北京交通环境PM_(10)分布特征及重金属形态分析

Distribution Characteristics and Speciation of Heavy Metals in PM_(10) near Urban Roads and Surrounding Areas of Beijing

以北京市西三环航天桥地区为对象,研究了城市交通环境大气可吸入颗粒物浓度及主要化学组成随时间和粒径的分布特征.结果表明:该地区大气中ρ(PM10)冬季略高于春季,秋季次之,夏季最低;颗粒物中ρ(PM2.5)/ρ(PM10)和ρ(PM1.0)/ρ(PM10)平均值分别为82.6%和70.3%;ρ(PM10)与ρ(PM2.5)和ρ(PM10)与ρ(PM1.0)之间均有显著的相关性.PM10中金属元素浓度冬春季较高,夏秋季较低;Mg,Ca和Fe等地壳元素浓度随粒径的减小而降低,而Pb,Zn和Ni等重金属元素浓度总体上随粒径的减小而增加.颗粒物中的Cr和Ni主要以有机物结合态存在,Cu,Zn和Cd主要以酸可提取态存在,Pb主要以酸可提取态和氧化物结合态存在;颗粒物中所含Cd和Zn元素的生物有效性最高.PM10中水溶性ρ(SO42-)在夏季和冬季最高,秋季最低,而水溶性ρ(NO3-)全年变化不大;[0.43～2.1μm)粒径段颗粒物中的水溶性ρ(SO42-)及ρ(NO3-)较高,分别占PM10中水溶性ρ(SO42-)及ρ(NO3-)总量的68.3%及57.6%;ρ(NO3-)/ρ(SO42-)平均值为0.659.

Taking the region surrounding Hangtian bridge in the West Third Ring Road of Beijing as the study object,we investigated the distribution characteristics of PM mass concentration and major chemical composition according to season and particle size.The results showed that the concentrations of PM10 changed with season,descending in the following order： winter,spring,autumn and summer.The average values of PM2.5 PM10 and PM1.0 PM10（mass concentration ratio） were 82.6% and 70.3%,respectively.The mass concentrations of PM2.5 and PM10 as well as PM1.0 and PM10 showed significant correlations.Generally,the mass concentrations of heavy metals in PM10 were higher in winter and spring and lower in summer and autumn.As particle size diminished,the concentrations of lithosphere elements like Mg,Ca and Fe decreased,while heavy metal elements like Pb,Zn and Ni increased.In the PM10,Cr and Ni existed mainly in organic form,Cu,Zn and Cd existed mainly in acid extractable form,and Pb existed mainly in acid extractable form and oxide form.Furthermore,the bioavailability of Cd and Zn in the PM were highest.The mass concentrations of SO42-in the PM10 were highest in summer and winter and lowest in autumn.The mass concentrations of NO3-changed slightly in different seasons.There were higher mass concentrations of SO42-and NO3-in the 0.43-2.1 μm PM,accounting for 68.3% and 57.6% of those in the PM10,respectively.The average ratio value of the mass concentration of NO3-to SO42-was 0.659.