共查询到20条相似文献,搜索用时 15 毫秒
1.
Tyler J. Johnson Martin Irwin Jonathan P. R. Symonds Jason S. Olfert Adam M. Boies 《Aerosol science and technology》2018,52(6):655-665
The Aerodynamic Aerosol Classifier (AAC) is a novel instrument that selects aerosol particles based on their relaxation time or aerodynamic diameter. Additional theory and characterization is required to allow the AAC to accurately measure an aerosol’s aerodynamic size distribution by stepping while connected to a particle counter (such as a Condensation Particle Counter, CPC). To achieve this goal, this study characterized the AAC transfer function (from 32 nm to 3 μm) using tandem AACs and comparing the experimental results to the theoretical tandem deconvolution. These results show that the AAC transmission efficiency is 2.6–5.1 times higher than a combined Krypton-85 radioactive neutralizer and Differential Mobility Analyzer (DMA), as the AAC classifies particles independent of their charge state. However, the AAC transfer function is 1.3–1.9 times broader than predicted by theory. Using this characterized transfer function, the theory to measure an aerosol’s aerodynamic size distribution using an AAC and particle counter was developed. The transfer function characterization and stepping deconvolution were validated by comparing the size distribution measured with an AAC-CPC system against parallel measurements taken with a Scanning Mobility Particle Sizer (SMPS), CPC, and Electrical Low Pressure Impactor (ELPI). The effects of changing AAC classifier conditions on the particle selected were also investigated and found to be small (<1.5%) within its operating range.
Copyright © 2018 American Association for Aerosol Research 相似文献
2.
《Journal of aerosol science》2006,37(10):1303-1325
A new instrument capable of measuring aerosol size distribution with high time and size resolution, and high signal-to-noise ratios is described. The instrument, referred to as Fast Integrated Mobility Spectrometer (FIMS), separates charged particles based on their electrical mobility into different trajectories in a uniform electric field. The particles are then grown into super-micrometer droplets, and their locations on the trajectories are recorded by a fast charge-coupled device (CCD) imaging system. Images captured by the CCD reveal mobility-dependent particle positions and their numbers, which are then used to derive a particle size distribution spectrum. By eliminating the need to scan over a range of voltages, FIMS significantly improves the measurement speed and counting statistics. A theoretical framework has been developed to quantify the measurement range, mobility resolution, and transfer function of FIMS. It is shown that FIMS is capable of measuring aerosol size distributions with high-time and size resolution. 相似文献
3.
Tamara Pinterich Steven R. Spielman Susanne Hering 《Aerosol science and technology》2017,51(10):1212-1222
A water-based fast integrated mobility spectrometer (WFIMS) with enhanced dynamic size range is developed. The WFIMS builds on two established technologies: the fast integrated mobility spectrometer and laminar flow water-based condensation methodology. Inside WFIMS, particles of differing electrical mobility are separated in a drift tube and subsequently enlarged through water condensation. Particle size and concentration are measured via digital imaging at a frame rate of 10 Hz. By measuring particles of different mobilities simultaneously, the WFIMS resolves particle diameters ranging from 8 to 580 nm within 1 s or less. The performance of WFIMS was characterized with differential mobility analyzer (DMA) classified (NH4)2SO2 particles with diameters ranging from 8 to 265 nm. The mean particle diameters measured by WFIMS were found to be in excellent agreement with DMA centroid diameters. Furthermore, detection efficiency of WFIMS was characterized using a condensation particle counter as a reference and is nearly 100% for particles with diameter greater than 8 nm. In general, measured and simulated WFIMS mobility resolutions are in good agreement. However, some deviations are observed at low particle mobilities, likely due to the non-idealities of the WFIMS electric field.
Copyright © 2017 American Association for Aerosol Research 相似文献
4.
Jian Wang 《Journal of aerosol science》2009,40(10):890-906
A fast integrated mobility spectrometer with wide size range (WSR-FIMS) is described. The WSR-FIMS greatly enhances the dynamic size range of the original FIMS [Kulkarni, P., & Wang, J. (2006a). New fast integrated mobility spectrometer for real-time measurement of aerosol size distribution—I: Concept and theory. Journal of Aerosol Science, 37, 1303—1325; Kulkarni, P., & Wang, J. (2006b). New fast integrated mobility spectrometer for real-time measurement of aerosol size distribution—II: Design, calibration, and performance characterization. Journal of Aerosol Science, 37, 1326—1339] by employing a non-uniform electric field. The strength of this electric field varies over three orders of magnitude along the width of the separator, allowing particles of a much wider size range to be classified and measured simultaneously. A theoretical framework is developed to derive the transfer function, resolution, and transmission efficiency of the WSR-FIMS. Two representative operation configurations are simulated, and the results show the WSR-FIMS can simultaneously measure particles ranging from 10 to 1470 nm, therefore greatly reducing the measurement time from minutes required by scanning mobility particle sizer (SMPS) to 1 s or less. The WSR-FIMS also has a higher size resolution than typical SMPS over most of its measurement size range. For typical ambient aerosols, the simulations show that 1 s measurements using the WSR-FIMS provide good counting statistics. 相似文献
5.
6.
Inversion to obtain aerosol size distributions from measurements with a differential mobility analyzer 总被引:1,自引:0,他引:1
To measure size distributions of submicrometer aerosols with an electrical differential mobility analyzer (DMA) requires an inversion procedure. The Knutson (1976) and the Hoppel (1978) inversion procedures were numerically investigated for the case of log-normal aerosol size distributions. It was found that the Hoppel procedure converges to the same result as that given by the Knutson procedure. The computational range for geometric mean diameter (
g) was 0.025-0.25 μm, and for geometric standard deviation (σg) was 1.1–2.4. The inversion error was found to be greater than 10% in certain “forbidden zones” of
g and σg values. For the case of an ideal DMA having no lower mobility limit, only one forbidden zone exists, this consisting of small σg values. The boundary of this forbidden zone intercepts the computational range boundaries at σg = 1.25,
and σg = 1.62,
. These results also apply to an actual DMA when the size distribution of particles larger than the DMA singly charged mobility limit is available a priori. If such information is not available, the concentration of these larger particles is assumed to be zero in performing the inversion. This assumption adds a second forbidden zone, consisting of large σg values and having the intercepts σg = 2.44,
and σg = 1.50,
. The first forbidden zone remains nearly the same. 相似文献
7.
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. 相似文献
8.
Pramod Kulkarni Chaolong Qi Nobuhiko Fukushima 《Aerosol science and technology》2016,50(11):1167-1179
We describe development of a portable aerosol mobility spectrometer (PAMS) for size distribution measurement of submicrometer aerosol. The spectrometer is designed for use in personal or mobile aerosol characterization studies and measures approximately 22.5×22.5×15 cm and weighs about 4.5 kg including the battery. PAMS uses electrical mobility technique to measure number-weighted particle size distribution of aerosol in the 10–855 nm range. Aerosol particles are electrically charged using a dual-corona bipolar corona charger, followed by classification in a cylindrical miniature differential mobility analyzer. A condensation particle counter is used to detect and count particles. The mobility classifier was operated at an aerosol flow rate of 0.05 L/min, and at two different user-selectable sheath flows of 0.2 L/min (for wider size range 15–855 nm) and 0.4 L/min (for higher size resolution over the size range of 10.6–436 nm). The instrument was operated in voltage stepping mode to retrieve the size distribution in approximately 1–2 min. Sizing accuracy and resolution were probed and found to be within the 25% limit of NIOSH criterion for direct-reading instruments. Comparison of size distribution measurements from PAMS and other commercial mobility spectrometers showed good agreement. The instrument offers unique measurement capability for on-person or mobile size distribution measurement of ultrafine and nanoparticle aerosol. 相似文献
9.
All aerosol formation and evolution processes, such as nucleation, condensation, fragmentation, etc., are understood and rationalized via fundamental probabilistic concepts such as probabilities of collision, coagulation, dispersion, etc. Therefore all theoretical size distribution functions (lognormal, modified gamma distribution, self-preserving particle size distribution for Brownian coagulation, etc.) are in fact size probability density functions pdf(r). Any (e.g., measured) size distribution f(r) of an aerosol system is some random realization of its pertinent size probability density function pdf(r). When pdf(r) is viewed as a continuous function, the corresponding size distribution vanishes almost everywhere excluding some randomly set of sizes where f(r)=1. We investigate proximity between f(r) and pdf(r) in finite size intervals and derive expressions for estimation of the standard deviations of several aerosol size-dependent properties arising from randomness of f(r). 相似文献
10.
11.
G.R. Johnson L. Morawska Z.D. Ristovski M. Hargreaves K. Mengersen C.Y.H. Chao M.P. Wan Y. Li X. Xie D. Katoshevski S. Corbett 《Journal of aerosol science》2011,42(12):839-851
An essential starting point when investigating the potential role of human expired aerosols in the transmission of disease is to gain a comprehensive knowledge of the expired aerosol generation process, including the aerosol size distribution, the various droplet production mechanisms involved and the corresponding sites of production within the respiratory tract. In order to approach this level of understanding we have integrated the results of two different investigative techniques spanning 3 decades of particle size from 700 nm to 1 mm, presenting a single composite size distribution, and identifying the most prominent modes in that distribution. We link these modes to specific sites of origin and mechanisms of production. The data for this were obtained using the Aerodynamic Particle Sizer (APS) covering the range 0.7≤d≤20 μm and Droplet Deposition Analysis (DDA) covering the range d≥20 μm.In the case of speech three distinct droplet size distribution modes were identified with count median diameters at 1.6, 2.5 and 145 μm. In the case of voluntary coughing the modes were located at 1.6, 1.7 and 123 μm. The modes are associated with three distinct processes: one occurring deep in the lower respiratory tract, another in the region of the larynx and a third in the upper respiratory tract including the oral cavity. The first of these, the Bronchiolar Fluid Film Burst (BFFB or B) mode contains droplets produced during normal breathing. The second, the Laryngeal (L) mode is most active during voicing and coughing. The third, the Oral (O) cavity mode is active during speech and coughing. The number of droplets and the volume of aerosol material associated with each mode of aerosol production during speech and coughing is presented. The size distribution is modeled as a tri-modal lognormal distribution dubbed the Bronchiolar/Laryngeal/Oral (B.L.O.) tri-modal model. 相似文献
12.
Yang Wang Guangjie Zheng Steven R. Spielman Tamara Pinterich Susanne V. Hering Jian Wang 《Aerosol science and technology》2013,47(9):1092-1106
Hygroscopicity describes the tendency of aerosol particle to uptake water and is among the key parameters in determining the impact of atmospheric aerosols on global radiation and climate. A hygroscopicity tandem differential mobility analyzer (HTDMA) system is the most widely used instrument for determining the aerosol hygroscopic growth. Because of the time needed to scan the classifying voltage of the DMA, HTDMA measurement often requires a minimum of 30?min to characterize the particle hygroscopic growth at a single relative humidity for five to six different sizes. This slow speed is often inadequate for measurements onboard mobile platforms or when aerosols evolve rapidly. Recently, a humidity-controlled fast integrated mobility spectrometer (HFIMS) was developed for measuring the hygroscopic growth of particles. The measurement speed of the HFIMS is about one order of magnitude faster than that of the conventional HTDMA. In this work, a data inversion routine is developed to retrieve the growth factor probability density function (GF-PDF) of particles measured by the HFIMS. The inversion routine considers the transfer functions of the upstream DMA and the downstream water-based fast integrated mobility spectrometer (FIMS), and derives the GF-PDF that reproduces the measured responses of the HFIMS. The performance of the inversion routine is examined using ambient measurements with different assumptions for the spectral shape of the particle GF-PDF (multimodal lognormal or piecewise linear). The influences of the data inversion parameters and counting statistics on the inverted GF-PDFs were further investigated, and an approach to determine the optimized inversion parameters is presented.Copyright © 2019 American Association for Aerosol Research 相似文献
13.
A multi-channel differential mobility analyzer (MCDMA) or aerosol spectrometer is widely used for classifying and measuring
nanometer aerosol particles in the size range from 1 nm to 1 μm because of its better time response than a typical differential
mobility analyzer. In the present study, the effect of Brownian diffusion on electrical mobility classification and trajectory
of nanometer aerosol particles in an electrical mobility spectrometer developed at Chiang Mai University has been analytically
investigated. Th Brownian diffusion of particles inside the spectrometer increased with decreasing particle size and flow
rates of aerosol and clean sheath air, and with increasing inner electrode voltage, and also decreased with decreasing operating
pressure. The particle trajectories considering Brownian diffusion motion inside the spectrometer were found to be broader
than those under no Brownian diffusion. Smaller particles were found to have higher degree of broadening of trajectory than
the larger particles. Brownian diffusion effect was found to be significant for particles smaller than 10 nm. 相似文献
14.
15.
In the Nano Aerosol Mass Spectrometer (NAMS), particles are irradiated with a high energy laser pulse to produce a plasma that quantitatively disintegrates each particle into positively charged atomic ions. Previous work with this method used electrodynamic focusing and trapping of particles 30 nm dia. and below. In the current work, an aerodynamic focusing inlet was used to study particles between 40 and 150 nm dia. The distribution of atomic ion charge states was found to be particle size dependent, shifting toward lower charges with increasing size. This shift also affected the calibration by which elemental composition was determined from atomic ion signal intensities. Size independent calibration could be achieved by restricting the analysis to particles that gave more than 90% of the total signal intensity as multiply charged ions. This approach worked best for particles smaller than about 100 nm dia. since most spectra met this criterion. For the nanoparticles studied, the elemental mole fractions of Group I and II metals, halogens, and low atomic mass nonmetals could be determined within 10% or less of the expected value when the mole fraction was at the 1% level or greater. Some transition and heavy metals could not be quantified, while others could. Quantification appeared to be dependent on the ability of the element to be vaporized. Elements with high melting and boiling points gave particle mass spectra similar to those obtained by laser desorption ionization—mostly singly charged ions with relative intensities strongly biased toward atoms with low ionization energies.
Copyright © 2017 American Association for Aerosol Research 相似文献
16.
The independent and the dependent models of light extinction methods were two new methods for measuring the particle size distribution. Some experiments were carried out to confirm these methods. The experimental results of the measurement of latex particles ranged from 0.091 to 9.85 μm and some samples of TiO2 powder were presented. Experimental results have shown that these methods have a larger measurable range from about 0.01 to 10 μm, high accuracy and a short measurement time. The optimum value of I/I0 in the measurement should lie between 0.4 and 0.9. The independent model of light extinction method can even measure ‘multi-peaks’ polydisperse aerosols. 相似文献
17.
Particle size distributions of nearly monodisperse dioctyl phthalate aerosols (dia. between 0–5 and 1–4 μm) have been determined using the Stöber aerosol spectrometer. The particle size distributions can be approximated very well by bimodal distribution functions. From a statistical analysis it turned out that the accuracy of the approximation is limited in case of small particles (dia. ~ 0·5 μm). This is due to evaporation of the particles during the analysis.The mean of the particle size distribution determined with the Stöber aerosol spectrometer was in fair agreement with the particle diameter determined with the higher order Tyndall spectrometer. 相似文献
18.
《Journal of aerosol science》2002,33(2):339-356
Elemental mass size distributions in aerosols collected at four different urban sites with gradually increasing overall aerosol mass concentration are presented, compared and discussed in the present paper. The aerosol samples were collected with cascade impactor and stacked filter unit samplers, and were analyzed by particle-induced X-ray emission spectrometry and instrumental neutron activation analysis. Typical coarse-mode elements, i.e., Na, Mg, Al, Si, P, Ca, Ti, Fe, Ga, Sr, Zr, Mo and Ba, exhibited unimodal size distributions at all four urban locations studied, and the mass median aerodynamic diameters were increased with aerosol pollution level. Elements typically related to high-temperature or anthropogenic sources, i.e., S, Cl, K, V, Cr, Mn, Ni, Cu, Zn, Ge, As, Se, Br, Rb and Pb, either had a unimodal size distribution with most or their mass in the fine size fraction or clearly showed a bimodal size distribution at the urban background site. However, significant differences between the size distributions of four sampling sites were noted. There was a clear tendency for the accumulation mode to decrease and for the coarse mode to increase with increasing total aerosol mass concentration. A pronounced resuspension of the soil and roadway dust associated with the fine aerosol particles that were deposited on the ground surface previously, and the condensation process of volatile precursor gases on the already existing aerosol particles can explain the observed tendencies. The elemental mass size distributions derived for the polluted urban environments differ from those typically observed for industrial, combustion or automotive sources. A consequence of the diversity in the size distributions on the PM2.5 speciation concept is also presented. 相似文献
19.
Aerosol mobility size spectrometers are commonly used to measure size distributions of submicrometer aerosol particles. Commonly used data inversion algorithms for these instruments assume that the measured mobility distribution is broad relative to the DMA transfer function. This article theoretically examines errors that are incurred for input distributions of any width with an emphasis on those with mobility widths comparable to that of the DMA's transfer function. Our analysis is valid in the limit of slow scan rates, and is applicable to the interpretation of measurements such as those obtained with tandem differential mobility analyzers as well as broader distributions. The analysis leads to expressions that show the relationship between the inverted number concentration, mean size, and standard deviation and true values of those parameters. For narrow distributions (e.g., for a mobility distribution produced by a DMA with a 1:10 aerosol:sheath air flow ratio) under typical operating conditions, number concentrations and mean mobility obtained with inversion algorithms are accurate to within 0.5% and 1.0%, respectively. This corresponds to mean diameter retrieval errors of 1.0% for large particles and 0.5% for small (kinetic regime) particles. The widths (i.e., relative mobility variance) of the inverted distributions, however, significantly exceed the true values.
Copyright © 2018 American Association for Aerosol Research 相似文献
20.
Current atmospheric observations tend to support the view that continental tropospheric aerosols, particularly urban aerosols, show multimodal mass distributions. One of the obvious mechanisms causing the multimodality is the mixing of different primary sources. Other modes involve dissimilar aerosol formation processes in the atmosphere. Fine aerosol particles are generated from secondary processes such as nucleation, condensation and chemical reaction, whereas coarse particles usually consist of dust, fly ash and mechanically generated aerosols. With the use of a newly developed computer code GROWTH in our laboratory, we report here the simulated results of Brownian coagulation dynamics involving multimodal mass density functions for long periods of time. In our model calculations we assume that the aerosol particles are well mixed in an atmospheric volume so that spatial variation in the distribution is negligible. Our accurate numerical simulation of the Brownian coagulation dynamics indicates that once formed, an atmospheric multimodal aerosol distribution in the range 0.1 to 100 μm will maintain its identity for a very long period of time (at least hours) unless “atmospheric perturbations” such as meteorological instabilities, rain-washout and gravitational settling occur. It is our belief that understanding the complex domain of atmospheric aerosols requires systematic investigation of each process. This paper is a continuation of such an investigation. 相似文献