Ultrafine Aerosol Particle Sizer Based on Piezoresistive Microcantilever Resonators with Integrated Air-Flow Channel

To monitor airborne nano-sized particles (NPs), a single-chip differential mobility particle sizer (DMPS) based on resonant micro cantilevers in defined micro-fluidic channels (µFCs) is introduced. A size bin of the positive-charged fraction of particles herein is separated from the air stream by aligning their trajectories onto the cantilever under the action of a perpendicular electrostatic field of variable strength. We use previously described µFCs and piezoresistive micro cantilevers (PMCs) of 16 ng mass fabricated using micro electro mechanical system (MEMS) technology, which offer a limit of detection of captured particle mass of 0.26 pg and a minimum detectable particulate mass concentration in air of 0.75 µg/m3. Mobility sizing in 4 bins of a nebulized carbon aerosol NPs is demonstrated based on finite element modelling (FEM) combined with a-priori knowledge of particle charge state. Good agreement of better than 14% of mass concentration is observed in a chamber test for the novel MEMS-DMPS vs. a simultaneously operated standard fast mobility particle sizer (FMPS) as reference instrument. Refreshing of polluted cantilevers is feasible without de-mounting the sensor chip from its package by multiply purging them alternately in acetone steam and clean air

Integral Measurement of Atmospheric Particulate Matter (PM)

Atmospheric aerosol particles also known as atmospheric particulate matter or particulate matter (PM) are microscopic particles (solid or liquid) suspended in air, which is one of six air pollutants in US air quality standard. PM is classified as coarse particles with diameters between 2.5 to 10 mm, fine particles with a diameter less than 2.5 mm (PM2.5), and ultrafine particles with the diameter less than 0.1 mm (PM0.1). Epidemiological studies have already showed the adverse health effects (such as asthma, lung cancer and respiratory and cardiovascular disease) resulted from exposure to the fine and ultrafine particles. Monitoring the PM concentration (i.e., either mass or surface area concentration of PM) is critical for the protection of public health and environment and for the regulatory control. Various PM sensors are now available in market. A majority of these PM sensors are optical sensors, whose readouts are highly depended on the physical property and composition of PM. Several PM monitors based on the measurement principle of electrical charging are also available. However, the empirical calibration of the readout of these electrical PM monitors via the use of standard dust particles makes it difficult to obtain the true mass concentration of PM when PM size distribution is different from that of standard dust. The overall objective of this dissertation is to advance our scientific knowledge on the performance of cost-effective PM monitors for measuring either mass or surface area concentration of fine and ultrafine PM. This thesis includes two parts: (1) is on the evaluation of existing PM sensor for PM mass concentration measurement; (2) is on the development of new PM monitor for PM surface area concentration measurement. For the first part of this dissertation, four low-cost optical sensors, one Personal Dust Monitor (PDM) and DustrakTM were experimentally evaluated. Particles in the size distribution having different mean size, standard deviation value and material were used as test aerosol particles. The readouts of these low-cost and portable sensors are compared to that of a standard TEOM (Tapered Element Oscillation Microbalance). For the second part of this dissertation, a new electrical PM monitor, consisting of a corona-based aerosol charger, a precipitator and high sensitive current meter, has been proposed for measuring surface area concentration of fine and ultrafine PM. Particles are electrically charged upon entering an electrical PM monitor. Instead of using Faraday cage and current meter to measure the charges carried by particles in existed electrical PM sensors, the new PM monitor measures the current carried by particles deposited directly on the wall of the precipitator. A thorough evaluation has been carried out to evaluate the fundamental performance of this new PM monitor. In addition, small cyclones (i.e., quadru-inlet and tapered-body cyclones) were also evaluated as the size-selective inlet of these PM sensors/monitors to minimize the potential interface from the presence of PM with large sizes in the air. The small quadru-inlet cyclone is to resolve the issue of directional sampling; and the tapered-body cyclones is to reduce the cyclone pressure drop while having small cyclone cutoff particle size. Each cyclone has been evaluated via the measurement of particle penetration curve and pressure drop. Semi-empirical models have been obtained for the prediction of cyclone performance

Приборы и методы измерений запылённости окружающей воздушной среды. Краткий обзор

The main characteristics of airborne micro/nanoparticles, their impact on human health and air quality standards are presented. International standards classify microparticles by size (PM10, PM2.5, PM1, UFP), establish maximum allowable concentrations and control methods. Particular attention is paid to carbonand virus-containing microparticles control. To monitor the air environment in enclosed spaces and in transport, the portable sensors of micro-, nanoparticles are required with the ability to classify them by size and electrophysical characteristics.Detection of microparticles includes the sorting of particles entering the sensor by size and material type, subsequent actual detection of particles of the same kind, with subsequent classification by size, electrical and morphological characteristics. Separation of nanoand microparticles by size before detection improves the sensitivity and selectivity of the detector both in size and material. The virtual impactor and dielectrophoresis method are considered for integration in a Lab-on-Chip type sensor. Detection of microparticles is performed by separating the dispersed phase from the aerosol followed by the analysis, or directly in the air flow. The classification of detection methods according to speed and functionality is given. Among the methods allowing detection of micrometer and submicrometer size particles, the most suitable for miniaturization and serial production of Lab-on-Chip sensors are the multi-wavelength photoelectric, MEMS, and capacitor elements.The microelectromechanics, microfluidics and microoptics technologies make it possible to create portable sensor systems of the Lab-on-Chip type to detect particulates matter of micrometer and submicrometer size. A micro-, nanoparticles detector prototype based on alumina technology using MEMS elements for a compact Lab-on-Chip type sensor is presented. The proposed design for multifunctional portable detector of airborne micro/nanoparticles is prospective for industry, transport, medicine, public and residential buildings applications.Представлены основные характеристики переносимых воздухом микро/наночастиц, их влияние на здоровье человека и нормативы качества воздушной среды. Международные стандарты классифицируют микрочастицы по размеру (PM10, PM2,5, PM1, UFP), определяют предельно допустимые концентрации и методики их контроля. Особое внимание уделяется контролю углероди вируссодержащих микрочастиц. Для мониторинга воздушной среды в закрытых помещениях, в транспорте требуются портативные датчики микро-, наночастиц с возможностями их классификации по размеру и электрофизическим характеристикам.Детектирование микрочастиц включает сортировку попадающих в детектор микро/наночастиц по размеру и типу материала и собственно детектирование однотипных частиц с последующей классификацией по размеру, электрофизическим и морфологическим характеристикам. Разделение нано и микрочастиц по размеру перед детектированием повышает чувствительность и селективность детектора как по размерам, так и по материалу. Для интеграции в сенсоре Lab-on-Chip типа рассмотрены методы виртуального импактора и диэлектрофореза. Детектирование микрочастиц осуществляется с выделением дисперсной фазы из аэрозоля с последующим анализом либо непосредственно в воздушном потоке. Приведена классификация методов детектирования по быстродействию и функциональным возможностям. Среди методов детектирования частиц микронных и субмикронных размеров наиболее пригодны для миниатюризации и серийного изготовления Lab-on-Chip сенсоров мультиволновые фотоэлектрические, МЭМС, конденсаторные элементы.Технологии микроэлектромеханики, микрофлюидики и микрооптики позволяют создавать портативные сенсорные системы типа Lab-on-Chip для детектирования твёрдых частиц микронного и субмикронного размера. Представлен прототип детектора микро-, наночастиц на основе алюмооксидной технологии с использованием МЭМС элементов для компактного сенсора Lab-on-Сhip типа. Предлагаемая конструкция многофункционального портативного детектора микро/наночастиц воздушной (газовой) среды перспективна для применения в промышленности, транспорте, медицине, общественных и жилых помещениях

A Simple Method for Measuring Fine-to-Ultrafine Aerosols Using Bipolar Charge Equilibrium.

Low-cost methods for measuring airborne microparticles and nanoparticles (aerosols) have remained elusive despite the increasing concern of health impacts from ambient, urban, and indoor sources. While bipolar ion sources are common in smoke alarms, this work is the first to exploit the mean charge on an aerosol resulting from a bipolar charge equilibrium and establish experimentally its correlation to properties of the aerosol particle size distribution. The net current produced from this mean particle charge is demonstrated to be linearly proportional to the product of the mean particle diameter and total number concentration (i ∼ Nd̅) for two bipolar ion sources (85Kr and 241Am). This conclusion is supported by simple equations derived from well-established bipolar charging theory. The theory predicts that the mean charge on the aerosol particles reaches an equilibrium, which, importantly, is independent of the concentration of charging ions. Furthermore, in situ measurements of a roadside aerosol demonstrate that the sensing method yields results in good agreement (R2 = 0.979) with existing portable and laboratory-grade aerosol instruments. The simplicity, stability, and cost of the bipolar ion source overcome challenges of other portable sensors, increasing the feasibility of widespread sensor deployment to monitor ultrafine particle characteristics, which are relevant to lung deposition and by extension, human health

Differential Mobility Classifiers in the Non-Ideal Assembly

The differential mobility classifier (DMC) is one of the core components in electrical mobility particle sizers for sizing sub-micrometer particles. Designing the DMC requires knowledge of the geometrical and constructional imperfection (or tolerance). Studying the effects of geometrical imperfection on the performance of the DMC is necessary to provide manufacturing tolerance and it helps to predict the performance of geometrically imperfect classifiers, as well as providing a calibration curve for the DMC. This thesis was accomplished via studying the cylindrical classifier and the parallel plate classifier. The numerical model was built using the most recent versions of COMSOL Multiphysics® and MATLAB®. For the cylindrical DMC, two major geometrical imperfections were studied: the eccentric annular classifying channel and the tilted inner cylinder/rod. For the parallel-plates DMC, the first study examined for the perfectly designed plates to optimize its dimensions and working conditions, while the second study conducted the plates’ parallelism. For both DMCs, a parametric study was conducted for several tolerances under various geometrical factors (i.e., channel length, width, spacing, cylinders radii, etc…), flow conditions (i.e., sheath-to-aerosol flow ratio, total flow rate), and several particles sizes. The results show that the transfer function deteriorated as the geometrical imperfection increased (i.e., the peak is reduced and the width at the half peak height is broadened). The parallel- plates DMC results show that the aspect ratio of the classifying channel cross-section (width-to-height) was recommended to be above 8. Particle diffusivity reduces the effect of geometrical imperfection, especially for particle sizes less than 10 nm

Selective Characterisation of Engineered Nanoparticles in Aerosols using Nucleation and Optical Techniques

The aim of this project is to develop novel approaches for the detection and characterisation of engineered and other potentially harmful nanoparticles in the air. In particular we wish to distinguish specific nanomaterials from the background atmospheric aerosol to provide a means of measuring human exposure to nanomaterials that may present a risk to health. Ideally, solutions should be practically deployable in the field. The metrics considered for measurement across this project are: size, number, chemical nature and surface area. Two main approaches are chosen to address these requirements: online size selective surface area controlled nucleation, and quantitative assessment of size resolved Raman spectroscopic maps. The first approach is based on the discovery of a different regime type of heterogeneous nucleation. In this case nucleation probability is determined by the surface area of the aerosol rather than the number of nuclei present. A portable DMA has also been developed allowing for the pre-separation of particles according to size in a compact package. Combining this DMA with the novel nucleation technology provides a means of measuring surface area distributions of particles. Finally, a novel Raman spectroscopic methodology is presented for the chemically specific quantification of aerodynamically size selected samples. Particles are first aerodynamically size segregated from the air in a wide size range sampler. These size fractionated samples are analysed by Raman spectroscopy. Imaging analysis is then applied to Raman spatial maps to provide chemically specific quantification against the substrate as a proxy for background aerosol. Analysing this data in combination with the known deposition efficiency of aerosols in the respiratory tract (provided by the sampling method), can then provide a complete exposure measurement approach

Measuring Aerosol Nanoparticles By Ultraviolet Photoionisation

Aerosol particulate matter adversely affects the climate, environment and human health. Mechanistic studies have indicated that ultrafine aerosol nanoparticles, those under 100 nm in diameter, may have significant health impacts due to their relatively high number concentration, surface area and potential for deep penetration into the human lung. However, epidemiological evidence remains limited due to the lack of measurement networks that monitor local concentrations of ultrafine particles. Direct ultraviolet (UV) photoionisation electrically charges aerosol nanoparticles for subsequent detection by a mechanism distinct from the ion-particle collisions of conventional methods. The aim of this work is to evaluate photoionisation theory in order to understand and interpret measurements from a low-cost aerosol particle sensor. To accomplish this, theoretical equations are analysed, modelled and compared with experimental results for validation. The photoelectric yield of aerosol particles is explored in terms of particle size, concentration, material, and morphology giving insight into the interaction of light and particles. This thesis introduces the first analysis of photoionisation, recombination, convection/diffusion and transport of particles in an electric field using analytical, numerical, and computational fluid dynamics (CFD) techniques. Characteristic times and dimensionless parameters are defined to determine regimes under which the measurement system is dominated by each of the charging or transport mechanisms. The level of modelling detail required for accurate prediction of aerosol charging and capture methods is demonstrated over a range of conditions. In a continuous flow of aerosol particles, an electric field is applied to capture charge as it is photoemitted from particles and before the emitted charge and particles can recombine. This method yields a novel current measurement directly representative of photoemission. The CFD model agrees well with electrical current measurements demonstrating that the physics of the problem is suitably represented. It is demonstrated that photoemission is linearly proportional to total (mobility) surface area for a large range of sizes and concentrations of particles of self-similar material and morphology, with agglomerated silver particles having 5$\times$ yield of agglomerated carbon from a propane flame. It is shown for the first time that agglomerated particles have a significantly higher photoelectric yield (2.6$\times$) than sintered, close-packed spheres of the same mobility diameter and material, directly contradicting two of the three previous relevant studies. Close-packed spheres have less material exposed to both the photon flux and the particle's surroundings than an agglomerate of the same particle mobility diameter, thereby reducing photoelectric activity. The photoelectrically active area is defined explicitly in this work to reflect the effect of a particle's morphology; the revised definition produces good agreement with experimental results.Alphasense Ltd., Cambridge Trust, Natural Sciences and Engineering Research Council of Canada (NSERC

Diffusion Charging-Based Aerosol Instrumentation: Design, Response Characterisation and Performance

The growing concern for the air quality in urban areas and the subsequent development of measurement networks has increased the need for lightweight and cost-effective air quality instrumentation. In urban areas, traffic-related emissions are one of the major contributors to the worsened air quality, which in turn has led to the stringed emission regulations set for vehicles. These regulations necessitate both on-board monitoring of the operation of the exhaust after-treatment devices and measurement of the real-word driving emissions with portable emission measurement systems. Both of these aspects increase the demand for sensor-type instrumentation for emission measurement.This thesis focusses on the development of diffusion charging–based aerosol instrumentation towards more compact and sensor-type instruments. The work was started by developing an add-on module for the electrical low-pressure impactor. This extended the instrument measurement capabilities by enabling the measurement of the effective density of particles in real-time. Focussing more on the sensor-type instrumentation, three different sensors were presented for measuring particle emission directly from the exhaust line: Two of them targeting the engine laboratory work or for the portable emission measurement and one designed for on-board diagnostics. The instrument developed for the on-board emission measurement provided a very good temporal performance owing to the miniaturisation of the instrument design. Lastly, a new sensor design approach was presented in which the flow rate dependence of the instruments response is minimised. This, together with the minimised pressure drop in the design, helps in lowering the instrument cost by promoting the use of a low-cost fan for generating the sample flow.Instrument response characterisation and response modelling made a central part of the study. Results from the characterisation measurements were presented for all instruments, and comprehensive response models were built for the sensor-type instruments. Depending on the instrument, both simplified approximations and theoretical responses of the instrument components were used as the starting point for the response models. Additionally, the instrument performance was demonstrated in practical measurements related to the application of each instrument. The obtained response models provide necessary information for the instrument performance evaluation and the measurement data processing

Electrical And Magnetic Separation Of Particles

Particle separation technologies have been utilized in many industrial fields, such as pigment and filler production, mineral processing, environmental protection, the food and beverage industry, and the chemical industry, as well as in biomedical application, such as cell biology, molecular genetics, biotechnological production, clinical diagnostics, and therapeutics. A lot of particle separation technologies using various mechanics in terms of the differences in the physical or physico-chemical properties of the particles have been developed. Among these categories, electrical and magnetic separations are of great interest in recent researches. The overall objective of this dissertation is to advance our current knowledge on these two particle separation technologies. Accordingly, it has two major parts:: 1) Charge Conditioning for Particle Separation, and: 2) Magnetic Filtering for Particle Separation. In the first part, a new DC-corona-based charge conditioner for critical control of electrical charges on particles and a UV aerosol charger for fundamental investigation particle photocharging process were developed. The chargers\u27 performances including charging efficiencies and charge distributions were evaluated upon different operational conditions such as aerosol flow rates, corona operations, and ion-driving voltages for the charge conditioner, particle material and irradiation intensity for the UV charger. The birth-and-death charging model with the Fuchs limiting sphere theory for calculating the ion-particle combination coefficient was applied to obtain the charging ion concentration inside the charge conditioner. The UV charging model with the photoemission rely on the Fowler-Nordheim law was applied to predict the charging performance of the UV charger. In the second part, a magnetic filter system has been constructed, and its performance has been investigated. To retrieve the magnetic property of characterized particles from the measured penetration data, a numerical model was further developed using the finite element package COMSOL Multiphysics 3.5. The numerical model was first validated by comparing the experimental penetration with the simulation results for the cases of 100, 150, and 250 nm r-Fe2O3 particles having the magnetic susceptibility characterized by Vibrating Sample Magnetometer: VSM). The magnetic susceptibilities of other sizes from 100 to 300 nm were then derived from this model according to the measured penetration data. To control or remove the lunar dust through a magnetic approach, eight samples: three JSC-1A series lunar dust simulants, two NU-LHT series lunar dust simulants, and three minerals) in the size range from 150 to 450 nm were characterized. Magnetic susceptibilities were obtained from the difference in particle penetration through magnetic mesh filters with and without an applied external magnetic field