秦岭主峰太白山北麓降水化学特征分析

利用太白山北麓2011年12月-2013年7月共39次降水样品数据资料, 定量分析了该区域降水化学的特征和时间变化规律. 结果表明: 太白山北麓地区降水中, 除常量离子Na⁺、NH₄⁺、K⁺、Mg²⁺、Ca²⁺、F^-、Cl^-、SO₄^2-、NO₃^-外, CO₃^2-、HCO₃^-、PO₄^3-及低分子有机酸也占有相当比例. 研究区降水常量离子浓度的顺序依次为: NH₄⁺ > SO₄^2- > Ca²⁺ > NO₃^- > Na⁺ > Cl^- > Mg²⁺ > K⁺ > F^-, 离子总浓度表现出明显的季节变化: 夏季(轻度污染) < 秋季(中等污染) < 春季(严重污染) < 冬季(极重污染). 利用因子分析法得出太白山北麓地区降水组分主要有三种来源; Na⁺、Cl^-、Mg²⁺、Ca²⁺主要来自地壳源, SO₄^2-、NO₃^-、NH₄⁺主要来自人为源, K⁺和F^-主要由海盐源和人为源共同贡献. 根据Hysplit 后向气流轨迹分析, 得出不同路径气团降水离子组分不同: 受地形等因素影响, 北方路径的气团比南方路径气团离子总浓度较高; 受土壤类型影响, 西北方向气团降水Na⁺、Mg²⁺、Ca²⁺浓度较高; 受人为活动影响, 东北方向SO₄^2-、NO₃^-、NH₄⁺浓度较高.

Chemical characteristics of precipitation on the northern slope of the Mount Taibai,Qinling Mountains

In this paper, chemical characteristics and their temporal variation are analyzed using a set of data of 39 precipitation samples from the northern slope of the Taibai Mountain, the peak of the Qinling Mountains. The data duration is from December 2012 to July 2013. Results show that besides the normal ions of Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, F^-, Cl^-, SO₄^2- and NO₃^-, the composition of the precipitation there also contains a certain proportion of CO₃^2-, HCO₃^-, PO₄^3- and organic acids with low molecular weight. Ionic concentration in precipitation may be ranked as NH₄⁺ > SO₄^2- > Ca²⁺ > NO₃^- > Na⁺ > Cl^- > Mg²⁺ > K⁺ > F^-. The total ionic concentration shows seasonal difference significantly, ranking as summer (light pollution) < autumn (moderate pollution) < spring (serious pollution) < winter (heavy pollution). Three sources of precipitation are demonstrated by the chemical composition analyses. They are respectively the crust source (Na⁺, Cl^-, Mg²⁺ and Ca²⁺), the anthropogenic source (SO₄^2-, NO₃^- and NH₄⁺) and the sea-salt source (mainly K⁺ and F^-), of which K⁺ partly may come from the crust source and biomass combustion. It is found that the precipitation ionic components are different under different atmospheric transmission paths. Partly due to the landform effects, the total ionic concentration is higher in the air mass from north than that from south. Mainly depending on soil type, concentrations of Na⁺, Mg²⁺ and Ca²⁺ are higher in precipitation of northwest airflow than that of southeast airflow. Due to different intensities of human activities, concentrations of SO₄^2-, NO₃^- and NH₄⁺ are higher in northeast airflow than that in northwest air mass.