北京市城区两个典型站点PM2.5浓度和元素组成差异研究

采用rp TEOM^® 1400a颗粒物测定系统,于2008年1月到2010年12月,对北京城市生态系统研究站和北京教学植物园周边大气中细颗粒物(PM_2.5)的浓度进行了连续监测.2010年,利用rp TEOM1400系统的旁路采样器同步采集PM_2.5样品,经微波消解后采用ICP-MS和ICP-OES方法测定样品中的Al、As、Ca、Cd、Co、Cr、Cu、Fe、K、Mg、Mn、Na、Ni、Pb、Se、V、Zn等17种元素的浓度.结果表明,2008年1月至2009年3月,北京城市生态系统研究站的PM_2.5平均浓度为59.1 μg·m^-3,比北京教学植物园低36%.2009年4月至2010年12月,北京城市生态系统研究站的PM_2.5平均浓度为95.5 μg·m^-3,比北京教学植物园高60%.施工工地的土方作业可能对两站点PM_2.5浓度的差异有重要贡献.地壳元素Al、Fe、Mg、K、Ca、Na浓度在两站点的差异最大.北京城市生态系统研究站其余污染元素的富集因子一般也高于北京教学植物园,尤其是Pb、As元素,可能与被污染土壤和建筑物等的二次污染有关.两站点的PM_2.5污染状况均在建筑施工期较严重,来自地表和建筑工地的扬尘可能是造成PM_2.5污染严重的主要原因.

Comparison of PM2.5 concentrations and elemental compositions in two typical sites in Beijing urban area

From January 2008 to December 2010,the fine particulate matter(PM2.5) concentrations in Beijing Urban Ecosystem Research Station(UERS) and Beijing Teaching Botanical Garden(TBG) were continuously monitored with rp TEOM1400a particulate measurement system.PM2.5 samples were also collected by rp TEOM1400 bypass sampler at both sites in 2010.With microwave digestion of the samples,we measured the concentrations of seventeen elements(i.e.Al、As、Ca、Cd、Co、Cr、Cu、Fe、K、Mg、Mn、Na、Ni、Pb、Se、V and Zn) by ICP-MS and ICP-OES and analyzed the elemental composition of PM2.5.The results showed that,from January 2008 to March 2009,the average mass concentration of PM2.5 in UERS site was 59.1 μg·m-3,which was 36% lower than that in TBG.However,from March 2009 to December 2010,the average mass concentration of PM2.5 in UERS was 95.5 μg·m-3,which was 60% higher than that in TBG.Earthwork construction might be a major contribution to the large differences of PM2.5 mass concentrations between the two sites and the distinct patterns in the two periods.In 2010,the differences of Al,Fe,Mg,K,Ca and Na concentrations of the PM2.5 samples between the two sites were the largest.The enrichment factors of the other elements in UERS were generally higher that in TBG,especially for Pb and As,which might be related to secondary pollution of contaminated soil and buildings near UERS.The PM2.5 pollution in the site with construction nearby was more serious than the other.Dust from the surface and construction sites may be the main reason for the serious PM2.5 pollution in the two sites.