Transmission Electron Microscopic Observations on Technegas and Pertechnegas

ABSTRACT

We examined the features of technegas, pertechnegas, and related nonradioactive aerosols using transmission electron microscopy. Samples of technegas, pertechnegas and unlabeled saline aerosols were created and collected within the Technegas Generator. The samples were examined by transmission electron microscopy and electron energy-loss spectroscopy (EELS). Technegas, pertechnegas, and the unlabeled saline aerosol particles have the same ultrastructure. Heating by the electron beam produces damage in some of these particles, revealing an opaque core material that is water soluble, and a thin surface layer. Disappearance of chlorine is noted by EELS during heating. We conclude that all of the examined aerosols have the same ultrastructure, regardless of the presence of small concentrations of oxygen during particle formation, and regardless of the presence of the technetium-99m label. We also note that some particles are susceptible to damage by heating; these consist of a thin surface layer and an opaque core substance that is dissipated upon heating.     

Evaluation of a High Volume Aerosol Concentrator

A virtual impactor sampler, which is designed to concentrate aerosols from a 1000 L/min ambient air sample into a 1 L/min exhaust airflow stream, was tested with near monodisperse aerosols in aerosol wind tunnels to characterize sampling performance. New methodology is introduced to correct results for the presence of doublet and satellite aerosol particles that can be present in the particle size distribution from a vibrating jet atomizer. Aerosol penetration from the free stream near the sampler inlet to the outlet of the device has a peak value of 78% at a particle size of 3.9 w m AD. Sampling effectiveness, which is the mean penetration over the size range of 2.5 to 10 w m AD, is 48%. There are 4 virtual impaction stages in the sampler, and examination of the regional losses shows that most of the aerosol deposition occurs on surfaces of the last 2 stages. The ideal power expenditure of the sampler (excluding electrical and frictional losses in the motor and bearing losses in the blower) is 58 watts as compared to the actual power consumption of 320 watts.     

Generation of Radiolabeled "Soot-Like" Ultrafine Aerosols Suitable for Use in Human Inhalation Studies

We have developed a method for radiolabeling ultrafine carbon particle aggregates with technetium-99m. The carbon aggregate aerosol was chosen to mimic the physical properties of urban combustion or ''soot-like'' particulate. The radioisotope is a short lived (t_1/2 = 6.02 h) gamma emitter commonly used in human studies where scintigraphic methods are employed. Primary carbon parti cles, the aggregation of which is controlled by concentration and time, were produced by arcing between graphite electrodes under an argon atmosphere. Radiolabeling of particles was accomplished by applying a pertechnetate solution onto the tips of electrodes prior to arcing. The activity median diameter of experimental aerosols could be varied from 50 to 150 nm. The specific activity of aerosols increased with the amount of activity applied to the electrodes and decreased with time of generator operation. In-vitro leaching of the radioisotope from particles into solution was also measured. Leaching appeared to increase with the specific activity of the aerosol but was not affected by particle size.     

Low Pressure Aerosol Flow Reactor

In this work we report the development of a novel low pressure aerosol flow reactor for the determination of the kinetic parameters of fast heterogeneous processes. The experimental apparatus consists of a spray atomizer to introduce aerosols into a low pressure zone; a fast flow reactor for kinetic measurements and an IR spectrometer and mass spectrometer for concentration measurements. The surface area distribution and number density of the aerosol particles are determined from their infrared spectra and the decay kinetics are determined by monitoring the disappearance rates of the gas phase species (with a mass spectrometer) as a function of the aerosol properties. We report the application of this apparatus to the investigation of the uptake of acetone by liquid water aerosols (0.1–20 μ m diameter) at room temperature and a pressure of 35 Torr. These measurements yielded a value of the mass accommodation coefficient, α, of 3.6 _{? 2} ^{+ 3.1} × 10 ^{? 3} .     

Characteristics of Fine Particle Growth Events Observed Above a Forested Ecosystem in the Sierra Nevada Mountains of California

Atmospheric aerosols from natural and anthropogenic processes have both primary and secondary origins, and can influence human health, visibility, and climate. One key process affecting atmospheric concentrations of aerosols is the formation of new particles and their subsequent growth to larger particle sizes. A field study was conducted at the Blodgett Forest Research Station in the Sierra Nevada Mountains of California from May through September of 2002 to examine the effect of biogenic volatile organic compounds on aerosol formation and processing. The study included in-situ measurements of concentration and biosphere-atmosphere flux of VOCs, ozone, aerosol size distribution, aerosol physical and optical properties, and meteorological variables. Fine particle growth events were observed on approximately 30 percent of the 107 days with complete size distribution data. Average particle growth rates measured during these events were 3.8 ± 1.9 nm hr^?1. Correlations between aerosol properties, trace gas concentrations, and meteorological measurements were analyzed to determine conditions conducive to fine particle growth events. Growth events were typically observed on days with a lesser degree of anthropogenic influence, as indicated by lower concentrations of black carbon, carbon monoxide, and total aerosol volume. Days with growth events also had lower temperatures, increased wind speeds, and larger momentum flux. Measurements of ozone concentrations and ozone flux indicate that gas phase oxidation of biogenic volatile organic compounds occur in the canopy, strongly suggesting that a significant portion of the material responsible for the observed particle growth are oxidation products of naturally emitted very reactive organic compounds.     

MADM-A New Multicomponent Aerosol Dynamics Model

A Multicomponent Aerosol Dynamics Model (MADM) capable of solving the condensation/evaporation equation of atmospheric aerosols is presented. Condensable species may be organic and/or inorganic. For the inorganic constituents the equilibrium model ISORROPIA is used to predict the physical state of the particle, i.e., whether the aerosol is liquid or solid. The mass transfer equations for the fluxes for solid atmospheric particles are developed. MADM is able to simulate aerosol deliquescence, crystallization, solid to solid phase transitions, and acidity transitions. Aerosols of different sizes can be in different physical states (solid, liquid, or partially solid and partially liquid). Novel constraints on the electroneutrality of the species flux between the gas and aerosol phases are presented for both liquid and solid aerosols. These constraints aid in the stability of the algorithm, yet still allow changes in aerosol acidity. As an example, MADM is used to predict the dynamic response of marine aerosol entering an urban area.     

Method to Determine the Number of Bacterial Spores Within Aerosol Particles

We describe methodology to reveal the number of microbial spores within aerosol particles. The procedure involves visualization under differential- interference-contrast microscopy enhanced by high-resolution photography and further analysis by computer-assisted imaging. The method was used to analyze spore of Bacillus globigii in aerosols generated by a small (pressured metered-dose inhaler type) generator. Particles consisting in 1 or 2 spores accounted for 85% of all generated particles. This percentage rose to 91% when the same aerosol was collected on an Andersen cascade impactor that collected particles larger than 0.65 μm and was even higher (96%) when particles larger than 3.3 μm were also eliminated. These results demonstrate that the imaging analysis of aerosol particles collected on glass slides is sensitive to even relatively small changes in aerosol particle composition. The accuracy of the enhanced microscopic method described herein (differences between visual and computer analysis were approximately 3% of the total particle counts) seems adequate to determine the spore composition of aerosols of interest in biodefense.     

A novel high-volume Photochemical Emission Aging flow tube Reactor (PEAR)

Aerosols emitted from various anthropogenic and natural sources undergo constant physicochemical transformations in the atmosphere, altering their impacts on health and climate. This article presents the design and characteristics of a novel Photochemical Emission Aging flow tube Reactor (PEAR). The PEAR was designed to provide sufficient aerosol mass and flow for simultaneous measurement of the physicochemical properties of aged aerosols and emission exposure studies (in vivo and in vitro). The performance of the PEAR was evaluated by using common precursors of secondary aerosols as well as combustion emissions from a wood stove and a gasoline engine. The PEAR was found to provide a near laminar flow profile, negligible particle losses for particle sizes above 40?nm, and a narrow residence time distribution. These characteristics enable resolution of temporal emission patterns from dynamic emission sources such as small-scale wood combustion. The formation of secondary organic aerosols (SOA) in the PEAR was found to be similar to SOA formation in a smog chamber when toluene and logwood combustion emissions were used as aerosol sources. The aerosol mass spectra obtained from the PEAR and smog-chamber were highly similar when wood combustion was used as the emission source. In conclusion, the PEAR was found to plausibly simulate the photochemical aging of organic aerosols with high flow rates, needed for studies to investigate the effects of aged aerosols on human health. The method also enables to study the aging of different emission phases in high time resolution, and with different OH-radical exposures up to conditions representing long-range transported aerosols.

Copyright © 2019 American Association for Aerosol Research     

Development of an Aerosol Mass Spectrometer for Size and Composition Analysis of Submicron Particles

The importance of atmospheric aerosols in regulating the Earth's climate and their potential detrimental impact on air quality and human health has stimulated the need for instrumentation which can provide real-time analysis of size resolved aerosol, mass, and chemical composition. We describe here an aerosol mass spectrometer (AMS) which has been developed in response to these aerosol sampling needs and present results which demonstrate quantitative mea surement capability for a laboratory-generated pure component NH₄ NO₃ aerosol. The instrument combines standard vacuum and mass spectrometric technologies with recently developed aerosol sampling techniques. A unique aerodynamic aerosol inlet (developed at the University of Minnesota) focuses particles into a narrow beam and efficiently transports them into vacuum where aerodynamic particle size is determined via a particle time-of-flight (TOF) measurement. Time-resolved particle mass detection is performed mass spectrometrically following particle flash vaporization on a resistively heated surface. Calibration data are presented for aerodynamic particle velocity and particle collection efficiency measurements. The capability to measure aerosol size and mass distributions is compared to simultaneous measurements using a differential mobility analyzer (DMA) and condensation particle counter (CPC). Quantitative size classification is demonstrated for pure component NH₄ NO₃ aerosols having mass concentrations 0.25_mu g m -3. Results of fluid dynamics calculations illustrating the performance of the aerodynamic lens are also presented and compared to the measured performance. The utility of this AMS as both a laboratory and field portable instrument is discussed.     

Conditions for Cloud Settling and Rayleigh-Taylor Instability

Most aerosol motion can be analyzed by individual particle motion or by the motion of the suspending gas. There are, however, two related situations in which an aerosol can exhibit bulk motion: cloud settling and Rayleigh-Taylor instability. In both cases, the aerosol particles move faster as a cloud than they do as individual particles. In the case of cloud settling, the aerosol is usually a spheroidal cloud surrounded by clean air. Rayleigh-Taylor instability occurs when a dense aerosol layer overlies a layer of clean air. This instability is characterized by abrupt breakthrough of the aerosol layer into the clean air layer at multiple points. High-concentration, submicrometer test aerosols were generated in two experimental systems that permitted observation of the transition from particle-dominated motion to cloud, or bulk, dominated motion and measurement of cloud settling velocities and characteristics. In both systems aerosol concentration could be controlled over two orders of magnitude. One system used commercial ventilation smoke tubes to release a dense stream of aerosol into a low velocity wind tunnel. The other used diluted mainstream cigarette smoke from a smoking machine in an aerosol centrifuge. Based on these experiments, theoretical equations for cloud settling predict cloud settling velocity within an order of magnitude. The transition from individual particle motion to observable bulk motion occurs when predicted cloud settling velocity is from 0.01 to 0.05 m/s. Cloud settling appears to be initiated from an aerosol stream or layer by Rayleigh-Taylor instability. The ratio of cloud settling velocity to particle settling velocity does not appear to be a reliable predictor of the transition from particle to bulk motion.     

Numerical Simulation of the Conditioning of Volatile Particles in Laminar Flow Tube Reactors

The conditioning of aerosol particles to a predefined composition and size can be considered as a standard problem in aerosol technology. Quite often aerosols generated by dispersing diluted solutions are conditioned in a subsequent flow reactor.To make the design of such reactors easier, a computer model was developed to simulate the behavior of particles with a volatile component during their passage through the reactor. The model is based on the assumption that part of the surface of the reactor is covered with a layer of the requested activity of the volatile component whose fraction has to be adjusted. The diffusion to or from this surface and the corresponding change of the particle size and composition is calculated for each streamline of the flow on the basis of a laminar flow profile. At the moment data for the system H 2 O/H 2 SO 4 are implemented in the model, but an extension to other systems can easily be done. Circular as well as annular flow cross sections can be taken into account.     

Particle Charge Distribution Measurement for Commonly Generated Laboratory Aerosols

ABSTRACT

An improved particle charge analyzer system has been developed to measure the absolute charge distribution of common generated laboratory aerosols. The charge analyzer system consists of an integral cylindrical mobility analyzer used in conjunction with an optical aerosol spectrometer, with computer assisted operation and data reduction. The charge analyzer collects aerosol particles over an absolute electrical mobility range from 4.2*10^?4 to 400 cm²/(stat · Volt second) and flow rates that can vary from 0.3 to 30 liters per minute. The charge analyzer has been used to investigate the nature of spray and contact electrification during aerosol generation by measuring the residual charge distribution on the liquid and solid generated particles. In addition, the neutralization of charged particles by bipolar ions also was studied using conventional neutralizers that use ionizing radiation from alpha and beta sources. Charge distribution measurements were performed on alumina dust (Al), Arizona road dust (ARD), potassium chloride (KCl), sodium chloride (NaCl) and di-octyl sebacate (DOS) liquid particles. Aerosol generation devices include a Collison atomizer, a condensation aerosol generator and a fluidized bed dust generator. Our work provides experimental charge distribution data for comparison with simple models of electrification theory. Experimental results showed that charge levels of atomized KCl and NaCl particles were high and decreased as the dissolved ion concentration increased. DOS particles generated by evaporation-condensation were both neutral and moderately charged. These conclusions support the existence of a dipole layer at the liquid-gas interface that interacts with dissolved particles and changes their charge state. Alumina and ARD generated by the fluidized bed disperser are highly charged due to strong contact electrification during dispersion. In most cases, the charge on generated aerosols could be reduced to Boltzmann charge equilibrium conditions by commonly used radioactive neutralizers.     

A Versatile Flat-Deposit Impactor-Type Aerosol Collector Part 2: Calibration and Quantitative Study

The SPAL collector is a versatile impactor-type aerosol collector with rotatable substrate plates and radially aligned slot orifices. The airflow, controlled with a critical orifice at the last stage, becomes choked for an exit pressure of 0.5 atm or less. Monodisperse latex and methylene blue aerosols sampled on coated and uncoated aluminum foil substrates were used to determine the particle cutpoint diameters of each stage (9.0-0.07 mu m aed), loss on walls (3-7% for 0.054 mu m particles), and overall efficiency (97% from 0.3 to 7 mu m). Quantitative measurements were made with a spectrophotometer after recovering aerosols with a water and surfactant solution and with a semiautomated particle counting system using phase contrast microscopy. The experimental cutpoints and mea sured interstage pressures compare well with theory.     

Online Analysis of Atmospheric Particles with a Transportable Laser Mass Spectrometer

A new mobile mass spectrometrical acquisition and evaluation system for on-line analysis of single airborne particles and for characterization of particle populations (aerosols), ''LAMPAS 2,'' is described. The modular aerosol inlet system of the instrument can be quickly exchanged with an alternate unit, providing for quasi-continuous long-term operation. The technical design allows for field operation with only a 9 A single phase power supply. Statistical evaluation of large numbers of single particle spectra is performed immediately after acquisition, resulting in a time course resolution for aerosol characterization of about 1 hr. The instrument was first employed in a joint field experiment ''LACE 98'' in July and August 1998, providing for chemical and physical characterization within the framework of other state-of-the-art technologies of characterizing the atmospheric aerosol.     

Simultaneous Use of Polystyrene Latex Particles of Different Sizes to Evaluate Performance of a Cyclone and Impactor

Monodisperse and polydisperse aerosols were produced to evaluate the effect of particle size on cyclone and impactor performance. Monodisperse aerosols were generated from polystyrene latex and divinylbenzene particles. Polystyrene aerosols were also generated by mixing several monodisperse aerosols of different sizes. The mixture ratio of monodisperse aerosols was found by trial and error to generate polydisperse aerosols. Generated polydisperse aerosols had multimodal aerosol size distribution, which had the same peak point as shown in the size distribution of monodisperse particles. The results show the collection efficiency curves of a cyclone and impactor, when generating monodisperse particles were coherent with those for polydisperse ones. Our findings show that the size distribution and the size range of test aerosols can be easily determined by mixing monodisperse particles of known particle sizes, using a time saving procedure.     

Generation of TiO2 Aerosols from Liquid Suspensions: Influence of Colloid Characteristics

The influence of the colloidal characteristics of aqueous TiO₂ nanoparticle suspensions and of the operating conditions on the total particle concentration and the particle size distribution of aerosols generated by nebulization has been studied. A commercial nebulization unit coupled to a diffusion dryer was used to generate aerosols using two different sources of titanium dioxide nanoparticles. Stable, concentration-tunable aerosols could be obtained for both types of nanoparticle suspensions. The effect of operating conditions during nebulization (air flow rate, purity of water source, nanoparticle concentration, and pH of the precursor suspension) was studied. The results obtained indicate that the degree of agglomeration in the liquid phase previous to aerosol formation has a direct influence both on the total nanoparticle count and on the particle size distribution of the generated aerosols.

Copyright 2013 American Association for Aerosol Research     

An Intensive Study of the Size and Composition of Submicron Atmospheric Aerosols at a Rural Site in Ontario,Canada

Atmospheric sampling was conducted at a rural site near Egbert, about 70 km north of Toronto, Ontario, Canada from March 27 to May 8, 2003 to characterize the physical and chemical properties of the ambient aerosol in near real-time. The instrumentation included a tapered element oscillating microbalance (TEOM), an ultrafine condensation particle counter (UCPC), a scanning mobility particle sizer (SMPS), an aerodynamic particle sizer (APS), an aerosol mass spectrometer (AMS), and a particulate nitrate monitor (R&P 8400N) for aerosol measurements. Gas-phase non-methane hydrocarbon compounds (NMHCs) were measured by gas chromatograph-flame ionization detection (GC-FID). Filter samples were also collected for analysis of inorganic ions by ion chromatography (IC). Aerosol properties varied considerably depending upon meteorological conditions and airmass histories. For example, urban and industrial emissions advected from the south strongly influenced the site occasionally, resulting in higher particulate mass with the higher fractions of nitrate and organics. Cleaner northwesterly winds carried aerosols with relatively higher fractions of organics and sulfate. The AMS derived mass size distributions showed that the inorganic species in the particles with vacuum aerodynamic diameters between about 60 nm and 600 nm had mass modal vacuum aerodynamic diameters around 400–500 nm. The particulate organics often exhibited two modes at about 100 nm and 425 nm, more noticeable during fresh pollution events. The small organic mode was well correlated with gas-phase nonmethane hydrocarbons such as ethylbenzene, toluene, and propene, suggesting that the likely sources of small organic particles were combustion related emissions. The particulate nitrate exhibited a diurnal variation with higher concentrations during dark hours and minima in the afternoon. Particulate sulfate and organics showed evidence of photochemical processing with higher levels of sulfate and oxygenated organics in the afternoon. Reasonable agreement among all of the co-located measurements is found, provided the upper size limit of the AMS is considered.     

Evolution of the Efficiency and Pressure Drop of a Filter Media with Loading

A model for calculating the filtration efficiency and the pressure drop of a fiber filter media in dynamic regime was used and modified to take account of both the fiber and the particle size distributions. Measurements were carried out on two medias employed in industry and two loading aerosols to test the possibilities offered by the model to predict the evolution of both the efficiency and pressure drop characteristics. The results show that the model satisfactorily reflects the variations in efficiency and pressure drop of a media with respect to the loading if its structure is homogeneous and if the deposit of particles takes place within the thickness of the filtering layer. On the other hand, the divergence between the model and practical experience becomes significant as soon as surface filtration regime occurs or when the media has a heterogeneous structure. A test rig was developed to determine the filtering characteristics, such as fractional efficiency and pressure drop in relation to the degree of loading, from aerosols of various particle sizes. This study has highlighted the necessity of taking into account the influence of loading in the methods for testing filters, especially those used in the industry, and demonstrates that the particle size of the test aerosol is a very sensitive parameter.     

Detection and Analysis of Aerosol Particles by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) was evaluated as a means for quantitative analysis of the size, mass, and composition of individual micron-to submicron-sized aerosol particles over a range of well-characterized experimental conditions. Conditional data analysis was used to identify LIBS spectra that correspond to discrete aerosol particles under low aerosol particle loadings. The size distributions of monodisperse particle source flows were measured using the LIBS technique for calcium- and magnesium-based aerosols. The resulting size distributions were in good agreement with independently measured size distribution data. A lower size detection limit of 175 nm was determined for the calcium- and magnesium-based particles, which corresponds to a detectable mass of approximately 3 femtograms. In addition, the accuracy of the LIBS technique for the interference-free analysis of different particle types was verified using a binary aerosol system of calcium-based and chromium particles.     

Combustion Generated Nickel Species Aerosols: Role of Chemical and Physical Properties on Lung Injury

Systematic manipulation of furnace temperature, residence time, and dilution air was used to study the formation of submicrometer nickel oxide (NiO) or nickel sulfate hexahydrate (NiSO 4 ) particles in a horizontal, laminar flow tube reactor. Chemical speciation, morphological changes, and aerosol size distributions were measured using x-ray diffraction, transmission electron microscopy, and diffusion mobility analysis, respectively. A technique was developed to use these submicrometer nickel species aerosols in animal inhalation studies. Representative aerosols were administered to C57BL/6J mice by intratracheal instillation or whole-body inhalation to study the effect of submicrometer particles on pulmonary injury. For instillation, NiO particles having a geometric mass mean diameter ( d pg ) of 40, 300, and 1000 nm were generated by pyrolysis of nickel nitrate hexahydrate aerosol suspended in physiological saline and administered at a dose corresponding to 3, 30, 300, or 3000 w g Ni/kg body weight. Bronchoalveolar lavage fluid was collected 18 hr after instillation and analyzed for total and differential cell counts, cell viability, and total protein. For inhalation experiments, an acute, whole-body exposure was conducted, exposing mice to 6, 24, 48, or 72 hr of continuous submicrometer NiO aerosol ( d pg = 50 nm; 340 w g Ni/m 3 ) or 24, 48, or 72 hr of NiSO 4 aerosol ( d pg = 60 nm; 420 w g Ni/m 3 ; d pg = 250 nm; 480 w g Ni/m 3 ). Exposure to NiO produced no significant lung injury when either instilled or inhaled, whereas inhaled NiSO 4 caused significant increases in protein content and neutrophil count in lavage following 48 or 72 hr of exposure. These findings suggest that submicrometer NiSO4 aerosols generated in combustion processes are more acutely injurious to the lung than an equivalent mass of NiO aerosol.