Chemical Characteristics and Trends of Atmospheric Precipitation in Lhasa from 2009 to 2018
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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