Last data update: Sep 16, 2024. (Total: 47680 publications since 2009)
Records 1-18 (of 18 Records) |
Query Trace: Turkevich L [original query] |
---|
Numerical investigation of powder aerosolization in a mining rock dust dispersion chamber
Chen H , Turkevich LA , Jog MA , Ghia U . J Loss Prev Process Ind 2023 83 We have conducted numerical simulations of dust dispersion within the NIOSH Rock Dust Dispersion Chamber. The apparatus consists of a low-speed background ventilation flow down a long box in which is placed a tray containing a rock dust powder. A nozzle upstream of the tray introduces a short pulse of a turbulent horizontal jet flow just above the powder surface. We have utilized an incompressible Reynolds-Averaged Navier-Stokes k-ω model for the turbulent flow; particles are incorporated within a one-way Euler-Lagrangian formalism. The Rock Dust Dispersion Chamber ventilation flow exhibits a recirculation zone just above the powder-containing tray. Aerosolization proceeds via the interplay of the jet pulse flow with the background recirculation flow. The air flow is not well-mixed. The aerosolized dust is convected as a concentration cloud downstream towards the detection zone. For larger particles, gravitational settling depletes the convected cloud, so the instrument behaves as a horizontal elutriator. The instrument is robust with respect to misalignment of the jet nozzle. However, reduced streamwise drift velocity allows mixing to disperse the optically detected dust cloud concentration pulse. Our large particle simulation results compare favorably with published experimental results for large, polydisperse calcium carbonate rock dust. © 2023 |
Numerical investigation of aerosolization in the Venturi Dustiness Tester: Aerodynamics of a particle on a hill
Palakurthi NK , Ghia U , Turkevich LA . J Fluids Eng 2022 144 (6) Understanding particle detachment from surfaces is necessary to better characterize dust generation and entrainment. Previous work has studied the detachment of particles from flat surfaces. The present work generalizes this to investigate the aerodynamics of a particle attached to various locations on a model hill. The present work serves as a model for dust aerosolization in a tube, as powder is injected into the Venturi Dustiness Tester. The particle is represented as a sphere in a parallel plate channel, or, in two dimensions, as a cylinder oriented perpendicular to the flow. The substrate is modified to include a conical hill (3D) or wedge (2D), and the test particle is located at various positions on this hill. The governing incompressible Navier-Stokes equations are solved using the finite-volume FLUENT code. The coefficients of lift and drag are compared with the results on the flat substrate. Enhanced drag and significantly enhanced lift are observed as the test particle is situated near the summit of the hill. |
Computational fluid dynamics simulations of aerosol behavior in a high-speed (Heubach) rotating drum dustiness tester
Chen H , Jog MA , Turkevich LA . Particuology 2023 72 68-80 Potential exposure from hazardous dust may be assessed by evaluating the dustiness of the powders being handled. Dustiness is the tendency of a powder to aerosolize with a given input of energy. Previously we used computational fluid dynamics (CFD) to numerically investigate the flow inside the European Standard (EN15051) rotating drum dustiness tester during its operation. The present work extends those CFD studies to the widely used Heubach rotating drum. Air flow characteristics are investigated within the Abe-Kondoh-Nagano k-epsilon turbulence model; the aerosol is incorporated via a Euler-Lagrangian multiphase approach. The air flow inside these drums consists of a well-defined axial jet penetrating relatively quiescent air. The spreading of the Heubach jet results in a fraction of the jet recirculating as back-flow along the drum walls; at high rotation rates, the axial jet becomes unstable. This flow behavior qualitatively differs from the stable EN15051 flow pattern. The aerodynamic instability promotes efficient mixing within the Heubach drum, resulting in higher particle capture efficiencies for particle sizes d < 80 μm. © 2022 |
Numerical investigation of powder aerosolization in a rotating drum apparatus
Chen H , Jog MA , Evans DE , Turkevich LA . Powder Technol 2021 390 62-72 Essential to estimating the potential exposure from dusts of toxic, hazardous or irritant powders is the evaluation of the dustiness of the powders being handled. Dustiness is the tendency of a powder to aerosolize with a given input of energy. Evaluating dustiness of a manufactured powder can alert to a potential exposure to workers. It can also aid in the selection of manufacturing processes/operations which generate less dust for a particular substance and can provide vital information to guide selecting/creating powders which generate less dust. A widely used (but marginally understood) instrument to evaluate powder dustiness is the Rotating Drum. Using computational fluid dynamics, we have numerically investigated the flow inside the Rotating Drum dustiness tester during its operation. A complete description of the flow aerodynamics associated with operation of this instrument will assist in the interpretation of dustiness measurements conducted with this instrument. © 2021 |
Periodic flow purging system for harvesting fibers from screens
Ku BK , Deye G , Turkevich LA . Aerosol Air Qual Res 2021 21 (6) Fiber length is believed to be an important factor in determining various toxicological responses to asbestos and other bio-persistent fibers. Length classification of fibers thus is crucial for toxicological assessment. Nylon mesh screens have been shown to be effective in separating fibers by length. In this note, we report development of a purging flow system for harvesting fibers from a nylon net screen, with the aim of separating airborne fibers by length. We evaluated the performance of this purging flow system by examining the lengths of glass fibers collected on a screen. Fibers aerosolized by vortex shaking were provided to 10 µm and 20 µm mesh screens, and the fibers collected on each screen were purged periodically with a backflow. The length of the purged fibers was measured and compared to that of fibers washed from the screen. The mean length of fibers on the screen is larger than that of the fibers in the original test aerosol. The mean length of the backflow purged fibers is smaller than that of the fibers from the washed screen. The results indicate that the purging flow system with screens can harvest the longer fibers from the original aerosol. © U.S. Government work. |
Screen collection efficiency of airborne fibers with monodisperse length
Ku BK , Deye G , Turkevich LA . J Aerosol Sci 2017 114 250-262 Fiber length is believed to be an important variable in determining various toxicological responses to asbestos and other elongate mineral particles. In this study we investigated screen collection characteristics using monodisperse-length glass fibers (i.e., 11, 15, 25, and 53 µm in length), to better understand the collection of fibers with different lengths on screens with different mesh sizes. A well-dispersed aerosol of glass fibers (geometric mean length ~ 20 µm), generated by vortex shaking, was fed directly into the Baron Fiber Length Classifier, in order to produce monodisperse length fibers. With nylon mesh screens (10, 20, 30, 41 and 60 µm mesh sizes), the screen collection efficiency was measured using an aerodynamic particle sizer. As the screen mesh size decreases from 60 µm to 10 µm, the screen collection efficiency for 53 µm fibers increases (from 0.3 to 0.9) while 11 µm fibers exhibited a collection efficiency independent of screen mesh size. The collection efficiency for the longest fibers was found to be nearly constant for aerodynamic diameters 1–4 µm for screens 20 and 30 µm, but to rise significantly at aerodynamic diameters larger than 4 µm. For the 20 µm screen, the collection efficiency for fibers with lengths > 20 µm is a factor of two to five larger than that for spherical particles with the same aerodynamic diameter. We believe that fibers are collected on the screen primarily by interception below 4 µm in aerodynamic diameter, and by impaction above 4 µm. This study represents a fundamental advance in the understanding of the interaction of screens with a fibrous aerosol. |
Direct measurement of aerosol glass fiber alignment in a DC electric field
Ku BK , Deye G , Turkevich LA . Aerosol Sci Technol 2017 52 (2) 123-135 We report non-conducting aerosol fiber (i.e., glass fiber) alignment in a DC electric field. Direct observation of fiber orientation state is demonstrated and quantitative analysis of fiber alignment is made using phase contrast microscopy in four different conditions; i) dry air and naturally charged fibers, ii) humid and naturally charged, iii) humid and neutralized (Boltzmann charge distribution) and iv) humid and neutralized with an electrostatic precipitator upstream electrodes (i.e., non-charged). The glass fiber aerosols generated by a vortex shaking method were conditioned using a Po-210 neutralizer or humidifier and were provided into a test unit where cylindrical or parallel plate electrodes are used and high voltage is applied to them. Fibers were collected on a filter immediately downstream from the electrodes and their images were taken through an optical microscope to visualize the fiber orientation and measure the alignment angles and lengths of the fibers. The results showed that under all four conditions tested, airborne glass fibers could be aligned to the electric field with different alignment quality, indicating that the glass fibers can be polarized in a steady electric field. In humid air, the fiber alignment along the field direction was observed to be much better and the number of uniform background particles (i.e., randomly oriented fibers) in angular distributions is smaller than that in dry air. Also, it was found that charged fibers in humid air could be better aligned with negligible uniform background than neutralized and non-charged fibers. Possible mechanisms about humidity and charge effects on enhanced fiber alignment are discussed to support the observations. The results indicate that the enhancement of alignment in an electric field would be possible in humid air for other non-conducting fibrous particles having surface chemistry similar to glass fibers. |
Computational fluid dynamics analysis of the Venturi Dustiness Tester
Dubey P , Ghia U , Turkevich LA . Powder Technol 2017 312 310-320 Dustiness quantifies the propensity of a finely divided solid to be aerosolized by a prescribed mechanical stimulus. Dustiness is relevant wherever powders are mixed, transferred or handled, and is important in the control of hazardous exposures and the prevention of dust explosions and product loss. Limited quantities of active pharmaceutical powders available for testing led to the development (at University of North Carolina) of a Venturi-driven dustiness tester. The powder is turbulently injected at high speed (Re ~ 2 × 104) into a glass chamber; the aerosol is then gently sampled (Re ~ 2 × 103) through two filters located at the top of the chamber; the dustiness index is the ratio of sampled to injected mass of powder. Injection is activated by suction at an Extraction Port at the top of the chamber; loss of powder during injection compromises the sampled dustiness. The present work analyzes the flow inside the Venturi Dustiness Tester, using an Unsteady Reynolds-Averaged Navier-Stokes formulation with the k-ω Shear Stress Transport turbulence model. The simulation considers single-phase flow, valid for small particles (Stokes number Stk < 1). Results show that ~ 24% of fluid-tracers escape the tester before the Sampling Phase begins. Dispersion of the powder during the Injection Phase results in a uniform aerosol inside the tester, even for inhomogeneous injections, satisfying a necessary condition for the accurate evaluation of dustiness. Simulations are also performed under the conditions of reduced Extraction-Port flow; results confirm the importance of high Extraction-Port flow rate (standard operation) for uniform distribution of fluid tracers. Simulations are also performed under the conditions of delayed powder injection; results show that a uniform aerosol is still achieved provided 0.5 s elapses between powder injection and sampling. |
Quantitative analysis of the role of fiber length on phagocytosis and inflammatory response by alveolar macrophages
Padmore T , Stark C , Turkevich LA , Champion JA . Biochim Biophys Acta 2016 1861 (2) 58-67 BACKGROUND: In the lung, macrophages attempt to engulf inhaled high aspect ratio pathogenic materials, secreting inflammatory molecules in the process. The inability of macrophages to remove these materials leads to chronic inflammation and disease. How the biophysical and biochemical mechanisms of these effects are influenced by fiber length remains undetermined. This study evaluates the role of fiber length on phagocytosis and molecular inflammatory responses to non-cytotoxic fibers, enabling development of quantitative length-based models. METHODS: Murine alveolar macrophages were exposed to short and long populations of JM-100 glass fibers, produced by successive sedimentation and repeated crushing, respectively. Interactions between fibers and macrophages were observed using time-lapse video microscopy, and quantified by flow cytometry. Inflammatory biomolecules (TNF-alpha, IL-1alpha, COX-2, PGE2) were measured. RESULTS: Uptake of short fibers occurred more readily than for long, but long fibers were more potent stimulators of inflammatory molecules. Stimulation resulted in dose-dependent secretion of inflammatory biomolecules but no cytotoxicity or strong ROS production. Linear cytokine dose-response curves evaluated with length-dependent potency models, using measured fiber length distributions, resulted in identification of critical fiber lengths that cause frustrated phagocytosis and increased inflammatory biomolecule production. CONCLUSION: Short fibers played a minor role in the inflammatory response compared to long fibers. The critical lengths at which frustrated phagocytosis occurs can be quantified by fitting dose-response curves to fiber distribution data. GENERAL SIGNIFICANCE: The single physical parameter of length can be used to directly assess the contributions of length against other physicochemical fiber properties to disease endpoints. |
Potential explosion hazard of carbonaceous nanoparticles: screening of allotropes
Turkevich LA , Fernback J , Dastidar AG , Osterberg P . Combust Flame 2016 167 218-227 There is a concern that engineered carbon nanoparticles, when manufactured on an industrial scale, will pose an explosion hazard. Explosion testing has been performed on 20 codes of carbonaceous powders. These include several different codes of SWCNTs (single-walled carbon nanotubes), MWCNTs (multi-walled carbon nanotubes) and CNFs (carbon nanofibers), graphene, diamond, fullerene, as well as several different control carbon blacks and graphites. Explosion screening was performed in a 20L explosion chamber (ASTM E1226 protocol), at a concentration of 500g/m3, using a 5kJ ignition source. Time traces of overpressure were recorded. Samples typically exhibited overpressures of 5-7 bar, and deflagration index K St = V 1/3 (dP/dt)max ∼10-80barm/s, which places these materials in European Dust Explosion Class St-1. There is minimal variation between these different materials. The explosive characteristics of these carbonaceous powders are uncorrelated with primary particle size (BET specific surface area). © 2016. |
Potential explosion hazard of carbonaceous nanoparticles: explosion parameters of selected materials
Turkevich LA , Dastidar AG , Hachmeister Z , Lim M . J Hazard Mater 2015 295 97-103 Following a previous explosion screening study, we have conducted concentration and ignition energy scans on several carbonaceous nanopowders: fullerene, SWCNT, carbon black, MWCNT, graphene, CNF, and graphite. We have measured minimum explosive concentration (MEC), minimum ignition energy (MIE), and minimum ignition temperature (MITcloud) for these materials. The nanocarbons exhibit MEC ~101-102g/m3, comparable to the MEC for coals and for fine particle carbon blacks and graphites. The nanocarbons are confirmed mainly to be in the St-1 explosion class, with fullerene, at KSt~200bar-m/s, borderline St-1/St-2. We estimate MIE~102-103J, an order of magnitude higher than the MIE for coals but an order of magnitude lower than the MIE for fine particle graphites. While the explosion severity of the nanocarbons is comparable to that of the coals, their explosion susceptibility (ease of ignition) is significantly less (i.e., the nanocarbons have higher MIEs than do the coals); by contrast, the nanocarbons exhibit similar explosion severity to the graphites but enhanced explosion susceptibility (i.e., the nanocarbons have lower MIEs than do the graphites). MITcloud>550 degrees C, comparable to that of the coals and carbon blacks. |
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 48 (8) 896-905 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. |
Comment on comparison of powder dustiness methods
Evans DE , Turkevich LA , Roettgers CT , Deye GJ . Ann Occup Hyg 2014 58 (4) 524-8 We have read with interest the recent work by the University of Wuppertal group (Bach et al., 2013) on dustiness determination using the University of North Carolina (UNC) Dustiness Testing Device (Boundy et al., 2006). We have referred to the UNC device as the ‘Venturi’ device (Evans et al., 2013), as that describes the underlying dispersal mechanism; we continue with this terminology. The Wuppertal paper is presented in two parts. In Part 1, the dustiness of nine industrial powders was measured with the Venturi device, and results compared with their earlier measurements (Bach and Schmidt, 2008) using macroscopic techniques: EN 1505 standardized continuous drop (CEN 2006, 2013) and the commercial Heubach rotating drum and commercial Palas single drop. In Part 2, dustiness values for 11 pharmaceutical powders were determined solely with the Venturi device. We would like to comment on these Wuppertal results, especially in light of our previous and extensive use of the Venturi device for fine and nanoscale powders (Evans et al., 2013). | Unfortunately, insufficient detail is provided on the provenance of the Wuppertal powders (Bach and Schmidt, 2008; Bach et al., 2013), to allow an inter-laboratory comparison with identical materials. (By contrast, our measurements (Evans et al., 2013) for Holland lactose of Dtot = 5.2 (0.4)% and Dresp = 0.9 (0.1)% are fully consistent with those of the UNC group (Boundy et al., 2006), with Dtot = 5.1 (0.9)% and Dresp = 1.3 (0.5)% for the same material.) In the technique comparison, Part 1, of the Wuppertal study, only three Venturi measurements were made for each powder, and no ranges or statistics were reported. In the pharmaceutical, Part 2, of their study, five Venturi measurements were made for each powder, and standard deviations were reported, permitting some analysis of possible error. Finally, we observed an empirical correlation between respirable and total dustiness, as measured with the Venturi device, to hold for a wide range of powders (Evans et al., 2013). It is informative to test that empirical correlation with these additional Wuppertal results. |
Efficacy of screens in removing long fibers from an aerosol stream - sample preparation technique for toxicology studies
Ku BK , Deye GJ , Turkevich LA . Inhal Toxicol 2014 26 (2) 70-83 Fiber dimension (especially length) and biopersistence are thought to be important variables in determining the pathogenicity of asbestos and other elongate mineral particles. In order to prepare samples of fibers for toxicology studies, it is necessary to develop and evaluate methods for separating fibers by length in the micrometer size range. In this study, we have filtered an aerosol of fibers through nylon screens to investigate whether such screens can efficiently remove the long fibers (L >20 microm, a typical macrophage size) from the aerosol stream. Such a sample, deficient in long fibers, could then be used as the control in a toxicology study to investigate the role of length. A well-dispersed aerosol of glass fibers (a surrogate for asbestos) was generated by vortex shaking a Japan Fibrous Material Research Association (JFMRA) glass fiber powder. Fibers were collected on a mixed cellulose ester (MCE) filter, imaged with phase contrast microscopy (PCM) and lengths were measured. Length distributions of the fibers that penetrated through various screens (10, 20 and 60 microm mesh sizes) were analyzed; additional study was made of fibers that penetrated through double screen and centrally blocked screen configurations. Single screens were not particularly efficient in removing the long fibers; however, the alternative configurations, especially the centrally blocked screen configuration, yielded samples substantially free of the long fibers. |
Characterization of a vortex shaking method for aerosolizing fibers
Ku BK , Deye G , Turkevich LA . Aerosol Sci Technol 2013 47 (12) 1293-1301 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 (t < 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 (Q > 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 (Q ~ 0.1 lpm) only aerosolizes the shorter fibers. These results have implications for the use of the vortex shaker as a standard aerosol generator. |
Penetration of fiber versus spherical particles through filter media and faceseal leakage of N95 filtering facepiece respirators with cyclic flow
Cho KJ , Turkevich L , Miller M , McKay R , Grinshpun SA , Ha KC , Reponen T . J Occup Environ Hyg 2012 10 (3) 109-15 This study investigated differences in penetration between fibers and spherical particles through faceseal leakage of an N95 filtering facepiece respirator. Three cyclic breathing flows were generated corresponding to mean inspiratory flow rates (MIF) of 15, 30, and 85 L/min. Fibers had a mean diameter of 1 um and a median length of 4.9 um (calculated aerodynamic diameter, d(ae) = 1.73 um). Monodisperse polystyrene spheres with a mean physical diameter of 1.01 um (PSI) and 1.54 um (PSII) were used for comparison (calculated d(ae) = 1.05 and 1.58 um, respectively). Two optical particle counters simultaneously determined concentrations inside and outside the respirator. Geometric means (GMs) for filter penetration of the fibers were 0.06, 0.09, and 0.08% at MIF of 15, 30, and 85 L/min, respectively. Corresponding values for PSI were 0.07, 0.12, and 0.12%. GMs for faceseal penetration of fibers were 0.40, 0.14, and 0.09% at MIF of 15, 30, and 85 L/min, respectively. Corresponding values for PSI were 0.96, 0.41, and 0.17%. Faceseal penetration decreased with increased breathing rate for both types of particles (p≤0.001). GMs of filter and faceseal penetration of PSII at an MIF of 30 L/min were 0.14% and 0.36%, respectively. Filter penetration and faceseal penetration of fibers were significantly lower than those of PSI (p < 0.001) and PSII (p < 0.003). This confirmed that higher penetration of PSI was not due to slightly smaller aerodynamic diameter, indicating that the shape of fibers rather than their calculated mean aerodynamic diameter is a prevailing factor on deposition mechanisms through the tested respirator. In conclusion, faceseal penetration of fibers and spherical particles decreased with increasing breathing rate, which can be explained by increased capture by impaction. Spherical particles had 2.0-2.8 times higher penetration through faceseal leaks and 1.1-1.5 higher penetration through filter media than fibers, which can be attributed to differences in interception losses. |
Dustiness of fine and nanoscale powders
Evans DE , Turkevich LA , Roettgers CT , Deye GJ , Baron PA . Ann Occup Hyg 2012 57 (2) 261-77 Dustiness may be defined as the propensity of a powder to form airborne dust by a prescribed mechanical stimulus; dustiness testing is typically intended to replicate mechanisms of dust generation encountered in workplaces. A novel dustiness testing device, developed for pharmaceutical application, was evaluated in the dustiness investigation of 27 fine and nanoscale powders. The device efficiently dispersed small (mg) quantities of a wide variety of fine and nanoscale powders, into a small sampling chamber. Measurements consisted of gravimetrically determined total and respirable dustiness. The following materials were studied: single and multiwalled carbon nanotubes, carbon nanofibers, and carbon blacks; fumed oxides of titanium, aluminum, silicon, and cerium; metallic nanoparticles (nickel, cobalt, manganese, and silver) silicon carbide, Arizona road dust; nanoclays; and lithium titanate. Both the total and respirable dustiness spanned two orders of magnitude (0.3-37.9% and 0.1-31.8% of the predispersed test powders, respectively). For many powders, a significant respirable dustiness was observed. For most powders studied, the respirable dustiness accounted for approximately one-third of the total dustiness. It is believed that this relationship holds for many fine and nanoscale test powders (i.e. those primarily selected for this study), but may not hold for coarse powders. Neither total nor respirable dustiness was found to be correlated with BET surface area, therefore dustiness is not determined by primary particle size. For a subset of test powders, aerodynamic particle size distributions by number were measured (with an electrical low-pressure impactor and an aerodynamic particle sizer). Particle size modes ranged from approximately 300nm to several micrometers, but no modes below 100nm, were observed. It is therefore unlikely that these materials would exhibit a substantial sub-100nm particle contribution in a workplace. |
Paul Baron (1944-2009)
Kulkarni P , Grinshpun SA , Turkevich LA , Schlecht PC , Birch ME , Willeke K . J Aerosol Sci 2009 40 (9) 731-32 Dr. Paul Andrew Baron died on May 20, 2009 at his residence in Cincinnati, OH, USA after a long battle with cancer. With his passing we have lost a leading scholar in aerosol science and occupational health research. |
- Page last reviewed:Feb 1, 2024
- Page last updated:Sep 16, 2024
- Content source:
- Powered by CDC PHGKB Infrastructure