Major ionic composition of precipitation in the Shigatse region, Southern Tibetan Plateau

摘要

In order to investigate the chemical characteristics of precipitation on Tibetan Plateau, a total of 34 precipitation samples have been collected from individual precipitation events at the Shigatse Meteorological Station located in the south Tibetan Plateau in 2008. All samples were analyzed for major cations ((NH_4)~+, Na~+, K~+, Ca~(2+) and Mg~(2+)) and anions (Cl~-, (NO_3)~- and (SO_4)~(2-)), conductivity and pH. The result showed that precipitation pH values ranged from 6.79 to 9.21 with an average value of 7.86. (HCO_3)~- and Ca~(2+) were the major ions detected in the samples, occupied 39% and 35% of the total ion mass, 80% of the total anion mass and 69% of the total cations mass, respectively. Factor analysis indicated that regional crustal dust, lake salt and local combustion products of residents were the main sources of the ionic compositions of precipitation of Shigatse region. Trajectory cluster analysis indicated that 97.1% of the air masses reaching Shigatse originated from the south, which passed through some pollution regions, as southeast Indian, Bangladesh.