基于Micro-PIXE能谱的大气单颗粒物污染源模式识别研究

来自不同排放源的大气气溶胶,其化学组成特别是微量元素组成具有各自的特征,在Micro-PIXE上呈现不同的特征峰。因此单个气溶胶颗粒物的Micro-PIXE能谱特征可作为其指纹,查找污染源。本文提出了适应于Micro-PIXE谱的模式识别算法,并对这种以Micro-PIXE能谱特征溯源的方法进行了可靠性检验。结果表明以此种方法进行源解析具有较高的可信度。相应的模式识别算法具有准确,快速的特点。     

气溶胶中钋-210的分析

采用α能谱示踪法进行了大气气溶胶中的210Po分析方法研究。气溶胶滤膜样品经剪碎后加入209Po示踪剂,在硝酸-硫酸-高氯酸体系中湿式消化,用0.5 mol/L盐酸反复浸取,在高温高速搅拌的水浴中置入银片自沉积,样品源银片在α能谱仪上测量。建立的分析测量方法,对于采样体积大于500m3的气溶胶样品,探测下限可达0.01 m Bq/m3,回收率接近95%。本方法经多项质量控制措施验证,现已在国家辐射监控点大气气溶胶测量和铀矿污染源监测项目中得到应用。     

PIXE和XRF用于北京新镇地区PM2.5源解析研究

大气颗粒物(APM)对人体健康和环境的影响越来越受重视,我国增设了PM2.5标准,同时提出了大气污染的专项治理措施。本文采用GENT二级取样器在北京郊区新镇进行连续取样,并用质子激发X射线荧光分析和能量色散X射线荧光分析对北京新镇地区收集到的140个大气颗粒物样品进行了多元素分析,对测量数据进行了可靠性评价和数据重组,结合取样、气象等参数建立了新镇地区大气颗粒物污染成分数据库,利用正矩阵因子模型进行污染源解析研究。初步认定了5个主要污染源,即燃煤源(29.2%)、汽车尾气和垃圾焚烧源(26.2%)、建筑工业源(23.3%)、土壤源(15.4%)以及含氯工业源(5.9%)。并结合气象数据进行了污染源来源研究,根据条件概率函数和潜在源贡献函数的计算结果作出了污染源来源分布图,发现污染来源与周围环境基本符合。     

核事故条件下的大气扩散模式及应用

本文介绍一个适用于核事故条件的大气扩散模式(粒子-烟团模式)的建立与调试。模式在模拟大气扩散的粒子随机游走方法中引入类似于扩散烟团的核函数概念，用以反映单个随机游走粒子所代表的污染物质的空间影响范围。模式解决了随机游走粒子与核函数“烟团”耦合后反映扩散物理真实过程的一致性问题，在约200km的范围内模拟结果与理论结果相一致。与代表实际大气典型扩散状况的高斯烟羽模式的结果进行定量比较，表明本模式结果在10km的范围内总体合理，但在近源处有系统偏小。模式瞬时浓度的涨落相对于平均轴线浓度大体控制在20％～30％的范围内。将模式应用于秦山地区的实际地形和气象条件进行实例测试表明，其结果可以反映当地复杂的大气扩散过程和特性。     

PIXE分析与统计处理相结合研究大气污染

采用分粒径采样器和步进式时间序列自动采样器分别在珠峰、戈壁沙漠边缘的张掖和北京等三个地点进行了大气气溶胶采样,用PIXE分析法进行了多元素浓度测定,然后对测定的数据进行了绝对主成分分析,并对这三个地区大气气溶胶的主要来源及其贡献率等进行了讨论。结果表明,PIXE分析技术具有灵敏度高、多元素同时分析能力强、分析速度快和对样品无破坏性等一系列优点。PIXE分析与统计处理相结合能有效地分析上面三个地区大气气溶胶的主要成分。对于都市地区大气气溶胶,绝对主成分分析能有效解出各主要成分,对于离污染源较远的洁净地区,绝对主成分分析能区分出当地的和从远地输送过来的成分。     

SF_6大气扩散示踪实验初步研究

一、引言 大气扩散示踪实验是直接模拟污染物的输送、扩散和沉降以测定大气扩散特征的方法。它对于验证和发展大气扩散理论、建立某特定地区大气污染予报模式都有重要的作用。 大气扩散示踪实验使用的示踪剂主要分气溶胶和气体两类。以往应用较多的是ZnS、ZnS(Cd)、荧光素钠和油雾等气溶胶示踪剂,也有少量采用二氧化硫以及氩-41、氪-85氙-133一类放射性示踪气体的。通过实验,人们发现上述示踪剂都存在一些不足之处。例如:气溶胶示踪剂因沉积、碰并和雨淋而损失,在离源70公里处CdS粒子已沉积损失     

反应堆热工水力中CATHARE与TRIO_U程序耦合分析研究

采用区域覆盖的耦合方法对一维系统程序CATHARE与三维计算流体力学(CFD)程序TRIO_U进行耦合分析研究,对文中建立的简易模型进行稳态计算,通过耦合前程序误差、耦合平台误差测试,确认解析解、系统程序计算结果、TRIO_U程序计算以及单个程序均与耦合平台耦合计算结果吻合.分别对3个不同的源项区域(热源、动量源、热交换区域)进行耦合计算,并与CATHARE计算结果进行比较.研究结果表明,耦合方法可以模拟算例中所建立的整个反应堆的简易模型.     

基于风洞实验的丘陵下垫面气溶胶大气扩散特性研究

核电厂正常运行或发生核事故时,会向大气释放一定量的放射性气溶胶,研究气溶胶在复杂下垫面的大气扩散特性对实现气载流出物辐射影响的准确评价具有重要意义。高斯烟羽或烟团模型被广泛用于大气扩散评价中,模型中的扩散参数描述了气溶胶受湍流作用扩散的强弱,需要针对不同的地形如平坦、丘陵下垫面进行校正。本文针对典型下垫面开展了气溶胶大气扩散风洞实验,采用激光粒子图像扩散参数估计方法,针对释放源高度不同的多组工况,统计分析了竖直截面内高分辨率的气溶胶浓度,根据高斯分布估计了下风向烟羽的上下边界及垂直方向扩散参数。结果表明：烟羽经过山体会出现整体抬升现象,这将导致山体后近地表浓度有所下降;烟羽经过山体前后出现浓度中心线两侧浓度分布不均现象,远离山体烟羽轨迹回归类高斯分布;释放源高度小于山体1/2高度的烟羽经过山体后轨迹趋于一致。高斯模型在丘陵下垫面适用度有限。     

~(14)C加速器质谱测量装置的研发与应用

正碳是大气颗粒物中的主要成分,为开展大气颗粒物中碳的来源研究需对颗粒物中的~(14)C进行分析测定以研究其来源。加速器质谱是测量~(14)C最有效的分析仪器,因此本工作的目的就是研发一种加速器质谱分析装置,通过对大气颗粒物中~(14)C的含量分析以实现大气颗粒物中碳元素的源解析。为使研发的装置更能满足大气颗粒物源解析的需求,研发的加速器质谱采用小型低能量的单极静电型加速器质谱装置。通过加速器质谱系统的物理设计和束流光学的优化计算,设计并建造     

用核分析技术研究上海市空气和水环境污染

用扫描质子微探针对上海市中心区和若干排放大气气溶胶单颗粒的质子激发X射线能谱进行了测量和形貌分析,然后用人工神经网络计算机识别技术追踪市中心区污染的来源,确定各排放源对它的贡献;用穆斯堡尔效应研究了市中心高架桥和隧道内含铁大气气溶胶颗粒的铁化学形态、尺寸和浓度,以及使用低本底放射性测量技术研究了苏州河水的α、β放射性强度。     

Size-resolved source apportionment of aerosol particles using polycapillary X-ray lens with a plateau in its focal spot

A laboratory micro X-ray fluorescence spectrometer based on a special polycapillary X-ray lens (PXRL) was used to carry out the source apportionment of aerosol particles. In the curve of the distribution of the X-ray intensity in the focal spot of the special PXRL, there was a plateau with a diameter of 21.3 μm in which the distribution of the X-ray intensity was homogeneous. The gain in flux density in the plateau of the PXRL is 1490. The uniformity of this plateau was 2.9%. This was helpful for the quantitative X-ray fluorescence analysis of a single aerosol particle with smaller size than that of the plateau of the PXRL. The fingerprint database of aerosol particles with given sizes from various air pollution sources was established with the single particle analysis method. The size-resolved source apportionment of aerosol particles in haze in Beijing city was performed with this fingerprint database.     

Aerosol composition and source apportionment in Santiago de Chile

Santiago de Chile, São Paulo and Mexico City are Latin American urban areas that suffer from heavy air pollution. In order to study air pollution in Santiago area, an aerosol source apportionment study was designed to measure ambient aerosol composition and size distribution for two downtown sampling sites in Santiago. The aerosol monitoring stations were operated in Gotuzo and Las Condes during July and August 1996. The study employed stacked filter units (SFU) for aerosol sampling, collecting fine mode aerosol (dp<2 μm) and coarse mode aerosol (210 mass of particles smaller than 10 μm) and black carbon concentration were also measured. Particle-Induced X-ray Emission (PIXE) was used to measure the concentration of 22 trace elements at levels below 0.5 ng m⁻³. Quantitative aerosol source apportionment was performed using Absolute Principal Factor Analysis (APFA). Very high aerosol concentrations were observed (up to 400 μg/m³ PM₁₀). The main aerosol particle sources in Santiago are resuspended soil dust and traffic emissions. Coarse particles account for 63% of PM₁₀ aerosol in Gotuzo and 53% in Las Condes. A major part of this component is resuspended soil dust. In the fine fraction, resuspended soil dust accounts for 15% of fine mass, and the aerosols associated with transportation activities account for a high 64% of the fine particle mass. Sulfate particle is an important component of the aerosol in Santiago, mainly originating from gas-to-particle conversion from SO₂. In the Gotuzo site, sulfates are the highest aerosol component, accounting for 64.5% of fine mass. Direct traffic emissions are generally mixed with resuspended soil dust. It is difficult to separate the two components, because the soil dust in downtown Santiago is contaminated with Pb, Br, Cl, and other heavy metals that are also tracers for traffic emissions. Residual oil combustion is observed, with the presence of V, S and Ni. An aerosol components from industrial emissions is also present, with the presence of several heavy metals such as Zn, Cu and others. A factor with molybdenum, arsenic, copper and sulfur was observed frequently, and it results from emissions of copper smelters.     

Analysis of atmospheric aerosols by PIXE: the importance of real time and complementary measurements

Particle-Induced X-ray Emission (PIXE) has been used for more than 30 yr in many urban and background air pollution studies. The technique has certainly contributed to the understanding of source-receptor relationship for aerosol particles as well as to aerosol physics and chemistry. In the last few years, where aerosol issues were strongly linked to global climate change through the relationship between aerosol and atmospheric radiation points to new challenges in atmospheric sciences, where PIXE could play an important role. Also the recognition for the inter-relationship between aerosol and liquid and gas phases in the atmosphere makes important to integrate PIXE aerosol analysis with other complementary measurements. The use of Nephelometers and Aethalometers to measure scattering and absorption of radiation by aerosol particles can be done in parallel with particle filter collection for PIXE analysis. Parallel measurements of trace gases using traditional monitors as well as with new techniques such as Differential Optical Absorption Spectroscopy (DOAS) that can provide concentration of O₃, SO₂, NO₃, NO₂, HCHO, HNO₃, Benzene, Toluene, and Xylene, is also important for both urban and remote aerosol studies. They provide information that allows a much richer interpretation of PIXE data. Recently developed instruments that provide real time aerosol data such as the Tapered Element Oscillating Microbalance (TEOM) PM₁₀ monitor and automatic real time organic and elemental carbon analyzers provide extremely useful data to complement PIXE aerosol analysis. The concentrations of trace elements measured by PIXE comprise only 10–30% of the aerosol mass, leaving the organic aerosol characterization and measurement with an important role. The aerosol source apportionment provided by PIXE analysis can be extended with other aerosol measurements such as scattering and absorption, estimating for example, the radiative impact of each discriminated aerosol source. The aerosol bulk PIXE measurements can be complemented with soluble concentrations provided by Ion Chromatography (IC) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). Recent developments in remote sensing techniques and products also enhance significantly regional aerosol studies. Three-dimensional air mass trajectories should be integrated in aerosol studies for urban and remote areas. The applications of these techniques to study urban aerosols from São Paulo and Santiago de Chile have broadened extensively the scientific scope of these studies.     

The new sample preparation line for radiocarbon measurements on atmospheric aerosol at LABEC

Radiocarbon measurements on the carbonaceous aerosol fractions have been demonstrated as an effective tool for aerosol source apportionment. For these measurements, a new sample preparation facility was installed at the INFN-LABEC laboratory of Florence (Italy). The line was designed to allow the preparation of samples from different carbonaceous fractions: the combustion of the aerosol samples can be performed in helium or oxygen flows, according to thermal sequences. The evolved CO₂ is cryogenically trapped and reduced to graphite, which is the target material for following Accelerator Mass Spectrometry (AMS) ¹⁴C measurements. This preparation line is described in detail in the paper. As a first step, the line was tested by means of AMS measurements performed on standards to check the reproducibility and the accuracy of the system; moreover, preliminary measurements on the total carbon fraction in aerosol samples were made. Results of these measurements are also reported.     

Identification of origin of single aerosol particles using polycapillary X-ray lens

A micro X-ray fluorescence (Micro-XRF) spectrometer based on a polycapillary focusing X-ray lens (PFXRL) and a laboratory X-ray source was designed to carry out the XRF analysis of single aerosol particles. The minimum detection limit (MDL) of this Micro-XRF spectrometer was 9 ppm for the Fe-Kα. The percentage of the particles of vehicle exhaust among aerosol particles was studied in Beijing, Chinese capital, during the test of odd-even driving restrictions for Beijing 2008 Olympics Games. This Micro-XRF spectrometer had potential applications in the analysis of single aerosol particles.     

一种用于SPM分析的大气气溶胶单颗粒样品的制备方法

介绍了一种用于扫描质子微探针分析的大气气溶胶单颗粒样品的制备方法。通过实验摸索出一种适合于支撑颗粒物的材料聚乙烯醇缩丁醛(PVB)。大气颗粒物被直接采集在PVB薄膜上从而制成样品,保持了颗粒物的原始信息。用显微镜观察了采集的颗粒物,颗粒物之间完全分开,颗粒物间距合适。样品的扫描质子微探针试验结果表明,所制成的单颗粒样品能经受住质子束的长久轰击。对PVB薄膜的本底测试表明,这种膜的本底很小,不会对被测颗粒物的元素产生干扰。     

球形容器核材料滞留量探测器小角度转动发射层析测量方法

核材料生产线上很多设备（如混合器、反应器）是球形结构，在生产过程中，内部会有核材料滞留。了解内部核材料滞留量，对核材料管理与衡算和核材料临界安全至关重要。本工作针对球形反应器内部核材料滞留量的测量，提出探测器小角度转动发射层析方法。认为球形容器内部的核材料近似球形分布，并按一定的方式将其分割为若干体素。探测器在有限小角度范围内转动，对球形容器进行分层扫描测量，获取投影数据。应用最小二乘法或最大似然法，对核材料分布进行重建计算。这样，不仅可给出较为准确的反应器内部核材料的总量，而且可给出核材料在内部的分布情况。采用蒙特卡罗模拟计算技术，对该方法进行了验证，证明该方法合理可行。     

核材料炸药化学爆炸条件下烟云源项的实验与仿真

为获取核材料化学爆炸事故烟云参数和气溶胶扩散规律，本文理论分析了核材料化学爆炸事故烟云扩散过程与机理，建立了基于CFD技术的烟云扩散数值仿真方法，并通过爆炸烟云外场扩散实验对该方法进行了验证。研究结果表明：CFD方法能实现烟云扩散的数值仿真；实验和仿真均显示小当量TNT爆炸高度远小于Church经验公式，宽度比例却增加；气溶胶颗粒在蘑菇云形态的双涡环烟云流场中分布不均匀，粒径大于50 μm的颗粒物大多位于烟柱中，而大部分可吸入颗粒物在烟云顶部聚集；气溶胶在烟云稳定前的驱散与沉降会改变其源项参数，以Operation Roller Coaster实验气溶胶积累质量分布为例的计算显示，空载释放率约为地面气化率的58%，可吸入比率由20%升高至31%，可吸入释放率约为18%。     

Identification and characterization of fine and coarse particulate matter sources in a middle-European urban environment

In this work a source apportionment study is presented which aimed to characterize the PM_2.5 and PM_2.5–10 sources in the urban area of Debrecen, East-Hungary by using streaker samples, IBA methods and positive matrix factorization (PMF) analysis.Samples of fine (PM_2.5) and coarse (PM_2.5–10) urban particulate matter were collected with 2 h time resolution in the frame of five sampling campaigns during 2007–2009 in different seasons in the downtown of Debrecen.Elemental concentrations from Al to Pb of over 1000 samples were obtained by particle induced X-ray emission (PIXE); concentrations of black carbon (BC) were determined with a smoke stain reflectometer. On this data base source apportionment was carried out by using the PMF method.Seven factors were identified for both size fractions, including soil dust, traffic, secondary aerosol – sulphates, domestic heating, oil combustion, agriculture and an unknown factor enriched with chlorine. Seasonal and daily variation of the different factors was studied as well as their dependence on meteorological parameters.Besides determining the time patterns characteristic to the city, several emission episodes were identified including a Saharan dust intrusion on 21st–24th May, 2008.     

SPM analysis on groups of single aerosol particles around steel plant

Several methods for preparing samples of dispersed single aeroslo particles used in scanning proton microprobe(SPM) analysis were tested.Many elements such as Al,Si,S,Cl,Ca,Ti,Cr,Mn,Fe,Ni,Cu and Zn in the groups of different single aerosol particles from the Capital Steel Plant area were analyzed by SPM,The distributions of elemental contents in the group of single particles were mapped with three dimensional contour and the isometric.A new approach to study the group of different single aerosol particles for air pollution is developed in the present work.The results are significant to assessing the environmental impact of the dispersed single aerosol particles.