Design and Performance Evaluation of Low‐Volume PM2.5 Inlet for Analyzing Chemical Composition

A new PM_2.5 inlet, based on the particle cup impactor configuration, was designed for sampling fine particles smaller than 2.5 μm in aerodynamic diameter and for operating at a flow rate of 5 l/min, as the devices, which are used to analyze the chemical composition of the particles, have good efficiency only at low‐volume flow rates. The performance of the inlet was evaluated in a test chamber, and the optimum dimensions of the particle cup impactor were determined by varying the nozzle‐to‐cup distance. Additional experiments covering flow rates between 3 and 10 l/min with particle sizes between 0.8 and 5.0 μm were carried out in the test chamber. The performance indicated that a nozzle‐to‐cup distance of 1.1 mm would yield a sharp size cutoff. The results from the tests showed that the inlet had a cutoff size of 2.55 μm in aerodynamic diameter at a flow rate of 5 l/min.     

Identification of aerosol particle sources in semi‐rural area of Kwabenya,near Accra,Ghana, by EDXRF techniques

Small aerosol particles have for a long time been known to be harmful to humans, and are today regarded to cause a larger number of deaths than traffic accidents globally. Energy dispersive x‐ray fluorescence (EDXRF) is a well known method that has been used for identification of toxic as well as non‐toxic elements in the particles. The combination of elements will together with other information help to identify the sources and predict the effects of particles on environment and human health. The present work was conducted in Kwabenya, a suburb of the capital Accra of Ghana, which is frequently exposed to Harmattan dust from the Sahara–Sahel region. In total 171 filters each of PM2.5 and PM(2.5–10) were collected during 1 year. Levels of elements, black carbon (BC) and mass, were determined for both particle sizes. Principal component analysis (PCA) was performed on the datasets from Harmattan and non‐Harmattan periods. The daily average of PM10 was very high, 179 µg m^?3 and the BC contents were 4 µg m^?3. The presence of crustal elements was large in PM(2.5–10) as well as in PM2.5, and had a more than tenfold increase in PM(2.5–10) during the Harmattan period. Major characteristic elements for different sources were identified from correlation coefficients and regression analysis of the data. Sahara sand aerosol was the major source in both study periods, but influence from biomass burning, sea‐spray and metal industries was also observed. Copyright © 2009 John Wiley & Sons, Ltd.     

Transient Response of Particle Distribution in a Chamber to Transient Particle Injection

We inject a large number of newly created nano‐particle aggregates into a chamber for the purpose of removing harmful contents in an indoor environment. This study is to experimentally and numerically investigate transient response of particle distributions to particle injections. A room‐sized chamber of 4 m × 2.1 m × 2.4 m is connected to a specially designed particle‐injection system, with two Optical Particle Counters used to simultaneously measure particle‐number densities with the size range from 0.3 μm to 10 μm at the inlet and in the chamber. A velocity probe measures the flow that is up to 1 m/s. An Euler‐type particulate‐phase‐transport model is developed and validated by comparing with experimental data. The study shows that the transient behavior of particle distributions is determined by many factors, including particle size, particle settling speed, sampling location, and velocity distribution. Particle number densities decrease in time more quickly for large particles than for small particles, and locations farther downstream in the chamber correlate more weakly with the inlet injection.     

利用PM10和PM2．5反演大气能见度

为了研究PM10和PM2.5与能见度的关系,提出了利用PM10和PM2.5来计算能见度的方法。该方法利用PM10和PM2.5与粒子谱分布的关系对能见度进行了计算。采用2004年8月在北京的测量数据对其进行了验证,证明了该方法是可行的。     

超声波空气污染物颗粒采样器的新结构及其特性研究*

超声波空气污染物颗粒采样器具有可采集低浓度颗粒污染物、采样速度快、重复性好、结构简单、易分析被采集物以及不破坏污染物成分等优点。为了进一步提高其采样效率,该文提出了一种超声波空气污染物颗粒采样器的新结构。该采样器由超声换能器、被粘接在换能器声辐射面上的圆形声辐射板以及与声辐射板平行的采样板组成。该采样器利用声辐射力和声学流场驱动空气中的污染物颗粒快速聚集到采样板上。样机测试表明,该结构在空气污染物颗粒初始浓度为4 mg/L以及辐射板中心位置的振动速度为0.29 m/s时,对烟雾中PM2.5和PM2.5-10颗粒的采样效率为16.3 mg/m~2·min·W。与不采用高阶弯曲振动圆形声辐射板的结构相比,其采样效率增加了110%。     

A Sampling Approach for Evaluating Particle Loss During Continuous Field Measurement of Particulate Matter

A method for evaluating sample bias in field measurements is presented. Experiments were performed in the field and laboratory to quantify the bias as a function of particle size for the scanning mobility particle sizer and the aerodynamic particle sizer. Sources of bias and sample loss considered in this work were sampling line loss, instrumental differences and inlet efficiencies. Measurement of the bias and sample loss allow for correction of the data acquired in the field, so as to obtain more representative samples of atmospheric concentrations. Substantial losses of fine and ultrafine particle count were observed, with sampling line losses ranging from 10–50 %, dependent on particle size. Only minor line losses were observed for coarse particles (approximately 5 %) because the sampling line was oriented vertically. Please note: corrected DOI, in print wrong DOI (10.1002/ppsc.200400939)     

Elemental characterization of airborne particles in Khartoum,Sudan

The aim of this study was to investigate the elemental composition of airborne particles in the Khartoum area, particularly small inhalable particles of diameter ≤10 µm. Aerosol particles were collected during the period April–May 2001. The sampling was done using a dichotomous virtual impactor capable of separating airborne particles <2.5 µm in a fine mode and 2.5–10 µm particles in a coarse mode. Energy‐dispersive x‐ray fluorescence analysis was used to determine the elemental concentrations of 14 elements in the samples. Concentrations of black carbon were also measured on the two size fractions. The results obtained were compared with previous data from Khartoum and other African locations. Si, K, Ca, Ti, Mn, Fe, Zn and Sr were found to be dominant in the collected particulates. Day period collections were found to have higher elemental concentrations than those of night periods. This is attributed to higher traffic levels and wind speeds. The results show that dust aerosol transport and resuspension are the main sources that affect the quality of ambient air in the Khartoum area. The elemental concentrations from anthropogenic sources are generally low. Copyright © 2004 John Wiley & Sons, Ltd.     

Inlet Efficiency Study for the TSI Aerodynamic Particle Sizer

The paper reports on the particle. sampling efficiency of the inlet system for the Aerodynamic Particle Sizer (TSI, Inc., St. Paul MN). Large particles are depleted from the sampled aerosol by two mechanisms: super-isokinetic sampling at the entrance of the inlet, and inertial impaction on the inner nozzle. A fluorometric technique was used to separately characterize these mechanisms. Numerical studies were also performed. The experimental results show that the inlet's overall efficiency drops from around 90% for 3 μm particles to less than 45% for particles larger than 10 gm. Several high efficiency inlets were developed and tested. These inlets provide higher sampling efficiencies, but reduce the instrument's sizing resolution. Measurements of 7.3 μm oleic acid particles with a high efficiency inlet showed a 5% spread in measured diameter at 50% count, while less than a 1076 spread was observed using the standard inlet. It was also found that the super-isokinetic condition reduces particle losses on the inner nozzle. The standard inlet is recommended for verifying test aerosol monodispersity. An alternative to the standard inlet is suggested for measurement of size distributions.     

乌鲁木齐市采暖期大气PM10及PM2.5中Cd的形态分析

2009年12月14日—28日采集了新疆农业大学校园PM10和PM2.5样品,分析了重金属Cd的形态和风险指数。该采样点在冬季采暖期间PM10及PM2.5污染非常严重,PM10和PM2.5中Cd的含量分别为3.642和1.964ng.m-3,均以残渣态为主,但PM2.5中Cd的生物有效性高于PM10中Cd的生物有效性。PM10中Cd的致癌风险为6.56×10-6,而PM2.5中Cd的致癌风险为3.46×10-6,均处于可接受的风险水平。     

温度场内可吸入颗粒物运动特性的实验研究

对温度场内可吸入颗粒物的运动特性进行了实验研究,使用PDA测量了场内可吸入颗粒物的速度和浓度分布等参数,研究了实验段入口速度和温度等操作参数对温度场内颗粒相运动特性的影响.结果表明,在近冷壁区边界层内,PM2.5的轴向速度和脉动速度变化很大,颗粒因热泳力及扩散作用会向冷壁面运动并产生沉积.在实验研究的基础上,提出了计算温度场内PM2.5沉积效率的经验公式.     

EDXRF and TXRF analysis of elemental size distributions and environmental mobility of airborne particles in the city of Riga,Latvia

Airborne particles were investigated in the central part of Riga during October 2000. Mass, black carbon and elemental concentrations of airborne particles were measured on Teflon filters from a dichotomous impactor, which samples fine (<2.5 µm) and coarse (2.5–10 µm) fractions of particles. In order to obtain more detailed information on the size distributions of different elements, a seven‐stage Batelle cascade impactor was used, in which quartz plates treated with silicone grease were utilized as backing for the different stages. Total reflection x‐ray fluorescence (TXRF) and energy‐dispersive x‐ray fluorescence (EDXRF) spectrometry were used for elemental analysis on the quartz plates and Teflon filters. The environmentally mobile part of the fine particle elements in the aerosol was determined by subtraction of x‐ray spectra measured before and after sequential leaching of the aerosol filters. The results of the different measurements show that naturally generated street dust and soil particles are dominant in coarse particles, whereas particles generated by human activities are dominant in the size fraction <0.5 µm. Copyright © 2004 John Wiley & Sons, Ltd.     

Estimation of surface area concentration of workplace incidental nanoparticles based on number and mass concentrations

Surface area was estimated by three different methods using number and/or mass concentrations obtained from either two or three instruments that are commonly used in the field. The estimated surface area concentrations were compared with reference surface area concentrations (SA_REF) calculated from the particle size distributions obtained from a scanning mobility particle sizer and an optical particle counter (OPC). The first estimation method (SA_PSD) used particle size distribution measured by a condensation particle counter (CPC) and an OPC. The second method (SA_INV1) used an inversion routine based on PM1.0, PM2.5, and number concentrations to reconstruct assumed lognormal size distributions by minimizing the difference between measurements and calculated values. The third method (SA_INV2) utilized a simpler inversion method that used PM1.0 and number concentrations to construct a lognormal size distribution with an assumed value of geometric standard deviation. All estimated surface area concentrations were calculated from the reconstructed size distributions. These methods were evaluated using particle measurements obtained in a restaurant, an aluminum die-casting factory, and a diesel engine laboratory. SA_PSD was 0.7–1.8 times higher and SA_INV1 and SA_INV2 were 2.2–8 times higher than SA_REF in the restaurant and diesel engine laboratory. In the die casting facility, all estimated surface area concentrations were lower than SA_REF. However, the estimated surface area concentration using all three methods had qualitatively similar exposure trends and rankings to those using SA_REF within a workplace. This study suggests that surface area concentration estimation based on particle size distribution (SA_PSD) is a more accurate and convenient method to estimate surface area concentrations than estimation methods using inversion routines and may be feasible to use for classifying exposure groups and identifying exposure trends.     

Ash cenosphere fragmentation during pulverised pyrite combustion: Importance of cooling

This paper as the first time in the field reports the direct experimental evidence for demonstrating the important role of cooling in ash cenosphere fragmentation using a simple but unique combustion system. The combustion system used pulverised pyrite (38–45 µm) for combustion in drop-tube furnace under designed conditions (gas temperature: 1000 °C; residence time: 1.2 s), which produced dominantly ash cenosphere particles or fragments. The combustion products were quenched under various cooling conditions (represented by nominal cooling rates of 6400–11,800 °C/s) for sampling. The results show that increasing cooling rate from 6400 to 11,800 °C/s substantially intensifies ash cenosphere fragmentation. Such enhanced ash cenosphere fragmentation leads to a significant shift in the particle size distribution of ash collected in the cyclone (>10 µm) to much smaller sizes. It also produces considerably more particulate matter (PM) with aerodynamic sizes less than 10 µm (i.e., PM₁₀) that consists of dominantly PM with aerodynamic sizes between 1 and 10 µm (i.e., PM_1–10) and some PM with aerodynamic sizes less than 1 µm (i.e., PM₁). It is further noted that the PM₁ is mainly PM with aerodynamic sizes between 0.1 and 1 µm (i.e., PM_0.1–1) and to a considerably lesser extent PM with aerodynamic sizes less than 0.1 µm (i.e., PM_0.1). Chemical analyses further show that both ash and PM samples contain only Fe₂O₃, indicating that complete consumption of sulphur and full oxidation of iron have been achieved during pulverised pyrite combustion under the conditions.     

波长色散X射线荧光光谱法快速测定大气PM_(2.5)中Cu和Zn的含量

介绍采用波长色散X射线荧光光谱法测定大气PM_(2.5)中Cu和Zn含量的分析方法。采用聚四氟乙烯滤膜来制备标准样品和进行大气颗粒物采样;对大气颗粒物样品的装样杯结构进行了讨论,采用6.7μm的Polypropylene膜配合改进样杯来封装大气颗粒物样品,应用改进后的样杯对大气颗粒物中Cu和Zn进行测定,可明显降低背景,改善峰背比,降低检出限;讨论了大气PM_(2.5)中目标元素Cu和Zn的测量条件,其分析线都采用Kα线,分光晶体选用PX10,采用间距300μm的准直器,ZnKα线探测选用闪烁计数器,CuKα线的探测利用流气式正比计数器和封闭式正比计数器串联使用,工作电压、电流采用50kV和50mA。应用制备的Cu和Zn标准样品建立工作曲线,实验结果表明,其线性相关性较好,准确度较高,Cu和Zn的相对标准偏差分别为2.43%和2.00%(n=8),检出限分别为0.028和0.021μg·cm~(-2),且分析大气颗粒物单个样品时间为60s。综上所述,该方法能够实现PM_(2.5)中Cu和Zn含量的快速、准确分析,为研究PM_(2.5)中的元素含量特征及来源解析提供科学依据。     

PM2.5气溶胶光学特性研究

利用FA-3型Anderson撞击式气溶胶粒度分布采样器采集大气中的可吸入颗粒物。在实验室使用光学测量系统对粒径低于PM2.5的气溶胶颗粒物进行透过率测量。结果表明,透过率随气溶胶粒子粒径的增大具有逐渐增加的趋势。粒径低于PM2.5的气溶胶颗粒与PM10粒径范围内的透过率相比,具有明显的波长选择性。     

Thin Film Solar Cell Based on ZnSnN2/SnO Heterojunction

In this article, we report the growth of zinc‐tin nitride (ZnSnN₂) thin films as a potential absorber for photovoltaic applications by fabricating a heterojunction of n‐ZnSnN₂/p‐SnO. The performance of the heterojunction has been monitored through selective deposition of top electrode with different materials (Ni/Au or Al). The electron‐transfer process from the ZnSnN₂ layer to the cathode is facilitated by selecting metal electrode with relatively low work function, which also boosts up the electron injection or/and extraction. The diode exhibits a good J–V response in the dark with a rectification ratio of 3 × 10³ at 1.0 V and an ideality factor of 4.2 in particular with Al as the top electrode. Under illumination, the heterostructure solar cell demonstrates a power conversion efficiency of ≈0.37% with an open circuit voltage of 0.25 V and a short circuit current density of 4.16 mA cm^?2. The prime strategies, on how to improve solar cell efficiency concerning band offsets and band alignment engineering are also discussed.     

ED‐XRF set‐up for size‐segregated aerosol samples analysis

The knowledge of size‐segregated elemental concentrations in atmospheric particulate matter (PM) gives a useful contribution to the complete chemical characterisation; this information can be obtained by sampling with multi‐stage cascade impactors. In this work, samples were collected using a low‐pressure 12‐stage Small Deposit Impactor and a 13‐stage rotating Micro Orifice Uniform Deposit Impactor^?. Both impactors collect the aerosol in an inhomogeneous geometry, which needs a special set‐up for X‐ray analysis. This work aims at setting up an energy dispersive X‐ray fluorescence (ED‐XRF) spectrometer to analyse quantitatively size‐segregated samples obtained by these impactors. The analysis of cascade impactor samples by ED‐XRF is not customary; therefore, as additional consistency test some samples were analysed also by particle‐induced X‐ray emission (PIXE), which is more frequently applied to size‐segregated samples characterised by small PM quantities. A very good agreement between ED‐XRF and PIXE results was obtained for all the detected elements in samples collected with both impactors. The good inter‐comparability proves that our methodology is reliable for analysing size‐segregated samples by ED‐XRF technique. The advantage of this approach is that ED‐XRF is cheaper, easier to use, and more widespread than PIXE, thus promoting an intensive use of multi‐stage impactors. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrostatic abatement of airborne respirable dust emission from mechanized tree-nut harvesting: Theoretical basis

The mechanized harvesting of tree nuts relies upon mechanically collecting and aerodynamically separating the nuts from extraneous vegetative and soil matter within the orchard using mobile power equipment. Typically the associated high-volume, high-velocity exhaust air disperses into the ambient atmosphere excessive concentrations of respirable-size particulate matter in the PM10 and PM2.5 micrometer realm creating a significant community air-quality problem. Our work developed a cyclonic-separation process for removing the PM10 dust and several candidate electrostatic-abatement processes for the smaller PM2.5 dust. We present the theoretical basis, including relevant mass- and charge-balances, for electrostatically abating the PM2.5 airborne dust via: (a) Ionized-field charging of the dust plume and its space-charge deposition within adjacent grounded tree-leaf canopies as air velocity subsides; (b) Injection of induction-charged spray of like polarity into the ion-charged-dust plume for space-charge-field enhancement; (c) Injection of charged spray alone into the dust plume; and (d) Injection of (+) polarity charged spray into the (?) polarity ionized-field-charged plume for electrostatic wet scrubbing of the dust. In addition to the theoretical basis, we report the technical development of a full-scale prototype to implement these electrostatic-abatement approaches on a mechanical harvester having ～10 g/s PM2.5 dust emission at ～27 m/s in an ～7 m³/s exhaust plume.     

亚微米颗粒湍流团聚特性的实验研究

燃煤电厂亚微米颗粒物排放是造成大气环境污染和影响人体健康的重要因素。本文搭建亚微米颗粒湍流团聚实验平台,通过场发射扫描电镜(FESEM)对亚微米颗粒的团聚形貌进行微观表征以及扫描电迁移率粒径谱仪(SMPS)对亚微米颗粒团聚前后的粒径分布特性进行宏观测量。结果表明:亚微米颗粒湍流团聚形成多分叉颗粒树聚团结构,进口流速为0.8?5.3m/s条件下,PM1和PM0.1的脱除效率分别为5.6%?18.6%和7.0%?21.4%,且PM1和PM0.1的脱除效率曲线随速度变化呈现二次函数规律。     

Graphene Quantum Dots from Polycyclic Aromatic Hydrocarbon for Bioimaging and Sensing of Fe3+ and Hydrogen Peroxide

An easy approach for large‐scale and low‐cost synthesis of photoluminescent (PL) graphene quantum dots (GQDs) based on the carbonization of commercially available polycyclic aromatic hydrocarbon (PAH) precursors with strong acid and followed by hydrothermal reduction with hydrazine hydrate is reported. Transmission electron microscopy (TEM) and atomic force microscopy (AFM) characterizations indicate that the size and height of GQDs are in the range of 5–10 nm and 0.5–2.5 nm, respectively. PAH, which has more benzene rings, generally forms GQDs with relatively larger size. The GQDs show high water solubility, tunable photoluminescence, low cytotoxicity, and good optical stability, which makes them promising fluorescent probes for cellular imaging. In addition, the fluorescence of GQDs shows a sensitive and selective quenching effect to Fe³⁺ with a detection limit of 5 × 10^?9m . By combination with the Fe²⁺/Fe³⁺ redox couple, the PL GQDs are able to detect oxidant, using H₂O₂ as an example. This study opens up new opportunities to make full use of GQDs because of their facile availability, cost‐effective productivity, and robust functionality.