Electrical Mobility Spectrometer Research Articles

A bipolar SMPS network for measuring atmospheric aerosols using natural air ions

To study atmospheric aerosols, it is essential to build networks that are continuously monitoring particle number size distribution (PNSD). PNSDs are often measured using electrical mobility spectrometers such as scanning mobility particle sizer (SMPS) which includes a neutralizer that conditions the charge state of particles to the pre-assumed distributions. During long-term atmospheric measurement, the charge state can deviate from these assumed values. Measuring both positively and negatively charged particles using a bipolar SMPS helps to capture the variations in aerosol charge state. In this study, we set up a network of bipolar SMPSs at three urban sites and three suburban sites in six Chinese cities. Removing the conventional neutralizer, the bipolar SMPS utilizes the natural aerosol charging process by atmospheric ions. Newly developed aerosol classifiers and detectors were used. Harmonized quality assurance procedures were adopted to assure the performance and the data quality, including laboratory calibrations and intercomparisons, maintenance and monitoring during field measurements, and data inversion and validation. PNSDs are effectively measured by bipolar SMPSs using natural charging process at all six sites. During six months of field measurement in these sites, ion mobility ratios fluctuate significantly while the daily averaged values are stable around 1.0. Particle number concentrations integrated from PNSDs are consistent with those directly measured by the detectors (within a variation of 10%).

Modular Multiplatform Compatible Air Measurement System (MoMuCAMS): a new modular platform for boundary layer aerosol and trace gas vertical measurements in extreme environments

Abstract. The Modular Multiplatform Compatible Air Measurement System (MoMuCAMS) is a newly developed in situ aerosol and trace gas measurement platform for lower-atmospheric vertical profiling. MoMuCAMS has been primarily designed to be attached to a Helikite, a rugged tethered balloon type that is suitable for operations in cold and windy conditions. The system addresses the need for detailed vertical observations of atmospheric composition in the boundary layer and lower free troposphere, especially in polar and alpine regions. The MoMuCAMS encompasses a box that houses instrumentation, a heated inlet, a single-board computer to transmit data to the ground for in-flight decisions and a power distribution system. The enclosure can accommodate various combinations of instruments within its weight limit (e.g., 20 kg for a 45 m3 balloon). This flexibility represents a unique feature, allowing for the study of multiple aerosol properties (number concentration, size distribution, optical properties, chemical composition and morphology), as well as trace gases (e.g., CO, CO2, O3, N2O) and meteorological variables (e.g., wind speed and direction, temperature, relative humidity, pressure). Different instrumental combinations are therefore possible to address the specific scientific focus of the observations. It is the first tethered-balloon-based system equipped with instrumentation providing a size distribution for aerosol particles within a large range, i.e., from 8 to 3370 nm, which is vital to understanding atmospheric processes of aerosols and their climate impacts through interaction with radiation and clouds. Here we present a characterization of the specifically developed inlet system and previously unreported instruments, most notably the miniaturized scanning electrical mobility spectrometer and a near-infrared carbon monoxide monitor. As of December 2022, MoMuCAMS has been tested during two field campaigns in the Swiss Alps in winter and fall 2021. It was further deployed in Fairbanks, Alaska, USA, in January–February 2022, as part of the ALPACA (Alaskan Layered Pollution and Chemical Analysis) campaign and in Pallas, Finland, in September–October 2022, as part of the PaCE2022 (Pallas Cloud Experiment) study. Three cases from one of the Swiss Alpine studies are presented to illustrate the various observational capabilities of MoMuCAMS. Results from the first two case studies illustrate the breakup of a surface-based inversion layer after sunrise and the dilution of a 50–70 m thick surface layer. The third case study illustrates the capability of the system to collect samples at a given altitude for offline chemical and microscopic analysis. Overall, MoMuCAMS is an easily deployable tethered-balloon payload with high flexibility, able to cope with the rough conditions of extreme environments. Compared to uncrewed aerial vehicles (drones) it allows for observation of aerosol processes in detail over multiple hours, providing insights into their vertical distribution and processes, e.g., in low-level clouds, that were difficult to obtain beforehand.

Beyond size classification: The dynamic-aerosol-size electrical mobility spectrometer

This paper overviews an alternative operation mode of the Electrical Mobility Spectrometer (EMS), herein termed as the “Dynamic-aerosol-size Electrical Mobility Spectrometer (DEMS)” where the size of aerosol particles evolves during mobility classification in response to any chemical/physical processes taking place within the device's classification region. Unlike the conventional EMS designed to classify the aerosol particle size, the function of the DEMS is to probe the kinetics (in terms of corresponding growth/shrinkage rates) of aerosol related chemical/physical processes. This is achievable because the particle trajectory in the device's classification region contains full information about the particle size change history. A theoretical framework is developed for analyzing the transmission of size-changing particles in the device's classification region. Expressions for the particle mobility at the device outlet and size change rate are derived based on known initial mobility and DEMS response, using the evaporation of monodisperse and single-component aerosols as an example. The theoretical framework is applicable to the entire Knudsen number range and is compared against simulations and experiments, demonstrating excellent validity in the test conditions.

The nano-scanning electrical mobility spectrometer (nSEMS) and its application to size distribution measurements of 1.5–25 nm particles

Abstract. Particle size measurement in the low nanometer regime is of great importance to the study of cloud condensation nuclei formation and to better understand aerosol–cloud interactions. Here we present the design, modeling, and experimental characterization of the nano-scanning electrical mobility spectrometer (nSEMS), a recently developed instrument that probes particle physical properties in the 1.5–25 nm range. The nSEMS consists of a novel differential mobility analyzer and a two-stage condensation particle counter (CPC). The mobility analyzer, a radial opposed-migration ion and aerosol classifier (ROMIAC), can classify nanometer-sized particles with minimal degradation of its resolution and diffusional losses. The ROMIAC operates on a dual high-voltage supply with fast polarity-switching capability to minimize sensitivity to variations in the chemical nature of the ions used to charge the aerosol. Particles transmitted through the mobility analyzer are measured using a two-stage CPC. They are first activated in a fast-mixing diethylene glycol (DEG) stage before being counted by a second detection stage, an ADI MAGIC™ water-based CPC. The transfer function of the integrated instrument is derived from both finite-element modeling and experimental characterization. The nSEMS performance has been evaluated during measurement of transient nucleation and growth events in the CLOUD atmospheric chamber at CERN. We show that the nSEMS can provide high-time- and size-resolution measurement of nanoparticles and can capture the critical aerosol dynamics of newly formed atmospheric particles. Using a soft x-ray bipolar ion source in a compact housing designed to optimize both nanoparticle charging and transmission efficiency as a charge conditioner, the nSEMS has enabled measurement of the contributions of both neutral and ion-mediated nucleation to new particle formation.

Diffusional transfer function for the scanning electrical mobility spectrometer (SEMS)

The scanning electrical mobility spectrometer (SEMS), or scanning mobility particle sizer (SMPS), uses the differential mobility analyzer (DMA) operated in scanning mode to measure particle size di...

Scanning DMA Data Analysis I. Classification Transfer Function

The scanning electrical mobility spectrometer (SEMS; also known as the scanning mobility particle sizer, SMPS) enables rapid particle size distribution measurements with a differential mobility ana...

Scanning DMA data analysis II. Integrated DMA-CPC instrument response and data inversion

Analysis of scanning electrical mobility spectrometer (SEMS) or SMPS data requires coupling the scanning differential mobility analyzer (DMA) transfer function with the response functions for the instrument plumbing and the detector. In the limit of plug flow (uniform velocity) within the DMA, the scanning DMA transfer function has the same form as that for constant voltage. Most SEMS/SMPS data analysis uses this model, though previous studies have shown that boundary layers distort the transfer function during scanning DMA measurements. Part I determined the instantaneous transfer function during scanning of the TSI Model 3081 A long column DMA by modeling the flows, fields, and particle trajectories within the actual DMA geometry. This study (Part II) combines that transfer function with empirical data on the efficiencies and delay time distributions of the plumbing and detector of the SEMS/SMPS to determine the instantaneous rate at which particles are counted, and integrates the count rate over the finite counting time interval to obtain the integrated SEMS/SMPS response function. Simulations using this geometrical model are compared with those obtained using traditional, idealized DMA models for scan rates ranging from slow (240 s) to very fast (10 s), and with measurements of monodisperse calibration aerosols. Data inversion studies show that both increasing and decreasing voltage scans can be used to determine the particle size distribution, even with fast scans.

Parameters governing the performance of electrical mobility spectrometers for measuring sub-3 nm particles

Measuring aerosol size distributions accurately down to ~1 nm is a key to nucleation studies, and it requires developments and improvements in instruments such as electrical mobility spectrometers in use today. The key factors characterizing the performance of an electrical mobility spectrometer for sub-3 nm particles are discussed in this study. A parameter named as Π is proposed as a figure of merit for the performance of an electrical mobility spectrometer in the sub-3 nm size range instead of the overall detection efficiency. Π includes the overall detection efficiency, the measurement time in each size bin, the aerosol flow rate passing through the detector, and the aerosol-to-sheath flow ratio of the differential mobility analyzer. The particle raw count number recorded by the detector can be estimated using Π at a given aerosol size distribution function, dN/dlogdp. The limit of detection for the spectrometer and the statistical uncertainty of the measured aerosol size distribution can also be readily estimated using Π. In addition to Π, the size resolution of an electrical mobility analyzer is another factor characterizing the systematic errors originated from particle sizing. Four existing electrical mobility spectrometers designed for measuring sub-3 nm aerosol size distributions, including three scanning/differential mobility particle spectrometers and one differential mobility analyzer train, are examined. Their optimal performance is evaluated using Π and the size resolution. For example, the Π value and the size resolution of a diethylene-glycol differential mobility particle spectrometer for 1.5 nm particles are 8.0 × 10−4 cm3 and 5.7, respectively. The corresponding relative uncertainty of the measured size distribution is approximately 9.6% during an atmospheric new particle formation event with a dN/dlogdp of 5 × 105 cm−3. Assuming an adjustable sheath flow rate of the differential mobility analyzer, the optimal size resolution is approximately 5–9 when measuring atmospheric new particle formation events.

Towards near real-time SEMS size distribution measurements under up-scan operation

Near real-time particle size distribution measurements with a scanning electrical mobility spectrometer (SEMS) requires a fast scan DMA operation. The classification characteristics of the DMA when operated with an up-scan voltage can be established from calculations of particle arrival-times at the sample port of the DMA. This approach, referred to as the arrival-time transfer function (ATF) calculation approach, has been shown to accurately calculate DMA mobility transfer functions under up-scan operation for a range of scan times. Fast SEMS operation, however, are further complicated by downstream effects of particle smearing, plumbing delays (offset time) and counting time interval of the particle counter. These effects have thus far been quantified empirically. In this paper, a theoretical framework is proposed to minimize empirical corrections. The effects of particle smearing, plumbing delays (offset time) and counting time interval are incorporated in determining SEMS transfer functions, which are then used to predict the signal response to a known upstream size distribution under different operating conditions. The predicted signals are then validated with experimental data with scan times as fast 5 s. Using the calculated SEMS transfer functions and a regularization-based inversion algorithm, we are able to accurately invert SEMS signals from a scan as fast as 5 s. Our proposed SEMS transfer function calculation approach, thus, suggests that near real-time, accurate size distributions may be possible with SEMS measurements.

Interesterification optimization of waste cooking oil and ethyl acetate over homogeneous catalyst for biofuel production with engine validation

The interesterification of waste cooking oil (WCO) and ethyl acetate (ETA) are investigated in homogeneous catalyst system using sodium hydroxide (NaOH) and acetic acid (CH3COOH). Later on, the subsequent biofuel has been investigated for the combustion characteristics, gaseous and particulate matter related emissions in a single-cylinder agricultural diesel engine. In the reaction, fatty acid ethyl esters were the main product whereas triacetin by-product was formulated in a single phase biofuel. The parameters affected the free fatty acid (FFA) conversion were studied such as catalyst system, molar ratio of ETA:WCO, molar ratio of catalyst:WCO, reaction time, and temperature. The experimental results revealed that NaOH was more favorable than the acid catalyst counterpart. The 92% biofuel yield was reached from the optimization at the NaOH:WCO of 0.015:1 M ratio and the ETA:WCO of 30:1 M ratio at 80 °C in 3 h. In the engine validation at 3.4 and 6.6 bar IMEP loads, 1700 rpm speed, the results from the combustion analysis using an indicating system reveal that the WCO biofuel initiates the combustion faster with pronounce premixed combustion regime than that of diesel fuel. The specific fuel consumption of WCO biofuel was greater, leading to a slight reduction in brake thermal efficiency by 4% and 10% at 3.4 and 6.6 bar IMEP loads, respectively compared with diesel fuel. The nano-particle emissions was characterized by an electrical mobility spectrometer and analyzed in terms of particle number. The total particle number increased with smaller size when fueling with WCO biofuel. In comparison over the loads tested, the total particle number concentrations were in the ranges of 8.1 × 1011 to 1.1 × 1012 m−3 for WCO biofuel and 4.8 × 1011 to 5.7 × 1011 m−3 for diesel fuel. Meanwhile, the particle sizes were in the ranges of 182–251 nm for WCO biofuel and 279–402 nm for diesel fuel. Summarily, for the biofuel production, this homogeneous process is beneficial in terms of low-cost feedstock, glycerol-free and mild reaction condition.

Data inversion methods to determine sub-3 nm aerosol size distributions using the particle size magnifier

Abstract. Measuring particle size distribution accurately down to approximately 1 nm is needed for studying atmospheric new particle formation. The scanning particle size magnifier (PSM) using diethylene glycol as a working fluid has been used for measuring sub-3 nm atmospheric aerosol. A proper inversion method is required to recover the particle size distribution from PSM raw data. Similarly to other aerosol spectrometers and classifiers, PSM inversion can be deduced from a problem described by the Fredholm integral equation of the first kind. We tested the performance of the stepwise method, the kernel function method (Lehtipalo et al., 2014), the H&A linear inversion method (Hagen and Alofs, 1983), and the expectation–maximization (EM) algorithm. The stepwise method and the kernel function method were used in previous studies on PSM. The H&A method and the expectation–maximization algorithm were used in data inversion for the electrical mobility spectrometers and the diffusion batteries, respectively (Maher and Laird, 1985). In addition, Monte Carlo simulation and laboratory experiments were used to test the accuracy and precision of the particle size distributions recovered using four inversion methods. When all of the detected particles are larger than 3 nm, the stepwise method may report false sub-3 nm particle concentrations because an infinite resolution is assumed while the kernel function method and the H&A method occasionally report false sub-3 nm particles because of the unstable least squares method. The accuracy and precision of the recovered particle size distribution using the EM algorithm are the best among the tested four inversion methods. Compared to the kernel function method, the H&A method reduces the uncertainty while keeping a similar computational expense. The measuring uncertainties in the present scanning mode may contribute to the uncertainties of the recovered particle size distributions. We suggest using the EM algorithm to retrieve the particle size distributions using the particle number concentrations recorded by the PSM. Considering the relatively high computation expenses of the EM algorithm, the H&A method is recommended for preliminary data analysis. We also gave practical suggestions on PSM operation based on the inversion analysis.

LEVELS AND WATER SOLUBLE ORGANIC CARBON OF ATMOSPHERIC NANOPARTICLES IN A LOCATION OF HA NOI, VIET NAM

Atmospheric nanoparticles (NPs or PM0.1) were investigated at a site inside the campus of Ha Noi University of Science and Technology (HUST) in Ha Noi, Viet Nam. The sampling was conducted during a rainy season (August, 2015) and a dry season (October to December, 2015). Mass was weighed by an electronic micro-balance, Sartorius ME2, 10-6 g. Number concentrations were measured by an electrical mobility spectrometer (NanoScan, SMPS TSI Model 3910). Water soluble organic carbon (WSOC) was analyzed by a total carbon analyzer (TOC-VCHP, Shimazu). The correlations between WSOC and other components were studied to primarily identify the sources of atmospheric nanoparticles. Secondary organic carbon (SOA) was estimated using elemental carbon (EC) – tracer method. Selected characteristics of nanoparticles including mass concentrations, number concentrations, and WSOC were determined.

Performance study of portable devices for the real-time measurement of airborne particle number concentration and size (distribution)

The aim of this experimental study was to investigate the performance of both portable and transportable devices devoted to the real-time measurement of airborne particle number concentration and size (distribution). Electrical mobility spectrometers (SMPS, FMPS, Nanoscan) as well as diffusion chargers (DiSCmini, Nanotracer) were studied. Both monodisperse and polydisperse aerosols were produced within the CAIMAN facility to challenge the instruments. The monodisperse test aerosols were selected in the 15-400 nm diameter range using a differential mobility analyser (DMA), and presented number concentrations of between 6.102 and 2.105 cm−3. The polydisperse test aerosols presented modal diameters of between 8 and 270 nm and number concentrations between 4.103 to 106 cm−3. The behavior of the different devices is expressed as (1) the ratio of the reported diameter to the reference diameter, and (2) the ratio of the reported number concentration to the reference concentration. These results are displayed as boxplots to better represent the statistical distribution of the experimental results. For the group of electrical mobility spectrometers, a good agreement between SMPS and FMPS and the reference was demonstrated. A slight tendency for the Nanoscan to underestimate particle size distribution for particles above around 100 nm was observed. The data reported for the group of diffusion chargers demonstrate that all, except the Nanotracer, show a tendency to underestimate particle diameter, by a factor around −40% to −10%. In the case of particle concentration, larger deviations were observed.

CFD Aided Procedure for Optimizing Electrical Mobility Spectrometer

Aerosol measurement is used in a variety of fields such as nanotechnology, materials science, pollution monitoring, air quality measurements, combustion and engine exhaust analysis, inhalation toxicology, and medical studies. One of the most prevalent methods for aerosol measurement is to use electrical mobility. An electrical mobility spectrometer (EMS) is used to measure aerosol particles size distribution ranging from 10 – 1000 nanometers, under the influence of an electric field. The accuracy of this distribution is influenced by flow conditions, the geometry of the EMS, the electric field, and the number of electrode rings. In this work, a multi-channel EMS is studied using computational fluid dynamics to numerically simulate the flow pattern, electric field and particle trajectories in the device. We found that neglecting the effect of the electric field on particles outside the sizing region generates an oversimplified model leading to high particle loss to the flow guide. In order to reduce the number of particle losses and obtaining a more realistic particle distribution we proposed a modification to the electrode electric potential which effectively reduces the particle loss. The applied modification has quintupled the number of particles which are classified by the EMS.

A multiple charging correction algorithm for scanning electrical mobility spectrometer data

Accuracy of particle size distribution measurements from scanning electrical mobility spectrometers (SEMS) is critically dependent on the quality of SEMS data inversion. A critical element of SEMS data inversion is the consideration of the charged particle fraction in the sample flow. In particular, when larger, multiply-charged particles are present in the measured aerosol, significant errors in the calculation of size distributions are possible if their contribution is not correctly accounted for. While ignoring the contribution of multiply charged particles may be acceptable when the particles are mostly in the ultrafine size range, a substantial error is possible when a significant fraction of particles are larger than 100nm. Accurate calculation of size distributions from SEMS data is possible when an inertial impactor is used to eliminate the contribution of multiply-charged particles larger than a cut-size and an iterative multiple-charge correction (MCC) algorithm is used during the data inversion process. The effectiveness of this approach is, however, strongly dependent on the relationship between the aerodynamic and the electrical mobility diameters of the particles. Here, we demonstrate the limitations of the existing inversion algorithms and propose an alternative MCC algorithm for size distribution calculation from non-ideal SEMS data. In the proposed approach, the zeroth order singly charged particle size distribution is fit using a Gumbel distribution function, and the resultant fit is used to correct for the multiply-charged contribution to the SEMS data. The effectiveness of the proposed approach is tested for a range of particle size distribution scenarios and validated with experimental data.

Improved Inversion of Scanning Electrical Mobility Spectrometer Data Using a New Multiscale Expectation Maximization Algorithm

The accuracy of particle size distributions obtained from scanning electrical mobility spectrometer (SEMS) measurements is strongly dependent on the accurate consideration of the instrument characteristics in the formulation of the SEMS problem and the effective inversion of the resulting SEMS equation. The estimation of size distributions from SEMS measurements requires a solution of the discretized form of the Fredholm integral equation of the first kind. The often ill-conditioned nature of the linear inverse problem coupled with the possible presence of measurement noise complicates these calculations. The use of standard inversion approaches, such as nonnegative least squares (NNLS) or regularization-based algorithms, requires SEMS measurements with significant signal-to-noise ratio or some a priori knowledge of the shape of the sampled size distribution. These severe constraints for SEMS measurements can be relaxed with the new multiscale expectation-maximization SEMS inversion method introduced here...

Size and time-resolved growth rate measurements of 1 to 5 nm freshly formed atmospheric nuclei

Abstract. This study presents measurements of size and time-resolved particle diameter growth rates for freshly nucleated particles down to 1 nm geometric diameter. Novel data analysis methods were developed, de-coupling for the first time the size and time-dependence of particle growth rates by fitting the aerosol general dynamic equation to size distributions obtained at an instant in time. Size distributions of freshly nucleated total aerosol (neutral and charged) were measured during two intensive measurement campaigns in different environments (Atlanta, GA and Boulder, CO) using a recently developed electrical mobility spectrometer with a diethylene glycol-based ultrafine condensation particle counter as the particle detector. One new particle formation (NPF) event from each campaign was analyzed in detail. At a given instant in time during the NPF event, size-resolved growth rates were obtained directly from measured size distributions and were found to increase approximately linearly with particle size from ~1 to 3 nm geometric diameter, increasing from 5.5 ± 0.8 to 7.6 ± 0.6 nm h−1 in Atlanta (13:00) and from 5.6 ± 2 to 27 ± 5 nm h−1 in Boulder (13:00). The resulting growth rate enhancement Γ, defined as the ratio of the observed growth rate to the growth rate due to the condensation of sulfuric acid only, was found to increase approximately linearly with size from ~1 to 3 nm geometric diameter. For the presented NPF events, values for Γ had lower limits that approached ~1 at 1.2 nm geometric diameter in Atlanta and ~3 at 0.8 nm geometric diameter in Boulder, and had upper limits that reached 8.3 at 4.1 nm geometric diameter in Atlanta and 25 at 2.7 nm geometric diameter in Boulder. Nucleated particle survival probability calculations comparing the effects of constant and size-dependent growth indicate that neglecting the strong dependence of growth rate on size from 1 to 3 nm observed in this study could lead to a significant overestimation of CCN survival probability.

10.2478/s11814-009-0261-0

A prototype of a short column electrical mobility spectrometer (EMS) for size measurement of aerosol particle was design, constructed, and experimentally characterized. The short EMS consists of a particle charger, a size classifier column, and a multi-channel electrometer. Its particle size resolution is derived from a 10 channel electrometer detector. The short EMS is capable of size measurements in the range between 10 nm to 1,000 nm with a time response of about 50 s for full up and down scan. Particle number concentration in which the short EMS can measure ranges from 1011 to 1013 particles/m3. The operating flow rate of the short EMS is set for the aerosol flow rate of 1.0–2.0 l/min and the sheath air flow rate fixed at 10.0 l/min. The inner electrode voltage of the classifier can be varied between 500–3,000 VDC. The short EMS operates at sub-atmospheric pressure, typically at 526 mbar. Validation of the short EMS performance was performed against a scanning electron microscope (SEM). Good agreements were obtained from comparison between sizes determined from the short EMS classifier and the SEM analysis. Signal current from the detector was also analyzed to give rise to number concentration of particles. Experimental results obtained appeared to agree well with the theoretical predictions.

Development of a fast-response, high-resolution electrical mobility spectrometer

A short electrical mobility spectrometer (EMS) for measuring aerosol size distribution has been developed and presented (Intra and Tippayawong, Korean J. Chem. Eng., 26, 1770, 2009). In this work, further improvement of the short EMS into a fast-response, and high resolution instrument is presented. This was done by (i) improvement in particle charging, (ii) utilization of faster flow rate, and (iii) adoption of higher number of electrode rings. The so-called "long" EMS consists of three main parts: a particle charger, a long multi-channel size classifier column, and a multi- channel electrometer. Performance of the long EMS was preliminarily tested using polydisperse, carbonaceous aerosol particles generated by a diffusion flame. Preliminary test results showed that the long EMS performed comparatively well, and gave faster response and higher resolution than the short EMS. It was a valuable aerosol instrument available for measuring size distribution of aerosol particles.

Experimental characterization of a short electrical mobility spectrometer for aerosol size classification

A prototype of a short column electrical mobility spectrometer (EMS) for size measurement of aerosol particle was design, constructed, and experimentally characterized. The short EMS consists of a particle charger, a size classifier column, and a multi-channel electrometer. Its particle size resolution is derived from a 10 channel electro- meter detector. The short EMS is capable of size measurements in the range between 10 nm to 1,000 nm with a time response of about 50 s for full up and down scan. Particle number concentration in which the short EMS can measure ranges from 10 11 to 10 13 particles/m 3 . The operating flow rate of the short EMS is set for the aerosol flow rate of 1.0- 2.0 l/min and the sheath air flow rate fixed at 10.0 l/min. The inner electrode voltage of the classifier can be varied between 500-3,000 VDC. The short EMS operates at sub-atmospheric pressure, typically at 526 mbar. Validation of the short EMS performance was performed against a scanning electron microscope (SEM). Good agreements were obtained from comparison between sizes determined from the short EMS classifier and the SEM analysis. Signal current from the detector was also analyzed to give rise to number concentration of particles. Experimental results obtained appeared to agree well with the theoretical predictions.