Number-weighted Particle Size Distribution Research Articles

Characterization of the Emissions and Crystalline Silica Content of Airborne Dust Generated from Grinding Natural and Engineered Stones.

In this study, we systematically characterized the airborne dust generated from grinding engineered and natural stone products using a laboratory testing system designed and operated to collect representative respirable dust samples. Four stone samples tested included two engineered stones consisting of crystalline silica in a polyester resin matrix (formulations differed with Stones A having up to 90wt% crystalline silica and Stone B up to 50wt% crystalline silica), an engineered stone consisting of recycled glass in a cement matrix (Stone C), and a granite. Aerosol samples were collected by respirable dust samplers, total dust samplers, and a Micro-Orifice Uniform Deposit Impactor. Aerosol samples were analyzed by gravimetric analysis and x-ray diffraction to determine dust generation rates, crystalline silica generation rates, and crystalline silica content. Additionally, bulk dust settled on the floor of the testing system was analyzed for crystalline silica content. Real-time particle size distributions were measured using an Aerodynamic Particle Sizer. All stone types generated similar trimodal lognormal number-weighted particle size distributions during grinding with the most prominent mode at an aerodynamic diameter of about 2.0-2.3 μm, suggesting dust formation from grinding different stones is similar. Bulk dust from Stone C contained no crystalline silica. Bulk dust from Stone A, Stone B, and granite contained 60, 23, and 30wt% crystalline silica, respectively. In Stones A and B, the cristobalite form of crystalline silica was more plentiful than the quartz form. Only the quartz form was detected in granite. The bulk dust, respirable dust, and total dust for each stone had comparable amounts of crystalline silica, suggesting that crystalline silica content in the bulk dust could be representative of that in respirable dust generated during grinding. Granite generated more dust per unit volume of material removed than the engineered stones, which all had similar normalized dust generation rates. Stone A had the highest normalized generation rates of crystalline silica, followed by granite, Stone B, and Stone C (no crystalline silica), which likely leads to the same trend of respirable crystalline silica (RCS) exposure when working with these different stones. Manufacturing and adoption of engineered stone products with formulations such as Stone B or Stone C could potentially lower or eliminate RCS exposure risks. Combining all the effects of dust generation rate, size-dependent silica content, and respirable fraction, the highest normalized generation rate of RCS consistently occurs at 3.2-5.6 µm for all the stones containing crystalline silica. Therefore, removing particles in this size range near the generation sources should be prioritized when developing engineering control measures.

Measuring the effect of fireworks on air quality in Minneapolis, Minnesota

Air quality was measured before, during, and after a 4th of July fireworks display in downtown Minneapolis, Minnesota using a mix of low-cost sensors (CO, CO2, and NO) for gases and portable moderate cost instruments for particle measurements (PM2.5, lung deposited surface area, and number weighted particle size distributions). Meteorological conditions—temperature, humidity, and vertical temperature profile were also monitored. Concentrations of particles and most gaseous species peak between 10 pm and midnight on July 4th, decrease in the middle of the night but increase again and by between 6 and 7 am reach concentrations as high or higher than during fireworks. This overnight increase is likely due to a temperature inversion trapping emissions. Between 10 pm and midnight on July 4th the measures of particle concentration increase by 180–600% compared to the same period on July 3rd. Particle size distributions are strongly influenced by fireworks, shifting from traffic-like bimodal distributions before to a nearly unimodal distribution dominated by a large accumulation mode during and after. The shape of the size distribution measured during the early morning peak is nearly identical to that observed during fireworks, suggesting that the early morning peak is mainly due to trapped fireworks emissions not early morning traffic. Gaseous species are less strongly influenced by fireworks than particles. Comparing measurements made between 10 pm and midnight on July 4th and the same period on July 3rd, the concentration of CO increases 32% while the CO2 increases only 2% but increases by another 15% overnight. The NO concentration behaves oddly, decreasing during fireworks, but then recovering the next morning, more than doubling overnight. Our measurements of CO, NO, and PM2.5 are compared with those made at the nearest (~ 2 km away) Minnesota Pollution Control Agency Air Monitoring Station. Their NO results are quite different from ours with much lower concentrations before fireworks, a distinct peak during, followed by a strong overnight increase and an early morning peak somewhat similar in shape and concentration to ours. These differences are likely due mainly to malfunction of our low-cost NO sensor. Concentrations of CO and PM2.5 track ours within 25% but peak shapes are somewhat different, which is not unexpected given the spatial separation of the measurements.Article highlightsLow-cost and moderate-cost sensors are used to monitor the impact of a 4th of July fireworks display on local air quality.Particle concentrations and size are more strongly influenced by fireworks than are concentrations gaseous pollutants.Particle size distributions produced by fireworks are distinctly different from those associated with urban traffic sources.

Estimating the number-weighted equivalents of the mass-weighted size distribution functions

The number-weighted particle size distributions are difficult to be estimated experimentally. This study offers a simple conversion method to convert mass-weighted distributions to their number-weighted equivalents. Besides, the number-weighted equivalents of the Gates-Gaudin-Schuhmann, Gaudin-Meloy, Pareto, and Rosin-Rammler distributions were determined by the conversion method. The accuracy of the method was successfully confirmed on the artificial populations generated from the Gates-Gaudin-Schuhmann, Rosin-Rammler (Weibull), and Pareto distributions. However, the number-weighted equivalent of the Gaudin-Meloy distribution was found to be trivial. The results also indicate that the conversion method may be applied to a wide range of sieve size distributions that are truncated with upper and lower bounds.

Spatial and Seasonal Variations of PM Concentration and Size Distribution in Manure-Belt Poultry Layer Houses

Abstract. Poultry layer houses are a significant source of particulate matter (PM) emissions, which potentially affect worker and animal health. Particulate matter characteristics, such as concentration and size distribution inside layer houses, are critical information for assessment of the potential health risks and development of effective PM mitigation technologies. However, this information and its spatial and seasonal variations are lacking for typical layer facilities. In this study, two TSI DustTrak monitors (DRX 8533) and an Aerodynamic Particle Sizer (APS 3321) were used to measure PM mass concentrations and number-weighted particle size distributions in two typical manure-belt poultry layer houses in Ohio in three seasons: summer, autumn, and winter. Bimodal particle size distributions were consistently observed. The average count median diameters (mean ±SD) were 1.68 ±0.25, 2.16 ±0.31, and 1.87 ±0.07 µm in summer, autumn, and winter, respectively. The average geometric standard deviations of particle size were 2.16 ±0.23, 2.16 ±0.18, and 1.74 ±0.17 in the three seasons, respectively. The average mass concentrations were 67.4 ±54.9, 289.9 ±216.2, and 428.1 ±269.9 µg m-3 for PM2.5; 73.6 ±59.5, 314.6 ±228.9, and 480.8 ±306.5 µg m-3 for PM4; and 118.8 ±99.6, 532.5 ±353.0, and 686.2 ±417.7 µg m-3 for PM10 in the three seasons, respectively. Both statistically significant (p < 0.05) and practically significant (difference of means >20% of smaller value) seasonal variations were observed. Spatial variations were only practically significant for autumn mass concentrations, likely due to external dust infiltration from nearby agricultural activities. The OSHA-mandated permissible exposure limit for respirable PM was not exceeded in any season. Keywords: Air quality, Particulate matter, Poultry housing, Seasonal variation, Spatial variation.

Validation of a particle tracking analysis method for the size determination of nano- and microparticles

Particle tracking analysis (PTA) is an emerging technique suitable for size analysis of particles with external dimensions in the nano- and sub-micrometre scale range. Only limited attempts have so far been made to investigate and quantify the performance of the PTA method for particle size analysis. This article presents the results of a validation study during which selected colloidal silica and polystyrene latex reference materials with particle sizes in the range of 20 nm to 200 nm were analysed with NS500 and LM10-HSBF NanoSight instruments and video analysis software NTA 2.3 and NTA 3.0. Key performance characteristics such as working range, linearity, limit of detection, limit of quantification, sensitivity, robustness, precision and trueness were examined according to recommendations proposed by EURACHEM. A model for measurement uncertainty estimation following the principles described in ISO/IEC Guide 98-3 was used for quantifying random and systematic variations. For nominal 50 nm and 100 nm polystyrene and a nominal 80 nm silica reference materials, the relative expanded measurement uncertainties for the three measurands of interest, being the mode, median and arithmetic mean of the number-weighted particle size distribution, varied from about 10% to 12%. For the nominal 50 nm polystyrene material, the relative expanded uncertainty of the arithmetic mean of the particle size distributions increased up to 18% which was due to the presence of agglomerates. Data analysis was performed with software NTA 2.3 and NTA 3.0. The latter showed to be superior in terms of sensitivity and resolution.

Performance of analytical centrifugation for the particle size analysis of real-world materials

Analytical centrifugation (AC) is a powerful technique for the measurement of particle size distributions. This study evaluates its performance for the grouping of particulate materials according to the European Commission's recommendation on the definition of a nanomaterial, which bases on the number-weighted median diameter. The focus lies on cuvette-type AC with turbidity detector and on the performance in the case of polydisperse, non-spherical real-world materials. Two grades of barium sulfate (nano and non-nano) were analysed. This study compares the repeatability of the measurement and the method precision including sample preparation, measurement and conversion into number-weighted particle size distributions. Experimental results show that the selected radiation wavelengths of 470nm and 865nm have only little impact on the number-weighted median diameter, but affect the intermediate precision of these values. However, the intermediate precision of the method is mainly determined by sample preparation up to 12.6% with respect to the number-weighted median diameter (x50,0). This paper provides information on particle sizing on real-world materials for the first time.

Investigation of nitrogen oxides, particle number, and size distribution on a light-duty diesel car with B10 and G10 fuels

Nitrogen oxides (NOx) and particle emissions from a light-duty diesel car with B10 (10% biodiesel from cooking oil +90% diesel, v/v) and G10 (10% GTL fuel +90% diesel, v/v) were investigated under the New European Driving Cycle (NEDC). The car was equipped with a high-pressure common rail system, cooled exhaust gas recirculation (EGR), and diesel oxidation catalyst (DOC). Results show that G10 has the lowest fuel consumption and B10 has the highest fuel consumption among the three fuels. B10 can increase the NOx emissions, and the G10 NOx emission is lower than diesel. The number-weighted particle size distribution shows that B10 and G10 can decrease the particle number at almost a full size range. In the four urban driving cycles (UDC), the geometric mean diameter (GMD) of B10 and G10 are both smaller than diesel. For the extra urban driving cycle (EUDC), the particle number concentration and emission rate are far higher than UDC cycle. The acceleration phase has a higher particle number emission rate and nucleation particle number than deceleration for the three fuels. Particle number emission is reduced when using B10 and G10 regardless of acceleration or deceleration. Number-weighted particle size distribution in acceleration and deceleration shows that the nucleation particle number in deceleration is far higher than acceleration, whereas accumulation particle shows the opposite tendency.

REMOVED: Experimental investigation of impacts of engine hardware, operating parameters and combustion performance on particulate emissions in a DISI engine

With increasing concern over ultrafine Particulate Matter (PM) emissions from Direct Injection Spark Ignition (DISI) engines and ever tightening emissions legislation, substantial research work is required to obtain a better understanding of influence of advanced engine technologies on particulate formation and oxidation. In this work, experimental investigation of engine-out particulate emissions were carried out on a single cylinder spray-guided DISI engine. With regard to effects of engine hardware on PM emissions; impacts of fuel spray angle, fuel flow rate and intake valves’ lift and camshaft phasing were examined over a wide start of injection sweep window. Injector tests highlighted a complex relation between injector characteristics and engine operating parameters with PM emissions as a result of fuel impingement and poor mixture preparation. Valvetrain tests indicated some benefits from engine throttling by valve lift and intake camshaft phasing in particulate number concentration reduction at low load. This was associated with increased intake flow turbulence and improved mixture preparation. Number-weighted particle size distribution was also affected by intake valve modes at low load. Nevertheless, at high load, impacts of variable valve lift and camshaft phasing on particulate number concentration and size distribution became negligible. Furthermore, combustion phase indicators were studied in order to probe impacts of combustion performance on PM emissions. While no satisfactory correlation of initial flame development with PM emissions was identified; shorter rapid-burning angles were observed with lower particulate number concentrations.

Avoiding drying-artifacts in transmission electron microscopy: Characterizing the size and colloidal state of nanoparticles.

Standard transmission electron microscopy nanoparticle sample preparation generally requires the complete removal of the suspending liquid. Drying often introduces artifacts, which can obscure the state of the dispersion prior to drying and preclude automated image analysis typically used to obtain number-weighted particle size distribution. Here we present a straightforward protocol for prevention of the onset of drying artifacts, thereby allowing the preservation of in-situ colloidal features of nanoparticles during TEM sample preparation. This is achieved by adding a suitable macromolecular agent to the suspension. Both research- and economically-relevant particles with high polydispersity and/or shape anisotropy are easily characterized following our approach (http://bsa.bionanomaterials.ch), which allows for rapid and quantitative classification in terms of dimensionality and size: features that are major targets of European Union recommendations and legislation.

Mechanochemical Approaches to Ceramic Ink Formulation for Digital Fabrication of Solid Oxide Fuel Cells

Four different ink processing protocols were investigated to control the particle size distribution of lab scale batches of inkjet inks used for printing Solid Oxide Fuel Cell (SOFC) anodes. The inks were composed of a mixture of commercial Nickel Oxide (NiO) and Yttria-stabilized Zirconia (YSZ) powders dispersed in organic solvents. Protocols incorporating high energy wet and dry milling using a SPEX 8000 mixer mill were compared to traditional low energy milling/dispersion methods. Brunauer-Emmett-Teller (B.E.T.) surface area measurements were used in conjunction with scanning electron microscopy (S.E.M.) to determine the effects of the milling protocols on the dry powder particle sizes and morphologies. Dynamic light scattering (D.L.S.) was used to measure the particle size distributions of the inks. Low energy dispersion of the NiO and YSZ powders produced an ink with a number weighted particle size distribution peaked ∼ 300 nm and a significant tail of particles as large as 1 μm. Adding high energy dry milling or high energy slurry dispersion to the process removed most of the large particle size tail, but the particle size distribution remained peaked at 250 – 300 nm. By combining high energy dry powder milling with high energy slurry dispersion, the main peak in the particle size distribution shifted to 180 nm with minimal particles above 600 nm. These results indicate that the combination of high energy milling and dispersion enable lab scale production of nanoscale NiO/YSZ inks from commercial powders. The protocols developed in this work provide a first step towards the goal of controlling the microstructure of inkjet printed solid oxide fuel cell (SOFC) anodes through control of the ink particle size distribution.

Characterizing Exposures to Airborne Metals and Nanoparticle Emissions in a Refinery

An air quality survey was conducted at a precious metals refinery in order to evaluate worker exposures to airborne metals and to provide detailed characterization of the aerosols. Two areas within the refinery were characterized: a furnace room and an electro-refining area. In line with standard survey practices, both personal and area air filter samples were collected on 37-mm filters and analyzed for metals by inductively coupled plasma-atomic emission spectroscopy. In addition to the standard sampling, measurements were conducted using other tools, designed to provide enhanced characterization of the workplace aerosols. The number concentration and number-weighted particle size distribution of airborne particles were measured with a fast mobility particle sizer (FMPS). Custom-designed software was used to correlate particle concentration data with spatial location data to generate contour maps of particle number concentrations in the work areas. Short-term samples were collected in areas of localized high concentrations and analyzed using transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) to determine particle morphology and elemental chemistry. Analysis of filter samples indicated that all of the workers were exposed to levels of silver above the Occupational Safety and Health Administration permissible exposure limit of 0.01 mg m(-3) even though the localized ventilation was functioning. Measurements with the FMPS indicated that particle number concentrations near the furnace increased up to 1000-fold above the baseline during the pouring of molten metal. Spatial mapping revealed localized elevated particle concentrations near the furnaces and plumes of particles rising into the stairwells and traveling to the upper work areas. Results of TEM/EDS analyses confirmed the high number of nanoparticles measured by the FMPS and indicated the aerosols were rich in metals including silver, lead, antimony, selenium, and zinc. Results of the survey were used to deduce appropriate strategies for mitigation of worker exposure to airborne metals.

Size Distributions of 0.5 to 20 μm Aerodynamic Diameter Lead-Containing Particles from Aerosol Sampler Walls and Filters

The study presented here investigates the number weighted particle size distributions of aerosols generated in the laboratory from lead oxide and lead sulfide dusts and sampled by Institute of Occupational Medicine (IOM) and closed face cassette (CFC) samplers as determined by scanning electron microscopy (SEM). The wall deposits and filter deposits from each sampler were characterized separately. A Mann-Whitney statistical analysis revealed that differences in the number weighted distributions of particles captured by the filter and the wall were not significant over the size range (up to 20 μm aerodynamic equivalent diameter) present in these laboratory-generated aerosols. Furthermore, for these samples it was not possible to distinguish an absolute difference between the IOM and CFC filter catches. By comparing direct measurements of aerodynamic equivalent diameter (AED) made by an Aerodynamic Particle Sizer (APS) to AEDs calculated from SEM images, empirical shape factors for lead oxide and lead sulfi...

The use of sedimentation field flow fractionation and photon correlation spectroscopy in the characterization of casein micelles.

Sedimentation Field Flow Fractionation (SdFFF) was combined with Photon Correlation Spectroscopy (PCS), to characterize changes in the structure of the colloidal particles of reconstituted skim milk of diameter >50 nm (aggregates of casein and calcium phosphate known as casein micelles) with the changes in partitioning (with the addition of salt) of calcium (Ca), inorganic phosphate (Pi) and casein between the serum and colloidal phases of the milk. The number weighted particle size distributions are determined. These are well represented by a log-normal distribution. Methods are presented for estimating the relative contributions of scattering and absorbance to the SdFFF detector signal and for taking both into account when analysing SdFFF data. The values found for the effective density of the casein micelles were in good agreement with the literature and ranged from (1.06-1.08 g cm(-3)) according to the composition of micelles. The changes in the scattering intensity as determined by PCS correlated with the changes in the particle composition. Although the concentrations of colloidal calcium phosphate (CCP) (1.1-3.5 g/kg milk) and micellar casein (18.1-27.2 g/kg milk) varied considerably only small changes in the size distribution of particles >50 nm diameter were observed except for milk to which 30 mmol Pi+10 mmol Ca/kg milk had been added where the particle size distribution shows a swelling of the particles consistent with a lower than expected value for the particle density. These observations suggest that the micelles have the ability to both lose (depleted micelles) and accommodate (enriched micelles) more casein, calcium and inorganic phosphate in their interior, thus confirming the model of the micelles which postulates an open structure allowing freedom of movement of casein and small ions.

Influences on the Particle Size Distribution of Diesel Particulate Emissions

Particulates give great concern for mankind health. Especially the nano size particles are under discussion. Therefore, the particle size distribution from the combustion chamber to tail pipe emissions are of great interest. With the aim of scanning mobility particle sizer the number weighted particle size distributions were measured in the combustion chamber as well as in the exhaust gas up and downstream of aftertreatment systems. Using the identical particle measurement technique results can be compared without changing the particle size definition. The particles in the cylinder of a modern serious DI diesel engine were sampled with a time resolved fast gas sampling valve. The Soot particles formed in the cylinder during the early combustion phase are oxidized by about 99% in the late combustion/early expansion phase, whereas the soot particle sizes distribution in the cylinder at the end of the expansion phase are equal to that in the tail pipe. DI diesel engines with high pressure injection system emit less numbers of particle with in tendency greater sizes compared to IDI diesel engines. Oxidation catalysts do not influence particle size distribution but particulate traps reduce particle number by up to two orders of magnitude. Detail analysis shows that an increase of nano size particle number downstream of an aftertreatment device results from artifacts.

Laser light scattering characterization of particle size distribution in porous silicon

We describe a purely optical technique, laser light scattering, to determine number-weighted particle size distribution in porous silicon (PS) with nanoscale resolution. Our result shows that the size of nanoscale particles in porous silicon is about 5.5 nm in diameter with distribution range from 3.5 to 14 nm. In the photoluminescence spectrum of this porous silicon sample, there appear two peaks, one peak locates at 658 nm, and the other locates at 805 nm. The information of particle size distribution in porous silicon holds much promise for elucidation of the visible light emission mechanism in porous silicon.