Paul A. Baron

Aerosol measurement : principles, techniques, and applications

In recent years, industry has become increasingly interested in modern aerosol measurement methods, not only to protect the health of their workers but also to augment productivity and thereby gain competitive advantage. Aerosol Measurement: Principles, Techniques, and Applications, Second Edition offers scientists and practitioners the fundamental principles used in deciding which aerosol properties to measure and how to interpret the results. Divided into three parts, the material reviews the physical understanding of aerosols, covers specific instrumental techniques, and explains applications in fields ranging from health care to mining and upper-atmosphere research. Leading experts contribute to the review of such areas as direct-reading techniques, bioaerosol sampling, indoor air evaluations, industrial aerosol processing, and measurement in semiconductor clean rooms. Plus, all the chapters in this latest edition have been updated and some have been rewritten by new authors. Two new chapters have been added: one on historical aspects of aerosol measurements and the other on real-time single particle analysis.

Exposure to Carbon Nanotube Material: Aerosol Release During the Handling of Unrefined Single-Walled Carbon Nanotube Material

Carbon nanotubes represent a relatively recently discovered allotrope of carbon that exhibits unique properties. While commercial interest in the material is leading to the development of mass production and handling facilities, little is known of the risk associated with exposure. In a two-part study, preliminary investigations have been carried out into the potential exposure routes and toxicity of single-walled carbon nanotube material (SWCNT)—a specific form of the allotrope. The material is characterized by bundles of fibrous carbon molecules that may be a few nanometers in diameter, but micrometers in length. The two production processes investi-gated use-transition metal catalysts, leading to the inclusion of nanometer-scale metallic particles within unrefined SWCNT material. A laboratory-based study was undertaken to evaluate the physical nature of the aerosol formed from SWCNT during mechanical agitation. This was complemented by a field study in which airborne and dermal exposure to SWCNT was investigated while handling unrefined material. Although laboratory studies indicated that with sufficient agitation, unrefined SWCNT material can release fine particles into the air, concentrations generated while handling material in the field were very low. Estimates of the airborne concen-tration of nanotube material generated during handling suggest that concentrations were lower than 53μg/m3 in all cases. Glove deposits of SWCNT during handling were estimated at between 0.2 mg and 6 mg per hand.

Inhalation vs. aspiration of single-walled carbon nanotubes in C57BL/6 mice: inflammation, fibrosis, oxidative stress, and mutagenesis

Nanomaterials are frontier technological products used in different manufactured goods. Because of their unique physicochemical, electrical, mechanical, and thermal properties, single-walled carbon nanotubes (SWCNT) are finding numerous applications in electronics, aerospace devices, computers, and chemical, polymer, and pharmaceutical industries. SWCNT are relatively recently discovered members of the carbon allotropes that are similar in structure to fullerenes and graphite. Previously, we (47) have reported that pharyngeal aspiration of purified SWCNT by C57BL/6 mice caused dose-dependent granulomatous pneumonia, oxidative stress, acute inflammatory/cytokine responses, fibrosis, and decrease in pulmonary function. To avoid potential artifactual effects due to instillation/agglomeration associated with SWCNT, we conducted inhalation exposures using stable and uniform SWCNT dispersions obtained by a newly developed aerosolization technique (2). The inhalation of nonpurified SWCNT (iron content of 17.7% by weight) at 5 mg/m(3), 5 h/day for 4 days was compared with pharyngeal aspiration of varying doses (5-20 microg per mouse) of the same SWCNT. The chain of pathological events in both exposure routes was realized through synergized interactions of early inflammatory response and oxidative stress culminating in the development of multifocal granulomatous pneumonia and interstitial fibrosis. SWCNT inhalation was more effective than aspiration in causing inflammatory response, oxidative stress, collagen deposition, and fibrosis as well as mutations of K-ras gene locus in the lung of C57BL/6 mice.

Calibration and use of the aerodynamic particle sizer (APS 3300)

The Aerodynamic Particle Sizer (APS) has been in use at the National Institute for Occupational Safety and Health (NIOSH) for over two years, beginning with a prototype model and more recently with a commercial version (Model 3300). The APS has been tested and used in a variety of laboratory and field situations. It has been a very useful instrument for testing aerodynamic sizing devices and provided a much needed means of rapid aerodynamic sizing of particles. Limits to the accuracy of the APS in determining aerodynamic diameter of particles were investigated. The calibration of the APS was originally carried out by using monodisperse di-octyl phthalate (DOP) oil aerosol in the 3–15 μm range. Using a laser imaging system, the flattening of droplets into oblate spheroids was observed for larger particles (20–100 μm). The APS was recalibrated with solid latex particles and the DOP particles were measured to determine the effect of the droplet flattening. A 15 μm droplet is measured as being 20% smaller by ...

The influence of operating parameters on number-weighted aerosol size distribution generated from a gas metal arc welding process

Abstract In light of recent research on the potential health problems associated with sub-micrometer aerosols, a study was conducted to determine the effect that droplet mass transfer mode, shield gas composition, and welding spatter had upon the aerosols generated from a Gas Metal Arc Welding (GMAW) Operation. The results revealed that the sub-micrometer aerosols produced during spray transfer resulted in markedly higher concentrations of nucleated particles than those produced during globular transfer. This probably resulted from a larger droplet surface area for vaporization of metallic species. The shield gas experiments results revealed that as the percentage of carbon dioxide increased the number of nucleated particles also increased. It appears that oxygen may have facilitated chemical reactions with the alloy constituents, thereby increasing the mass transfer rate from the evaporating metal droplets in the plasma. Finally, an attempt to characterize the spatter aerosol revealed a distinct particle size distribution with a mode particle diameter of 6.8 μm . This particle size distribution appeared to be independent of shield gas composition, and the particle number concentration was significantly smaller than the sub-micrometer aerosols formed during the GMAW process (i.e., two-orders of magnitude smaller when weighted by particle mass).

Electrical charges on airborne microorganisms

Abstract We have investigated the parameters affecting the magnitude and polarity of the electric charges carried by biological particles in the airborne state. A recently developed experimental setup through which we analyzed the electric charges imposed on airborne particles by a means of induction charging (Mainelis et al. (Aerosol Sci. Technol. 2001, submitted for publication)) was utilized for this research. In this study, the microorganisms were aerosolized under controlled conditions and an electric mobility analyzer extracted particles of specific electric mobility. The extracted microorganisms were then analyzed by an optical particle size spectrometer. The amount of electric charge carried by airborne microorganisms was found to depend on the dispersion method and can be more than 10,000 elementary electric charges. This finding contrasts with the low electric charge levels carried by non-biological particles. Our data show that repeated pneumatic dispersion of sensitive bacteria affects their structural integrity, which, in turn, changes the magnitude of electric charges carried by these bacteria. We have concluded that the amount of electric charge carried by aerosolized bacteria may be used as an indicator of mechanical stress. It was also found that the electrical conductivity and the pH level of a bacterial suspension increase during aerosolization from a Collison nebulizer. Thus, these two parameters may be used as indicators of the mechanical stress, injury and loss in viability, endured by bacteria during aerosolization, i.e., measuring the electrical conductivity and pH level of bacterial suspensions may be a simple and convenient method for monitoring the “wear and tear” of the bacteria suspended in deionized water.

Effect of fiber length on glass microfiber cytotoxicity.

Fiber length has been implicated as a determinant of fiber toxicity. Fibers of narrowly defined length can be generated by dielectrophoretic classifiers. Since the quantities of fibers produced are very small, we developed a rat alveolar macrophage microculture system to study the toxicity of these samples. The objective of this study was to examine the role of fiber length on the cytotoxicity of Manville code 100 (JM-100) fibers. Rat alveolar macrophages were cultured with 0-500 microg/ml of 5 lengths of JM-100 fibers on 96-well plates. After 18 h, well supernatants were removed and lactate dehydrogenase (LDH) activity was measured to assess cell damage. Chemiluminescence (CL), an assessment of macrophage function, was measured by adding lucigenin with or without zymosan, a particulate stimulus, to appropriate wells. For each fiber length the effects were concentration dependent: CL declined and LDH rose with increasing fiber concentration. Comparing the effects of different lengths showed the greatest toxicity from a relatively long fiber sample (mean length = 17 microm). Microscopic examination of the interaction of fibers with macrophages revealed multiple macrophages attached along the length of the long fibers. This suggests that frustrated, or incomplete, phagocytosis may be a factor in the increased toxicity of longer fibers. Overall the results demonstrate that length is an important determinant of toxicity for JM-100 fibers.

Critical role of glass fiber length in TNF-α production and transcription factor activation in macrophages

Recent studies have demonstrated that dielectrophoresis is an efficient method for the separation of fibers according to fiber length. This method allows the investigation of fiber-cell interactions with fiber samples of the same composition but of different lengths. In the present study, we analyzed the effects of length on the interaction between glass fibers and macrophages by focusing on production of the inflammatory cytokine tumor necrosis factor (TNF)-α in a mouse macrophage cell line (RAW 264.7). The underlying molecular mechanisms controlling TNF-α production were investigated at the gene transcription level. The results show that glass fibers induced TNF-α production in macrophages and that this induction was associated with activation of the gene promoter. Activation of the transcription factor nuclear factor (NF)-κB was responsible for this induced promoter activity. The inhibition of both TNF-α production and NF-κB activation by N-acetyl-l-cysteine, an antioxidant, indicates that generation of oxidants may contribute to the induction of this cytokine and activation of this transcription factor by glass fibers. Long fibers (17 μm) were significantly more potent than short fibers (7 μm) in inducing NF-κB activation, the gene promoter activity, and the production of TNF-α. This fiber length-dependent difference in the stimulatory potency correlated with the fact that macrophages were able to completely engulf short glass fibers, whereas phagocytosis of long glass fibers was incomplete. These results suggest that fiber length plays a critical role in the potential pathogenicity of glass fibers.

Recovery Efficiency and Limit of Detection of Aerosolized Bacillus anthracis Sterne from Environmental Surface Samples

ABSTRACT After the 2001 anthrax incidents, surface sampling techniques for biological agents were found to be inadequately validated, especially at low surface loadings. We aerosolized Bacillus anthracis Sterne spores within a chamber to achieve very low surface loading (ca. 3, 30, and 200 CFU per 100 cm2). Steel and carpet coupons seeded in the chamber were sampled with swab (103 cm2) or wipe or vacuum (929 cm2) surface sampling methods and analyzed at three laboratories. Agar settle plates (60 cm2) were the reference for determining recovery efficiency (RE). The minimum estimated surface concentrations to achieve a 95% response rate based on probit regression were 190, 15, and 44 CFU/100 cm2 for sampling steel surfaces and 40, 9.2, and 28 CFU/100 cm2 for sampling carpet surfaces with swab, wipe, and vacuum methods, respectively; however, these results should be cautiously interpreted because of high observed variability. Mean REs at the highest surface loading were 5.0%, 18%, and 3.7% on steel and 12%, 23%, and 4.7% on carpet for the swab, wipe, and vacuum methods, respectively. Precision (coefficient of variation) was poor at the lower surface concentrations but improved with increasing surface concentration. The best precision was obtained with wipe samples on carpet, achieving 38% at the highest surface concentration. The wipe sampling method detected B. anthracis at lower estimated surface concentrations and had higher RE and better precision than the other methods. These results may guide investigators to more meaningfully conduct environmental sampling, quantify contamination levels, and conduct risk assessment for humans.

Aerosolization of single-walled carbon nanotubes for an inhalation study.

Single-walled carbon nanotubes (SWCNT) are being produced in increasing quantities because of high interest in applications resulting from their unique properties. Because of potential respiratory exposures during production and handling, inhalation studies are needed to determine potential toxicity. A generation system was designed to produce respirable aerosol at 5 mg/m3 for a 1-wk animal (mouse) exposure. The starting material used in these experiments was as-produced powder from the high pressure carbon monoxide method that was sieved to number 6 mesh (< 2.3 mm). An acoustic feeder system was developed that handled the SWCNT powder without causing compaction of the material. The feed rate was adjustable, allowing output concentrations as high as 25 mg/m3. The powder particles were reduced in size using a mill that produced high shear forces, tearing the agglomerates apart. The resulting aerosol was size-separated using a settling chamber and two cyclones to produce a respirable aerosol. The mass output efficiency of the entire system for producing a respirable aerosol from bulk material was estimated to be about 10%.