，加权平均降水pH值为7.56；降水电导率的分布范围为33.9～1 011 μS·cm^-1，加权平均降水电导率为191.07 μS·cm^-1；降水中离子浓度SO₄^2- > Ca²⁺ > NO₃^- > Na⁺ > Cl^- > K⁺ > Mg²⁺ > NH₄⁺ > F^-。SO₄^2-、Ca²⁺、NO₃^-、Cl^-和Na⁺浓度占总离子浓度的92.14%；阴阳离子浓度随季节变化均表现出显著的波动，Na⁺、Ca²⁺、NH₄⁺均在春季出现最大值，K⁺、Mg²⁺、F^-、Cl^-、NO₃^-和SO₄^2-均在冬季出现最大值。人类活动产生的污染对武威市降水离子浓度有很大影响，特别是工农业生产以及人类活动排放SO₂、NO_x以及氯化物等污染物。据水汽通量、流线分布和后向轨迹将武威市的降水划分为西风源降水和混合源降水（受季风和西风共同影响）。

Precipitation Characteristics and the Water Vapor Source in Wuwei,Gansu, China

Precipitation samples were collected in Wuwei of Gansu from April 2013 to July 2014, and the major ions concentrations of the rainwater samples were measured, and the chemical characteristics of precipitation were analyzed using the correlation analysis, factor analysis, enrichment factor analysis and HYSPLIT trajectory analysis. The pH values of the precipitation were between 6.69 and 8.84, and its average value is 7.56. The electrical conductivity values of the precipitation was between 33.9 and 1 011 μs·cm^-1, and its average value is 191.07 μs·cm^-1. The order of the ion concentration in Wuwei was SO₄^2- > Ca²⁺ > NO₃^-> N a⁺ > Cl^- > K⁺ > Mg²⁺ > NH₄⁺ > F^-. Among them, SO₄^2-, Ca²⁺, NO₃^-, Cl^- and Na⁺ concentration accounted for 92.14% of the total ion concentration. The ion concentration changes with the seasons showed significant fluctuations, and the maximum values of Na⁺, Ca²⁺, NH₄⁺ all appeared in spring, and the maximum values of K⁺, Mg²⁺, F^-, Cl^-, NO₃^- and SO₄^2- all appeared in winter. The correlation analysis showed that pollution from human activity had a great influence on the ion concentration of the precipitation, especially emissions of pollutants such as SO₂, NO_x and chloride from industrial and agricultural production and other human activities. According to the distribution of water vapor flux and flow line and backward trajectory, sources of precipitation could be divided into two types:westerly wind source and mixed source (affected by the monsoon and westerly wind).