若尔盖高原土壤和近地表大气气溶胶铅同位素组成测试及示踪研究

摘要

若尔盖高原牧场处于中国偏远洁净高海拔地区,大气沉降是污染物主要来源途径之一.由于季风的影响,污染源的辨析较为困难.本文通过多点大气气溶胶不同季节同时采样方式,利用热电离固体同位素质谱仪可有效校正质谱分析中同位素分馏效应的优点,对若尔盖地区土壤和大气气溶胶的铅同位素比值进行精确分析,并结合季风特征对该地区污染物的来源进行解析.结果表明:土壤的208 pb/204 Pb比值变化范围为38.79059±0.00194 ～ 38.94461 ±0.00135,206pb/207 Pb为1.18551±0.00002 ～1.19362±0.00002;大气气溶胶的208 pb/204 Pb比值变化范围为37.49571±0.00117 ～38.48980±0.00105,206 pb/207 Pb为1.12894±0.00001～1.16734±0.00001.该地区土壤铅同位素的特征是放射成因铅高,来自于自身天然存在的岩石矿物,与大气污染关系不大;大气气溶胶的铅同位素组成与土壤差异较大,显示为多元混合模式,受到了天然物质和人类活动来源的混合影响,机动车尾气及来自北部(兰州)和西北部(青海、新疆、哈萨克斯坦、俄罗斯)的大气远程运移是若尔盖大气气溶胶及污染物质的主要来源.%The Ruoergai highland pasture is located in the remote,high altitude area of China.Atmospheric transport and precipitation is one of the major routes of pollutants to this area,but pollution source identification is difficult due to the monsoon.Atmospheric aerosol samples were taken in different seasons at multiple sites in Ruoergai.High precision Pb isotope analysis for soils and atmospheric aerosols was performed by using Thermal Ionization Mass Spectrometry (TIMS),which has the advantage of effectively removing the isotope fractionation effect in mass analysis.The sources of the aerosols were analyzed in association with the characteristics of the monsoon.The range of 208pb/204 Pb ratio is 38.79059 ± 0.00194-38.94461 ± 0.00135 and 206pb/207 Pb 1.18551 ±0.00002-1.19362 ±0.00002,208 pb/204 Pb in the atmospheric aerosol is 37.49571 ± 0.00117-38.48980 0.00105 and 206pb/207pb 1.12894 ± 0.00001-1.16734 ± 0.00001.The Pb isotopic composition of soil in Ruoergai is characterized by high radiogenic Pb,mainly from local rock and minerals.The Pb isotopic composition of aerosols differs from that of soil,showing a multiple mode of mixing of natural and anthropogenic sources.Automobile exhaust gas and long-range atmospheric transport mainly from the north (Lanzou) and northwest (Qinghai,Xinjiang,Kazakhstan and Russia) are possible sources of aerosols and pollutants.