Aerosol Science And Technology[JOURNAL]
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138 papers
An Method for Sizing Insoluble Residues in Precipitation and Other Aqueous Samples.
Axson JL, Creamean JM, Bondy AL … +3 more , Capracotta SS, Warner KY, Ault AP
Aerosol Sci Technol · 2015 Jan · PMID 25705069 · Full text
Particles are frequently incorporated into clouds or precipitation, influencing climate by acting as cloud condensation or ice nuclei, taking up coatings during cloud processing, and removing species through wet depositi...
Particles are frequently incorporated into clouds or precipitation, influencing climate by acting as cloud condensation or ice nuclei, taking up coatings during cloud processing, and removing species through wet deposition. Many of these particles, particularly ice nuclei, can remain suspended within cloud droplets/crystals as insoluble residues. While previous studies have measured the soluble or bulk mass of species within clouds and precipitation, no studies to date have determined the number concentration and size distribution of insoluble residues in precipitation or cloud water using in situ methods. Herein, for the first time we demonstrate that Nanoparticle Tracking Analysis (NTA) is a powerful in situ method for determining the total number concentration, number size distribution, and surface area distribution of insoluble residues in precipitation, both of rain and melted snow. The method uses 500 μL or less of liquid sample and does not require sample modification. Number concentrations for the insoluble residues in aqueous precipitation samples ranged from 2.0-3.0(±0.3)×10 particles cm, while surface area ranged from 1.8(±0.7)-3.2(±1.0)×10 μm cm. Number size distributions peaked between 133-150 nm, with both single and multi-modal character, while surface area distributions peaked between 173-270 nm. Comparison with electron microscopy of particles up to 10 μm show that, by number, > 97% residues are <1 μm in diameter, the upper limit of the NTA. The range of concentration and distribution properties indicates that insoluble residue properties vary with ambient aerosol concentrations, cloud microphysics, and meteorological dynamics. NTA has great potential for studying the role that insoluble residues play in critical atmospheric processes.
Physicochemical Characterization of Simulated Welding Fume from a Spark Discharge System.
Park JH, Mudunkotuwa IA, Kim JS … +4 more , Stanam A, Thorne PS, Grassian VH, Peters TM
Aerosol Sci Technol · 2014 Jul · PMID 25097299 · Full text
This study introduces spark discharge system (SDS) as a way to simulate welding fumes. The SDS was developed using welding rods as electrodes with an optional coagulation chamber. The size, morphology, composition, and c...
This study introduces spark discharge system (SDS) as a way to simulate welding fumes. The SDS was developed using welding rods as electrodes with an optional coagulation chamber. The size, morphology, composition, and concentration of the fume produced and the concentration of ozone (O) and nitrogen oxides (NO) were characterized. The number median diameter (NMD) and total number concentration (TNC) of fresh fume particles were ranged 10-23 nm and 3.1×10-6×10 particles/cm, respectively. For fresh fume particles, the total mass concentration (TMC) measured gravimetrically ranged 85-760 μg/m. The size distribution was stable over a period of 12 h. The NMD and TNC of aged fume particles were ranged 81-154 nm and 1.5×10-2.7×10 particles/cm, respectively. The composition of the aged fume particles was dominated by Fe and O with an estimated stoichiometry between that of FeO and FeO. Concentrations of O and NO were ranged 0.07-2.2 ppm and 1-20 ppm, respectively. These results indicate that the SDS is capable of producing stable fumes over a long-period that are similar to actual welding fumes. This system may be useful in toxicological studies and evaluation of instrumentation.
Design and Laboratory Evaluation of a Sequential Spot Sampler for Time-Resolved Measurement of Airborne Particle Composition.
Eiguren Fernandez A, Lewis GS, Hering SV
Aerosol Sci Technol · 2014 Jan · PMID 25045199 · Full text
A new sampling approach has been developed to enable affordable, time-resolved monitoring of particulate chemical compositions, and more generally to provide concentrated samples of airborne particles. Using a newly deve...
A new sampling approach has been developed to enable affordable, time-resolved monitoring of particulate chemical compositions, and more generally to provide concentrated samples of airborne particles. Using a newly developed, moderated water-based condensational growth technology, individual particle samples are deposited in a 1-mm diameter dry "spot". The moderated condensation technology enables this collection with minimal temperature rise, providing robust collection for volatile constituents. Measured collection efficiencies are above 95% for particles in the size range from 0.010 μm to 2.5 μm. A set of 20 or more time-resolved samples, plus blanks, may be collected onto a multiwell collection plate. For chemical analysis the plate is returned to the laboratory, and placed directly into a modified autosampler, without extraction or preparation. The autosampler handles the addition of eluent, extraction, and sample injection without user manipulation. This paper presents the design and laboratory evaluation of a 1.5 L/min sampling rate version of this system.
Targeted Lung Delivery of Nasally Administered Aerosols.
Tian G, Hindle M, Longest PW
Aerosol Sci Technol · 2014 · PMID 24932058 · Full text
Using the nasal route to deliver pharmaceutical aerosols to the lungs has a number of advantages including co-administration during non-invasive ventilation. The objective of this study was to evaluate the growth and dep...
Using the nasal route to deliver pharmaceutical aerosols to the lungs has a number of advantages including co-administration during non-invasive ventilation. The objective of this study was to evaluate the growth and deposition characteristics of nasally administered aerosol throughout the conducting airways based on delivery with streamlined interfaces implementing two forms of controlled condensational growth technology. Characteristic conducting airways were considered including a nose-mouth-throat (NMT) geometry, complete upper tracheobronchial (TB) model through the third bifurcation (B3), and stochastic individual path (SIP) model to the terminal bronchioles (B15). Previously developed streamlined nasal cannula interfaces were used for the delivery of submicrometer particles using either enhanced condensational growth (ECG) or excipient enhanced growth (EEG) techniques. Computational fluid dynamics (CFD) simulations predicted aerosol transport, growth and deposition for a control (4.7 μm) and three submicrometer condensational aerosols with budesonide as a model insoluble drug. Depositional losses with condensational aerosols in the cannula and NMT were less than 5% of the initial dose, which represents an order-of-magnitude reduction compared to the control. The condensational growth techniques increased the TB dose by a factor of 1.1-2.6x, delivered at least 70% of the dose to the alveolar region, and produced final aerosol sizes ≥2.5 μm. Compared to multiple commercial orally inhaled products, the nose-to-lung delivery approach increased dose to the biologically important lower TB region by factors as large as 35x. In conclusion, nose-to-lung delivery with streamlined nasal cannulas and condensational aerosols was highly efficient and targeted deposition to the lower TB and alveolar regions.
Moderated, Water-Based, Condensational Particle Growth in a Laminar Flow.
Hering SV, Spielman SR, Lewis GS
Aerosol Sci Technol · 2014 Jan · PMID 24839342 · Full text
Presented is a new approach for laminar-flow water condensation that produces saturations above 1.5 while maintaining temperatures of less than 30°C in the majority of the flow and providing an exiting dew point below 15...
Presented is a new approach for laminar-flow water condensation that produces saturations above 1.5 while maintaining temperatures of less than 30°C in the majority of the flow and providing an exiting dew point below 15°C. With the original laminar flow water condensation method, the particle activation and growth occurs in a region with warm, wetted walls throughout, which has the side-effect of heating the flow. The "moderated" approach presented here replaces this warm region with a two sections - a short, warm, wet-walled "initiator", followed by a cool-walled "moderator". The initiator provides the water vapor that creates the supersaturation, while the moderator provides the time for particle growth. The combined length of the initiator and moderator sections is the same as that of the original, warm-walled growth section. Model results show that this new approach reduces the added heat and water vapor while achieving the same peak supersaturation and similar droplet growth. Experimental measurements confirm the trends predicted by the modeling.
On-Roadway In-Cabin Exposure to Particulate Matter: Measurement Results Using Both Continuous and Time-Integrated Sampling Approaches.
Greenwald R, Bergin MH, Yip F … +5 more , Boehmer T, Kewada P, Shafer MM, Schauer JJ, Sarnat JA
Aerosol Sci Technol · 2014 May · PMID 35923760 · Full text
The Atlanta Commuters Exposure (ACE) Study was designed to measure in-cabin exposure to roadway particulate pollution and acute health response in a panel of adults with and without asthma following a 2-h scripted route...
The Atlanta Commuters Exposure (ACE) Study was designed to measure in-cabin exposure to roadway particulate pollution and acute health response in a panel of adults with and without asthma following a 2-h scripted route along major highways in Atlanta. This article focuses on methods and results of both continuous and integrated approaches used to measure the concentration of PM mass, particle number concentration (PNC), black carbon (BC) mass, and particle-bound PAHs, in-cabin noise, PM elemental composition, elemental carbon, organic carbon, water-soluble organic carbon (WSOC) content, and speciation of a broad range of organic compounds including alkanes, hopanes, and PAHs. Speciated PM data indicates that in-cabin particles derive from three non-co-varying processes: the resuspension of road dust containing crustal elements and previously-deposited brake pad residue with a contribution of normal fuel combustion, incomplete combustion processes producing PAHs and carbon particles, and particles ablated from brake pads that have not previously deposited to the roadside environment. Most in-cabin pollutants were elevated during the warm season with the notable exception of PNC. PNC was not found to be correlated with most other pollutants. In-cabin concentrations were marginally higher when windows were open.
LABORATORY EVALUATION OF A MICROFLUIDIC ELECTROCHEMICAL SENSOR FOR AEROSOL OXIDATIVE LOAD.
Koehler K, Shapiro J, Sameenoi Y … +2 more , Henry C, Volckens J
Aerosol Sci Technol · 2014 May · PMID 24711675 · Full text
Human exposure to particulate matter (PM) air pollution is associated with human morbidity and mortality. The mechanisms by which PM impacts human health are unresolved, but evidence suggests that PM intake leads to cell...
Human exposure to particulate matter (PM) air pollution is associated with human morbidity and mortality. The mechanisms by which PM impacts human health are unresolved, but evidence suggests that PM intake leads to cellular oxidative stress through the generation of reactive oxygen species (ROS). Therefore, reliable tools are needed for estimating the oxidant generating capacity, or oxidative load, of PM at high temporal resolution (minutes to hours). One of the most widely reported methods for assessing PM oxidative load is the dithiothreitol (DTT) assay. The traditional DTT assay utilizes filter-based PM collection in conjunction with chemical analysis to determine the oxidation rate of reduced DTT in solution with PM. However, the traditional DTT assay suffers from poor time resolution, loss of reactive species during sampling, and high limit of detection. Recently, a new DTT assay was developed that couples a Particle-Into-Liquid-Sampler with microfluidic-electrochemical detection. This 'on-line' system allows high temporal resolution monitoring of PM reactivity with improved detection limits. This study reports on a laboratory comparison of the traditional and on-line DTT approaches. An urban dust sample was aerosolized in a laboratory test chamber at three atmospherically-relevant concentrations. The on-line system gave a stronger correlation between DTT consumption rate and PM mass (R = 0.69) than the traditional method (R = 0.40) and increased precision at high temporal resolution, compared to the traditional method.
Minimizing Concentration Effects in Water-Based, Laminar-Flow Condensation Particle Counters.
Lewis GS, Hering SV
Aerosol Sci Technol · 2013 · PMID 24436507 · Full text
Concentration effects in water condensation systems, such as used in the water-based condensation particle counter, are explored through numeric modeling and direct measurements. Modeling shows that the condensation heat...
Concentration effects in water condensation systems, such as used in the water-based condensation particle counter, are explored through numeric modeling and direct measurements. Modeling shows that the condensation heat release and vapor depletion associated with particle activation and growth lowers the peak supersaturation. At higher number concentrations, the diameter of the droplets formed is smaller, and the threshold particle size for activation is higher. This occurs in both cylindrical and parallel plate geometries. For water-based systems we find that condensational heat release is more important than is vapor depletion. We also find that concentration effects can be minimized through use of smaller tube diameters, or more closely spaced parallel plates. Experimental measurements of droplet diameter confirm modeling results.
Size Distribution and Estimated Respiratory Deposition of Total Chromium, Hexavalent Chromium, Manganese, and Nickel in Gas Metal Arc Welding Fume Aerosols.
Cena LG, Chisholm WP, Keane MJ … +2 more , Cumpston A, Chen BT
Aerosol Sci Technol · 2014 · PMID 26848207 · Full text
A laboratory study was conducted to determine the mass of total Cr, Cr(VI), Mn, and Ni in 15 size fractions for mild and stainless steel gas-metal arc welding (GMAW) fumes. Samples were collected using a nano multi orifi...
A laboratory study was conducted to determine the mass of total Cr, Cr(VI), Mn, and Ni in 15 size fractions for mild and stainless steel gas-metal arc welding (GMAW) fumes. Samples were collected using a nano multi orifice uniform deposition impactor (MOUDI) with polyvinyl chloride filters on each stage. The filters were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) and ion chromatography. Limits of detection (LODs) and quantitation (LOQs) were experimentally calculated and percent recoveries were measured from spiked metals in solution and dry, certified welding-fume reference material. The fraction of Cr(VI) in total Cr was estimated by calculating the ratio of Cr(VI) to total Cr mass for each particle size range. Expected, regional deposition of each metal was estimated according to respiratory-deposition models. The weight percent (standard deviation) of Mn in mild steel fumes was 9.2% (6.8%). For stainless steel fumes, the weight percentages were 8.4% (5.4%) for total Cr, 12.2% (6.5%) for Mn, 2.1% (1.5%) for Ni and 0.5% (0.4%) for Cr(VI). All metals presented a fraction between 0.04 and 0.6 m. Total Cr and Ni presented an additional fraction <0.03 m. On average 6% of the Cr was found in the Cr(VI) valence state. There was no statistical difference between the smallest and largest mean Cr(VI) to total Cr mass ratio (-value D 0.19), hence our analysis does not show that particle size affects the contribution of Cr(VI) to total Cr. The predicted total respiratory deposition for the metal particles was ∼25%. The sites of principal deposition were the head airways (7-10%) and the alveolar region (11-14%). Estimated Cr(VI) deposition was highest in the alveolar region (14%).
Numerical Investigation of Sheath and Aerosol Flows in the Flow Combination Section of a Baron Fiber Classifier.
Dubey P, Ghia U, Turkevich LA
Aerosol Sci Technol · 2014 · PMID 26388662 · Full text
The Baron fiber classifier is an instrument used to separate fibers by length. The flow combination section (FCS) of this instrument is an upstream annular region, where an aerosol of uncharged fibers is introduced along...
The Baron fiber classifier is an instrument used to separate fibers by length. The flow combination section (FCS) of this instrument is an upstream annular region, where an aerosol of uncharged fibers is introduced along with two sheath flows; length separation occurs by dielectrophoresis downstream in the flow classification section. In its current implementation at NIOSH, the instrument is capable of processing only very small quantities of fibers. In order to prepare large quantities of length-separated fibers for toxicological studies, the throughput of the instrument needs to be increased, and hence, higher aerosol flow rates need to be considered. However, higher aerosol flow rates may give rise to flow separation or vortex formation in the FCS, arising from the sudden expansion of the aerosol at the inlet nozzle. The goal of the present investigation is to understand the interaction of the sheath and aerosol flows inside the FCS, using computational fluid dynamics (CFD), and to identify possible limits to increasing aerosol flow rates. Numerical solutions are obtained using an axisymmetric model of the FCS, and solving the Navier-Stokes equations governing these flows; in this study, the aerosol flow is treated purely aerodynamically. Results of computations are presented for four different flow rates. The geometry of the converging outer cylinder, along with the two sheath flows, is effective in preventing vortex formation in the FCS for aerosol-to-sheath flow inlet velocity ratios below ~ 50. For higher aerosol flow rates, recirculation is observed in both inner and outer sheaths. Results for velocity, streamlines, and shear stress are presented.
Optimization approaches to ameliorate humidity and vibration related issues using the microAeth black carbon monitor for personal exposure measurement.
Cai J, Yan B, Kinney PL … +9 more , Perzanowski MS, Jung KH, Li T, Xiu G, Zhang D, Olivo C, Ross J, Miller RL, Chillrud SN
Aerosol Sci Technol · 2013 Nov · PMID 25558122 · Full text
Exposure to ambient black carbon (BC) is associated with adverse health effects. Black carbon levels display large spatial and temporal variability in many settings, such as cities and rural households where fossil fuel...
Exposure to ambient black carbon (BC) is associated with adverse health effects. Black carbon levels display large spatial and temporal variability in many settings, such as cities and rural households where fossil fuel and biomass, respectively, are commonly burned for transportation, heat and cooking. This paper addresses the optimization of the miniaturized personal BC monitor, the microAeth® for use in epidemiology studies. To address false positive and negative peaks in real time BC concentrations resulting from changes in temperature and humidity, an inlet with a diffusion drier was developed. In addition, we developed data cleaning algorithms to address occasional false positive and negative fluctuations in BC readings related to physical vibration, due in part to both dirt accumulations in the optical inserts and degraded components. These methods were successfully used to process real-time BC data generated from a cohort of 9-10 year old children (N= 54) in NYC, who wore 1 or 2 microAeth units for six 24hr time periods. Two hour and daily BC averages after data cleaning were consistent with averaged raw data (slopes near 1 with R =0.99, <0.001; R= 0.95, <0.001, respectively), strongly suggesting that the false positive and negative excursions balance each other out when averaged for at least 2 hrs. Data cleaning of identified suspect events allows more confidence in the interpretation of the real-time personal monitoring data generated in environmental exposure studies, with mean percent difference <10% for 19 duplicate deployments.
Arsenic removal from water using flame-synthesized iron oxide nanoparticles with variable oxidation states.
Abid AD, Kanematsu M, Young TM … +1 more , Kennedy IM
Aerosol Sci Technol · 2013 Feb · PMID 23645964 · Full text
We utilized gas-phase diffusion flame synthesis, which has potential for large-scale production of metal oxide nanoparticles, to produce iron oxide nanoparticles (IONPs) with variable oxidation states. The efficacy of th...
We utilized gas-phase diffusion flame synthesis, which has potential for large-scale production of metal oxide nanoparticles, to produce iron oxide nanoparticles (IONPs) with variable oxidation states. The efficacy of these materials in removal of arsenate (As(V) ) from water was assessed. Two different flame configurations, a diffusion flame (DF) and an inverse diffusion flame (IDF), were employed to synthesize six different IONPs by controlling flame conditions. The IONPs produced in the IDF configuration (IDF-IONPs) had smaller particle diameters (4.8 - 8.2 nm) and larger surface areas (141-213 m/g) than the IONPs produced in the DF configuration (29 nm, 36 m/g), which resulted in their higher adsorption capacities. As(V) adsorption capacities of the IDF-IONPs increased when the IONPs were synthesized in more oxidizing conditions. The fully oxidized IDF-IONPs, maghemite (γ-FeO), showed the highest As(V) adsorption capacity, comparable to that of magnetite nanocrystals synthesized by thermal decomposition of iron pentacarbonyl and equivalent to three to four times higher capacity than that of a commonly used goethite-based adsorbent. All IONPs were magnetically responsive, which is of great importance for solid-liquid separation. This study demonstrates that the IONPs synthesized in gas-phase flame, particularly IDF-IONPs, are excellent adsorbents because of their high As(V) sorption capacity, potential for large-scale production, and useful magnetic property.
Development and Performance Evaluation of an Exhaled-Breath Bioaerosol Collector for Influenza Virus.
McDevitt JJ, Koutrakis P, Ferguson ST … +5 more , Wolfson JM, Fabian MP, Martins M, Pantelic J, Milton DK
Aerosol Sci Technol · 2013 Jan · PMID 23418400 · Full text
The importance of the aerosol mode for transmission of influenza is unknown. Understanding the role of aerosols is essential to developing public health interventions such as the use of surgical masks as a source control...
The importance of the aerosol mode for transmission of influenza is unknown. Understanding the role of aerosols is essential to developing public health interventions such as the use of surgical masks as a source control to prevent the release of infectious aerosols. Little information is available on the number and size of particles generated by infected persons, which is partly due to the limitations of conventional air samplers, which do not efficiently capture fine particles or maintain microorganism viability. We designed and built a new sampler, called the G-II, that collects exhaled breath particles that can be used in infectivity analyses. The G-II allows test subjects to perform various respiratory maneuvers (i.e. tidal breathing, coughing, and talking) and allows subjects to wear a mask or respirator during testing. A conventional slit impactor collects particles > 5.0 μm. Condensation of water vapor is used to grow remaining particles, including fine particles, to a size large enough to be efficiently collected by a 1.0 μm slit impactor and be deposited into a buffer-containing collector. We evaluated the G-II for fine particle collection efficiency with inert particle aerosols and evaluated infective virus collection using influenza A virus aerosols. Testing results showed greater than 85% collection efficiency for particles greater than 50nm and influenza virus collection comparable with a reference SKC BioSampler®. The new design will enable determination of exhaled infectious virus generation rate and evaluate control strategies such as wearing a surgical type mask to prevent the release of viruses from infected persons.
Effect of Particle Size on the Performance of an N95 Filtering Facepiece Respirator and a Surgical Mask at Various Breathing Conditions.
He X, Reponen T, McKay RT … +1 more , Grinshpun SA
Aerosol Sci Technol · 2013 · PMID 31548759 · Full text
The effect of aerosol particle size on the performance of an N95 filtering facepiece respirator (FFR) and a surgical mask (SM) was evaluated under different breathing conditions, including breathing frequency and mean in...
The effect of aerosol particle size on the performance of an N95 filtering facepiece respirator (FFR) and a surgical mask (SM) was evaluated under different breathing conditions, including breathing frequency and mean inspiratory flow (MIF) rate. The FFR and SM were sealed on a manikin headform and challenged with charge-equilibrated NaCl aerosol. Filter penetration (P) was determined as the ratio of aerosol concentrations inside and outside the FFR/SM size-selectively (28 channels) within a range of 20 to 500 nm. In addition, the same models of the FFR and SM were donned, but not sealed, on an advanced manikin headform covered with skin-like material. Total inward leakage (TIL), which represents the total particle penetration, was measured under conditions identical to the filter penetration experiment. Testing was conducted at four mean MIFs (15, 30, 55 and 85 L/min) combined with five breathing frequencies (10, 15, 20, 25 and 30 breaths/min). The results show that SM produced much higher P and TIL values, and thus provide little protection against aerosols in the size range tested. P was significantly affected by particle size and breathing flow rate ( <0.05) for the tested FFR and SM. Surprisingly, for both devices, P as a function of the particle size exhibited more than one peak under all tested breathing conditions. The effect of breathing frequency on P was generally less pronounced, especially for lower MIFs. For the FFR and SM, TIL increased with increasing particle size up to about 50 nm; for particles above 50 nm, the total penetration was not significantly affected by particle size and breathing frequency; however, the effect of MIF remained significant.
Design and Evaluation of a Personal Diffusion Battery.
Vosburgh DJ, Klein T, Sheehan M … +2 more , Anthony TR, Peters TM
Aerosol Sci Technol · 2013 · PMID 26900207 · Full text
A four-stage personal diffusion battery (pDB) was designed and constructed to measure submicron particle size distributions. The pDB consisted of a screen-type diffusion battery, solenoid valve system, and electronic con...
A four-stage personal diffusion battery (pDB) was designed and constructed to measure submicron particle size distributions. The pDB consisted of a screen-type diffusion battery, solenoid valve system, and electronic controller. A data inversion spreadsheet was created to solve for the number median diameter (NMD), geometric standard deviation (GSD), and particle number concentration of unimodal aerosols using stage number concentrations from the pDB combined with a handheld condensation particle counter (pDB+CPC). The inversion spreadsheet included particle entry losses, theoretical penetrations across screens, the detection efficiency of the CPC, and constraints so the spreadsheet solved to values within the pDB range. Size distribution parameters (NMD, GSD, and number concentration) measured with the pDB+CPC with inversion spreadsheet were within 25% of those measured with a scanning mobility particle sizer (SMPS) for 5 of 12 polydisperse combustion aerosols. For three tests conducted with propylene torch exhaust, the pDB+CPC with inversion spreadsheet successfully identified that the NMD was smaller than the constraint value of 16 nm. The ratio of the nanoparticle portion of the aerosol compared to the reference () was calculated to determine the ability of pDB+CPC with inversion spreadsheet to measure the nanoparticle portion of the aerosols. The ranged from 0.87 to 1.01 when the inversion solved and from 0.06 to 2.01 when the inversion solved to a constraint. The pDB combined with CPC has limited use as a personal monitor but combining the pDB with a different detector would allow for the pDB to be used as a personal monitor.
Deposition Uniformity of Coal Dust on Filters and Its Effect on the Accuracy of FTIR Analyses for Silica.
Miller AL, Drake PL, Murphy NC … +3 more , Cauda EG, LeBouf RF, Markevicius G
Aerosol Sci Technol · 2013 · PMID 26719603 · Full text
Miners are exposed to silica-bearing dust which can lead to silicosis, a potentially fatal lung disease. Currently, airborne silica is measured by collecting filter samples and sending them to a laboratory for analysis....
Miners are exposed to silica-bearing dust which can lead to silicosis, a potentially fatal lung disease. Currently, airborne silica is measured by collecting filter samples and sending them to a laboratory for analysis. Since this may take weeks, a field method is needed to inform decisions aimed at reducing exposures. This study investigates a field-portable Fourier transform infrared (FTIR) method for end-of-shift (EOS) measurement of silica on filter samples. Since the method entails localized analyses, spatial uniformity of dust deposition can affect accuracy and repeatability. The study, therefore, assesses the influence of radial deposition uniformity on the accuracy of the method. Using laboratory-generated Minusil and coal dusts and three different types of sampling systems, multiple sets of filter samples were prepared. All samples were collected in pairs to create parallel sets for training and validation. Silica was measured by FTIR at nine locations across the face of each filter and the data analyzed using a multiple regression analysis technique that compared various models for predicting silica mass on the filters using different numbers of "analysis shots." It was shown that deposition uniformity is independent of particle type (kaolin vs. silica), which suggests the role of aerodynamic separation is negligible. Results also reflected the correlation between the location and number of shots versus the predictive accuracy of the models. The coefficient of variation (CV) for the models when predicting mass of validation samples was 4%-51% depending on the number of points analyzed and the type of sampler used, which affected the uniformity of radial deposition on the filters. It was shown that using a single shot at the center of the filter yielded predictivity adequate for a field method, (93% return, CV approximately 15%) for samples collected with 3-piece cassettes.
Aerosol Generation by Modern Flush Toilets.
Johnson D, Lynch R, Marshall C … +2 more , Mead K, Hirst D
Aerosol Sci Technol · 2013 · PMID 26635429 · Full text
A microbe-contaminated toilet will produce bioaerosols when flushed. We assessed toilet plume aerosol from high efficiency (HET), pressure-assisted high efficiency (PAT), and flushometer (FOM) toilets with similar bowl w...
A microbe-contaminated toilet will produce bioaerosols when flushed. We assessed toilet plume aerosol from high efficiency (HET), pressure-assisted high efficiency (PAT), and flushometer (FOM) toilets with similar bowl water and flush volumes. Total and droplet nuclei "bioaerosols" were assessed. Monodisperse 0.25-1.9- m fluorescent microspheres served as microbe surrogates in separate trials in a mockup 5 m water closet (WC). Bowl water seeding was approximately 10 particles/mL. Droplet nuclei were sampled onto 0.2- m pore size mixed cellulose ester filters beginning 15 min after the flush using open-face cassettes mounted on the WC walls. Pre- and postflush bowl water concentrations were measured. Filter particle counts were analyzed via fluorescent microscopy. Bowl headspace droplet count size distributions were bimodal and similar for all toilet types and flush conditions, with 95% of droplets m. Up to 145,000 droplets were produced per flush, with the high-energy flushometer producing over three times as many as the lower energy PAT and over 12 times as many as the lowest energy HET despite similar flush volumes. The mean numbers of fluorescent droplet nuclei particles aerosolized and remaining airborne also increased with flush energy. Fluorescent droplet nuclei per flush decreased with increasing particle size. These findings suggest two concurrent aerosolization mechanisms-splashing for large droplets and bubble bursting for the fine droplets that form droplet nuclei.
Characterization of a Vortex Shaking Method for Aerosolizing Fibers.
Ku BK, Deye G, Turkevich LA
Aerosol Sci Technol · 2013 · PMID 26635428 · Full text
Generation of well-dispersed, well-characterized fibers is important in toxicology studies. A vortex-tube shaking method is investigated using glass fibers to characterize the generated aerosol. Controlling parameters th...
Generation of well-dispersed, well-characterized fibers is important in toxicology studies. A vortex-tube shaking method is investigated using glass fibers to characterize the generated aerosol. Controlling parameters that were studied included initial batch amounts of glass fibers, preparation of the powder (e.g., preshaking), humidity, and airflow rate. Total fiber number concentrations and aerodynamic size distributions were typically measured. The aerosol concentration is only stable for short times ( < 10 min) and then falls precipitously, with concomitant changes in the aerosol aerodynamic size distribution; the plateau concentration and its duration both increase with batch size. Preshaking enhances the initial aerosol concentration and enables the aerosolization of longer fibers. Higher humidity strongly affects the particle size distribution and the number concentration, resulting in a smaller modal diameter and a higher number concentration. Running the vortex shaker at higher flow rates ( > 0.3 lpm), yields an aerosol with a particle size distribution representative of the batch powder; running the vortex shaker at a lower aerosol flow rate ( ~ 0.1 lpm) only aerosolizes the shorter fibers. These results have implications for the use of the vortex shaker as a standard aerosol generator.
Miniature Dual-Corona Ionizer for Bipolar Charging of Aerosol.
Qi C, Kulkarni P
Aerosol Sci Technol · 2013 Jan · PMID 26512158 · Full text
A corona-based bipolar charger has been developed for use in compact, field-portable mobility size spectrometers. The charger employs an aerosol flow cavity exposed to two corona ionizers producing ions of opposite polar...
A corona-based bipolar charger has been developed for use in compact, field-portable mobility size spectrometers. The charger employs an aerosol flow cavity exposed to two corona ionizers producing ions of opposite polarity. Each corona ionizer houses two electrodes in parallel needle-mesh configuration and is operated at the same magnitude of corona current. Experimental measurement of detailed charge distribution of near-monodisperse particles of different diameter in the submicrometer size range showed that the charger is capable of producing well-defined, consistent bipolar charge distributions for flow rates up to 1.5 L/min and aerosol concentration up to 10 per cm. For particles with preexisting charge of +1, 0, and -1, the measured charge distributions agreed well with the theoretical distributions within the range of experimental and theoretical uncertainties. The transmission efficiency of the charger was measured to be 80% for 10 nm particles (at 0.3 L/min and 5 A corona current) and increased with increasing diameter beyond this size. Measurement of uncharged fractions at various combinations of positive and negative corona currents showed the charger performance to be insensitive to fluctuations in corona current. Ion concentrations under positive and negative unipolar operation were estimated to be 8.2 × 10 and 3.37 × 10 cm for positive and negative ions; the · product value under positive corona operation was independently estimated to be 8.5 × 10 s/cm. The ion concentration estimates indicate the charger to be capable of "neutralizing" typical atmospheric and industrial aerosols in most measurement applications. The miniature size, simple and robust operation makes the charger suitable for portable mobility spectrometers.
A Cough Aerosol Simulator for the Study of Disease Transmission by Human Cough-Generated Aerosols.
Lindsley WG, Reynolds JS, Szalajda JV … +2 more , Noti JD, Beezhold DH
Aerosol Sci Technol · 2013 · PMID 26500387 · Full text
Aerosol particles expelled during human coughs are a potential pathway for infectious disease transmission. However, the importance of airborne transmission is unclear for many diseases. To better understand the role of...
Aerosol particles expelled during human coughs are a potential pathway for infectious disease transmission. However, the importance of airborne transmission is unclear for many diseases. To better understand the role of cough aerosol particles in the spread of disease and the efficacy of different types of protective measures, we constructed a cough aerosol simulator that produces a humanlike cough in a controlled environment. The simulated cough has a 4.2 l volume and is based on coughs recorded from influenza patients. In one configuration, the simulator produces a cough aerosol containing particles from 0.1 to 100 µm in diameter with a volume median diameter (VMD) of 8.5 µm and a geometric standard deviation (GSD) of 2.9. In a second configuration, the cough aerosol has a size range of 0.1-30 µm, a VMD of 3.4 µm, and a GSD of 2.3. The total aerosol volume expelled during each cough is 68 µl. By generating a controlled and reproducible artificial cough, the simulator allows us to test different ventilation, disinfection, and personal protection scenarios. The system can be used with live pathogens, including influenza virus, which allows isolation precautions used in the healthcare field to be tested without risk of exposure for workers or patients. The information gained from tests with the simulator will help to better understand the transmission of infectious diseases, develop improved techniques for infection control, and improve safety for healthcare workers and patients.
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