Individual Particle Analysis Research Articles

Optical trapping and coherent anti-Stokes Raman scattering (CARS) spectroscopy of submicron-size particles

Optical trapping combined with coherent anti-Stokes Raman scattering (CARS) spectroscopy is demonstrated for the first time as a new technique for the chemical analysis of individual particles over an extended period of time with high temporal resolution. Single submicron-size particles suspended in aqueous media are optically trapped and immobilized using two tightly focused collinear laser beams from two pulsed Ti:Sapphire laser sources. The particles can remain stably trapped at the focus for many tens of minutes. The same lasers generate a CARS vibrational signal from the molecular bonds in the trapped particle when the laser frequencies are tuned to a vibrational mode of interest, providing chemical information about the sample. The technique is characterized using single polystyrene beads and unilamellar phospholipid vesicles as test samples and can be extended to the study of living biological samples. This novel method could potentially be used to monitor rapid dynamics of biological processes in single particles on short time scales that cannot be achieved by using other vibrational spectroscopy techniques.

Inorganic tripton in the Finger Lakes of New York: importance to optical characteristics

Inorganic particles in the upper waters of the 11 Finger Lakes of New York are morphometrically and elementally characterized by individual particle analysis conducted with scanning electron microscopy interfaced with automated image and X-ray analyses (IPA/SAX). Coupled measurements of Secchi disk transparency (SD), the attenuation coefficient for downwelling irradiance (Kd), the beam attenuation coefficient at 660 nm, and turbidity (Tn) were made to support evaluation of the importance of non-living, inorganic particles (inorganic tripton) in regulating these optical features of water quality. Wide differences in levels of inorganic tripton, represented in terms of particle projected area per unit volume (PAVin), and the optical measures are reported for these lakes. However, generally similar size distributions are observed for the inorganic tripton for the lakes. Terrigenous suspensoids, in the form of clay minerals, dominated the inorganic tripton particle assemblage of nine lakes, while CaCO3, formed autochthonously, dominated in the other two and was a noteworthy contributor in four others. PAVin is demonstrated to be an important regulator of the optical properties of these lakes, performing substantially better than chlorophyll in predicting SD, and Tn, and interlake differences in these optical measures.

Flow cytometric analysis of fine particles in a eutrophic lake

Fine particles play an important role, not only in aquatic biogeochemical processing but also in the distribution, transfer and transformation of pollutants in the aquatic environment. Flow cytometry, widely used in biomedical research, allows fast counting and optical analysis of individual particles. Organic autotrophic particles contain naturally fluorescing pigments, such as chlorophyll and phycoerythrin. Different populations have different sizes and pigments. They also have different ratios of pigments. In general, side angle scatter (SSC) is related to the size, shape and refractive index of particles. When a 488 nm wavelength was used to excite chlorophyll and phycoerythrin fluorescence, the pigments of organic autotrophic particles emitted red and orange light. Fine particles were detected by flow cytometry (FCM) in the southern part of a eutrophic lake in winter. We found that organic autotrophic particles belonged to three populations, which represented only 15.89% of total fine particles. Organic non-living particles and inorganic particles represented the greater part (84.11%) of total fine particles. This study also demonstrated that flow cytometry is well suited to the dynamic monitoring and analysis of natural water aquatic particles that were difficult to study with traditional methods.

Microstrain and Defect Analysis of CL-20 Crystals by Novel X-Ray Methods

ABSTRACT Microstrains and defects are introduced during synthesis and crystal-growth stages of energetic particles and increase during processing stages such as grinding, mixing, and extrusion. The detection and quantification of these microstrains and defects in a given particle population is a difficult task that requires highly sensitive techniques. In this study a novel X-ray diffraction technique (XAPS) based on simultaneous rocking-curve analysis of individual particles was successfully applied to CL-20 powders. The effects of synthesis, grinding, and static loads on the extent of microstrain and defect development in CL-20 particles were quantitatively determined as frequency versus half-width of rocking curves. The greater half-width values observed for the samples subjected to grinding and static loads indicated greater microstrain and defect density in comparison to the as-received samples of CL-20. It may be possible to relate the findings of such analysis to combustion calculations for energetic particles in general and to CL-20 particles in particular.

Surfactant—Dispersion of Metal Oxide Fume Particles

Fume agglomeration frustrates electron microscopy of individual primary particles. Lauric acid was added to an ethanol suspension of metal oxide fume particles collected from arc welding in order to create a dense suspension that minimized interparticle contact. Evaluation of transmission electron micrographs demonstrated that the surfactant aided dispersion and therefore analysis of individual particles.

Synthesis of Kaolinite with a High Level of Fe3+ for Al Substitution

AbstractFe-rich kaolinites were synthesized at 225°C in distilled water from gels with different Fe/Al ratios (0.15, 0.25, 0.35) and with Si/(Al + Fe) = 2. X-ray diffraction patterns of the reaction products showed that kaolinite was the only long-range crystalline phase synthesized. Analytical electron microscopy analyses of individual particles and Fourier transform infrared spectra indicated that Fe3+ was isomorphously incorporated into the kaolinite octahedral sheet and that tetrahedral substitution did not occur. The Fe content hosted in the synthetic kaolinites was similar to that incorporated into its corresponding starting gel. The highest Fe content in the particles reached 30 mol.% of the octahedral occupancy. Increases in the b parameter are proportional to increases in Fe for Al substitution. The extent of isomorphic substitution of Al by Fe is the highest ever reported for both natural and synthetic samples. At the nano-scale, there is no evidence of discontinuity in the solid-solution between the Si2Al2O7 and Si2Al1.4Fe0.6O7 end-members, such as short-range disorder or clustering of Fe and Al in domains.

Microscopy and mineralogy of airborne particles collected during severe dust storm episodes in Beijing, China

Asia dust storm (ADS) samples were collected during two severe dust storm episodes in Beijing, China. High‐resolution field emission scanning electron microscopy (FESEM) and environmental scanning electron microscopy‐energy dispersive X‐ray detector (ESEM‐EDX) coupled with an image analysis system were used to study the morphology, chemical compositions, and number‐size distributions of ADS particles. FESEM analysis indicated that Beijing ADS samples were mainly composed of irregularly shaped mineral particles. More than 50% of the ADS particles were larger than 1 μm, measured as equivalent spherical diameter (ESD). Image analysis showed that when the dust storm episodes ended in Beijing, the number of anthropogenic particles, such as soot aggregates and coal fly ash, in the samples increased, and the number of mineral particles decreased. Analysis of individual ADS particles showed that about one fifth of all the particles were mineral aggregates, and at least one fourth of the particles contained sulfur. X‐ray diffraction (XRD) was used to quantify the phase and the clay mineral compositions of ADS samples. Phases in the ADS sample collected during the 20 March 2002 dust storm episode included clay minerals, noncrystalline materials, quartz, calcite, plagioclase, potassium feldspar, pyrite, hornblende, and gypsum in descending order. Clay minerals were mainly illite/smectite mixed layers (78%), followed by illite (9%), kaolinite (6%), and chlorite (7%). Particulate matter (PM) less than 10 μm were enriched with clay minerals and deficient with quartz by mass compared with the total suspended particulates collected during an ADS episode. The PM less than 10 μm collected during the two severe dust storm episodes was characterized by the absence of dolomite, high quartz/clay ratio, and dominance of illite/smectite mixed layers in clay minerals.

Variations of constituents of individual sea-salt particles at Syowa station, Antarctica

Sampling of atmospheric aerosol particles was carried out at Syowa station, Antarctica (39.58°E, 69.00°S) in 1998. For a better understanding of sea-salt chemistry in the coastal Antarctic regions, individual sea-salt particles were analysed using a scanning electron microscope equipped with energy dispersive X-ray spectrometer (SEM-EDX). Individual particle analysis indicates that more sea-salt particles were modified in fine particles (0.2–2 µm in diameter) through heterogeneous reactions mainly with gaseous sulfur species in the summer and reactive nitrogen oxides in the winter—spring. In particular, sea-salt particles in the coastal Antarctic atmosphere may be modified by heterogeneous reactions with not only SO2 and H2SO4 but also volatile sulfur species (e.g. CH3SO3H, DMS and DMSO) derived from bioactivity on the ocean surface during the summer. Also, low air temperature and a larger extent of sea ice offshore Syowa probably enhanced release of fractionated sea-salt particles (S-rich, Mg-rich, K-rich and Ca-rich) from the surface of snow and sea ice, particularly in September—October 1998. In addition, we attempt to estimate the scavenging rate of atmospheric sulfur species and reactive nitrogen oxides by dry deposition of sea-salt particles. Our estimation suggests that the upper limit of the scavenging rate of atmospheric sulfur species by sea-salt particles could rise to approximately 0.5 nmol m−2 day−1 at Syowa station during the summer. This value corresponded to about 30% of the concentration of particulate sulfur species such as non-sea-salt (nss)-SO2−4 and CH3SO−3 and ~10% of total atmospheric sulfur species (nss-SO2−4, CH3SO−3 and SO2). In contrast, the estimated NO−3 scavenging rate by sea-salt particles was ~0.2 nmol m−2 day−1, which is similar to the dry deposition rate of HNO3+N2O5 (approximately 0.2–0.3 nmol m−2 day−1). Hence, sea-salt particles probably play an important role as scavengers of acidic species in the coastal Antarctic regions.

Automated analysis of individual particles using a commercial capillary electrophoresis system

Capillary electrophoretic analysis of individual submicrometer size particles has been previously done using custom-built instruments. Despite that these instruments provide an excellent signal-to-noise ratio for individual particle detection, they are not capable of performing automated analyses of particles. Here we report the use of a commercial Beckman P/ACE MDQ capillary electrophoresis (CE) instrument with on-column laser-induced fluorescence (LIF) detection for the automated analysis of individual particles. The CE instrument was modified with an external I/O board that allowed for faster data acquisition rates (e.g. 100 Hz) than those available with the standard instrument settings (e.g. 4 Hz). A series of eight hydrodynamic injections expected to contain 32 +/- 6 particles, each followed by an electrophoretic separation at -300 V cm(-1) with data acquired at 100 Hz, showed 28 +/- 5 peaks corresponding to 31.9 particles as predicted by the statistical overlap theory. In contrast, a similar series of hydrodynamic injections followed by data acquisition at 4 Hz revealed only 8 +/- 3 peaks suggesting that the modified system is needed for individual particle analysis. Comparison of electropherograms obtained at both data acquisition rates also indicate: (i) similar migration time ranges; (ii) lower variation in the fluorescence intensity of individual peaks for 100 Hz; and (iii) a better signal-to-noise ratio for 4 Hz raw data. S/N improved for 100 Hz when data were smoothed with a binomial filter but did not reach the S/N values previously reported for post-column LIF detection. The proof-of-principle of automated analysis of individual particles using a commercially available CE system described here opens exciting possibilities for those interested in the study and analyses of organelles, liposomes, and nanoparticles.

The chemical composition and complex refractive index of rural and urban influenced aerosols determined by individual particle analysis

Abstract From July 1997 to June 1998 aerosol particle samples (diameter 0.1–25 μm) were collected at Kleiner Feldberg (Taunus mountains, Germany), a rural location that is temporarily influenced by the nearby urban Rhein-Main area and/or by long-range transport from East Germany and Eastern Europe. The atmospheric concentrations of the elements sodium to lead (11⩽Z⩽83) were determined by total reflection X-ray fluorescence analysis. Size, morphology and chemical composition of more than 27,000 individual aerosol particles were determined by high-resolution scanning electron microscopy and energy-dispersive X-ray microanalysis. Based on morphology and chemical composition the particles were classified in the particle groups: ammonium sulfates, calcium sulfates, sea salt, alumosilicates, silica, metal oxides/hydroxides, soot, biological particles, carbon/sulfate mixed particles, and remaining carbon-rich particles (Crest). Polluted air masses at Kleiner Feldberg are characterized by high number concentrations of soot (up to 80% in the size range from 0.1 to 0.2 μm), metal oxides and sulfates. Anthropogenic and natural sources of alumosilicates, silica and metal oxides/hydroxides are easily distinguished by their morphology. From the size resolved relative abundance of the different particle groups the total and the size resolved complex refractive index (CRI) of the dry particulate matter ( λ = 550 nm ) was calculated for the different sampling days. Urban influenced air masses are characterized by high real (1.60–1.73) and imaginary parts (0.034–0.086) of the total CRI, rural air masses by lower real (1.54–1.61) and imaginary parts (0.001–0.021). The high real parts of the CRI of polluted air masses are predominantly caused by the high abundance of metal oxide/hydroxide particles, the high imaginary parts by high abundances of soot.

Receptor Modeling of Toronto PM2.5 Characterized by Aerosol Laser Ablation Mass Spectrometry

Urban Toronto fine particulate matter (PM2.5) was physically and chemically characterized by online aerosol laser ablation mass spectrometry (LAMS) between January 2002 and February 2003. The mass spectra from the analysis of individual aerosol particles were classified according to chemical composition by a neural network approach called adaptive resonance theory (ART-2a). Temporal trends of the hourly analysis rate of over 120 different particles types were constructed and subjected to positive matrix factorization (PMF). This receptor modeling technique enabled the identification of nine distinct emission sources responsible for these particle types: biogenic, mixed crustal, organic nitrate, construction dust, Toronto soil/road salt, secondary salt, wood burning, intercontinental dust, and an unknown source of aluminum fluoride dust. Episodic events occurred with the wood burning, intercontinental dust, and unknown dust sources. This is the first paper reporting the application of PMF to single-particle spectral data.

Characterization and source identification of a fine particle episode in Finland

Abstract A strong long-range transported (LRT) fine particle (PM 2.5 ) episode occurred from March 17–22, 2002 over large areas of Finland. Most of the LRT particle mass was in the submicrometre size fraction. The number of concentrations of 90–500 nm particles increased by a factor of 5.6 during the episode, but the concentrations of particles smaller than 90 nm decreased. This reduction of the smallest particles was caused by suppressed gas-to-particle conversion due to the vapour uptake of LRT particles. Individual particle analyses using SEM/EDX showed that the proportion of sulphur-rich particles rose strongly during the episode and that the relative weight percentage of potassium was unusually high in these particles. The median S/K ratios of S-rich particles were 2.1 at the beginning of the episode, 5.2 at the peak stage of the episode and 8.9 during the reference days. The high proportion of K is a clear indication of emissions from biomass burning, because K is a good tracer of biomass-burning aerosols. Trajectories and satellite detections of fire areas indicated that the main source of biomass-burning aerosols was large-scale agricultural field burning in the Baltic countries, Belarus, Ukraine and Russia. The higher S/K ratio of S-rich particles during the peak stage was obviously due to the increased proportion of fossil fuel-burning emissions in the LRT particle mass, since air masses arrived from the more polluted areas of Europe at that time. The concentrations of sulphate, total nitrate and total ammonium increased during the episode. Our results suggest that large-scale agricultural field burning may substantially affect PM 2.5 concentrations under unfavourable meteorological conditions even at distances over 1000 km from the burning areas.

Elemental and Single Particle Aerosol Characterisation at a Background Station in Kazakhstan

Aerosol sampling in Kazakhstan was performed at a remote astronomical observatory in the Tien Shan mountain region. The background character of the site was considered by comparing the elemental concentrations, obtained by Energy Dispersive X-Ray Fluorescence (EDXRF), with those reported for other remote stations. On the basis of the variability of the elemental concentrations and the source of origin, the elements could be classified into two main groups. These findings, complemented with enrichment factor calculations revealed the first group of elements to be originating mainly from local sources, and the second group to be related to long-range transport of anthropogenic aerosol. Automated individual particle analysis by electron probe X-ray microanalysis (EPXMA) and subsequent cluster analysis resulted in the identification of 12 distinct aerosol particle types. Relative particle type abundances were converted to absolute abundances by estimating the particle number concentrations for the detected particles, exploring the seasonal particle variation. Based on the absolute abundances, a strong seasonal pattern was found for Si-Al-Fe-, Si-, Ca-S-Si-, Ca-Si-, Fe-Si- and Ti-Si-rich particles. These particle types can mainly be attributed to the local soil source. For most of the remaining particle types, a completely different seasonal trend was found, which can be related to anthropogenic emissions. Their abundance in winter can be related to long-range transport of anthropogenic aerosols. As a result, these data can be representative for the Tien Shan site and may be useful to climate modellers and environmentalists.

CHARACTERIZATION OF INORGANIC PARTICLES IN SELECTED RESERVOIRS AND TRIBUTARIES OF THE NEW YORK CITY WATER SUPPLY1

ABSTRACT: Individual particle analysis (IPA) by scanning electron microscopy interfaced with automated image and X‐ray analyses was used to characterize inorganic particles in five reservoirs and four tributaries located within the Catskill and Delaware systems of the New York City water supply. Individual particle analysis provides combined elemental and morphologic characterizations. Results are presented in terms of particle projected area per unit volume (PAV), consistent with optical impacts, and partitioned into seven generic particle types according to composition. Minerals of terrigenous origins, particularly clay minerals, dominated the inorganic particle populations of all the study systems except one downstream reservoir. Higher PAV levels were observed in the Catskill system. Particle dynamics represented by PAV were driven primarily by runoff, while the reservoirs were also greatly influenced by the timing of sediment resuspension promoted by drawdown of the surface and fall mixing. The benefit of the serial configuration of the reservoirs in decreasing inorganic particles with progression downstream towards the city is demonstrated. The patterns in PAV levels among the study systems generally tracked those of more common metrics of impacts of suspensoids, including mass concentrations of suspended solids, turbidity, and Secchi disc transparency.

Pilot study of a fluidized-pellet-bed technique for simultaneous solid/liquid separation and sludge thickening in a sewage treatment plant

A fluidized-pellet-bed separator with movable sludge hoppers was applied in pilot scale for the separation and thickening of activated sludge mixture liquid. Under the condition of suspension SS around 4,000 mg/L, polymer (CJX103, cationic, MW 5 x 10(6)) dose at a dry solid ratio of 0.003 and upward flow rate at 5.4 m/hr, the fluidized pellet bed performed solid/liquid separation and sludge thickening well. The SS concentration of the treated water was about 5 mg/L on average and the moisture content of the sludge after screening for 5 min was less than 94%, which is much lower than that after conventional settling and thickening and easy to be finally disposed. At a higher upward flow rate of 7.2 m/hr, similar results could also be obtained but higher polymer dose (solid ratio of 0.004) was required. The morphological characteristics and density-size relationship of the granular particles formed in the fluidized pellet bed were also investigated by image analysis and settling velocity measurement of individual particles. The two-dimensional fractal dimension was evaluated to be 1.6-1.8, showing a good quasi-spherical morphology of the granular particles with their density much higher than the conventional flocs. The results of the pilot study indicate a possible way to innovate the conventional secondary settling and gravitational thickening processes for solid/liquid separation and sludge handling, especially for small scale wastewater treatment plants to reach the goal of space saving and higher treatment efficiency.

TOF-SIMS analysis of sea salt particles: imaging and depth profiling in the discovery of an unrecognized mechanism for pH buffering

As part of a broader effort at understanding the chemistry of sea salt particles, we have performed time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis of individual sea salt particles deposited on a transmission electron microscopy (TEM) grid. Scanning electron microscopy (SEM) and TOF-SIMS analysis have, in conjunction with OH exposure studies, led to the discovery of an unrecognized buffering mechanism in the uptake and oxidation of SO 2 in sea salt particles in the marine boundary layer. This chemistry may resolve some discrepancies in the atmospheric chemistry literature. Several challenges during the acquisition and interpretation of both imaging and depth profiling data on specific particles on the TEM grid identified by the SEM were overcome. A description of the analysis challenges and the solutions ultimately developed to them is presented here, along with an account of how the TOF-SIMS data were incorporated into the overall research effort. Several issues unique to the analysis of high aspect ratio particles are addressed.

Measurement of fine particulate matter using electron microscopy techniques

Ambient fine particulate matter, defined as material with an aerodynamic diameter less than or equal to 2.5 μm (PM 2.5), comprises a broad range of primary and secondary particles that are dispersed through the atmosphere from a variety of sources. Attention has recently shifted to investigating ambient PM 2.5 because fine particles are thought to have a greater influence on health effects. Of particular interest are sources of fossil fuel combustion because they have been hypothesized as potentially contributing to the observed link between atmospheric particulate matter and health effects. Current studies are focused on the use of multiple analytical techniques to assist in the characterization of particulate matter to gain a better understanding of the relationship between anthropogenic emission sources and ambient PM 2.5. Electron microscopy techniques are being employed to provide information on the size, morphology, and elemental composition of individual particles. Individual particle data offers the potential to more specifically identify and quantify sources of particulate matter contributing to ambient air quality. However, electron microscopy has not been widely utilized in air quality studies because of the difficulties associated with collecting a sample that is well suited for individual particle analysis. Recent improvements in sampling technology, specifically the speciation sampler, permit collection of samples that are more amenable for electron microscopy analysis. This paper discusses the application of electron microscopy in environmental studies for individual particle analysis using scanning electron microscopy (SEM), computer-controlled scanning electron microscopy (CCSEM), and transmission electron microscopy (TEM) techniques. The paper also addresses managing the difficulties associated with the characterization of fine particulate matter using electron microscopy due to substrate interference and describes the benefits of sample collection with speciation samplers.

The effect of traction sanding on urban suspended particles in Finland.

Springtime urban road dust forms one of the most serious problems regarding air pollution in Finland. The composition and origin of springtime dust was studied in southern Finland with two different methods. Suspended particles (PM10 and TSP) were collected with high volume particle samplers and particle deposition was collected with moss bags. The composition of the PM(1.5-10) fraction was studied using individual particle analysis with SEM/EDX. The deposition in the moss bags was analysed with ICP-MS. The results showed that during the study period, approximately 10% of both PM(1.5-10) particles and the deposition originated from sanding. Other sources in the springtime PM(1.5-10) were e.g. asphalt aggregate or soil and combustion processes. It can be concluded that sanding produced a relatively small amount of particulate matter under the investigated circumstances.

Characterization of individual particles in a PM2.5 fraction of an urban air sample

The analysis of individual particles in a PM2.5 fraction of an urban air sample was carried out using scanning electron and electron microprobe analysis. Sampling was done using a portable cascade impactor with a silver substrate to obtain information about some lighter elements(C, N and O). It was found that particles in PM2.5 could be classified into 6 groups based on their shape and composition. Some of the groups could be attributed to specific anthropogenic origins. We observed a difference in the deformation of particles during the microprobe analysis, which might provide unique additional information concerning the classification protocols in the future.

Evaluation of diesel exhaust particle pollution using the source apportionment of PM2.5 in an urban atmospheric environment

We performed a source apportionment for particulate matter under 2.5 μm with the diameter (PM2.5) based on individual particle analyses using an electron probe microanalyzer (FE-SEM/EPMA). The analyzed particles were collected from the air environment near to a traffic route in June (before diesel vehicle emissions control regulations) and December (after regulations) 2003. From the results of the size, shape, and components of the particles, five or more sources of the particles were estimated. The rates for the contribution of diesel exhaust particle (DEP) were higher than that of the other sources. DEPs were further classified based on information concerning light elements according to the X-ray spectrum patterns. The X-ray spectrum patterns of DEPs collected before diesel vehicle emissions control regulations were different from that collected after the regulations. We could obtain this information about PM2.5 and DEPs, which could not be obtained by the conventional method. Therefore, it is concluded that the combination of individual particle analysis based on FE-SEM and EPMA is one of the most powerful techniques for obtaining detailed information about PM2.5.