Collection Of Aerosol Particles Research Articles

The investigation of traceable preparation technique of submicron particle number concentration standards in liquids

The concentration of particles at the nano- and submicron-meter scale in liquid is crucial in multiple fields including the biomedical and semiconductor industry. However, there is still a lack of metrological standards or Certified Reference Materials (CRMs) for liquid-borne particle number concentration (PNC) which could be traceable to the International System of Units (SI). To address this issue, a quantitative and value-traceable preparation technique for liquid-borne particle number concentration CRMs (PNC-CRMs) in a submicron-meter scale based on controllable aerosol generation and collection was developed in this study. In this technique, by using commercial differential electrostatic mobility analyzer (DMA) and calibrated condensation particle counter (CPC), monodisperse aerosol particle with known concentration was initially generated. Then for quantitatively transforming the aerosol particles to the liquid, an aerosol particle collection system was designed and developed by hydrodynamic (CFD) simulations and experiment conducting, and crucial parameters of the collection system, e.g. the nozzle diameter of the aerosol particle outlet, the distance from the nozzle to the liquid surface, and the state of the liquid interface, were investigated and optimized. Under the optimized collected parameters, the collection efficiency for aerosol particles of the newly-developed system could reach over 90%. Because the PNC in aerosol is SI-traceable, combined with the obtained collection efficiency and collection time, the PNC in the collection liquid with could be obtained finally and trace to SI unit. Using this technique, two kinds of PNC-CRMs with nominal sizes of 100 and 500 nm were developed successfully, where, certified values were (7–9) × 106 particles/mL and 1.7 × 106 particles/mL, and standard uncertainties are 4.2%.

Direct Observation of Particle-To-Particle Variability in Ambient Aerosol pH Using a Novel Analytical Approach Based on Surface-Enhanced Raman Spectroscopy.

The pH of atmospheric aerosols is a key characteristic that profoundly influences their impacts on climate change, human health, and ecosystems. Despite widely performed aerosol pH research, determining the pH levels of individual atmospheric aerosol particles has been a challenge. This study presents a novel analytical technique that utilizes surface-enhanced Raman spectroscopy to assess the pH of individual ambient PM2.5-10 aerosol particles in conjunction with examining their hygroscopic behavior, morphology, and elemental compositions. The results revealed a substantial pH variation among simultaneously collected aerosol particles, ranging from 3.3 to 5.7. This variability is likely related to each particle's unique reaction and aging states. The extensive particle-to-particle pH variability suggests that atmospheric aerosols present at the same time and location can exhibit diverse reactivities, reaction pathways, phase equilibria, and phase separation properties. This pioneering study paves the way for in-depth investigations into particle-to-particle variability, size dependency, and detailed spatial and temporal variations of aerosol pH, thus deepening our understanding of atmospheric chemistry and its environmental implications.

Characterization of a multi-stage focusing nozzle for collection of spot samples for aerosol chemical analysis

Concentrated collection of aerosol particles on a substrate is essential for their chemical analysis using various microscopy and laser spectroscopic techniques. An impaction-based aerosol concentration system was developed for focused collection of particles using a multi-stage nozzle that consists of a succession of multiple smooth converging stages. Converging sections of the nozzle were designed to focus and concentrate a particle diameter range of 900–2500 nm into a relatively narrower particle beam to obtain particulate deposits with spot diameters of 0.5–1.56 mm. A slightly diverging section before the last contractions was included to allow for better focusing of particles at the lower end of the collectable diameter range. The characterization of this multi-stage nozzle and the impaction-based aerosol concentration system was accomplished both numerically and experimentally. The numerical and experimental trends in collection efficiency and spot diameters agreed well qualitatively; however, the quantitative agreement between numerical and experimental results for wall losses was poor, particularly for larger particle diameters. The resulting concentrated particulate deposit, a spot sample, was analysed using Raman spectroscopy to probe the effect of spot size on analytical sensitivity of measurement. The method's sensitivity was compared against other conventional techniques, such as filtration and aerosol focused impaction, implementing condensational growth. Impaction encompassing the multi-stage focusing nozzle is the only method that can ensure high sensitivity at Reynolds numbers greater than 2000, that can be supported by small pumps which renders such method suitable for portable instrumentation.

Optimization of the QuEChERS extraction method to determine Polycyclic Aromatic Hydrocarbons (PAHs) in powder aerosol particles collected by cyclone

Conventional methods for collecting and extracting aerosol particles are challenging in accurately characterizing particle-bound polycyclic aromatic hydrocarbons (PAHs) contamination and conducting cellular exposure studies. Therefore, developing direct aerosol sample collection and simple pretreatment analytical methods is necessary. This study describes the optimization of the QuEChERS (quick, easy, cheap, effective, rugged, and safe) extraction method for the determination of PAHs in powder-form environmental standard materials (SRM1944) and proves it is also effective for analyzing PAHs in powder aerosol particle samples collected by cyclone. In this study, we used an I-optimal design response surface method combined with a desirability function to investigate the extraction effect of PAHs under different combinations of QuEChERS extraction factors, including extraction solvent, salt, and clean-up reagent. The optimized conditions of the method were determined using the 2-factor interaction (2FI) model combined with boundary conditions, resulting in acetonitrile/dichloromethane (7:1, v/v), Na2SO4/NaCl (1:1, w/w), and primary and secondary amine (PSA) as extraction solvents, extraction salts, and clean-up reagent, respectively. The optimized method showed good recoveries of PAHs reaching 76%–118% and 85%–121% for SRM1944 and standard solution. The results for cyclone-collected ambient powder aerosol particles extracted by the optimized QuEChERS illustrated that this improved procedure has good PAHs extraction efficiency as the traditional Soxhlet method, while reducing hazardous organic solvents usage, experimental cost (per mg sample) by 97% and sample pretreatment time. Overall, this combination of “powder aerosol particle collection and modified QuEChERS extraction” provides new insight on aerosol sample collection, extraction, and in vitro/in vivo exposure studies.

Development of a microsampler suitable for aerial collection of aerosol particles

A microsampler for collecting aerosol particles on an unmanned aerial system (UAS) was designed and evaluated in the laboratory for dry (no condensed water) and wet (foggy, misty, or rainy) air conditions.

SARS-CoV-2 in Exhaled Aerosol Particles from COVID-19 Cases and Its Association to Household Transmission.

BackgroundCoronavirus disease 2019 (COVID-19) transmission via exhaled aerosol particles has been considered an important route for the spread of infection, especially during super-spreading events involving loud talking or singing. However, no study has previously linked measurements of viral aerosol emissions to transmission rates.MethodsDuring February–March 2021, COVID-19 cases that were close to symptom onset were visited with a mobile laboratory for collection of exhaled aerosol particles during breathing, talking, and singing, respectively, and of nasopharyngeal and saliva samples. Aerosol samples were collected using a BioSpot-VIVAS and a NIOSH bc-251 2-stage cyclone, and all samples were analyzed by RT-qPCR for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) RNA detection. We compared transmission rates between households with aerosol-positive and aerosol-negative index cases.ResultsSARS-CoV-2 RNA was detected in at least 1 aerosol sample from 19 of 38 (50%) included cases. The odds ratio (OR) of finding positive aerosol samples decreased with each day from symptom onset (OR 0.55, 95 confidence interval [CI] .30–1.0, P = .049). The highest number of positive aerosol samples were from singing, 16 (42%), followed by talking, 11 (30%), and the least from breathing, 3 (8%). Index cases were identified for 13 households with 31 exposed contacts. Higher transmission rates were observed in households with aerosol-positive index cases, 10/16 infected (63%), compared to households with aerosol-negative index cases, 4/15 infected (27%) (χ2 test, P = .045).ConclusionsCOVID-19 cases were more likely to exhale SARS-CoV-2-containing aerosol particles close to symptom onset and during singing or talking as compared to breathing. This study supports that individuals with SARS-CoV-2 in exhaled aerosols are more likely to transmit COVID-19.

Study on the Collection Efficiency of Bioaerosol Nanoparticles by Andersen-Type Impactors.

Airborne transmission is much more common than previously thought. Based on our knowledge about SARS-COV-2 (COVID-19) infection, the aerosol transmission routes for all respiratory infections must be reassessed. Thus far, the COVID-19 outbreak has caused catastrophic public health and economic crises, posing a serious threat to the lives and health of people around the world and directing public attention toward the airborne transmission of pathogens. The novel coronavirus transmission in the form of nanoaerosols in a wider range hinders prevention and early warning efforts. As a classical bioaerosol sampler, the Andersen six-stage sampler is widely used in the collection and research of aerosol particles. In this study, the physical and biological collection efficiency of the six-stage sampler was explored by qPCR and colony counting method. Results showed that the physical collection efficiency reached more than 50% when the particle size was larger than 0.75 μm. However, the overall biological collection efficiency was only 0.25%. In addition, fluorescence microscopy and flow cytometry were used to detect the microbial state after sampling, and the results showed that the proportion of the collected live bacteria was less than 15% of the total. This result is of great significance not only for the application of the Andersen six-stage sampler in collecting nanosized bioaerosols, but also provides reference for the selection of subsequent detection technologies for effective collection.

Effect of Double Masking with Silk or Cotton Over-masks on the Source Control Capabilities of a Surgical Mask

In spite of the remarkable progress made in the development of safe and effective vaccines against COVID-19, deployment of respiratory protective devices remains vital for mitigating the transmission of SARS-CoV-2 during the ongoing pandemic. In this study, we evaluated double masking, which entails layering a fitted over-mask on top of a surgical mask. A previously validated manikin-based protocol was used to evaluate the performance of a surgical mask with an over-mask made of silk or cotton. We showed that double masking can significantly enhance the mask’s source control capabilities by reducing an aerosol emission from a coughing or sneezing wearer while maintaining a reasonable breathability and comfort level. The data obtained in this study, as well as the results recently reported by other investigators, suggest that an over-mask made of silk fabric has several advantages over one made of cotton. Moreover, silk over-masks have the added benefit of providing a reusable protective outer layer for surgical masks as silk is hydrophobic and increases aerosol particle collection. Not only can double masking reduce viral or bacterial transmission, but it can also promote surgical mask longevity, thereby reducing global waste and pollution associated with the use of disposable surgical masks. Finally, an additional study with five human subjects revealed no significant differences in perceived comfort (measured by proxies such as relative humidity, temperature, and CO2 level inside the mask) between single masking and double masking, as well as between double masking with either a silk or cotton over-mask.

A combined virtual impactor and field-effect transistor microsystem for particulate matter separation and detection

Ambient suspended particulate matter (PM) (primarily with particle diameter 2.5 µm or less, i.e., PM2.5) can adversely affect ecosystems and human health. Currently, optical particle sensors based on light scattering dominate the portable PM sensing market. However, the light scattering method has poor adaptability to different-sized PM and adverse environmental conditions. Here, we design and develop a portable PM sensing microsystem that consists of a micromachined virtual impactor (VI) for particle separation, a thermophoretic deposition chip for particle collection, and an extended-gate field-effect transistor (FET) for particle analysis. This system can realize on-site separation, collection, and analysis of aerosol particles without being influenced by environmental factors. In this study, the design of the VI is thoroughly analyzed by numerical simulation, and mixtures of different-sized silicon dioxide (SiO2) particles are used in an experimental verification of the performance of the VI and FET. Considering the low cost and compact design of the whole system, the proposed PM analysis microsystem has potential for PM detection under a wide range of conditions, such as heavily polluted industrial environments and for point-of-need outdoor and indoor air quality monitoring.

Contribution of Phoretic and Electrostatic Effects to the Collection Efficiency of Submicron Aerosol Particles by Raindrops

This article presents an experimental study, performed in the BERGAME setup, dedicated to studying the collection of submicron aerosol particles by raindrops. The initial aim was to focus on the influence of the electrical charges of raindrops on the efficiency with which they collect aerosol particles. However, in the relative humidity range considered in this article (26–36%), measurements highlight a first-order role of phoretic effect for submicron aerosol particles. Indeed, measurements highlight a 100% increase in the collection efficiency for each percentage decrease in the atmospheric relative humidity. Phoretic effects are known to play a role in collection by drops; however, none of the models found in the literature predicts the same magnitude as the one presently measured. Characterization of the aerosol trajectories around the drop, accelerated to terminal velocity, seems to show a coupling between phoretic effects and rear capture. This interaction, already suggested by Grover et al., is a line of explanation for such a sharp unpredicted increase of the collection efficiency with moisture decrease.

Effect of micropillars with varying geometry and density on the efficiency of impaction-based quartz crystal microbalance aerosol sensors

Inertial impaction is frequently used for the collection and subsequent measurement of aerosol particles in resonator-based airborne particulate matter (PM) sensors. However, particle bounce is known to significantly reduce particle collection efficiency (CE) on surfaces exhibiting low roughness, such as those present in quartz crystal microbalance (QCM) PM sensors. This paper shows that the addition of micropillars to impaction surfaces can significantly enhance their particle collection. Similarities in particle capture mechanisms between fibrous filters and pillar-enhanced surfaces are explained, and we show the adaptability of fibrous filter theory to pillared surface collection efficiency. Experiments confirm that the micropillar cross section and spacing have a significant role in particle capture. Pillars with circular, rectangular, and cross-shaped horizontal cross sections with 15 μm height and 12 μm (dense), 20 μm (nominal), and 27 μm (sparse) center-to-center spacings were printed using two-photon micro stereolithography. The efficiency increased by 35%–52% in the dense case, while the effect of the pillar shape was negligible. At nominal spacing, CE depended heavily on the pillar shape. The cross-shaped and circular pillars improved the CE by 26%–29%, although the rectangular pillars were as efficient as the bare surface. No significant difference between the bare and pillar-enhanced surfaces was visible in sparse spacing. We further show that, upon addition of a nominal distribution of micropillars to the surface of a QCM sensor for real-time mass measurements, the sensor response improved significantly (approximately 2.5 times) compared to a QCM with a bare surface.

Capturing heavy loading microparticles using electrostatic precipitator with square-wave collecting electrode

Collecting aerosol particles is important in public health viewpoint because aerosol particles have been resulting in million deaths every year. Electrostatic precipitators (ESPs) are widely used to deal with massive particles at a given airflow rate because of several advantages attributed to ESPs' low pressure drop. However, the collection efficiency of an ESP decays quickly when demanding a higher airflow rate. This paper presents the characteristics of a two-stage ESP that has a square-wave collecting electrode proposed to handle massive particles while preventing the collection efficiency from decreasing too fast when the airflow rate increases. The results show that, when almost doubling the airflow rate, the decreasing of the collection efficiency of an ESP using the square-wave collecting electrode is 8.4%, while that using the conventional flat-plate collecting electrode is 17.5%. The visual examinations of the particle depositions suggest that large particles likely impact the upstream walls of the square-wave structure, whereas small particles tend to recirculate and deposit on the downstream walls of the square-wave structure. Moreover, because of the increasing resistivity, it was observed that the massive particles accumulating in the charger causes the corona voltage increase when the corona current keeps at a constant.

Collection of Aerosol Particles by Filters Composed of Whisker-Coated Fibers

The deposition of submicron aerosol particles in model fibrous filters consisting of composite fibers coated with coaxial porous permeable shells composed of thin whiskers directed perpendicularly to the fiber surface has been considered. The viscous drag of the composite fibers and the efficiency of the diffusion collection of nanosized (point) and submicron particles from a three-dimensional flow have been calculated taking into account the finite sizes of the latter particles at small Reynolds numbers and Peclet diffusion numbers Pe = 1–106. Filter quality criterion γ, i.e., the ratio between the logarithmic penetration of the particles and the pressure drop across the filter, has been calculated as depending on the particle size and the parameters of the composite fibers. It has been shown that, when filtering aerosols of submicron particles, the γ value of the filters consisting of the composite fibers increases with Pe, markedly exceeds the γ values for point nanoparticles, and may be several times higher than the quality criterion of filters composed of fibers without porous shells.

Aerosol Particle Collection by Filters Composed of Fibers Coated with Porous Permeable Shells

Filtration of fine aerosols with model filters formed from composite fibers coated with porous permeable shells (layers) of a discrete structure consisting of finer parallel fibers has been considered. Drag forces and efficiencies of diffusion collection of submicron particles have been calculated as depending on the porosity of the filters, parameters of the shells, and the Peclet diffusion numbers at which the filter performance is substantially increased.

Sources of Airborne Norovirus in Hospital Outbreaks.

BackgroundNoroviruses are the major cause of viral gastroenteritis. Disease transmission is difficult to prevent and outbreaks in health-care facilities commonly occur. Contact with infected persons and contaminated environments are believed to be the main routes of transmission. However, noroviruses have recently been found in aerosols and airborne transmission has been suggested. The aim of our study was to investigate associations between symptoms of gastroenteritis and the presence of airborne norovirus, and to investigate the size of norovirus-carrying particles.MethodsAir sampling was repeatedly performed close to 26 patients with norovirus infections. Samples were analyzed for norovirus RNA by reverse transcription quantitative polymerase chain reaction. The times since each patient’s last episodes of vomiting and diarrhea were recorded. Size-separating aerosol particle collection was performed.ResultsNorovirus RNA was found in 21 (24%) of 86 air samples from 10 different patients. Only air samples during outbreaks, or before a succeeding outbreak, tested positive for norovirus RNA. Airborne norovirus RNA was also strongly associated with a shorter time period since the last vomiting episode (odds ratio 8.1; P = .04 within 3 hours since the last vomiting episode). The concentrations of airborne norovirus ranged from 5–215 copies/m3, and detectable amounts of norovirus RNA were found in particles <0.95 µm and >4.51 µm.ConclusionsThe results suggest that recent vomiting is the major source of airborne norovirus and imply a connection between airborne norovirus and outbreaks. The presence of norovirus RNA in submicrometre particles indicates that airborne transmission can be an important transmission route.

Effect of dry or wet substrate deposition on the organic volume fraction of core–shell aerosol particles

Abstract. Understanding the impact of sea spray aerosol (SSA) on the climate and atmosphere requires quantitative knowledge of their chemical composition and mixing states. Furthermore, single-particle measurements are needed to accurately represent large particle-to-particle variability. To quantify the mixing state, the organic volume fraction (OVF), defined as the relative organic volume with respect to the total particle volume, is measured after generating and collecting aerosol particles, often using deposition impactors. In this process, the aerosol streams are either dried or kept wet prior to impacting on solid substrates. However, the atmospheric community has yet to establish how dry versus wet aerosol deposition influences the impacted particle morphologies and mixing states. Here, we apply complementary offline single-particle atomic force microscopy (AFM) and bulk ensemble high-performance liquid chromatography (HPLC) techniques to assess the effects of dry and wet deposition modes on the substrate-deposited aerosol particles' mixing states. Glucose and NaCl binary mixtures that form core–shell particle morphologies were studied as model systems, and the mixing states were quantified by measuring the OVF of individual particles using AFM and compared to the ensemble measured by HPLC. Dry-deposited single-particle OVF data positively deviated from the bulk HPLC data by up to 60 %, which was attributed to significant spreading of the NaCl core upon impaction with the solid substrate. This led to underestimation of the core volume. This problem was circumvented by (a) performing wet deposition and thus bypassing the effects of the solid core spreading upon impaction and (b) performing a hydration–dehydration cycle on dry-deposited particles to restructure the deformed NaCl core. Both approaches produced single-particle OVF values that converge well with the bulk and expected OVF values, validating the methodology. These findings illustrate the importance of awareness in how conventional particle deposition methods may significantly alter the impacted particle morphologies and their mixing states.

A new multicopter-based unmanned aerial system for pollen and spores collection in the atmospheric boundary layer

Abstract. The application of a new particle collection system (PCS) developed in-house and operated on board a commercially available multicopter unmanned aerial vehicle (UAV) is presented as a new unmanned aerial system (UAS) approach for in situ measurement of the concentration of aerosol particles such as pollen grains and spores in the atmospheric boundary layer (ABL). A newly developed impactor is used for high-efficiency particle extraction on board the multicopter UAV. An airflow volume of 0.2 m3 min−1 through the impactor is provided by a battery-powered blower and measured with an on-board mass flow sensor. A bell-mouth-shaped air inlet of the PCS is arranged and oriented on the multicopter UAV to provide substantial isokinetic sampling conditions by advantageously using the airflow pattern generated by the propellers of the multicopter UAV. More than 30 aerosol particle collection flights were carried out near Tübingen in March 2017 at altitudes of up to 300 m above ground level (a.g.l.), each with a sampled air volume of 2 m3. Pollen grains and spores of various genera, as well as large (&gt;20 µm) opaque particles and fine dust particles, were collected, and specific concentrations of up to 100 particles per m3 were determined by visual microscopic analysis. The pollen concentration values measured with the new UAS match well with the pollen concentration data published by the Stiftung Deutscher Polleninformationsdienst (PID) and by MeteoSwiss. A major advantage of the new multicopter-based UAS is the possibility of the identification of collected aerosol particles and the measurement of their concentration with high temporal and spatial resolutions, which can be used inter alia to improve the database for modelling the propagation of aerosol particles in the ABL.

The Influence of Air Flow Velocity and Particle Size on the Collection Efficiency of Passive Electrostatic Aerosol Samplers

ABSTRACT Electrostatic sampling is a promising method for the collection of bioaerosol particles. Although the underlying physics responsible for particle collection are well understood, the collection efficiency of simple passive electrostatic samplers is difficult to predict. Under these conditions, the collection efficiency becomes very sensitive to ambient air current and particle size, especially for submicron particles relevant for airborne virus transmission. In this paper, we compare two electrostatic aerosol sampler designs, a commercial product consisting of a flat collector plate located in the same plane as the charging needles and an axisymmetric design sampling directly to a liquid droplet. The aerosol particle collection efficiency of the samplers is investigated for particle size ranging from 0.25 to 2 µm while the air flow velocity surrounding the samplers is varied from 0.3 to 1 m s–1. For the planar design, at all ambient flow velocities, the submicron fraction of the particles captured originates in streamlines up to a maximum of 75 mm above the surface of the device collector, which greatly limits the volume of air being effectively sampled. The axisymmetric design features a non-monotonic capture efficiency as a function of particle size, with a minimum between 0.4 and 0.8 µm. The flow field in the inter-electrode region, captured using particle image velocimetry (PIV) reveals the presence of strong recirculation zones that can be responsible for the increased collection efficiency for very small particles.

Collection of soot particles into aqueous suspension using a particle-into-liquid sampler.

Steam collection devices collecting aerosol particles into liquid samples are frequently used to analyze water-soluble particulate material. The fate of water-insoluble components is often neglected. In this work, we show that fresh soot particles can be suspended into pure water using a steam collection device, the particle-into-liquid sampler (PILS, Weber et al. 2001). The overall collection efficiency of freshly generated soot particles was found to be on the order of 20%. This shows that, depending on the analytic technique employed, the presence of insoluble, and/or hydrophobic particles in liquid samples from steam collection cannot be neglected.Copyright © 2018 The Author(s). Published with license by Taylor & Francis Group, LLC

Correlation between inorganic pollutants in the suspended particulate matter (SPM) and fine particulate matter (PM2.5) collected from industrial and residential areas in Greater Cairo, Egypt

Simultaneous sampling collection of suspended particulate matter (SPM) and fine aerosol particles with an aerodynamic diameter equal or less than 2.5 μm (PM2.5) from industrial and residential areas of Greater Cairo, Egypt, has been carried out during two different seasons namely autumn 2014 and winter 2014/2015. The average mass concentrations of both SPM and PM2.5 samples are higher than the annual mean levels, especially for the samples collected from the industrial area. In addition, the mass concentrations of SPM are much higher than the PM2.5 mass concentrations during the whole sampling period. The ratios of the mass concentration between the SPM and PM2.5 were determined to be equal to 20 ± 6 and 17 ± 4 for the residential and industrial areas, respectively, and these ratios seem to be constant during the two mentioned seasons. Based on our previous elemental analysis results using multiple secondary target energy dispersive X-ray fluorescence (EDXRF), 18 elements in both SPM and PM2.5 samples have been quantified. Remarkable variations in the elemental concentrations between the SPM and PM2.5 samples were obtained. Comparison and statistical analysis of the elemental composition of both SPM and PM2.5 have been investigated. The PMF model EPA 5.0 was utilized for source identification on both PM fractions. Seven sources were identified and their relative contributions in the two areas of the study were investigated.