摘要
基于 2009-2018 年采集的拉萨市 270 个降水样品,分析了降水的pH、电导率、水溶性离子浓度特征及变化趋势;应用相关性分析和主成分分析等溯源方法,探讨了降水中水溶性离子的潜在来源.结果表明:拉萨市降水年均 pH 变化范围为 7.34～7.87,平均值为 7.56,呈弱碱性;电导率变化范围为 1.24～5.64 mS/m,平均值为 3.91 mS/m,低于北京市、西安市等大部分城市.降水中水溶性离子平均浓度大小顺序为 Ca2+＞SO2-4＞Cl-＞K+＞Mg2+＞NO-3＞Na+＞NH4+＞F-.近年SO2-4、Cl-、NO-3 等阴离子浓度占比迅速升高的趋势需要格外警惕.来源分析表明:阴离子的来源较为一致,主要来自汽车尾气排放;阳离子 Ca2+和 Mg2+主要来自地表土壤和浮尘,它们对降水 pH起到了中和作用.
Abstract
In this study,we analyze 270 precipitation samples collected in Lhasa city over the past decade(2009-2018)to examine the characteristics and trends of pH,conductivity,and water-soluble ion concentrations in precipitation.By employing traceability methods such as correlation analysis and principal component analysis,we explore the potential sources of water-soluble ions in precipitation.The findings reveal that the annual average pH of precipitation in Lhasa ranges from 7.34 to 7.87,with a mean value of 7.56,indicating weak alkalinity.The conductivity variation ranges from 1.24 to 5.64 mS/m,with an average of 3.91 mS/m,which is lower than that of major cities like Beijing and Xi'an.The average concentration of water-soluble ions in precipitation follows the order:Ca2+＞SO2-4＞Cl-＞K+＞Mg2+＞NO-3＞Na+＞NH+4＞F-.Notably,the percentage of anion concentrations,including SO2-4、Cl-、NO-3,has shown a rapid increase in recent years,highlighting a concerning trend that warrants additional attention.Source analysis suggests that anions likely originate from vehicle emissions,exhibiting a more consistent source,while cations such as Ca2+and Mg2+primarily come from surface soil and floating dust,acting as neutralizers of precipitation pH.
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