Particle Aerodynamic Diameter Research Articles

Understanding regional aerosol deposition in pediatric airways during oral breathing: Insights from computational modeling

While there has been considerable investigation into the deposition of inhaled aerosols in the airways of adults, less is known about where aerosols deposit in the lungs of children. Clinical investigation into aerosol deposition in children is complicated by ethical concerns surrounding ionizing radiation studies in children. To meet the need for non-clinical methods of estimating regional deposition in pediatric airways, multiple in silico models were developed to represent the lungs of girls and boys aged 6, 8, 10 and 12 years. The models were symmetric and used a single-path deterministic approach to calculate aerosol deposition in the airways. Regional deposition estimates were provided for children using a fixed set of controlled breathing patterns before characterizing regional deposition during typical tidal breathing in each age group. Deposition patterns were found to be strongly influenced by inhalation flow rate and aerodynamic particle size. Differences between boys and girls in the fraction of inhaled aerosol depositing were minimal during fixed breathing patterns, with higher deposition in all regions of the younger age groups. However, when breathing patterns were adjusted to represent typical tidal breathing in each age group, age differences in the regional fraction of particles depositing became negligible. Moreover, peak deposition fractions in both the conducting and peripheral airways occurred within a narrow range of aerodynamic particle diameters between 2.4 and 2.6 μm, a smaller size range than for adults. During exposure over a fixed period of time, age-related differences in minute ventilation resulted in a larger aerosol dose depositing in the intrathoracic airways of older children. Such differences suggest that to achieve comparative dosing in this age range, older children should inhale aerosols for a shorter time. These findings provide an improved understanding of regional deposition in pediatric airways and will assist in optimizing regional drug delivery to children.

Modelling Drug Delivery to the Small Airways: Optimization Using Response Surface Methodology

AimThe aim of this in silico study was to investigate the effect of particle size, flow rate, and tidal volume on drug targeting to small airways in patients with mild COPD.MethodDesign of Experiments (DoE) was used with an in silico whole lung particle deposition model for bolus administration to investigate whether controlling inhalation can improve drug delivery to the small conducting airways. The range of particle aerodynamic diameters studied was 0.4 – 10 µm for flow rates between 100 – 2000 mL/s (i.e., low to very high), and tidal volumes between 40 – 1500 mL.ResultsThe model accurately predicted the relationship between independent variables and lung deposition, as confirmed by comparison with published experimental data. It was found that large particles (~ 5 µm) require very low flow rate (~ 100 mL/s) and very small tidal volume (~ 110 mL) to target small conducting airways, whereas fine particles (~ 2 µm) achieve drug targeting in the region at a relatively higher flow rate (~ 500 mL/s) and similar tidal volume (~ 110 mL).ConclusionThe simulation results indicated that controlling tidal volume and flow rate can achieve targeted delivery to the small airways (i.e., > 50% of emitted dose was predicted to deposit in the small airways), and the optimal parameters depend on the particle size. It is hoped that this finding could provide a means of improving drug targeting to the small conducting airways and improve prognosis in COPD management.

Assessment of personal deposited dose and particle size distribution of bacterial aerosol in kindergarten located in southern Poland

The study's primary focus lies in examining the relationship between respiratory and deposition doses of bacterial aerosols in urban kindergarten, providing valuable insights into the specific doses absorbed by individuals in different sections of their respiratory systems based on the aerodynamic diameter of bacterial particles. Samples were collected twice a week, using by an Andersen cascade impactor during autumn and winter seasons 2018/2019 resulting in a total of 1152 Petri dishes analyzed. The highest average concentration of bacterial aerosol was observed during autumn (1698 ± 663 CFU/m3) in comparison to winter months (723 ± 134 CFU/m3). Respirable doses for children and staff were 2945 and 2441 CFU/day during winter and 5988 and 4964 CFU/day during autumn, respectively. Deposition doses incorporated from empirical models for regional deposition in the respiratory tract showed that children in kindergarten absorb 33% less of bacteria into alveolar region if breath by nose instead of mouth. Additionally, risk assessment results indicate that the hazard indices for children attending kindergartens for 3 years and for staff working 25 years are below 1, suggesting minor risks associated with the inhalation of bioaerosols during autumn and winter. HI was <1, so the non-carcinogenic effects are on an acceptable level, but the indoor/outdoor ratio were 3.5 and 2.4 for autumn and winter, respectively, indicating children's and adult's exposure to bacterial aerosol should be reduced.

Elemental composition of particles formed during welding with stick electrodes

The elemental composition of welding fume (WF) respirable particles formed in carbon and low-alloy steels welding with stick electrodes with rutile (ANO-4) and the basic (UONI 13/45) type of coating was studied by X-ray-spectral electron-probe microanalysis. In the range from 0.25 to 16 µm aerodynamic diameter, all WF particles were divided into three groups according to their iron content: low (Fe≤20%), medium (20%&lt;Fe&lt;40%) and high (Fe≥40%). Each group contains various amounts of elements originating from the welding materials, which reflects their formation mechanism. Their relative abundance in WF depends on the particles aerodynamic diameter, type of electrode coating and the arc power. Particles with the medium iron content (agglomerates of nanosized primary particles) formed the largest group (over 70%) of respirable WF particles. For each electrode type, their average elemental composition does not depend on the size of the agglomerates. The low iron particles contain various combinations of electrode coating elements, and the variety of combinations increases with their aerodynamic diameter grows.These WF particles can be identified as aggregates of primary particles agglomerates and microspatters formed by disintegration of the electrode coating. WF particles with a high iron content are formed by aggregation of molten electrode metal microdroplets and nanosized primary particles agglomerates. They mainly contain iron (60–70%)and oxygen (15–35%). Their average elemental composition does not depend on the size of the aggregates, type of electrode coating and the arc power. The obtained results can be useful for the analysis and assessment of health risks for welders.

Using particle dimensionality-based modeling to estimate lung carcinogenicity of 3D printer emissions.

The use of 3D printing technologies by industry and consumers is expanding. However, the approaches to assess the risk of lung carcinogenesis from the emissions of 3D printers have not yet been developed. The objective of the study was to demonstrate a methodology for modeling lung cancer risk related to specific exposure levels as derived from an experimental study of 3D printer emissions for various types of filaments (ABS, PLA, and PETG). The emissions of 15 filaments were assessed at varying extrusion temperatures for a total of 23 conditions in a Class 1,000 cleanroom following procedures described by ANSI/CAN/UL 2904. Three approaches were utilized for cancer risk estimation: (a) calculation based on PM2.5 and PM10 concentrations, (b) a proximity assessment based on the pulmonary deposition fraction, and (c) modeling based on the mass-weighted aerodynamic diameter of particles. The combined distribution of emitted particles had the mass median aerodynamic diameter (MMAD) of 0.35 μm, GSD 2.25. The average concentration of PM2.5 was 25.21 μg/m3 . The spline-based function of aerodynamic diameter allowed us to reconstruct the carcinogenic potential of seven types of fine and ultrafine particles (crystalline silica, fine TiO2 , ultrafine TiO2 , ambient PM2.5 and PM10, diesel particulates, and carbon nanotubes) with a correlation of 0.999, P < 0.00001. The central tendency estimation of lung cancer risk for 3D printer emissions was found at the level of 14.74 cases per 10,000 workers in a typical exposure scenario (average cumulative exposure of 0.3 mg/m3 - years), with the lowest risks for PLA filaments, and the highest for PETG type.

Mobile measurements for distribution and attribution of particulate matter in urban environments

Particulate matter (PM) sources differ in urban environments and may show spatiotemporal distinct patterns for varying particle aerodynamic diameters (DP). We here assess such patterns using high-resolution PM ≤10 μm data recorded with a cargo bike along a 14 km route through urban, suburban, and rural areas in Mainz (Germany). The measurements conducted twice a day between May and August 2021 reveal decreasing particle number concentration (PNC) with increasing DP including ∼6000 times higher particle numbers at DP 0.22–0.25 μm compared to DP 4–5 μm. Total mass concentration is bi-modally distributed and dominated by particles <0.3 μm and from 3 to 5 μm representing 36 and 22% of the entire air load, respectively. PM concentrations in Mainz are significantly higher in the morning than in the afternoon, and PM1 and PM10 are 13 and 31% higher in urban compared to surrounding suburban and rural areas. The high-resolution measurements also revealed 30% higher PM concentrations at DP 3–5 μm in the urban compared to the rural sectors, which is indicative for road dust, brake and tyre abrasion as the main source. DP distribution in rural hotspots is generally shifted toward larger particles >3 μm, most likely related to natural dust from agricultural fields. These findings show that high-resolution PM profiles can skillfully be recorded using bikes as mobile platform to identify spatial pollution patterns and attribute DP spectra to particular emission sources.

ALKBH5 mediates silica particles-induced pulmonary inflammation through increased m6A modification of Slamf7 and autophagy dysfunction

Silica particles are commonly encountered in natural and industrial activities. Long-term environmental exposure to silica can result in silicosis, which is characterized by chronic inflammation and abnormal tissue repair in lung. To uncover the role of m6A modification in silica-induced pulmonary inflammation, we conducted this study using established mouse and macrophage models. In this study, the aerodynamic diameter of silica particles was approximately 1–2 µm. We demonstrated that silica exposure in mice caused pulmonary inflammation and increased global m6A modification levels, the downregulation of alkB homolog 5 (ALKBH5) might contribute to this alteration. Besides, we found that F4/80, a macrophage-specific biomarker, was co-expressed with ALKBH5 through dual immunofluorescent staining. In vitro studies using MeRIP assays suggested that Slamf7 was a target gene regulated by m6A modification, and specific inhibition of ALKBH5 increased Slamf7 expression. Mechanistically, ALKBH5 promoted m6A modification of Slamf7, which decreased Slamf7 mRNA stability in an m6A-dependent manner, ultimately regulating Slamf7 expression. In addition, silica exposure activated PI3K/AKT and induced macrophage autophagy. Inhibition of Slamf7 promoted autophagy, reduced the secretion of pro-inflammatory cytokines, and improved silica-induced pulmonary inflammation. In summary, ALKBH5 can regulate silica-induced pulmonary inflammation by modulating Slamf7 m6A modification and affecting the function of macrophage autophagy.

Effect of forceful suction and air disinfection machines on aerosol removal

BackgroundsDental procedures involving drilling and grinding can produce a significant amount of suspended aerosol particles (PM) and bioaerosols. This study aims to analyze the size and concentration of aerosol particles generated during drilling and to investigate the effectiveness of two air exchange systems, namely forceful suction (FS) and air disinfection machines (DM), in removing PM.MethodsFor this study, 100 extracted permanent teeth were collected and divided into three groups: without suction (n = 50), suction with forceful suction (n = 25), and suction with air disinfection machines (n = 25). The removal rate of suspended aerosol particles was analyzed using particle counters and air data multimeter.ResultsWhen drilling and grinding were performed without vacuum, 0.75% of the aerosol particles generated were PM2.5-10, 78.25% of total suspended aerosol particles (TSP) were PM2.5, and 98.68% of TSP were PM1. The nanoanalyzer measurements revealed that the aerodynamic diameter of most aerosol particles was below 60 nm, with an average particle diameter of 52.61 nm and an average concentration of 2.6*1011 ultrafine aerosol particles. The air change per hour (ACH) was significantly lower in the air disinfection machines group compared to the forceful suction group. Additionally, the number of aerosol particles and mass concentration was significantly lower in the air disinfection machines group compared to the forceful suction group in terms of PM2.5 levels. However, the forceful suction group also reduced the mass concentration in PM10 level than the air disinfection machines group.ConclusionIn conclusion, the air exchange system can reduce the aerosol particles generated during drilling and grinding. Comparing the two air exchange systems, it was found that the air disinfection machines group reduces the number of aerosol particles and mass concentration in PM2.5 levels, while the forceful suction group reduces the mass concentration in PM10 level.

PM0.1 non-bouncing impactor (NBI) for ultrafine particle mass and number measurements

This study designed and tested a 30 L/min PM0.1 non-bouncing impactor (PM0.1 NBI) for ultrafine particle (UFP) mass concentration measurement. The PM0.1 NBI uses a wetted glass fiber filter with continuous water injection to maintain a clean surface, preventing particle loading and bounce effects. Lab tests showed the 30 L/min PM0.1 NBI outperformed the PM0.1 stage of NCTU micro-orifice cascade impactor (NMCI, non-rotating) with a silicon oil-coated aluminum foil substrate in collecting solid particles, as the particle collection efficiency of the latter decreased obviously with increasing particle aerodynamic diameter for particles larger than ca. 300 nm, an apparent particle bounce phenomenon. The ambient field tests showed very close UFP mass concentrations between the PM0.1 NBI sampler (the PM0.1 NBI preceded by 3 stages with 18, 10, and 2.5 μm cutoff sizes) and the reference rotating 10-stages NMCI with the difference of ±0.5 μg/m3 only. In addition, the 3 L/min PM0.1 NBI was combined with a condensation particle counter to measure the UFP number concentrations which were shown to be very close to those of the reference with the difference of ±5% only in the laboratory tests for loaded particle mass up to 300 μg. Good agreement was also found in the field tests. Therefore, the current 3 L/min PM0.1 NBI and the future PM NBI with smaller flow rates (0.2–2.1 L/min) and larger cut-sizes (such as 0.4–0.9 μm) can be used as viable UFP classifiers for improving UFP measurement accuracy both in mass concentrations and number concentrations and reducing the maintenance needs for the UFP classifiers which are important to long-term sampling and monitoring.

Identifying patterns of aerosols formation during contact butt fusion welding

The object of research is the hygienic characteristics of harmful substances that pollute the air during contact butt welding with continuous and pulsating melting. The task to be solved is the lack of such information for devising appropriate measures to protect operators of contact welding of railroad rails. A description of the methods of researching the chemical composition of welding aerosols and gases, the dispersed composition of nano-sized fractions of aerosols and assessing their impact on the body of welders is given. It was established that contact butt welding by melting P65 rails is accompanied by the release of harmful substances into the air of the working zone in the form of aerosols at the nano range level, which are characterized by high biological activity. The research results showed that during continuous melting, the intensity of welding aerosol release is lower than during pulsating melting. It is shown that the toxicity of the aerosol during contact welding belongs to the moderately dangerous class. It was established that during contact butt welding by melting, an aerosol is formed, the composition of which contains nano-sized components of manganese and iron in concentrations that exceed the calculated approximately safe levels of human exposure. In the aerosol sample, particles ranging in size from 70.8 to 1071.8 nm were detected, and the average aerodynamic diameter of the aerosol particles was 295.2 nm. The studies have shown that melting butt welding is accompanied by the formation of such toxic gases as nitrogen dioxide and carbon monoxide in concentrations that exceed the maximum permissible. The results of a comprehensive hygienic assessment of aerosols during contact butt fusion welding provided comprehensive information about the level of harmful effects of these aerosols on the body of welders

Estimation of the activity median aerodynamic diameter of plutonium particles using image analysis

ABSTRACT The aerodynamic radioactive median diameter (AMAD) and the absorption type are necessary information for internal exposure assessment. In 2017, at a plutonium-handling facility in the Oarai site of the Japan Atomic Energy Agency, an accidental contamination occurred, and five workers were contaminated with radioactive materials, including plutonium. In this study, some smear papers and a dust sampling filter were measured with the imaging plate, and some particles were observed with an electron microscope. The minimum AMADs for the two absorption types of plutonium were estimated for the conservative dose assessment. Two AMADs were calculated for Type M as plutonium nitrate and Type S as plutonium dioxide. Excluding the extremely large particle found in a smear sample, the AMAD estimation results showed that the minimum AMADs of plutonium nitrate from smear papers were 4.3–11.3 μm, while those of plutonium dioxide were 5.6–14.4 μm. Moreover, the minimum AMAD of plutonium nitrate from a dust sampling filter was 3.0 μm, while that of plutonium dioxide was 3.9 μm.

Distribution and bioavailability of mercury in size-fractioned atmospheric particles around an ultra-low emission power plant in Southwest China

Ultra-low emission (ULE) technology retrofits significantly impact the particulate-bound mercury (Hg) emissions from coal-fired power plants (CFPPs); however, the distribution and bioavailability of Hg in size-fractioned particulate matter (PM) around the ULE-retrofitted CFPPs are less understood. Here, total Hg and its chemical speciation in TSP (total suspended particles), PM10 (aerodynamic particle diameter ≤ 10 µm) and PM2.5 (aerodynamic particle diameter ≤ 2.5 µm) around a ULE-retrofitted CFPP in Guizhou Province were quantified. Atmospheric PM2.5 concentration was higher around this ULE-retrofitted CFPP than that in the intra-regional urban cities, and it had higher mass Hg concentration than other size-fractioned PM. Total Hg concentrations in PM had multifarious sources including CFPP, vehicle exhaust and biomass combustion, while they were significantly higher in autumn and winter than those in other seasons (P < 0.05). Regardless of particulate size, atmospheric PM-bound Hg had lower residual fractions (< 21%) while higher HCl-soluble fractions (> 40%). Mass concentrations of exchangeable, HCl-soluble, elemental, and residual Hg in PM2.5 were higher than those in other size-fractioned PM, and were markedly elevated in autumn and winter (P < 0.05). In PM2.5, HCl-soluble Hg presented a significantly positive relationship with elemental Hg (P < 0.05), while residual Hg showed the significantly positive relationships with HCl-soluble Hg and elemental Hg (P < 0.01). Overall, these results suggested that atmospheric PM-bound Hg around the ULE-retrofitted CFPP tends to accumulate in finer PM, and has higher bioavailable fractions, while has potential transformation between chemical speciation.

СОВРЕМЕННЫЕ АСПЕКТЫ НЕБУЛАЙЗЕРНОЙ ТЕРАПИИ

Nebulizer therapy is widely used in modern respiratory medicine. Nebulizers are devices that convert a liquid into a suitable for inhalation by a patient aerosol, which meets the requirements of the European standard for nebulizer therapy prEN 13544-1. The fundamental differences between nebulizers and other inhalation devices (metered aerosol inhalers, powder inhalers) are the possibility to perform maneuvers on spontaneous breathing, the use of drugs, which do not involve the use of other inhalers, and the possibility to select drug doses depending on patients need. Although this delivery method is effective for many respiratory diseases, and it is preferred for special groups (children, the elderly, as well as severe exacerbations, etc.), there are some peculiarities and limitations of its use, which should be taken into account by clinicians. According to the principle of operation, nebulizers are divided into compressor, ultrasonic and electronic-mesh, which differ in technical characteristics and indications for use. Compressor nebulizers are most widely used in medical institutions (intensive care units, hospitals, offices) and at home, relatively inexpensive, simple and easy to maintain, have additional components (chambers with inhalation-exhalation valves, masks for children and children) adults, nasal aspirator, etc.). Modern jet nebulizers are equipped with spray mode switches, so that the aerosol feed rate and the aerodynamic diameter of particles of an average mass from 2-3 to 10 microns can be adjusted. Depending on the selection of the switch mode and the corresponding medication, the nebulizer can be used in the treatment of rhinitis, laryngitis, bronchitis, asthma and other diseases of both upper and lower respiratory tract.

In silico investigation of the effect of particle diameter on deposition uniformity in pulmonary drug delivery

Systemic drug delivery via the pulmonary route has a critical limitation because dose uniformity is strongly dependent upon patient inhalation technique. The most frequent and critical errors in inhalation technique are overly forceful inspiration and insufficient breath-holding. In this study, response surface methodology was used with an in silico whole lung particle deposition model for bolus administration to investigate whether varying the inhaled drug particle size could reduce the dependence of deposition upon flow rate and/or breath-holding duration. The range of particle aerodynamic diameters studied was 0.1–10 µm for flow rates between 500–2000 mL/s and breath-holding duration between 0–15 seconds. Comparison with published experimental data showed that this modeling approach can accurately predict the lung deposition. The simulation results indicated that the deposition of particles with aerodynamic diameter in the range of 0.1–1.5 µm should be minimally affected by flow rate over the 500–2000 mL/s range. There was found to be no particle size whose deposition was completely independent of breath-holding duration. The smallest particles, whose deposition is diffusion-driven, were found to be the least sensitive to breath-holding time, but this size is of limited practical use. On the other hand, the simulations indicated that particles with a 1.5 µm diameter would provide acceptable consistency in dose reaching the acini region when the breath-holding duration was greater than 10 seconds. It is hoped that this finding could provide a means of improving dose uniformity for systemic delivery via the pulmonary route by facilitating simplified patient instructions.

Size-specific filtration efficiency and pressure drop of school-aged children's woven and nonwoven masks at varying face velocities

BackgroundDifferences in physiology and breathing patterns between children and adults lead to disparate responses to aerosols of varying sizes. No standardized method exists for measuring the filtration efficiency (FE) of children's masks to reflect such differences. MethodsUsing an adult N95 mask as a control and two different face velocities (vf) (9.3 cm/s representing adults and 4.0 cm/s representing school-aged children), we tested the pressure drop (ΔP) through children's nonwoven masks (surgical and KN95) and children's woven masks (100% cotton and partially-cotton-based masks), as well as their size-specific FE between aerodynamic particle diameters of 0.02 and 2.01 μm. ResultsAll three types of mask showed a 1 to 9% absolute increase in minimum FE at the lower vf and a significant decrease in ΔP. For children's surgical masks the increase in FE was significant for most of the examined particle sizes, but for children's woven masks the increase was limited to particles smaller than 0.04 μm. ConclusionsLower vf for children is likely to lead to a higher FE, lower ΔP, and consequently higher filter qualities in children's masks. For woven masks, the FE for particles larger than 0.04 μm was low (typically <50%) for both vf‘s studied.

Design of Round-Nozzle Inertial Impactors Review with Updated Design Parameters

Round-nozzle inertial impactors are widely used aerosol measuring instruments to characterize the mass and chemical composition of airborne aerosol particles as a function particle aerodynamic diameter. This article summarizes the most important design considerations with updated recommended design parameters taken from our review of published research articles, and discusses some of the more common non-idealities seen in the operation and performance of inertial impactors. With this information, it is now possible to design a cascade impactor with near-ideal particle separation performance, and with stage cutpoints that can be predicted with excellent accuracy, and verified experimentally using state-of-the-art calibration techniques.

Developing mucociliary clearance model for the numerical simulation of two-way coupling particulate flow inside the nasal cavity in the presence of deep breathing

Generally, it is essential to investigate mucociliary clearance as a defensive mechanism for drug delivery through the respiratory tract system. However, regarding the vicinity of micro-macro scales inside the respiratory system, typically, it has been neglected in numerical simulations. Hence, in the current research, a new boundary condition is developed to consider the effects of mucociliary clearance on deposited particles inside the nasal cavity. The two main components in developing the mucociliary clearance model are, namely, the cilia metachronal wave and wall-adjacent cell information. The cilia metachronal wave and wall-adjacent cell velocity generally determine the velocity and direction of the mucociliary clearance model, respectively. Therefore, the new boundary condition does not create an extra computational cost. Accordingly, all developing procedures are performed using the open-source toolbox (OpenFOAM 7). Herein, by applying the new boundary condition to the nasal wall, it is observed that each deposited particle is trapped and followed a different path alongside the nasal wall. Moreover, the initial deposition location of particles is changed up to 3% by means of the new implemented boundary condition based on the particle aerodynamic diameter. Based on the results, tracking of particles for 5 min indicated that 42% of deposited particles inside the nasal valve are transferred to the main airway. This means that drug absorption locations change with the consideration of the mucociliary clearance model. The results reveal that such a simplified strategy to account for mucociliary clearance can contribute to the prediction accuracy of the transport of sprayed therapeutic drug particles through the nasal cavity.

Performance of Textile Mask Materials in Varied Humidity: Filtration Efficiency, Breathability, and Quality Factor

During the COVID-19 pandemic, reusable masks became ubiquitous; these masks were made from various fabrics without guidance from the research community or regulating agencies. Though reusable masks reduce the waste stream associated with disposable masks and promote the use of masks by the population, their efficacy in preventing the transmission of infectious agents has not been evaluated sufficiently. Among the unknowns is the effect of relative humidity (RH) on fabrics’ filtration efficiency (FE) and breathability. This study evaluates the FE and breathability of several readily accessible mask materials in an aerosol chamber. Sodium chloride aerosols were used as the challenge aerosol with aerodynamic particle diameter in the 0.5 to 2.5 µm range. To mimic the variability in RH in the environment and the exhaled-breath condition, the chamber was operated at RH of 30% to 70%. The face velocity was varied between 0.05 m/s and 0.19 m/s to simulate different breathing rates. The FE and pressure drop were used to determine the quality factor of the materials. Among the tested materials, the 3M P100 filter has the highest pressure drop of 140 Pa; the N95 mask and the 3M P100 have almost 100% FE for all sizes of particles and tested face velocities; the surgical mask has nearly 90% FE for all the particles and the lowest pressure drop among the certified materials, which ranks it the second to the N95 mask in the quality factor. Other material performance data are presented as a function of relative humidity and aerosol size. The quality factor for each material was compared against reference filtration media and surgical masks. Multiple layers of selected materials are also tested. While the additional layers improve FE, the pressure drop increases linearly. Additionally, the certified materials performed approximately three times better than the highest performing non-certified material.

A numerical study of reducing the concentration of O3 and PM2.5 simultaneously in Taiwan.

Since the 24-hr PM2.5 (particle aerodynamic diameter less than 2.5μm) concentration standard was regulated in Taiwan in 2012, the PM2.5 concentration has been decreasing year by year, but the ozone (O3) concentration remains almost the same. In particular, the daily maximum 8-hr average O3 (MDA8 O3) concentration frequently exceeds the standard. The goal of this study is to find a solution for reducing PM2.5 and O3 simultaneously by numerical modeling. After the Volatile Organic Compounds (VOCS)-limited and nitrogen oxides (NOX)-limited areas were defined in Taiwan, then, in total, 50 scenarios are simulated in this study. In terms of the average in Taiwan, the effect of VOCS emission reduction is better than that of NOX on the decrease in PM2.5 concentration, when the same reduction proportion (20%, 40%) is implemented. While the effect of further NOX emission reduction (60%) will exceed that of VOCS. The decrease in PM2.5 is proportional to the reduction in precursor emissions such as NOX, VOCS, sulfur dioxides (SO2), and ammonia (NH3). The lower reduction of NOX emission for whole Taiwan caused O3 increases on average but higher reduction can ease the increase, which suggests the implement of NOX emission reductions must be cautious. When comparing administrative jurisdictions in terms of grids, districts/towns, and cities/counties, it was found that controlling NOX and VOCS at a finer spatial resolution of control units did not benefit the decrease in PM2.5 but did benefit the decrease in O3. The enhanced O3 control strategies obviously cause a higher decrease of O3 throughout Taiwan due to NOX and VOCS emission changes when they are implemented in the right places. Finally, three sets of short-term and long-term goals of controlling PM2.5 and O3 simultaneously are drawn from the comprehensive rankings for all simulated scenarios, depending on whether PM2.5 or O3 control is more urgent. In principle, the short-term scenarios could be ordinary or enhanced version of O3 decrease with lower NOX/VOCS emissions, while the long-term scenario is enhanced version of O3 decrease plus high emission reductions for all precursors.

Revisiting the CFD modeling of a virtual impactor with inverted split ratio: Highlighting some determinants of representativeness

Dichotomous sampling of a mixture of gas and aerosol is looked for in many applications such as airborne SVOC (semivolatile organic compound) sampling. This article revisits the computational fluid dynamics simulation of the original SVOC aerosol dichotomous sampler (Kim & Raynor, 2009) to investigate which among some factors influence most the representativeness of such simulations. Considered modeling factors of influence are the 2D-axisymmetric reduction of space and the choice of turbulence model (realizable k-ε vs. k-ω BSL or k-ω SST). Considered physical factors of influence are the particles aerodynamic diameter (range 50 nm to 20 μm), the type of inlet condition for gas and particles (uniform or free-sampling condition), the particles turbulent dispersion and the particles initial radial position at inlet. Results are supported by an extensive numerical verification procedure and by available validation data. In this specific confined transitional two-phase flow, it is found that the axisymmetric simplification holds, that the turbulence model affects significantly the predicted flow pattern but less pressure drops and marginally the fate of aerosol particles. Turbulent dispersion of aerosols is found negligible, but the effect of inlet boundary condition appears decisive on aerosol motion despite a marginal influence on the flow pattern. In particular, for aerodynamic diameters above 2 μm, free-sampling conditions produce a strong focusing effect of particles which drastically helps in limiting wall deposition. These findings highlight particularly the importance of using a physically sound inlet condition for aerosol particles when simulating aerosol samplers, rejecting the usual simplistic uniform condition. Results also particularly emphasize the necessity of a thorough verification procedure for the computation of both phases when using CFD for similar samplers. Regarding the application to dichotomous sampling, it appears that any process that moves particles away from the wall upon entry improves the separation efficiency of the device while decreasing deposition.