Individual Particle Analysis Research Articles

The effects of non‐sphericity on geostationary satellite retrievals of dust aerosols

Using data collected during the Puerto Rico Dust Experiment (PRIDE), we examine the effect of non‐spherical phase functions on dust aerosol retrievals from geostationary satellites. We utilize a statistical model based on Scanning Electron Micrograph (SEM) analysis of individual dust particles. Using T‐matrix calculations and assuming that dust particles are randomly‐orientated oblate spheroids we compute the dust phase function and scattering properties. Although the non‐spherical function developed in this study compares well with the synthetic non‐spherical phase functions [Liu et al., 2003], new retrievals using the non‐spherical phase function only show slight improvement at scattering angles (Θ) from 110° ∼ 150°, and become worse for Θ between 150° ∼ 170°. However the retrievals are greatly improved at all angles when retrieval algorithms account for the combined effect of both spherical and non‐spherical phase functions.

Measurement of Efficiency of Distribution of Liquid Feed in a Gas-Solid Fluidized Bed Reactor

A technique has been developed to give a quantitative measure of the contacting efficiency of liquid feed onto particles in a hot fluidized bed for petroleum applications. Copper naphthenate was used as a tracer to measure the coating of atomized bitumen feed onto solid coke particles in a fluid coking pilot plant. The pilot plant consisted of a reactor vessel, where bitumen was injected into the reactor as feed, and a regeneration vessel, where coke particles were heated and circulated back to the reactor. Atomized bitumen droplets were injected through a feed nozzle into the reactor section. A small concentration of copper naphthenate tracer, pre-diluted with bitumen, was injected upstream of the nozzle, following a step function with time. As the bitumen reacted, the copper formed solid deposits on the surface of the particles, effectively labeling the particles that had been contacted by the bitumen droplets. Frequent coke samples from the solids exiting and entering the reactor were taken during and after the injection of the tracer.Two types of measurements were conducted on the coke samples; bulk copper concentration in the samples, using Inductively Coupled Plasma (ICP), and copper concentration on individual coke particles using energy-dispersive X-ray (EDX) analysis. The data for bulk copper concentration confirmed that the solids were mixed rapidly in the reactor, approximating a Continuous Stirred Tank Reactor (CSTR). The EDX analysis of individual coke particles demonstrated, however, that a significant fraction of the coke particles within the samples were not labeled with copper. This result indicated that many of the particles in the fluidized bed were not contacted by bitumen in the reactor. Consequently, the tracer technique was used to compare the coating efficiency of bitumen on coke particles by operation of different nozzle designs.

Speciation of Aerosols by Combining Bulk Ion Chromatography and Thin-Window Electron Probe Micro Analysis

Size-fractionated aerosol samples were collected at De Panne, a coastal village east of the French industrial area of Dunkerque. The samples were treated and analysed with conventional ion chromatography (IC) analysis and with the relatively new and promising thin-window electron probe microanalysis (EPMA) technique. The output data of the chromatographic bulk analysis technique were compared with the results from the individual particle analysis technique after statistical processing. Both methods give specific and complementary information concerning the aerosol composition. Statistically interpreted information on the single particle scale can give a more qualitative interpretation of the quantitative bulk analysis data. In fact, it becomes possible to define and quantify a certain compound as a constituent of different aerosol types. On the other hand, the quantitative data of the bulk analysis helps the interpretation, validation and quantification of the output from the single particle technique. Especially in the case of coagulated aerosols, the IC technique is able to define and to quantify irresolvable clusters.

Speciation of lead in ambient air dust combining individual particle analysis by ESEM-EDS, micro-Raman, micor-PIXE and bulk analysis by ICP-MS and selective chemical extractions

In order to determine the speciation of lead in ambient air dust, a combination of two complementary levels of investigation is used. The first one consists in a quantitative bulk analysis of the samples by applying selective chemical extractions followed by ICP-MS analysis. The second one is an individual particle analysis done by ESEM-EDS, micro-PIXE and micro-Raman. This paper presents the results from initial studies aiming to demonstrate the relevance of our methodology. Primary information about the main physico-chemical species of lead found in ambient air particulate matter, collected in the vicinity of a lead and zinc smelter, are given.

Thermal stability of beam sensitive atmospheric aerosol particles in electron probe microanalysis at liquid nitrogen temperature

Thin-window electron probe X-ray microanalysis offers new analytical possibilities for low- Z detection (i.e. elements with low atomic number; such as C, N and O). However, the quantitative analysis of individual particles raises some practical questions concerning the technique. From the analytical point of view, beam damage is one of the most important problems due to its big impact on the analysis of individual atmospheric particles. The dependence of the beam-damage effect on the type of collection substrate was studied using standard aerosol particles. Different metallic substrates were rigorously tested in relation to the beam damage effects to different kinds of beam sensitive particles. Ammonium sulfate, ammonium nitrate, sodium nitrate as well as sulfuric acid droplets were analyzed using a liquid nitrogen cooled sample stage on different metallic substrates such as Be, Al, Si and Ag. The obtained results confirm that the use of Be as a collection surface offers some advantages in order to minimize the damage to beam sensitive particles, as suggested in earlier research.

X-ray fluorescence tomography of individual waste fly ash particles

, Fluorescence tomography is a non-destructive, non-invasive technique that provides information about the internal spatial distribution of each element that emits a detectable fluorescence signal from the measured slice of the sample. The reconstruction problem for fluorescence tomography is much more difficult than it is for transmission tomography, due to the absorption of the photons within the excitation and detection paths. The present work presents a reconstruction technique that is based on the SART (Simultaneous Algebraic Reconstruction Technique) algorithm, which has been modified in order to take into account absorption corrections. This technique has been applied to the analysis of individual waste fly ash particles of about 8O 150 micron diameters, which have been scanned using an X-ray beam of V*H=2*5 μm 2 spot-size and placing an energy dispersive Si(Li) X-ray detector at 90 degrees to the incoming excitation beam. From previous scanning μ-SRXRF measurements it is clear that the elemental distribution within individual fly ash particles is highly inhomogeneous but no information could be obtained on the location of the different investigated elements (within/on the surface of the particle). On the other hand the location of toxic elements within individual fly ash particles affects the possible fate of these elements during e.g. fly-ash recycling. Thus the aim of this study was to investigate the 2D internal elemental distribution of the particles, with special attention to that of the toxic metals, such as Zn, Cd, Pb.

A Monte Carlo program for quantitative electron-induced X-ray analysis of individual particles.

A versatile Monte Carlo program for quantitative particle analysis in electron probe X-ray microanalysis is presented. The program includes routines for simulating electron-solid interactions in microparticles lying on a flat surface and calculating the generated X-ray signal. Simulation of the whole X-ray spectrum as well as phi(z) curves is possible. The most important facility of the program is the reverse Monte Carlo quantification of the chemical composition of microparticles, including low-Z elements, such as C, N, O, and F. This quantification method is based on the combination of a single scattering Monte Carlo simulation and a robust successive approximation. An iteration procedure is employed; in each iteration step, the Monte Carlo simulation program calculates characteristic X-ray intensities, and a new set of concentration values for chemical elements in the particle is determined. When the simulated X-ray intensities converge to the measured ones, the input values of elemental concentrations used for the simulation are determined as chemical compositions of the particle. This quantification procedure was evaluated by investigating various types of standard particles, and good accuracy of the methodology was demonstrated. A methodology for heterogeneity assessment of single particles is also described.

Comparison of nuclear and X-ray techniques for actinide analysis of environmental hot particles

Actinide-containing radioactive hot particles have been dispersed into the environment during atmospheric nuclear tests, accidents of the nuclear fuel cycle and authorized discharges from nuclear reprocessing plants. Several other activities like illicit trafficking of radioactive material or the use of depleted uranium in shielding, weapons can also be considered as possible sources of contamination by actinides. The paper compares detection limits for actinide analysis by nuclear spectroscopy as well as various X-ray micro-fluorescence and absorption techniques using laboratory and synchrotron sources. The detection limits for X-ray techniques were calculated using Monte Carlo simulations. Detection limits obtained for X-ray microanalysis using synchrotron sources were close to that of nuclear analysis. For long half-life nuclides (more than 105 years), X-ray spectrometry was more sensitive, while being non-destructive and offering additional information on oxidation states using X-ray absorption. For U, α spectrometry resulted only in 10−7 g (238U) contrasting 10−13 g obtained for monochromatic beam µ-XRF (micro X-ray fluorescence) at HASYLAB Beamline L. Using the combination of autoradiography and µ-XRF, identification and quantitative analysis of individual radioactive particles of 20 µm diameter were possible. Despite the strong spectral overlap with the Rb-Kα characteristic line, in fluorescence mode µ-XANES (micro X-ray absorption near-edge structure) it was possible to determine the oxidation state of 15 µg g−1 U in a single hot particle.

The Analysis of Particles at Low Accelerating Voltages (≤ 10 kV) With Energy Dispersive X-Ray Spectroscopy (EDS).

In recent years, there have been a series of advancements in electron beam instruments and x-ray detectors which may make it possible to improve significantly the quality of results from the quantitative electron-probe analysis of individual particles. These advances include: (1) field-emission gun electron beam instruments such as scanning electron microscopes (FEG-SEMs) that have high brightness electron guns with excellent performance at low beam energies, E0 ≤ 10 keV and (2) high-resolution energy-dispersive x-ray spectrometers, like the microcalorimeter detector, that provide high-resolution (< 10 eV) parallel x-ray collection. These devices make it possible to separate low energy (< 4 keV) x-ray lines including the K lines of carbon, nitrogen and oxygen and the L and M lines for elements with atomic numbers in the range of 25 to 83. In light of these advances, this paper investigates the possibility of using accelerating voltages ≤ 10 kV, as a method to improve the accuracy of elemental analysis for micrometer-sized particles.

Concentration trends and mixing states of particulate oxalate in Arctic boundary layer in winter/spring

Particulate organic species contribute to the formation of cloud condensation nuclei and may play a role in the formation/growth of condensation nuclei. The field measurements in this paper investigated size distribution and mixing states of particulate oxalate (one of major organic compounds in aerosol particles) in the Arctic boundary layer in during the winter and spring. The variation of particulate oxalate concentration correlated well with nss‐SO42− concentration. This correlation may be due to the direct emissions of oxalate and its precursors of oxalate from anthropogenic sources. The molar ratio of oxalate to nss‐SO42− was found to gradually increase from winter to early spring with the recovery of solar radiation to the Arctic Circle. Individual aerosol particle analysis by means of laser microprobe mass spectrometry showed that most of the oxalate was internally mixed with sulfate in fine particle mode (0.2–2.0 μm).

SUSPENSOIDS IN NEW YORK CITY'S DRINKING WATER RESERVOIRS: TURBIDITY APPORTIONMENT1

ABSTRACT: The technique of individual particle analysis conducted by scanning electron microscopy interfaced with automated X‐ray microanalysis (IPA/SAX) was used to characterize suspended particulate matter in New York City's drinking water reservoirs and their tributaries. The study covered a two year period and involved analyses of more than 300 samples. The particle cross sectional area per unit volume (PAV), or area concentration, was measured to account for the observed turbidity, a representation of light scattering property of the studied medium. A simple linear model with a nearly zero intercept was able to explain more than 85 percent of the variation in the measured turbidity. Moreover, the particle assemblage was categorized into generic particle types with distinctive geochemical or geological origins. Thus, PAV compositions in terms of particle types could be apportioned into turbidity components based on the model. Inorganic tripton, dominated by aluminosilicate (clay) and silicate of nonbiological nature, was found to be the major turbidity causing constituent in most cases. With the exception of one reservoir where organic detritus was significant, the predicted inorganic particle turbidity agreed with the measured turbidity within experimental error.

Atmospheric inorganic chlorine and bromine species in Arctic boundary layer of the winter/spring

Atmospheric aerosol particles and inorganic acidic gases were simultaneously collected in Ny‐Ålesund (78°55'N, 11°56'E), Svalbard, during the winter/early‐spring seasons. Inorganic chlorine species were predominantly distributed in the particulate phase, which consisted of sea‐salt particles. Gaseous inorganic chlorine species probably arise via Cl− liberation from sea‐salt particles by acidic species such as sulfate. On the other hand, inorganic bromine species were mostly found in the gaseous phase. Moreover, the concentration of gaseous inorganic bromine species gradually increased from winter to early spring. The major particulate constituent was Br−, whose concentration exceeded to sea‐salt Br− concentration, whereas bromate (BrO3−) was also found as a minor particulate bromine constituent. Thus, inorganic bromine species were suggested to be accumulated in the boundary layer during the winter/early‐spring. Halogen liberation from sea‐salt particles was often observed in analyses of individual aerosol particles and size fractionation of aerosol constituents. Chlorine liberation mostly occurred in the fine particle mode (0.2 – 2.0 μm), while Br− liberation occurred in both coarse particle (&gt;2.0 μm) and fine modes. Non‐sea‐salt Br− was predominantly distributed in fine and backup modes and internally mixed with fine sulfate particles.

Complex refractive index of aerosols during LACE 98#x2010; as derived from the analysis of individual particles

During the Lindenberger Aerosol Characterization Experiment (LACE 98), impactor sampling of aerosol particles in the size range of 0.1 to 25 μm was performed. The atmospheric concentrations of the elements sodium to lead (11 ≤ Z ≤ 83) were determined by total reflection X‐ray fluorescence analysis. Approximately 15,500 individual particles were examined by high‐resolution scanning electron microscopy and energy‐dispersive X‐ray microanalysis, and about 3800 particles were examined by transmission electron microscopy combined with energy‐dispersive X‐ray microanalysis. On the basis of morphology and chemical composition the particles were classified into 10 different groups: ammonium sulfates, calcium sulfates, sea salt, metal oxides/hydroxides, carbonates, silicates, soot, biological particles, carbon/sulfate mixed particles, and rest of carbon‐rich particles Crest. The phases present in the different particle groups were determined by selected area electron diffraction in the transmission electron microscope. In addition, the heterogeneous phase composition of agglomerates was studied in detail. On the basis of the size distribution and the relative abundance of the particle groups, the average and size‐resolved complex refractive index of the total aerosol were calculated. The real part of the average refractive index mainly depends on the abundance of metal oxide/hydroxide particles and varied between 1.52 and 1.57 on the different sampling days. The average imaginary part varied between 0.031 and 0.057 depending on the amounts of soot and carbon/sulfate mixed particles. The average complex refractive index deduced from the analysis of individual aerosol particles is in good agreement with the results of photometer measurements of dried filter samples.

Vertical variations of sea-salt modification in the boundary layer of spring Arctic during the ASTAR 2000 campaign

Airborne and ground-based aerosol/gas measurements were carried out in Svalbard between mid-March and mid-April 2000. From the viewpoint of vertical features of sea-salt modification in the lower troposphere (1500 m) of the Arctic spring, more than 1000 individual sea-salt particles were analyzed with scanning electron microscopy energy dispersive X-ray spectrometry (SEM-EDX) in the present study. Individual particle analysis suggested a vertical gradient of sea-salt modification in fine sea-salt particles with an altitude of 59–1485 m above sea level (asl), e.g. chlorine liberation rates of 33.0% (212 m asl) and 81.0% (1266 m asl) on 15 March, and 72.7% (100 m asl), 83.8% (495 m asl) and 95.8% (1411 m asl) on 26 March. Sea salts may be dominantly modified with SO2 and SO42− under Arctic haze conditions with higher SO2 concentration (≥2 nmol m−3), whereas they are dominantly modified with NO3− and reactive nitrogen oxides under Arctic background conditions, with [HNO3] of 0.15–1.3 nmol m−3 and [SO2] of 0.04–2 nmol m−3. Vertical trends in sea-salt modification suggested that it makes a significant contribution to the formation of reactive halogen species in the upper boundary layer and the lower free troposphere of the spring Arctic.

An integrated intelligence system for wear debris analysis

Wear debris generated from two moving surfaces inside a machine is a direct wear product of operating machinery. The study of the debris can reveal wear mechanisms, wear modes and wear phases undergoing in the machine. Hence, wear debris analysis can be a very useful means to assess the condition of the machine. However, the current techniques for individual particle analysis are usually time-consuming and costly due to the requirement of analyst’s expertise to perform particle inspection, morphology characterisation and data interpretation. The limitation has obstructed the wide application of this method. Therefore, it is necessary to develop effective, reliable and cost-efficient techniques to perform wear debris analysis for industrial application. This paper presents a fully computerised package for wear debris analysis. The package includes three major systems corresponding to a three-dimensional particle analysis system, an automatic particle identification system and an expert system, communicating with each other through user-friendly interfaces. The successful development of such a system has demonstrated the possibility to achieve a fully computerised analysis system for routine and in-depth wear debris study for machine condition monitoring and fault diagnosis.

Quantitative trace element analysis of individual fly ash particles by means of X-ray microfluorescence.

A new quantification procedure was developed for the evaluation of X-ray microfluorescence (XRF) data sets obtained from individual particles, based on iterative Monte Carlo (MC) simulation. Combined with the high sensitivity of synchrotron radiation-induced XRF spectroscopy, the method was used to obtain quantitative information down to trace-level concentrations from micrometer-sized particulate matter. The detailed XRF simulation model was validated by comparison of calculated and experimental XRF spectra obtained for glass microsphere standards, resulting in uncertainties in the range of 3-10% for the calculated elemental sensitivities. The simulation model was applied for the quantitative analysis of X-ray tube and synchrotron radiation-induced scanning micro-XRF spectra of individual coal and wood fly ash particles originating from different Hungarian power plants. By measuring the same particles by both methods the major, minor, and trace element compositions of the particles were determined. The uncertainty of the MC based quantitative analysis scheme is estimated to be in the range of 5-30%.

The Characterisation of Settled Dust by Scanning Electron Microscopy and Energy Dispersive X-ray Analysis

Settled dust has been collected inside the main foyers ofthree University buildings in Wolverhampton City Centre,U.K. Two of the three buildings are located in a streetcanyon used almost exclusively by heavy duty dieselvehicles. The dust was collected on adhesive carbonspectro-tabs to be in a form suitable for analysis byscanning electron microscope and energy dispersive X-rayanalysis. Using these analytical techniques, individualparticle analysis was undertaken for morphology andchemistry. Seasonal variations and variations due tolocation were observed in both the morphologicalmeasurements and chemical analysis. Many of the differencesappear attributable to the influence of road traffic, inparticular, the heavy duty diesel vehicles, travellingalong the street canyon.

The Role of Atmospheric Aerosols in the Origin Of Life

Recent results from the real time analysis of individual aerosol particles by laser mass spectrometry have revived interest in the inverted micelle structure for aerosols containing organic molecules; indeed for many aerosols the organic content is high enough, for example ∼50% by mass in the tropical upper troposphere, that it is likely to be the only viable structure. It is pointed out that atmospheric aerosols would have had many advantages as prebiotic chemical reactors, having the potential to address several key problems in a way arising naturally from the probable geophysical and chemical environment on the prebiotic planet. Bacterial and viral size can be predicted for these structures by an equation combining atmospheric aerodynamics and gravity, and which is therefore applicable to other astronomical objects which are candidates for supporting life. Experimental tests and mathematical modelling of the early stages of the chemical evolution of aerosols should be possible.

Composition, size distribution and lung deposition distribution of aerosols collected in the atmosphere of a speleotherapeutic cave situated below Budapest, Hungary

Elemental composition and mass size distribution of cave aerosols were determined by PIXE on seven-stage cascade impactor samples collected in two different sites of the Szemlőhegy-cave, a speleotherapeutic cave situated below Budapest, Hungary. In addition, individual particle analysis was also performed on about 450 aerosol particles. Significant differences were found between the two sampling sites and also in comparison with the external air in both the size distribution and in the composition of the aerosol. On the basis of the obtained data a stochastic lung deposition model was used to calculate total and regional deposition efficiencies of the different types of particles along the human respiratory system. One can conclude that the extrathoracic deposition is quite significant and its role increasing with increasing respiratory minute volume. The regional thoracic deposition is not very sensitive to the size distribution and it has a maximum around the 15–20th airway generations.

Source apportionment of gasoline and diesel by multivariate calibration based on single particle mass spectral data

The mass apportionment of gasoline and diesel particles in ambient aerosol samples is a difficult problem because both sources exhibit very similar chemical composition. However, individual particle analysis could provide additional information and help achieve source apportionment with good accuracy. Aerosol time-of-flight mass spectrometry (ATOFMS) has proven to be a powerful technique capable of simultaneously determining both the size and chemical composition of single particles in real time. Thus, samples of gasoline and diesel particles were analyzed by ATOFMS for their single particle information. In addition to the aerodynamic diameter from which the individual particle mass can be estimated, positive and negative mass spectra were obtained for each particle. A novel data analysis approach based on the combination of an adaptive resonance theory-based neural network (ART-2a), and a multivariate calibration method, partial least squares (PLS), has been developed to apportion the mass contributions of gasoline and diesel sources to mixture samples. The ART-2a neural network was used first to classify the particle-by-particle mass spectral data. The source profile for each source (gasoline/diesel) was obtained in terms of the mass fractions of the classified particle types. Next, PLS was applied to build a model relating the mass fractions of different particle classes and the mass contributions of the two sources to mixture samples. Artificial mixture samples obtained by randomly mixing some particles from the two source samples have been used to examine the feasibility of the proposed method. Satisfactory predictions for the mass contributions of gasoline and diesel exhaust to the mixture samples have been obtained. A recently proposed formula for prediction error variance is successfully modified to quantify the uncertainty in the PLS predictions. This study exemplifies the potential promise of multivariate calibration as applied to the aerosol source apportionment problem.