新疆春季两次沙尘暴过程中大气PM2.5元素组成特征分析

Characteristics of Elemental Compositions of Ambient PM2.5 during Sandstorm in Spring in Xinjiang

目的研究新疆沙尘天气发生频次最高的中心区和田市和沙尘天气发生频次较低的地区库尔勒市大气PM2.5表面和整体元素组成特征。方法于2008年4—5月对和田、库尔勒市的大气PM2.5进行同时段采样,分别用X射线光电子能谱(XPS)分析两城市大气PM2.5表面元素组成及价态特征,用X-射线荧光法(XRF)分析两城市大气PM2.5整体各元素的质量分数。结果和田大气PM2.5整体5种元素(Si、Al、Na、Ca、Mg)的质量分数超过1%,库尔勒大气PM2.5整体3种元素(Si、Al、Na)的质量分数超过1%,两城市大气PM2.5整体元素质量分数的差异均没有统计学意义;库尔勒市大气PM2.5表面Zn、S的质量分数较高,和田市大气PM2.5表面K、Al、Mg的质量分数较高,其差异有统计学意义(P<0.05)。在两城市大气PM2.5整体和表面都检测到的元素中,元素Fe、Mg、K在PM2.5表面发生了富集。沙尘天气发生时,大气PM2.5整体元素,除Si外,其他元素的质量分数均升高;大气PM2.5表面元素Na、Ca、K、Al、Mg、Fe的质量分数升高,脂肪族碳、和氮结合的碳、羰基碳、铵盐、硫酸盐、Cl的质量分数降低。结论和田大气PM2.5整体主要由5种元素(Si、Al、Na、Ca、Mg)组成,库尔勒大气PM2.5整体主要由3种元素(Si、Al、Na)组成。两城市大气PM2.5表面的主要元素相同,均为O、C、N、Si、Al、Mg。沙尘天气多发区和田市大气PM2.5整体和表面的自然源的元素质量分数较高;沙尘天气发生频次较低的库尔勒大气PM2.5整体和表面来自污染源的元素质量分数较高。沙尘天气时,大气PM2.5整体和表面的自然源元素质量分数升高;大气PM2.5表面污染元素(脂肪族碳、和氮结合的碳、羰基碳、铵盐、S、Cl)质量分数降低。

Objective To study the characteristics of bulk and surface elemental compositions of ambient PM2.5 collected in Hetian where sand-dust weather happened frequently and Kuerle as the control in southern Xinjiang.Methods From April to May 2008,ambient PM2.5 samples were collected in Hetian and Kuerle in the same period.X-ray photoelectron spectroscopy（XPS） was employed to analyze the surface components of PM2.5 and their valence states,while X-ray fluorescence（XRF） was applied to analyze the overall elemental compositions of the PM2.5 samples in those two cities.Results In PM2.5,the elements with mass fraction of higher than 1% were Si,Al,Na,Ca and Mg in Hetian and Si,Al and Na in Kuerle,respectively.There was no significant difference in the bulk elemental compositions of PM2.5 between the two cities.The mass fraction of Zn,S were higher in Kuerle and K,Al,Mg were higher in Hetian for the surface of PM2.5 during dust weather and the significant differences could be found statistically between the two cities.Elements Fe,Mg,K were found to be enriched on the surface of PM2.5 in the two cities.All elements except silicon increased on PM2.5 bulk with sandstorm weather;while on PM2.5 surface elements such as Na,Ca,K,Al,Mg,Fe increased;Aliphatic C,carbon combined with nitrogen,carbonyl carbon,ammonium,sulfate and Cl decreased.Conclusion In Hetian,the major elements on PM2.5 overall are Si,Al,Na,Ca,Mg;while in Kuerle are Si,Al,Na.The dominant elements on the surface of PM2.5 collected in the two cities are O,C,N,Si,Al,and Mg.In Hetian,the elemental compositions of PM2.5 are mainly from natural sources.While in Kuerrle area,they are mainly from anthropogenic sources.The elemental mass fraction of PM2.5 in natural resources may increase,however,the pollutants,e.g.aliphatic C,carbon combined with nitrogen,carbonyl carbon,ammonium,sulfate and Cl decrease with sandstorm weather.