Measuring Particulate Mass Emissions with the Electrical Low Pressure Impactor

The electrical low pressure impactor (ELPI) is a useful tool for recording transient particle size distributions, such as in motor vehicle emissions. But for sub-micron aerosols, the straightforward mass weighting and integration of these size distributions overestimates the particulate matter (PM) mass by a factor of two or more. The present article examines the sources of this discrepancy and develops an analysis that allows quantitative PM mass measurement with an accuracy of about 20%. This procedure is applied to measure motor vehicle PM emissions, and the results are compared with filter-based gravimetric determinations. Good agreement is achieved for diesel and direct injection gasoline vehicles. For particulate trap equipped diesel vehicles and conventional gasoline vehicles, the PM mass recorded by the ELPI is often substantially lower than the filter based mass owing to the gaseous adsorption artifact of the latter. Accurate work at very low emissions levels, less than ～ 1 mg/mi, requires further study of how reliably the ELPI can provide semivolatile nanoparticle mass as well as an improved understanding of filter-based vehicle exhaust measurement.     

Size Characterization of Carbonaceous Particles Using a Lovelace Multijet Cascade Impactor / Parallel-Flow Diffusion Battery Serial Sampling Train

A serial sampling train consisting of a Lovelace multijet cascade impactor (LMJI) and a seven cell parallel-flow diffusion battery (PFDB) has been used to provide a comprehensive method for sizing aerosols with a wide size distribution ranging from less than 0.01 μm to over 10 μm. The fraction of the aerosol greater than 0.7 μm is collected by the impactor. The remaining fraction of the aerosol is sampled by the PFDB. Design of the PFDB is based on the theory of a screen-type diffusion battery. The concept of parallel flow is employed to provide a method for sampling aerosols that fluctuate too rapidly in concentration and size distribution to be measured by conventional methods. The LMJI/PFDB sampling system is useful for characterizing multimodel size distributions such as those that occur in ambient aerosols. It can also be used to determine the chemical composition of collected samples as a function of particle size. This sampling system has been used to size classify diesel and diesel-oil shale exposure atmospheres, and benzo(a)-pyrene-coated carbon black aerosols. The diffusion equivalent diameter (D _de) of the diesel exhaust was 0.07–0.08 μm, and the oil-shale dust had a mass median aerodynamic diameter (MMAD) of 2.6–2.9 μm. The size distribution of the carbon black aerosol was bimodal, with the fine fraction having a D _de of 0.2 μm, and the coarse fraction having a MMAD of 2.0 μm.     

北京市火电厂排放颗粒物的粒径分布

本文重点研究了北京市燃煤、燃油电厂锅炉的颗粒物排放及其粒径分布,静电除尘器的分级效率.文中对所采用的WY-Ⅱ型冲击式尘粒分级仪进行简要介绍,指出存在的问题,并提出建议.     

A New Method to Measure Aerosol Particle Bounce Using a Cascade Electrical Low Pressure Impactor

The phase state of secondary organic aerosol (SOA) in the atmosphere is of scientific interest as it can impact SOA growth and reactivity. For this purpose, a simplified method is described herein to estimate SOA bounce factor to gain an improved understanding of the phase state of atmospheric aerosols. This new method involves the use of a multistage electrical low pressure cascade impactor operating with either smooth or sintered impaction plates. Measurement of the raw current on smooth and sintered plates allows one to calculate the bounce factor, eliminating the need for a scanning mobility particle sizer to independently measure the SOA aerodynamic size distribution. The proposed method provides the temporal resolution necessary to measure phase changes in a continuously evolving SOA parcel.

We validate our method by measuring the bounce factor of solid and liquid aerosols, namely ammonium sulfate (AS), dioctyl sebacate (DOS), oleic acid (OA) and ozonized OA, and also present bounce factor evolution of aging α-pinene-derived aerosols. The results suggest that the new method can be used to understand the phase state of amorphous and crystalline substances, as well as distinguish between liquid and nonliquid particles.

Copyright 2015 American Association for Aerosol Research     

Capillary Impactor with Optical Detection in Collection of Carbonaceous Particles

A new single-orifice capillary system for optical analysis of carbonaceous matter is reported. The special feature of this system is the use of long, flexible capillary tubing for sampling.     

Deposition Uniformity and Particle Size Distribution of Ambient Aerosol Collected with a Rotating Drum Impactor

Rotating drum impactors (RDI) are cascade type impactors used for size and time resolved aerosol sampling, mostly followed by spectrometric analysis of the deposited material. They are characterized by one rectangular nozzle per stage and are equipped with an automated stepping mechanism for the impaction wheels. An existing three-stage rotating drum impactor was modified, to obtain new midpoint cutoff diameters at 2.5 μm, 1 μm, and 0.1 μm, respectively. For RDI samples collected under ambient air conditions, information on the size-segregation and the spatial uniformity of the deposited particles are key factors for a reliable spectrometric analysis of the RDI deposits. Two aerodynamic particle sizers (APS) were used for the determination of the RDI size fractionation characteristics, using polydisperse laboratory room air as quasi-stable proxy for urban ambient air. This experimental approach was suitable for the scope of this study, but was subject to numerous boundary conditions that limit a general use. Aerodynamic stage penetration midpoint diameters were estimated to be 2.4 and 1.0 μm for the first two RDI stages. Additionally, the spatial uniformity and geometrical size distribution of the deposited aerosol were investigated using micro-focus synchrotron radiation X-ray fluorescence spectrometry (micro-SR-XRF) and transmission electron microscopy (TEM), respectively. The size distribution of the particles found on the TEM samples agreed well with the results from the APS experiments. The RDI deposits showed sufficient uniformity for subsequent spectrometric analysis, but in the 2.5–10 μm size range the particle area density was very low. All of the applied methods confirmed the theoretical cutoff values of the modified RDI and showed that compared to other cascade impactors, the determined stage penetration sharpness was rather broad for the individual impactor stages.     

Size Distributions of Species in Fine Particles in Denver Using a Microorifice Impactor

Size-fractionated fine particles in Denver, Colorado, were collected by a microorifice impactor and analyzed for mass and elemental composition by a β-gauge and an X-ray fluorescence spectrometer. A least-squares procedure was used to fit a lognormal distribution function to the data in order to determine values and uncertainties for the mass median aerodynamic diameter and geometric standard deviation. The validity of the uncertainties so determined was tested by comparing them to uncertainties derived from Monte Carlo simulations.     

颗粒物再悬浮和检测系统的性能指标

系统地提出了颗粒物再悬浮和检测系统的性能指标,指标至少应包括5方面：颗粒物浓度稳定性、浓度调节平衡时间与连续运行时间、浓度可调范围、颗粒物采样均匀度、粒径分布的一致性. 根据干粉气动再分散方法和气溶胶力学理论,集成了一款颗粒物再悬浮和检测系统,并按照指标评估了该系统. 结果表明,浓度可调范围为0.1~12000 mg/m3,连续运行时间至少可达1~7 d,浓度调节平衡时间≤1 min;浓度稳定性较好,各种运行状态对应的浓度相对标准偏差(RSD)的平均值≤10%;各采样点采样均匀度好,RSD≤1.5%;混合箱内颗粒物在空气动力学直径0~40 mm范围内的粒径分布与待测粉尘一致.     

一种纳米颗粒粒度分布的非接触测量方法

研究了基于高频宽带超声衰减谱非接触式方法测量纳米颗粒悬浊液中颗粒相粒度分布问题. 通过理论分析和数值计算,选择ECAH模型作为反演计算的理论模型. 以1%(j)的纳米银水悬浊液作为实验样品,采用标称中心频率为50 MHz的超声换能器和变声程脉冲回波法进行了非接触测量,获得了可利用的高频宽带(10~50 MHz)超声衰减谱,结合理论模型和最优正则化算法反演出纳米颗粒的粒度分布. 实验结果与透射电子显微镜法和高速离心沉降法的测定结果吻合较好,表明该方法可测量悬浊液中纳米颗粒粒度分布.     

Reduction of Particulate Matter Emissions from a Pellet Boiler Using Primary Measures

The use of primary measures to reduce particulate matter, CO, and NO_x emissions can be feasible for pellet boilers fired with a standardized fuel with low quality variations. At the same time, the use of lower-quality pellets such as A2 or I2 can be realized without the need for secondary emission reduction measures. Here, the possibility of particulate matter reduction through the use of primary measures is discussed, demonstrating that particulate matter emissions can be significantly reduced with the aid of primary measures such as air staging and exhaust gas recirculation. However, the use of these measures also influences other emissions, such as CO and NO_x from the furnace.     

Comparison and Combination of Aerosol Size Distributions Measured with a Low Pressure Impactor,Differential Mobility Particle Sizer,Electrical Aerosol Analyzer,and Aerodynamic Particle Sizer

Data from a different mobility particle sizer (DMPS) or an electrical aerosol analyzer (EAA) has been combined with data from an aerodynamic particle sizer (APS) and converted to obtain aerosol mass distribution parameters on a near real-time basis. A low pressure impactor (LPI), a direct and independent measure of this mass distribution, provided information for comparison.

The number distribution of particles within the electrical measurement range was obtained with the DMPS and EAA. Data from the APS for particles greater than that size were used to complete the number distribution. Two methods of obtaining mass distribution parameters from this number data were attempted. The first was to convert the number data, channel by channel, to mass data and then fit a log-normal function to this new mass distribution. The second method was to fit a log-normal function to the combined number distribution and then use the Hatch-Choate equations to obtain mass parameters.

Both the DMPS / APS and the EAA / APS systems were shown to successfully measure aerosol mass distribution as a function of aerodynamic diameter. Careful operation of the measurement equipment and proper data manipulation are necessary to achieve reliable results. A channel-by-channel conversion from number to mass distribution provided the best comparison to the LPI measurement. The DMPS / APS combination furnishes higher-size resolution and accuracy than the EAA / APS system. A small gap was observed in the EAA / APS combined data; however, this did not seem to adversely affect the determination of mass distribution parameters.     

基于超声衰减谱的脂肪乳粒度分布测量方法

研究了超声衰减法测量高浓度多分散脂肪乳浊液的粒径分布问题. 在理论分析的基础上,实验测量了多个浓度(1%~20%)下脂肪乳试样在2~13 MHz频带下的超声衰减谱,结合反演算法,由实验数据计算出乳浊液颗粒的粒径及其分布. 将用超声衰减法对脂肪乳试样在原始浓度(20%)下测得的粒径分布与用消光法超细颗粒粒径分析仪在稀释条件下对试样的测量结果作对比,粒径均小于1 mm时,二者比较吻合. 超声法测得的浓度与给定值误差约3%,反演谱误差率小于10%,表明此法可在无需稀释的高浓度条件下准确测得乳浊液的粒径分布和浓度.     

Measuring the Size Distribution of Atmospheric Organic and Black Carbon Using Impactor Sampling Coupled with Thermal Carbon Analysis: Method Development and Uncertainties

A method for determining the mass size distribution of organic and black carbon (OC and BC) in atmospheric aerosols is introduced. The method relies on a particle sampling with 2 parallel size-segregating devices, a 12-stage Small Deposit area low pressure impactor (SDI) and a virtual impactor (VI), and the subsequent analysis of the samples with thermal and thermal-optical methods, respectively. The method development revealed that SDI is, like other sampling methods, susceptible to serious sampling artifacts and OC pyrolysis during thermal analysis. However, some of the SDI's limitations can be overcome by parallel VI measurements. The good correlation between the SDI and the VI data for most of the samples collected here indicates that under most conditions, the lack of the pyrolysis correction for the SDI samples does not cause significant errors in the OC/BC split. Valuable features of this method are that it offers a good size resolution in both sub- and supermicron size fractions, indicates if there has been serious positive or negative artifacts for OC during sampling, reveals if the samples have been affected by OC pyrolysis during thermal analysis, and provides semiquantitative means by which the OC and BC size distributions can be corrected for the samples being affected by OC pyrolysis. Application of the method to real atmospheric samples is demonstrated, and the major areas requiring further research and/or method development are identified.     

A Moment Method for Evaporation Using a Logarithmic Size Distribution with the Smallest Size

A moment method of the log-normal distribution with the smallest size is applied to evaporation by newly introducing correction factors obtained from the error function. In this article, the improved moment method is tested for the evaporation, and is compared with the exact solutions calculated by the CIP semi-Lagrangian (CIP-SL) method. In small particle regime, the size distributions and the time histories of the total number and volume per unit volume are reproduced by the moment method for the evaporation near the smallest size. In large particle regime, however, the differences between the moment and exact solutions are larger with time, after the exact distribution spreads to the smallest size. This new moment solver can reproduce the evaporation near the smallest size even when large time step size is given, and thus is expected to be used for the parameterization of the evaporation of small particles in aerosol-transport model.     

Influences on the Particle Size Distribution of Diesel Particulate Emissions

Particulates give great concern for mankind health. Especially the nano size particles are under discussion. Therefore, the particle size distribution from the combustion chamber to tail pipe emissions are of great interest. With the aim of scanning mobility particle sizer the number weighted particle size distributions were measured in the combustion chamber as well as in the exhaust gas up and downstream of aftertreatment systems. Using the identical particle measurement technique results can be compared without changing the particle size definition. The particles in the cylinder of a modern serious DI diesel engine were sampled with a time resolved fast gas sampling valve. The Soot particles formed in the cylinder during the early combustion phase are oxidized by about 99% in the late combustion/early expansion phase, whereas the soot particle sizes distribution in the cylinder at the end of the expansion phase are equal to that in the tail pipe. DI diesel engines with high pressure injection system emit less numbers of particle with in tendency greater sizes compared to IDI diesel engines. Oxidation catalysts do not influence particle size distribution but particulate traps reduce particle number by up to two orders of magnitude. Detail analysis shows that an increase of nano size particle number downstream of an aftertreatment device results from artifacts.     

Automated Measurement of the Size and Concentration of Airborne Particulate Nitrate

A three-stage, cascaded integrated collection and vaporization system has been developed to provide automated, 10 min resolution monitoring of the size and concentration of fine particulate nitrate in the atmosphere. Particles are collected (7 min) by a humidified impaction process, and analyzed in place (3 min) by flash vaporization and chemiluminescent detection of the evolved nitrogen oxides. The three size fractions, < 0.45 w m, 0.45-1.0 w m, and 1.0-2.5 w m, are chosen to distinguish the condensation, droplet, and coarse components of PM 2.5 . The size precut at 2.5 w m is done at ambient conditions, while the size fractionation at 1.0 w m and 0.45 w m is done at a constant relative humidity of 65%. The system is calibrated with laboratory aerosols, including comparison of sizing for hygroscopic salt and hydrophobic organic aerosols. The complete system is tested with monodisperse ammonium nitrate aerosol generated with a high-flow differential mobility analyzer coupled with an impactor precut and yields results consistent with the calibration of the individual stages.     

Size Distribution of Health-Relevant Trace Elements in Airborne Particulate Matter During a Severe Winter Stagnation Event: Implications for Epidemiology and Inhalation Exposure Studies

Size distributions for As, Cd, Bi, Br, Fe, Mn, S, Sb, Tl, K, V, Rb, elemental carbon (EC), organic carbon (OC), sulfate (SO ^2? ₄ ), chloride (Cl^?), and nitrate (NO^? ₃ ) were measured at Bakersfield and Modesto CA between 12/15/2000–01/07/2001. S and V size distributions were highly correlated with little diurnal variation suggesting that, during stagnant winter conditions, inhalation exposure and epidemiological studies can choose exposure/analysis times of several days during which population exposure will be relatively uniform. In contrast, the size distribution and temporal patterns of Fe are highly variable requiring more frequent measurements and shorter health analysis periods to adequately characterize exposure concentrations. K and Rb (tracers for wood smoke) exhibited nearly identical diurnal size distribution shifts (R ²  > 0.99) with smaller particles emitted at night and larger aged particles evident during the day. This pattern suggests that the health effects of fresh wood smoke could be studied through nighttime inhalation exposure experiments and aged wood smoke could be evaluated through daytime experiments. All of the components’ size distributions were consistent with production by combustion sources and/or secondary chemistry. Future inhalation exposure studies should use a combustion source to generate these particles. Lung deposition calculations predict that 32 ± 11% of PM deposition occurs in the pulmonary region, 61 ± 23% occurs in the respiratory region, and 6 ± 2% occurs in the tracheo-bronchial region for all components. Deposition patterns were highly correlated with PM _1.8 concentrations suggesting that exposure estimates can be developed with bulk filter samples during the current episode.     

Characterization of Porous Carbonaceous Sorbents Using High Pressure CO2 Adsorption Data

In this paper we present adsorption isotherms of carbon dioxide on five different activated carbons from CHEMVIRON CARBON Belgium (Centaur HSV, BPL 410, F30-470, WS 42, Reactivated) and on a carbon molecular sieve from BERGBAU FORSCHUNG Gmbh (CMS II). The temperature is 303 K and the pressure ranges from 100 kPa up to 4000 kPa. Such conditions correspond to relative pressures ranging from 0.01 to 0.5. We also provide, for the same six sorbents, the nitrogen isotherms at 77 K (pressure: 0.001 to 100 kPa, relative pressure: 10^-5 to 1). A theoretical treatment based on the Dubinin-Radushkevich and Stoeckli concept is presented and applied to the experimental results in order to obtain the micropore size distribution function (considered as Gaussian) of each sorbent. Using the CO₂ data, it is possible to point out important structural differences between the six carbons. The theoretical treatment provides micropore size distribution functions in agreement with what is physically expected. Using N₂ data, the structural differences are not so well marked. As a consequence, the structural parameters provided by the theoretical treatment are not reliable: except for the total micropore volume, they fluctuate strongly when changing the relative pressure domain of the used data.