北京市冬季大气细颗粒物中二■英的污染特征

Profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in atmospheric fine particulate matter of Beijing in winter

为了解北京市大气细颗粒物(PM2.5)中二噁英(PCDD/Fs)的污染特征,利用中流量大气颗粒物采样器,在北京市3个功能区5个采样点(两个市区点、两个工业区点和一个背景点),同步连续采集了大气细颗粒物PM2.5样品.参照US EPA 1613B标准方法,应用高分辨率气相色谱/高分辨率质谱(HRGC/HRMS),分析了PM2.5中17种PCDD/Fs的浓度水平和区域分布特征,并对PCDD/Fs的污染来源做了初步探讨.结果表明,5个采样点PM2.5的日均质量浓度范围102—146μg·m-3,平均日均值119μg·m-3,超出国家二级标准(75μg·m-3)59%,污染较重.在空间分布上,PM2.5的日均浓度表现为工业区大于背景点大于市区的特征.所有采样点17种PCDD/Fs的总浓度范围∑PCDD/Fs是1.60—4.09 pg·m-3,平均值3.23 pg·m-3,PCDD/Fs总毒性当量∑TEQ范围是140.54—275.69 fg I-TEQ·m-3,平均值233.18 fg I-TEQ·m-3.与国内外其他城市相比,北京市大气PM2.5中PCDD/Fs污染处于相当或略高水平.OCDD、OCDF和1,2,3,4,7,8-HpCDF是PCDD/Fs的主要组成成分,分别占总浓度∑PCDD/Fs的10%、19%和24%.对于总毒性当量∑TEQ贡献最大的是2,3,4,7,8-PeCDF,占总毒性当量的48.3%,∑PCDDs/∑PCDFs比值范围为0.19—0.23,平均值0.22,属于典型的'热源'特征.在浓度变化上, PCDDs呈现为随氯取代个数的增加而增加,除OCDF外, PCDFs的各单体浓度也随着取代氯原子个数的增加而增大.在区域分布上,PCDD/Fs浓度表现为工业区高于市区,市区大于背景点,充分体现了局地源的特点.采样期间工业热过程(化石燃料燃烧、电弧炉、烧结和冶炼等)、机动车排放和固体垃圾焚烧是北京冬季大气PM2.5中PCDD/Fs和PM2.5污染水平的主要影响因素.

Atmospheric PM2.5 samples were collected concurrently with middle-volume active sampler at five contrasting sites(two urban sites,two industrial sites,and a background site)to investigate the level and distribution of PCDD/Fs in air of Beijing.The concentrations and spatial distributions of 17 PCDD/F congeners were analyzed with isotope dilution high resolution gas chromatography/high resolution mass spectrometry(HRGS/HRMS)based on US EPA 1613 B method.The results showed that PM2.5 concentrations for different districts were in the range of 102—146μg·m-3 with mean value of 119μg·m-3,which was 59%higher than the second class daily average standards(75μg·m-3).The∑17PCDD/Fs concentrations ranged 1.60—4.09 pg·m-3 with an average concentration of 3.23 pg·m-3.The TEQs varied from 140.54 to 275.69 fg I-TEQ·m-3 with an average value of 233.18 fg I-TEQ·m-3.For individual PCDD/Fs,1,2,3,4,6,7,8-HpCDF showed higher concentrations than other congeners and accounted for 24%of∑17PCDD/Fs,followed by OCDF(19%)and OCDD(10%).The 2,3,4,7,8-PeCDF was the largest contributor to∑TEQ,which accounted for 48.3%of∑TEQ,the ratio of∑PCDDs/∑PCDFs varied from 0.19—0.23 with an average value of 0.22,which was classified as thermal source pollution profiles.Both the PCDDs and the PCDFs(except OCDF)concentrations increased with the increasing levels of chlorination.For spatial distribution,the highest PCDD/Fs concentration in PM2.5 was observed in industrial sites followed by urban sites and background site.The major factors affecting PM2.5 and PCDD/Fs levels were industrial thermal process,vehicle emissions and solid waste incinerators during sampling.