Ultrafine Size Range Research Articles

Aerosol size distribution and new particle formation events in the suburb of Xi'an, northwest China

Particle number concentration and size distribution are important for better understanding the characteristics of aerosols. However, their measurements are scarce in western China. Based on the first measurement of particle number size distribution (10–487 nm) in the suburb of Xi'an, northwest China from November 2013 to December 2014, the seasonal, monthly and diurnal average particle number concentrations were investigated, and the characteristics of new particle formation (NPF) events and their dependencies on meteorological parameters also discussed. The results showed that the annual average particle number concentrations in the nucleation (NNUC), Aitken (NAIT), and Accumulation (NACC) size ranges were 960 cm−3, 4457 cm−3, 3548 cm−3, respectively. The mean total particle number concentration (NTOT) was 8965 cm−3 and largely dominated by particles in Aitken mode. The number concentration was dominated by particles around 67.3 nm in spring, summer and fall, while about 89.8 nm in winter. The percentage of the ultrafine size range (UFP, particles of diameter below 100 nm) to total particle number concentration was 63.2%, 69.6%, 62.2% and 58.1% in four seasons. The diurnal variation of the nucleation mode particles was mainly influenced by NPF events in summer, while by both traffic densities and NPF events in spring, fall and winter. The diurnal variation of the number concentration of Aitken mode particles correlated with the traffic emission in spring, fall and winter, while in summer it more correlated with contribution of the growth of the nucleation mode particles. The burst of nucleation mode particles typically started in the daytime (08:15–16:05, LST). The growth rates of nucleated particles ranged from 2.8 to 10.7 nm h-1 with an average of 5.0 ± 1.9 nm h-1. Among observed 66 NPF events from 347 effective measurement days, 85 percent of their air masses came from north or northwest China, resulting in a low concentration of pre-existing particles, and only 15 percent came southerly from Qingling Mountains. Based on their growth rate, 64 and 36 percent of their subsequent particles, corresponding to types 1 and 2 NPF events, grew and seldom grew after the burst of nucleation mode particles. For type 1 NPF event, the nucleated particles could grow up to 40 nm or larger when surface winds shifted from westerly to easterly or southeasterly (from village areas). For type 2 NPF events, the particles kept almost unchanged when the winds stayed westerly. This implied that the surface wind direction with different emissions might play an important role in new particle growth in suburb of Xi'an.

Selective Flocculation of Iron Ore Slimes: Results of Successful Pilot Plant Trials at Tata Steel, Noamundi

A significant portion of currently mined iron ores, that is, 15–20% of run of mine ore, typically ends up as slimes—a slurry of fine particles (<45 micron) with relatively higher alumina contents (7–15% Al2O3). The only viable option currently is to dispose these slimes in tailing ponds for water recovery and future use. Due to increasing demand for steel and rapid consumption of high grade ores, processing and utilization of these slimes has become an urgent necessity. Traditional gravity and magnetic separation is not very effective in the ultrafine size range (less than 45 microns) and hence most of the flowsheets have a desliming step ahead of gravity and magnetic separation. Selective dispersion—flocculation is commercially proven technology to accomplish efficient separation in this size range, provided appropriate selective reagents are available. Our earlier work in TRDDC laboratories has demonstrated that selective flocculation with starch and guar gum is sufficiently selective for the reduction of alumina contents and thus this process should be scaled up for the processing of alumina rich Indian iron ore slimes. TRDDC has also designed a portable set-up which can be used to run pilot plant trials in a continuous mode onsite in the mines. The successful pilot plant trials of a selective flocculation separation process were completed by us at Noamundi mines recently. The results of these plant trials, using a portable pilot plant set up, designed by TRDDC, are summarized in this paper. The slimes sample for these plant trials, was withdrawn from one of the slimes stream at the Tata Steel’s iron ore beneficiation plant at Noamundi mines. Though there was considerable variation in the grade and pulp density of the slimes sample, it was possible to produce a concentrate of consistent quality in a continuous mode. It was for example demonstrated that one can produce a concentrate assaying 65.3% Fe and 2.5% alumina with a yield of 80.4% from a relatively richer grade slime sample containing 60.3% Fe and 4.8% alumina. More importantly, the corresponding tails contained less than 39.7% Fe. For a leaner grade slime sample assaying 53.4% Fe and 7.3% alumina, the corresponding concentrate grade was 63.5% Fe and 3.1% alumina, tailings grade 35.7% Fe and the yield achieved during the plant trials was 63.5%.

Online monitoring of nanoparticles formed during nanosecond laser ablation

The particle size distribution of dry aerosol originating from laser ablation of glass material was monitored simultaneously with Laser Ablation – Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analysis and two aerosol spectrometers – Fast Mobility Particle Sizer (FMPS) and Aerodynamic Particle Sizer (APS). The unique combination of LA-ICP-MS and FMPS offers the possibility of measuring the particle size distribution every 1s of the ablation process in the size range of 5.6–560nm. APS extends the information about particle concentration in the size range 0.54–17μm. Online monitoring of the dry aerosol was performed for two ablation modes (spot and line with a duration of 80s) with a 193nm excimer laser system, using the glass reference material NIST 610 as a sample. Different sizes of laser spot for spot ablation and different scan speeds for line ablation were tested. It was found that the FMPS device is capable of detecting changes in particle size distribution at the first pulses of spot laser ablation and is suitable for laser ablation control simultaneously with LA-ICP-MS analysis. The studied parameters of laser ablation have an influence on the resulting particle size distribution. The line mode of laser ablation produces larger particles during the whole ablation process, while spot ablation produces larger particles only at the beginning, during the ablation of the intact layer of the ablated material. Moreover, spot ablation produces more primary nano-particles (in ultrafine mode size range <100nm) than line ablation. This effect is most probably caused by a reduced amount of large particles released from the spot ablation crater. The larger particles scavenge the ultrafine particles during the line ablation mode.

Physical properties and lung deposition of particles emitted from five major indoor sources

The physical properties of indoor particles were measured with an Scanning Mobility Particle Sizer (SMPS) system (14.6–850 nm), an Aerodynamic Particle Sizer (APS, 0.54–18 μm) and an Hygroscopic Tandem Differential Mobility Analyzer (H-TDMA) in an apartment located in an urban background site in Prague (Czech Republic) from 15 August to 8 September, 2014. The total particle maximum number concentration was 9.38 × 104, 1.46 × 105, 2.89 × 104, 2.25 × 105 and 1.57 × 106 particles cm−3 for particles released from vacuum cleaning, soap/W5 cleaning spray, smoking, incense burning and cooking (frying) activities, respectively. Particles emitted from cleaning activities showed unimodal number size distributions, with the majority of particles (>98.2 %) in the ultrafine size range (Dp <100 nm) and modes at a diameter of 19.8 nm for vacuum cleaning and 30.6 nm for soap/W5 cleaning. Smoking and incense burning predominantly generated particles in the accumulation mode with a count median diameter around 90–150 nm while cooking emissions showed a bimodal structure with a main mode at 47.8 nm. Particles from vacuum cleaning, incense burning, smoking and cooking emissions were found to be “nearly hydrophobic” with an average growth factor (Gf) around 1.01–1.10, while particles emitted from desk cleaning using organic compounds were found to be “less-hygroscopic” (Gf ∼1.12–1.16). Based on an adjusted MPPD model with a consideration of the hygroscopic properties of particles, the total lung deposition fractions of these particles by number when they penetrate into the human lung were 0.73 ± 0.02, 0.62 ± 0.03, 0.37 ± 0.03, 0.32 ± 0.03 and 0.49 ± 0.02 for vacuum cleaning, desk cleaning, smoking, incense burning and cooking, respectively.

Smoking and Cerebral Oxidative Stress andAir Pollution: A Dreadful Equation withParticulate Matter Involved and One More Powerful Reason Not to Smoke Anything!

Smoking has serious health effects. Cigarettes, including tobacco, marijuana, and electronic nicotine delivery systems are very effective ways to inhale harmful amounts of fine and ultrafine particulate matter. Does size matter? Yes, indeed! The smaller the particle you inhale, the higher the ability to produce reactive oxygen species and to readily access the brain. In this issue of the Journal of Alzheimer's Disease, Durazzo provides evidence of an association between active cigarette tobacco smoking in cognitively-normal elders and increased cerebral oxidative stress, while in actively smoking Alzheimer's disease (AD) patients, the association was also seen with smaller left and total hippocampal volumes. This paper has highly relevant results of interest across the US and the world because millions of people are active smokers and they have other genetic and environmental risk factors that could play a key role in the development/worsening of brain oxidative stress and neurodegeneration. Smoking basically anything producing aerosols with particulate matter in the fine and ultrafine size range is detrimental to your brain. Marijuana and e-cigarette use has grown steadily among adolescents and young adults. Smoking-related cerebral oxidative stress is a potential mechanism promoting AD pathology and increased risk for AD. Current knowledge also relates fine and ultrafine particles exposures influencing neurodevelopmental processes in utero. The results from Durazzo et al. should be put in a broader context, a context that includes evaluating the oxidative stress of nano-aerosols associated with cigarette emissions and their synergistic effects with air pollution exposures. AD is expected to increase in the US threefold by the year 2050, and some of these future AD patients are smoking and vaping right now. Understanding the impact of everyday exposures to long-term harmful consequences for brain health is imperative.

Diesoline, Diesohol, and Diesosene Fuelled HCCI Engine Development

Compression ignition (CI) engines are facing strong restrictive emission norms globally, which demand extremely low oxides of nitrogen (NOx) and particulate matter (PM) emissions. Homogeneous charge compression ignition (HCCI) engine is a very attractive solution to meet these stringent emission challenges due to its capability to simultaneously reduce NOx and PM. In this study, HCCI combustion was investigated using different test fuels such as diesoline (15% v/v gasoline with diesel), diesohol (15% v/v ethanol with diesel), and diesosene (15% v/v kerosene with diesel) vis-a-vis baseline mineral diesel. A dedicated fuel vaporizer was used for homogeneous fuel–air mixture preparation. The experiments were performed at constant intake charge temperature (180 °C), fixed exhaust gas recirculation (EGR) (15%) at different engine loads. Stable combustion characteristics were determined for diesosene at lower engine loads, however, diesoline and diesohol yielded improved emissions compared to baseline diesel HCCI combustion. At higher loads, diesoline and diesosene showed higher knocking tendency compared to baseline diesel and diesohol. Diesohol showed lower NOx and smoke opacity, however, diesoline and diesosene showed slightly lower hydrocarbon (HC) and carbon monoxide (CO) emissions compared to baseline diesel HCCI combustion. Performance results of diesohol and diesosene were slightly inferior compared to diesel and diesoline HCCI combustion. Physical characterization of exhaust particulates was done for these test fuels using engine exhaust particle sizer (EEPS). Particle number-size distribution showed that most particles emitted from diesoline and diesohol were in ultrafine size range and baseline diesel and diesosene emitted relatively larger particles. Reduction in total particle number concentration with addition of volatile fuel components in mineral diesel was another important observation of this study.

Exposure to ultrafine particles, intracellular production of reactive oxygen species in leukocytes and altered levels of endothelial progenitor cells.

Exposure to particles in the fine and ultrafine size range has been linked to induction of low-grade systemic inflammation, oxidative stress and development of cardiovascular diseases. Declining levels of endothelial progenitor cells within systemic circulation have likewise been linked to progression of cardiovascular diseases. The objective was to determine if exposure to fine and ultrafine particles from indoor and outdoor sources, assessed by personal and residential indoor monitoring, is associated with altered levels of endothelial progenitor cells, and whether such effects are related to leukocyte-mediated oxidative stress. The study utilized a cross sectional design performed in 58 study participants from a larger cohort. Levels of circulating endothelial progenitor cells, defined as either late (CD34(+)KDR(+) cells) or early (CD34(+)CD133(+)KDR(+) cells) subsets were measured using polychromatic flow cytometry. We additionally measured production of reactive oxygen species in leukocyte subsets (lymphocytes, monocytes and granulocytes) by flow cytometry using intracellular 2',7'-dichlorofluoroscein. The measurements encompassed both basal levels of reactive oxygen species production and capacity for reactive oxygen species production for each leukocyte subset. We found that the late endothelial progenitor subset was negatively associated with levels of ultrafine particles measured within the participant residences and with reactive oxygen species production capacity in lymphocytes. Additionally, the early endothelial progenitor cell levels were positively associated with a personalised measure of ultrafine particle exposure and negatively associated with both basal and capacity for reactive oxygen species production in lymphocytes and granulocytes, respectively. Our results indicate that exposure to fine and ultrafine particles derived from indoor sources may have adverse effects on human vascular health.

What are the Driving Factors Influencing the Size Distribution of Airborne Synthetic Clay Particles Emitted from a Jet Milling Process?

In the field of workplace air quality, measuring and analyzing the size distribution of airborne particles to identify their sources and apportion their contribution has become widely accepted, however, the driving factors that influence this parameter, particularly for nanoparticles (< 100 nm), have not been thoroughly determined. Identification of driving factors, and in turn, general trends in size distribution of emitted particles would facilitate the prediction of nanoparticles’ emission behavior and significantly contribute to their exposure assessment. In this study, a comprehensive analysis of the particle number size distribution data, with a particular focus on the ultrafine size range of synthetic clay particles emitted from a jet milling machine was conducted using the multi-lognormal fitting method. The results showed relatively high contribution of nanoparticles to the emissions in many of the tested cases, and also, that both surface treatment and feed rate of the machine are significant factors influencing the size distribution of the emitted particles of this size. In particular, applying surface treatments and increasing the machine feed rate have the similar effect of reducing the size of the particles, however, no general trend was found in variations of size distribution across different surface treatments and feed rates. The findings of our study demonstrate that for this process and other activities, where no general trend is found in the size distribution of the emitted airborne particles due to dissimilar effects of the driving factors, each case must be treated separately in terms of workplace exposure assessment and regulations.

Air sampling filtration media: Collection efficiency for respirable size-selective sampling.

The collection efficiencies of commonly used membrane air sampling filters in the ultrafine particle size range were investigated. Mixed cellulose ester (MCE; 0.45, 0.8, 1.2, and 5 μm pore sizes), polycarbonate (0.4, 0.8, 2, and 5 μm pore sizes), polytetrafluoroethylene (PTFE; 0.45, 1, 2, and 5 μm pore sizes), polyvinyl chloride (PVC; 0.8 and 5 μm pore sizes), and silver membrane (0.45, 0.8, 1.2, and 5 μm pore sizes) filters were exposed to polydisperse sodium chloride (NaCl) particles in the size range of 10-400 nm. Test aerosols were nebulized and introduced into a calm air chamber through a diffusion dryer and aerosol neutralizer. The testing filters (37 mm diameter) were mounted in a conductive polypropylene filter-holder (cassette) within a metal testing tube. The experiments were conducted at flow rates between 1.7 and 11.2 l min-1. The particle size distributions of NaCl challenge aerosol were measured upstream and downstream of the test filters by a scanning mobility particle sizer (SMPS). Three different filters of each type with at least three repetitions for each pore size were tested. In general, the collection efficiency varied with airflow, pore size, and sampling duration. In addition, both collection efficiency and pressure drop increased with decreased pore size and increased sampling flow rate, but they differed among filter types and manufacturer. The present study confirmed that the MCE, PTFE, and PVC filters have a relatively high collection efficiency for challenge particles much smaller than their nominal pore size and are considerably more efficient than polycarbonate and silver membrane filters, especially at larger nominal pore sizes.

Characterization of the Ultrafine and Nano Particle Emissions on Modified Indian Driving Cycle for Passenger Cars Operating on CNG Phase Wise Analysis

The ultrafine and nano particles compared to larger particles are gaining high importance because of their vulnerable effects to environment and human health causing respiratory problems, cardiovascular disease, and various types of cancers leading to premature death [1]. WHO report points out that approximately, two thirds of the global burden of disease due to urban outdoor air pollution is mostly from the developing countries in Asia (Cohen et al. 2004)[2]. By number, nearly all of the particles emitted by a diesel engine are nanoparticles which are also true for gasoline engines [3]. This is addressed by new UN Regulations by introducing the emission norms for diesel and GDI vehicles for particle number and PM2.5 as 6 x 10 11 and 4.5 mg/km respectively [4]. However, other S.I. engines like CNG, even though they look clean as there is no visible smoke but emitting large number of particles is necessary to investigate. This research paper focuses on characterization of ultrafine and nano particle emissions from CNG vehicle on Indian driving cycle and it covers experimental Investigation to identify the significance of different operating phases viz. idling, acceleration, deceleration and cruising for their contributions to particle number and size distribution pattern over urban as well as on extra urban part of the cycle. CNG passenger car shows large peak of PN emissions during cold starting phase at the beginning of the test cycle which is almost twice that of diesel vehicle. However, this concentration peak will decrease near to 25% on light operating loads during urban part of the cycle, but during acceleration and cruising operation on extra urban cycle under heavy load the PN emissions from CNG car are higher in magnitude. The particles emitted from CNG buses are too small to contribute to PM10 as they are of ultrafine and nano size range.

Ultrafine Particles from Traffic Emissions and Children's Health (UPTECH) in Brisbane, Queensland (Australia): study design and implementation.

Ultrafine particles are particles that are less than 0.1 micrometres (µm) in diameter. Due to their very small size they can penetrate deep into the lungs, and potentially cause more damage than larger particles. The Ultrafine Particles from Traffic Emissions and Children’s Health (UPTECH) study is the first Australian epidemiological study to assess the health effects of ultrafine particles on children’s health in general and peripheral airways in particular. The study is being conducted in Brisbane, Australia. Continuous indoor and outdoor air pollution monitoring was conducted within each of the twenty five participating school campuses to measure particulate matter, including in the ultrafine size range, and gases. Respiratory health effects were evaluated by conducting the following tests on participating children at each school: spirometry, forced oscillation technique (FOT) and multiple breath nitrogen washout test (MBNW) (to assess airway function), fraction of exhaled nitric oxide (FeNO, to assess airway inflammation), blood cotinine levels (to assess exposure to second-hand tobacco smoke), and serum C-reactive protein (CRP) levels (to measure systemic inflammation). A pilot study was conducted prior to commencing the main study to assess the feasibility and reliably of measurement of some of the clinical tests that have been proposed for the main study. Air pollutant exposure measurements were not included in the pilot study.

Number and size distribution of airborne nanoparticles during summertime in Kuwait: first observations from the Middle East.

We made fast response measurements of size-resolved particle number concentrations (PNCs) and distributions (PNDs) in the 5-1000 nm range close to a busy roadside, continuously for 31 days, in Kuwait. The aims were to understand their dispersion characteristics during summertime and dust events, and association with trace pollutants (NOx, O3, CO, SO2, and PM10) and meteorological parameters. PNCs were found up to ∼19-times higher (5.98 × 10(5) cm(-3)) than those typically found in European roadside environments. Size distributions exhibited over 90% of PNCs in ultrafine size range (<100 nm) and a negligible fraction over 300 nm. Peak PNDs appeared at ∼12 nm, showing an unusually large peak in nucleation mode. Diurnal variations of PNCs coincided with the cyclic variations in CO, NOx, and traffic volume during morning and evening rush hours. Despite high traffic volume, PNC peaks were missing during noon hours due to high ambient temperature (∼48 °C) that showed an inverse relationship with the PNCs. Principal Component Analysis revealed three probable sources in the area--local road traffic, fugitive dust, and refineries. Dust events, categorized by PM10 with over 1000 μg m(-3), decreased PNCs by ∼25% and increased their geometric mean diameters (GMDs) by ∼66% compared with nondust periods.

Yielding Behavior and Its Effect on Uniform Elongation of Fine Grained IF Steel

Interstitial free (IF) steel specimens with different mean grain sizes ranging from 0.4 to 12µm were fabricated by the accumulative roll bonding (ARB) process and subsequent annealing. Tensile tests at room temperature have revealed that by decreasing the mean grain size down to an ultra-fine range, the yielding behavior gradually changes from the continuous yielding to the discontinuous yielding, accompanying a yield drop phenomenon. It has been found that the yield stress of specimens having fine grain sizes shows extra-hardening, deviated from the original Hall­Petch relation for coarse-grained specimens in accordance with the discontinuous yielding. The Hall­Petch analysis also has indicated that the loss in the uniform elongation in the ultrafine grain size range is related to the appearance of the discontinuous yielding behavior. [doi:10.2320/matertrans.MA201317]

Fine and ultrafine particle emissions from microwave popcorn

This study characterized fine (PM2.5 ) and ultrafine particle (UFP, diameter < 100nm) emissions from microwave popcorn and analyzed influential factors. Each pre-packed popcorn bag was cooked in a microwave oven enclosed in a stainless steel chamber for 3min. The number concentration and size distribution of UFPs and PM2.5 mass concentration were measured inside the chamber repeatedly for five different flavors under four increasing power settings using either the foil-lined original package or a brown paper bag. UFPs and PM2.5 generated by microwaving popcorn were 150-560 and 350-800 times higher than the emissions from microwaving water, respectively. About 90% of the total particles emitted were in the ultrafine size range. The emitted PM concentrations varied significantly with flavor. Replacing the foil-lined original package with a brown paper bag significantly reduced the peak concentration by 24-87% for total particle number and 36-70% for PM2.5 . A positive relationship was observed between both UFP number and PM2.5 mass and power setting. The emission rates of microwave popcorn ranged from 1.9×10(10) to 8.0×10(10) No./min for total particle number and from 134 to 249μg/min for PM2.5 .

A multiple charging correction algorithm for scanning electrical mobility spectrometer data

Accuracy of particle size distribution measurements from scanning electrical mobility spectrometers (SEMS) is critically dependent on the quality of SEMS data inversion. A critical element of SEMS data inversion is the consideration of the charged particle fraction in the sample flow. In particular, when larger, multiply-charged particles are present in the measured aerosol, significant errors in the calculation of size distributions are possible if their contribution is not correctly accounted for. While ignoring the contribution of multiply charged particles may be acceptable when the particles are mostly in the ultrafine size range, a substantial error is possible when a significant fraction of particles are larger than 100nm. Accurate calculation of size distributions from SEMS data is possible when an inertial impactor is used to eliminate the contribution of multiply-charged particles larger than a cut-size and an iterative multiple-charge correction (MCC) algorithm is used during the data inversion process. The effectiveness of this approach is, however, strongly dependent on the relationship between the aerodynamic and the electrical mobility diameters of the particles. Here, we demonstrate the limitations of the existing inversion algorithms and propose an alternative MCC algorithm for size distribution calculation from non-ideal SEMS data. In the proposed approach, the zeroth order singly charged particle size distribution is fit using a Gumbel distribution function, and the resultant fit is used to correct for the multiply-charged contribution to the SEMS data. The effectiveness of the proposed approach is tested for a range of particle size distribution scenarios and validated with experimental data.

Sources of ultrafine particles and chemical species along a traffic corridor: comparison of the results from two receptor models

Environmental context Identifying the sources responsible for air pollution is crucial for reducing the effect of the pollutants on human health. The sources of the pollutants were found here by applying two mathematical models to data consisting of particle size distribution and chemical composition data. The identified sources could be used as the basis for controlling or reducing emissions of air pollution into the atmosphere. Abstract Particulate matter is common in our environment and has been linked to human health problems particularly in the ultrafine size range. In this investigation, the sources of particles measured at two sites in Brisbane, Australia, were identified by analysing particle number size distribution data, chemical species concentrations and meteorological data with two source apportionment models. The source apportionment results obtained by positive matrix factorisation (PMF) and principal component analysis–absolute principal component scores (PCA–APCS) were compared with information from the gaseous chemical composition analysis. Although PCA–APCS resolved more sources, the results of the PMF analysis appear to be more reliable. Six common sources were identified by both methods and these include: traffic 1, traffic 2, local traffic, biomass burning and two unassigned factors. Thus motor vehicle related activities had the greatest effect on the data with the average contribution from nearly all sources to the measured concentrations being higher during peak traffic hours and weekdays. Further analyses incorporated the meteorological measurements into the PMF results to determine the direction of the sources relative to the measurement sites, and this indicated that traffic on the nearby road and intersection was responsible for most of the factors. The described methodology that utilised a combination of three types of data related to particulate matter to determine the sources and combination of two receptor models could assist future development of particle emission control and reduction strategies.

Microstructural evolution of pure silver during ECAP processing and subsequent heating

In recent years large research efforts have been focused on the development of severe plastic deformation (SPD) processes to produce ultrafine grained metals. One of the most studied methods for SPD processing is equal channel angular pressing, widely applied to different metals. Silver is one of the material recently subjected to this type of deformation process, since it is a representative FCC metal with low stacking fault energy (SFE). Limited information exists on structure evolution and deformation mechanisms of silver and its alloys in the ultrafine and nanoscale grain size range, and on thermal stability of these microstructures. In particular, low temperature, or even room-temperature, self-annealing is a fundamental issue to be faced for industrial applications. An evaluation of microstructure stability through X-ray diffraction measurements during step-heating treatments is proposed here, instead of multiple isothermal treatments. The method allowed to confirm that restoration temperature decreases for increasing deformation, and it achieves a saturation value after four ECAP passes.

3D air filtration modeling for nanofiber based filters in the ultrafine particle size range

In this work, 3D filtration modeling utilizing realistic SEM image-based 3D structure model, transition/free molecular flow regime, Brownian diffusion, particle–fiber interactions, aerodynamic slip and sieve has been proposed and used for different polyurethane nanofiber-based filters. For the model validation purposes, two polyurethane nanofiber layers prepared by the electrospinning process (having identical average fiber diameter, 120nm, but different average pore sizes) were combined to form two pairs of nanofiber-based filters; each pair consists of two filters having comparable mass area and thickness. Filtration characteristics of prepared filters were determined experimentally in the ultrafine particle size range (20–400nm). It has been found that the proposed model is able to reasonably predict the measured filtration efficiency, pressure drop and quality factor for all tested filter samples.

Levels of black carbon and their relationship with particle number levels—observation at an urban roadside in Taipei City

Information on the relationship between black carbon (BC) and particle number levels in urban areas is limited. Therefore, investigating the relationship between BC and particle number levels in different particle size ranges at an urban area is worthwhile. This study used an aethalometer and scanning mobility particle sizer to measure the levels of BC and particle number simultaneously at an urban roadside in Taipei City. Measurement results show that hourly BC levels are 0.62-8.80 μg m(-3) (mean=3.50 μg m(-3)) and hourly particle number levels are 4.21 × 10(3)-4.64 × 10(4) particles cm(-3) (mean=2.00 × 10(4) particles cm(-3)) in Taipei urban area. The BC and particle number levels peak during morning (7:00-9:00) and evening (16:00-18:00) rush hours on weekdays. Low BC and particle number levels exist in the early morning hours. Time variations in BC levels are the same as those of particle number levels in this study, clearly indicating that BC and particles are likely released from the same emission source. Additionally, BC levels in the urban area are more strongly associated with ultrafine particle levels than with total particle number levels, particularly in the size range of 56-180 nm. According to measurement results, most BC in aerosols in urban areas can be in the ultrafine size range.

Impact of two particle measurement techniques on the determination of N95 class respirator filtration performance against ultrafine particles

The purpose of this experimental study was to compare two different particle measurement devices; an Electrical Low Pressure Impactor (ELPI) and a Scanning Mobility Particle Sizer (SMPS), to measure the number concentration and the size distribution of NaCl salt aerosols to determine the collection efficiency of filtering respirators against poly disperse aerosols. Tests were performed on NIOSH approved N95 filtering face-piece respirators (FFR), sealed on a manikin head. Ultrafine particles found in the aerosols were also collected and observed by transmission electron microscopy (TEM). According to the results, there is a systematic difference for the particle size distribution measured by the SMPS and the ELPI. It is largely attributed to the difference in the measurement techniques. However, in spite of these discrepancies, reasonably similar trends were found for the number concentration with both measuring instruments. The particle penetration, calculated based on mobility and aerodynamic diameters, never exceeded 5% for any size range measured at constant flow rate of 85L/min. Also, the most penetrating particle size (MPPS), with the lowest filtration efficiency, would occur at a similar ultrafine size range <100nm. With the ELPI, the MPPS was at 70nm aerodynamic diameter, whereas it occurred at 40nm mobility diameter with the SMPS.