Journal of Aerosol Science

Published by Elsevier
Print ISSN: 0021-8502
We studied the effect of gravitational sedimentation on the dispersion of 0.5 and 1 micrometer-diameter particle boluses within a two-dimensional symmetric six-generation model of the human acinus. Boluses were introduced at the beginning of a 2-s inspiration immediately followed by a 4-s expiration, in normal gravity (1 G) and in the absence of gravity (0 G). The flow corresponded to a flow rate at the mouth of 500 ml/s. In 0 G, simulated dispersion (Hsim) was 16 ml for both particle sizes. In 1 G, Hsim was 71 and 242 ml for 0.5 and 1 micrometer-diameter particles, respectively, showing the effect of gravitational sedimentation. The difference between experimental data (J. Appl. Physiol. 86 (1999) 1402) and simulations was independent of particle size. This suggests that the residual dispersion was independent of the intrinsic properties of the particles and was more likely due to other mechanisms such as ventilation inhomogeneities, cardiogenic oscillations and alveolar wall motion.
A prototype instrument has been constructed to measure individual airborne particles based on their aerodynamic size and their intrinsic fluorescence at selected excitation and emission wavelength bands. The instrument combines features of an aerodynamic particle sizing device with capabilities similar to those of a liquid flow cytometer. The goal of the instrument is to provide real-time data indicative of particle characteristics, and it is especially targeted to respond to bioaerosols from 0.5 to 10 micrometers (aerodynamic diameter) with intrinsic fluorescence exited at a wavelength of 325 nm and emitting from 420 to 580 nm. This size range covers individual airborne bacteria and bacteria clusters, and the fluorescence sensitivity is selected for biological molecules commonly found in cellular systems, for example, reduced nicotinamide adenine dinucleotide phosphate [NAD(P)H] and riboflavin. Initial tests with nebulised Bacillus subtilis var. niger (BG, ATCC 9372) spores have shown that, for both individual spores and spore clumps, a low level of fluorescence is detected from 17% of the particles. This detection percentage is on the same order as previous experiments that have measured viability of about 12% for mechanically dispersed BG spores (Ho and Fisher (1993) Defense Research Establishment Suffield Memorandum 1421) and suggests a need for further investigation into the possible relationship between the detected fluorescence and viability of bacterial spores.
The performance of Grimm optical particle counters (OPC, models 1.108 and 1.109) was characterized under urban aerosol conditions. Number concentrations were well correlated. The different lower cut-off diameters (0.25 and 0.3 μm) give an average difference of 23.5%. Both detect less than 10% of the total particle concentration (0.01-1 μm; Differential Mobility Analyzer), but in the respective size ranges, differences are <10%. OPC number size distributions were converted to mass concentrations using instrument-specific factors given by the manufacturer. Mass concentrations for OPC1.108 were 60% higher than for OPC1.109 and (in case of OPC1.109) much lower than those measured with an impactor in the relevant size range or a TSP filter. Using the C-factor correction suggested by the manufacturer, OPC1.109 underestimated mass concentrations by 21% (impactor) and by about 36% (TSP filter), which is in the range of comparability of co-located different mass concentration methods (Hitzenberger, Berner, Maenhaut, Cafmeyer, Schwarz, & Mueller et al., 2004).
Core-shell, nano-sized LiFePO(4)-carbon particles were made in one step by scalable flame aerosol technology at 7 g/h. Core LiFePO(4) particles were made in an enclosed flame spray pyrolysis (FSP) unit and were coated in-situ downstream by auto thermal carbonization (pyrolysis) of swirl-fed C(2)H(2) in an O(2)-controlled atmosphere. The formation of acetylene carbon black (ACB) shell was investigated as a function of the process fuel-oxidant equivalence ratio (EQR). The core-shell morphology was obtained at slightly fuel-rich conditions (1.0<EQR<1.07) whereas segregated ACB and LiFePO(4) particles were formed at fuel-lean conditions (0.8<EQR<1). Post-annealing of core-shell particles in reducing environment (5 vol% H(2) in argon) at 700 °C for up to 4 h established phase pure, monocrystalline LiFePO(4) with a crystal size of 65 nm and 30 wt% ACB content. Uncoated LiFePO(4) or segregated LiFePO(4)-ACB grew to 250 nm at these conditions. Annealing at 800 °C induced carbothermal reduction of LiFePO(4) to Fe(2)P by ACB shell consumption that resulted in cavities between carbon shell and core LiFePO(4) and even slight LiFePO(4) crystal growth but better electrochemical performance. The present carbon-coated LiFePO(4) showed superior cycle stability and higher rate capability than the benchmark, commercially available LiFePO(4).
This work concentrates on the experimental determination of the properties of ionic molecular clusters that are produced in the bipolar ionic atmosphere of a radioactivity based (241)Am charger. The main scope of this study was to investigate the dependency of the ions' properties on carrier gas contaminants caused by the evaporation of trace gases from different kinds of frequently encountered tubing materials. A recently developed high resolution mobility spectrometer allows the precise determination of the ions' electrical mobility; an empirical mass-mobility relationship was used to approximate the corresponding ion masses. It was found that impurities in the carrier gas dramatically change the pattern of the ion mobility/size distribution, resulting in very different ion properties that strongly depend on the carrier gas composition. Since the ion properties control the charging process of aerosols, it was further investigated how the different ion properties affect the calculation of the charging probabilities of aerosols. The results show that despite large variations of the ions' properties, only a minor effect on the calculated charging probabilities can be found.
Submicrometer and nanoparticle aerosols may significantly improve the delivery efficiency, dissolution characteristics, and bioavailability of inhaled pharmaceuticals. The objective of this study was to explore the formation of submicrometer and nanometer aerosols from mesh nebulizers suitable for respiratory drug delivery using experiments and computational fluid dynamics (CFD) modeling. Mesh nebulizers were coupled with add-on devices to promote aerosol drying and the formation of submicrometer particles, as well as to control the inhaled aerosol temperature and relative humidity. Cascade impaction experiments were used to determine the initial mass median aerodynamic diameters of 0.1% albuterol aerosols produced by the AeroNeb commercial (4.69 μm) and lab (3.90 μm) nebulizers and to validate the CFD model in terms of droplet evaporation. Through an appropriate selection of flow rates, nebulizers, and model drug concentrations, submicrometer and nanometer aerosols could be formed with the three devices considered. Based on CFD simulations, a wire heated design was shown to overheat the airstream producing unsafe conditions for inhalation if the aerosol was not uniformly distributed in the tube cross-section or if the nebulizer stopped producing droplets. In comparison, a counter-flow heated design provided sufficient thermal energy to produce submicrometer particles, but also automatically limited the maximum aerosol outlet temperature based on the physics of heat transfer. With the counter-flow design, submicrometer aerosols were produced at flow rates of 5, 15, and 30 LPM, which may be suitable for various forms of oral and nasal aerosol delivery. Thermodynamic conditions of the aerosol stream exiting the counter-flow design were found be in a range of 21-45 °C with relative humidity greater than 40% in some cases, which was considered safe for direct inhalation and advantageous for condensational growth delivery.
The structure of fractal-like agglomerates (physically-bonded) and aggregates (chemically- or sinter-bonded) is important in aerosol synthesis of nanoparticles, and in monitoring combustion emissions and atmospheric particles. It influences also particle mobility, scattering, and eventually performance of nanocomposites, suspensions and devices made with such particles. Here, aggregate sintering by viscous flow of amorphous materials (silica, polymers) and grain boundary diffusion of crystalline ceramics (titania, alumina) or metals (Ni, Fe, Ag etc.) is investigated. A scaling law is found between average aggregate projected area and equivalent number of constituent primary particles during sintering: from fractal-like agglomerates to aggregates and eventually compact particles (e.g. spheres). This is essentially a relation independent of time, material properties and sintering mechanisms. It is used to estimate the equivalent primary particle diameter and number in aggregates. The evolution of aggregate morphology or structure is quantified by the effective fractal dimension (Df ) and mass-mobility exponent (Dfm ) and the corresponding prefactors. The Dfm increases monotonically during sintering converging to 3 for a compact particle. Therefore Dfm and its prefactor could be used to gauge the degree or extent of sintering of agglomerates made by a known collision mechanism. This analysis is exemplified by comparison to experiments of silver nanoparticle aggregates sintered at different temperatures in an electric tube furnace.
Accurate prediction of nanoparticle (1~100 nm) deposition in the rat nasal cavity is important for assessing the toxicological impact of inhaled nanoparticles as well as for potential therapeutic applications. A quasi-steady assumption has been widely adopted in the past investigations on this topic, yet the validity of such simplification under various breathing and sniffing conditions has not been carefully examined. In this study, both steady and unsteady computational fluid dynamics (CFD) simulations were conducted in a published rat nasal model under various physiologically realistic breathing and sniffing flow rates. The transient airflow structures, nanoparticle transport and deposition patterns in the whole nasal cavity and the olfactory region were investigated and compared with steady state simulation of equivalent flow rate. The results showed that (1) the quasi-steady flow assumption for cyclic flow was valid for over 70% of the cycle period during all simulated breathing and sniffing conditions in the rat nasal cavity, or the unsteady effect was only significant during the transition between the respiratory phases; (2) yet the quasi-steady assumption for nanoparticle transport was not valid, except in the vicinity of peak respiration. In general, the total deposition efficiency of nanoparticle during cyclic breathing would be lower than that of steady state due to the unsteady effect on particle transport and deposition, and further decreased with the increase of particle size, sniffing frequency, and flow rate. In the contrary, previous study indicated that for micro-scale particles (0.5~4μm), the unsteady effect would increase deposition efficiencies in rat nasal cavity. Combined, these results suggest that the quasi-steady assumption of nasal particle transport during cycling breathing should be used with caution for an accurate assessment of the toxicological and therapeutic impact of particle inhalation. Empirical equations and effective steady state approximation derived in this study are thus valuable to estimate such unsteady effects in future applications.
Accurate modeling of air flow and aerosol transport in the alveolated airways is essential for quantitative predictions of pulmonary aerosol deposition. However, experimental validation of such modeling studies has been scarce. The objective of this study is to validate CFD predictions of flow field and particle trajectory with experiments within a scaled-up model of alveolated airways. Steady flow (Re = 0.13) of silicone oil was captured by particle image velocimetry (PIV), and the trajectories of 0.5 mm and 1.2 mm spherical iron beads (representing 0.7 to 14.6 mum aerosol in vivo) were obtained by particle tracking velocimetry (PTV). At twelve selected cross sections, the velocity profiles obtained by CFD matched well with those by PIV (within 1.7% on average). The CFD predicted trajectories also matched well with PTV experiments. These results showed that air flow and aerosol transport in models of human alveolated airways can be simulated by CFD techniques with reasonable accuracy.
Enhanced condensational growth (ECG) is a newly proposed concept for respiratory drug delivery in which a submicrometer aerosol is inhaled in combination with saturated or supersaturated water vapor. The initially small aerosol size provides for very low extrathoracic deposition, whereas condensation onto droplets in vivo results in size increase and improved lung retention. The objective of this study was to develop and evaluate a CFD model of ECG in a simple tubular geometry with direct comparisons to in vitro results. The length (29 cm) and diameter (2 cm) of the tubular geometry were representative of respiratory airways of an adult from the mouth to the first tracheobronchial bifurcation. At the model inlet, separate streams of humidified air (25, 30, and 39 °C) and submicrometer aerosol droplets with mass median aerodynamic diameters (MMADs) of 150, 560, and 900 nm were combined. The effects of condensation and droplet growth on water vapor concentrations and temperatures in the continuous phase (i.e., two-way coupling) were also considered. For an inlet saturated air temperature of 39 °C, the two-way coupled numerical (and in vitro) final aerosol MMADs for initial sizes of 150, 560, and 900 nm were 1.75 μm (vs. 1.23 μm), 2.58 μm (vs. 2.66 μm), and 2.65 μm (vs. 2.63 μm), respectively. By including the effects of two-way coupling in the model, agreements with the in vitro results were significantly improved compared with a one-way coupled assumption. Results indicated that both mass and thermal two-way coupling effects were important in the ECG process. Considering the initial aerosol sizes of 560 and 900 nm, the final sizes were most influenced by inlet saturated air temperature and aerosol number concentration and were not largely influenced by initial size. Considering the growth of submicrometer aerosols to above 2 μm at realistic number concentrations, ECG may be an effective respiratory drug delivery approach for minimizing mouth-throat deposition and maximizing aerosol retention in a safe and simple manner. However, future studies are needed to explore effects of in vivo boundary conditions, more realistic respiratory geometries, and transient breathing.
Increasing evidence suggests that the physicochemical properties of inhaled nanoparticles influence the resulting toxicokinetics and toxicodynamics. This report presents a method using scanning transmission electron microscopy (STEM) to measure the Mn content throughout the primary particle size distribution of welding fume particle samples collected on filters for application in exposure and health research. Dark field images were collected to assess the primary particle size distribution and energy-dispersive X-ray and electron energy loss spectroscopy were performed for measurement of Mn composition as a function of primary particle size. A manual method incorporating imaging software was used to measure the primary particle diameter and to select an integration region for compositional analysis within primary particles throughout the size range. To explore the variation in the developed metric, the method was applied to 10 gas metal arc welding (GMAW) fume particle samples of mild steel that were collected under a variety of conditions. The range of Mn composition by particle size was -0.10 to 0.19 %/nm, where a positive estimate indicates greater relative abundance of Mn increasing with primary particle size and a negative estimate conversely indicates decreasing Mn content with size. However, the estimate was only statistically significant (p<0.05) in half of the samples (n=5), which all had a positive estimate. In the remaining samples, no significant trend was measured. Our findings indicate that the method is reproducible and that differences in the abundance of Mn by primary particle size among welding fume samples can be detected.
Computational fluid dynamics (CFD) predictions of inertial particle deposition have not compared well with data from nasal replicas due to effects of surface texture and the resolution of tomographic images. To study effects of geometric differences between CFD models and nasal replicas, nasal CFD models with different levels of surface smoothness were reconstructed from the same MRI data used to construct the nasal replica used by Kelly et al. (2004) [Aerosol Sci. Technol. 38:1063-1071]. One CFD model in particular was reconstructed without any surface smoothing to preserve the detailed topology present in the nasal replica. Steady-state inspiratory airflow and Lagrangian particle tracking were simulated using Fluent software. Particle deposition estimates from the smoother models under-predicted nasal deposition from replica casts, which was consistent with previous findings. These discrepancies were overcome by including surface artifacts that were not present in the reduced models and by plotting deposition efficiency versus the Stokes number, where the characteristic diameter was defined in terms of the pressure-flow relationship to account for changes in airflow resistance due to wall roughness. These results indicate that even slight geometric differences have significant effects on nasal deposition and that this information should be taken into account when comparing particle deposition data from CFD models with experimental data from nasal replica casts.
Iron oxide nanoparticles of reduced oxidation state, mainly in the form of magnetite, have been synthesized utilizing a new continuous, gas-phase, nonpremixed flame method using hydrocarbon fuels. This method takes advantage of the characteristics of the inverse flame, which is produced by injection of oxidizer into a surrounding flow of fuel. Unlike traditional flame methods, this configuration allows for the iron particle formation to be maintained in a more reducing environment. The effects of flame temperature, oxygen-enrichment and fuel dilution (i.e. the stoichiometric mixture fraction), and fuel composition on particle size, Fe oxidation state, and magnetic properties are evaluated and discussed. The crystallite size, Fe(II) fraction, and saturation magnetization were all found to increase with flame temperature. Flames of methane and ethylene were used, and the use of ethylene resulted in particles containing metallic Fe(0), in addition to magnetite, while no Fe(0) was present in samples synthesized using methane.
Experimentally determined total and regional deposition data are presented for breathing monodisperse aerosols of a wide particle size range at different patterns through the mouth and nose. From these data simple analytical expressions were derived for the efficiencies of the nasal passages, larynx, upper and lower ciliated thoracic airways and the nonciliated portion of the lungs in collecting particles from inspired aerosols. Thus, empirical expressions are now available for the calculation of total and regional deposition in the human respiratory tract for particles of any size and density inspired at any pattern through the mouth or nose.
Schematic drawing of the experimental set-up (not to scale). A/ The thermostatted chamber B/ Location of subject C/ high efficiency particle air (HEPA) filter D/ automatic 2-way non re-breathing valve E/ manual 2-way valve F/ table G/ ultrasonic flow meter H/ 30 l storage bag I/ pressure plate J/ two-way HEPA filter K/optical particle counter sizer L/ mobility analyser M/ condensation particle counter N/ mass flow controller for dry air.
Original and recalculated interval limits for the Grimm dust monitor data.
Characteristics of study objects.
Measurement data for each participant and breathing manoeuvre.
This study investigates the number size distribution of endogenously produced exhaled particles during tidal breathing and breathing with airway closure. This is the first time that the region below 0.4 μm has been investigated. The particle concentration was generally lower for tidal breathing than for airway closure, although the inter-individual variation was large. During tidal breathing, the size distribution peaks at around 0.07 μm. This peak is still present during the airway closure manoeuvre, but an additional broad and strong peak is found between 0.2 and 0.5 μm. This suggests that different mechanisms govern the generation of particles in the two cases. The particles produced from airway closure may be attributed to formation of film droplets in the distal bronchioles during inhalation. It is speculated that the very small particles are film droplets originating from the alveolar region.
Besides their effects on air hygiene and health, bioaerosol particles play an important role in cloud physics, for example, some bacteria are able to accumulate water and act as ice nuclei. For sampling aerosol particle impactors were used. The larger particles were sampled size fractionated with a free wing impactor while for the smaller ones an isokinetic two-stage impactor was constructed. The bioaerosol particles of the coarse fraction were stained with a protein dye and could be distinguished from the non-dyed particles using an optical light microscope. The small particles were examined in a scanning electron microscope (SEM) equipped with an energy-dispersive X-ray spectrometer (EDX). Three criteria were used to characterize the particles: morphology, elemental composition and behaviour during EDX. Literature and the results of our own experiments with test aerosols showed that biological particles have a special morphology together with a special elemental composition and also some of them change their form during EDX. Based on these criteria a scheme was developed dividing the atmospheric aerosol into six groups, each of them representing biological or non-biological particles.
The size distributions of droplets emitted from Taylor cones operating in the cone-jet regime are measured by sampling their electrosprays into an aerodynamic size spectrometer (API's Aerosizer). The sizing scheme is not affected by the large charge on the un-neutralized droplets in the range of diameters d explored, 0.3 μm < d < 4 μm. The diameters of the droplets electrosprayed from highly conducting liquids are found to be relatively insensitive to electrostatic variables, depending for a given liquid mostly on the flow rate Q pushed through the jet. At fixed Q, the size distributions consist of one or several fairly monodisperse classes of droplets with diameters di(Q); i = 1, 2, …, N(Q). Near the minimum flow rate Qmin at which the cone is stable, the spray tends to consist of “primary” and “satellite” droplets only, with N = 2. However, at larger flows, the modality of the distributions (N) increases. The largest size mode bifurcates into two branches at a critical flow rate Q1, coinciding with the onset of lateral oscillations of the jet. The diameter d1 of the largest drops scales approximately with , where τ is the electrical relaxation time of the fluid. Surprisingly, all the other size classes have diameters di (i ≠ l) nearly independent of flow rate, which scale as (γ= coefficient of surface tension; ρ=liquid density). Although the jet diameter dj appears to be unaffected by viscosity, its breakup mechanism, and thus the diameters di of all the droplet classes, do depend on the viscous parameters (μ = coefficient of viscosity of the liquid). The diameters of the smaller droplets are given by functions (i ≠ 1), which depend steeply on Πμ for values of this parameter below 0.06, but appear to level off above Πμ=0.15. An inviscid asymptote, in which , is approached also for d1 for sufficiently large values of Πμ where is nearly constant below the bifurcation, and seems to tend to the asymptote at large η, in qualitative agreement with the behavior of given by Fernández de la Mora and Loscertales (J. Fluid Mech. 260, 155–184, 1994). It follows from the scaling laws found that, by varying the electrical conductivity of a given liquid, it should be possible to generate monodisperse droplets with initial diameters of the order of dmin, which may span the whole range between 100 μm down to a few nanometers. The flow rate must, however, be between Qmin and its value at the bifurcation, which requires that η ∼ 1.
A new diffusion battery was designed to make precise measurements of the indoor activity size distribution of short-lived 222Rn decay products in the size range of 0.5–5 nm. It relies on the selection of particles by five annular diffusion channels (ADCs) and on the use of a non-linear inversion method, EVE, for the reconstruction of the particle size distributions. The ADC geometry proved to allow a better selection of the particles size compared to the wire screen and the implementation of an alpha detector set in front of the sampling filter for semi-continuous activity measurements. EVE algorithm was chosen in order to take into account the uncertainties of the measurement in the deconvolution process. The diffusion battery was tested in a radon chamber, and results showed a good reproducibility of the measurements. The degree of confidence on the obtained size distributions is then discussed. Results show that the relative uncertainty on the penetration data has to be less than 10% in order to obtain a reliable size distribution.
Electrostatic atomization of liquids has become a hot research area since the new and promising characteristics of the resulting spray have been brought to light, namely its fairly monodisperse size distribution, and its small and controllable droplet size. In the present work, using perturbation techniques and matched asymptotic analysis (Van Dyke, 1964; Kevorkian and Cole, 1980) based on a small parameter1, Taylor's electrostatic theory for electrified liquid cones (Taylor, 1964) has been extended in order to take into account liquid and charge emissions in the form of a capillary microjet.Our results show analytically for the first time the droplet size, its charge, and the emmited current as functions of the liquid properties (essentially the electric conductivity, surface tension, and density) and the injected flow rate. This allows for a serious approaching to the real design for an entirely new fuel injection device generation. This article was published in Journal of Aerosol Science, Vol. 24, A.M. Gañán-Calvo, A. Barrero, C. Pantano-Rubiño, The electrohydrodynamics of electrified conical menisci, Pages S19-S20, Copyright Elsevier 1993.
The high spectral resolution radiometer at the Indian Institute of Tropical Meteorology (IITM), Pune [18°, 32′N, 73° 51′ E, 559 m Above Mean Sea Level (AMSL)], India has been operated on 79 clear-sky days during April 1993–April 1995 in order to study the temporal-spectral variations in aerosol optical depth (AOD) at the station. From the records of solar irradiance at different zenith angles of the sun, AODs were estimated at a spectral interval of 5 nm in the wavelength region 400–700 nm. The temporal variations in AOD in different spectral regions showed a relationship with those observed in the concurrent surface-level meteorological parameters at the experimental site. The seasonal variations in AOD indicated maximum during summer months and minimum during winter months. In addition, the afternoon (AN) AODs are found to be higher as compared to the forenoon (FN) depths in summer months of the year, whereas the FN AODs dominate in winter months at almost all wavelengths over the observing station.
The use of electrostatic collection was investigated in quantifying airborne environmental allergens and toxins. The experiments were conducted with two 96-well plates filled with water and placed into the electrostatic sampler designed in this study. The combinations of different electrostatic fields: 0.63, 1.25 kV/cm, and different sampling flow rates: 5, 12.5 L/min, were tested with the electrostatic sampler. As a reference, a BioSampler operating at 12.5 L/min was simultaneously placed in the same environments. The sampling lasted for 40 min both for electrostatic sampler and the BioSampler in each test. House dust allergens, endotoxin and (1,3)-β-d-glucans in the air samples collected were analyzed using enzyme-linked immunosorbent assay (ELISA) and Limulus amebocyte lysate (LAL) method, respectively. The entire experiments were conducted both in office environment and hotel rooms.
An electrospraying system operated in the cone-jet mode is shown to produce monodisperse droplets in a wide size range and with good monodispersity. These highly charged droplets are rapidly discharged in a radioactive neutralizer. The produced droplet size can be further reduced by the evaporation process without experiencing the Rayleigh breakup. The experiment is performed using sucrose solutions and the liquid electrical conductivity is controlled by adding small amounts of nitric acid. The size distribution is quite monodisperse having a geometrical standard deviation of 1.1. The mean droplet size produced can be varied from 40 nm to 1.8 μm by changing the liquid feed rate and electrical conductivity. Using 0.1% sucrose concentration solution, the residue particle size is reduced by a factor of ten, in the range from 4 nm to 0.18 μm. The parameters affecting the particle size distribution, the measured spraying current, and the operating envelope have also been obtained and quantified.
The Electromobility Spectrometer is an automated measurement system for the size analysis of fine and ultrafine aerosols using Differential Mobility Analysers (DMA) for the classification of particles and an electrical sensor for their detection. To cover a particle size range from 1 to 1000 nm, new DMAs with different geometries have been designed to optimize performance for small and large particles. Key problems in the size characterization of particles smaller than 20 nm have been addressed. A Faraday cup electrometer with a sensitivity of 10−16 A is used as a particle sensor to avoid the deficiency of condensation nucleus counters with counting efficiencies decreasing with particle size. A new flow control technique allows the generation of stable air flows to further improve system performance. Additional improvements include the use of a multi-stage cascade impactor at the aerosol inlet, an instrument background correction mechanism and a refined data reduction algorithm. The computer controlled measurement program allows for variable size resolution, parallel operation of two DMAs and a time resolution for the measurement of size distributions of the order of 1 min.
The eruption of Mt Pinatubo (15.14°N, 120.35°E) in the Philippines on 15 June 1991 produced the largest volcanic effluents into the stratosphere as observed by satellite measurements. In this paper we demonstrate the application of an inversion technique to satellite observations to infer the stratospheric aerosol size distributions before and after the eruption. The U.S.A. NASA SAGE (Stratospheric Aerosol and Gas Experiment) 11 satellite data were used. As a result, the stratospheric aerosol size distributions were found to be bimodal due to the addition of larger particles from Mt Pinatubo ejection. In addition, aerosol parameters such as extinction coefficient, effective radius, total surface area, and mass loading were used to track the northward and southward dispersion of Pinatubo volcanic plume unmistakably. For example, by 18 July 1991, the Pinatubo plume had reached as high as 22 km in the stratosphere above Taiwan area. The extinction profiles for September and October 1991 cases were enhanced about two orders in magnitude at the altitude of 20–24 km owing to Pinatubo aerosols. Regarding the transport in the southern hemisphere, for five months after eruption, the plume had reached the Antarctic stratosphere, and dispersed vertically as high as 40 km. In middle Antarctic stratosphere, the aerosol extinctions were increased in general by an order of 103-105 due to the intrusion of Pinatubo plume. The second mode at 0.5 μm was found compared with the one at less than 0.1 μm, generally found in background stratosphere.
Previous work (Ahn and Liu (1990)J. Aerosol. Sci. 21, 249–261; Brockmann (1981) Ph.D. Thesis, University of Minnesota; Rebours et al. (1992)J. Aerosol. Sci. 23, S189–S192; Stolzenburg (1988) Ph.D. thesis, University of Minnesota) has shown that for particles smaller than about 15 nm, pulse heights produced by the optical detector in a white-light ultrafine condensation nucleus counter (UCNC; Stolzenburg and McMurry (1991)Aerosol. Sci. Technol. 14, 48–65) decrease with initial particle size. We have previously reported on the use of pulse heights from this instrument to determine the concentrations of freshly nucleated atmospheric nanoparticles in the 3–4 nm diameter range (Weber et al. (1995)J. Atm. Sci. 52, 2242–2257; Weber et al. (1997)J. Geophys. Res. 102, 4375–4385). In this paper we report on the inversion of measured pulse-height distributions to obtain size distributions of particles in the 3–10 nm diameter range. Using methods developed by Stolzenburg (Stolzenburg (1988) Ph.D. Thesis, University of Minnesota) the effect of diffusional broadening is taken into account so as to obtain monodisperse kernel functions from measured pulse-height distributions produced by DMA-generated calibration aerosols in the 3–50 nm diameter range. These kernel functions are then used with the MICRON algorithm described by Wolfenbarger and Seinfeld (1990, J. Aerosol. Sci. 21, 227–247) to obtain size distributions of nanoparticle aerosols from measured pulse height distributions. Calculations were done to ensure that assumed pulse-height data generated from selected known size distributions can be inverted to recover the original size distribution. Results from these validation studies are discussed. Applications of the inversion algorithm to data acquired in studies of homogeneous nucleation in the atmosphere are also presented.
A representative human tracheobronchial tree has been geometrically represented with adjustable triple-bifurcation units (TBUs) in order to effectively simulate local and global micron particle depositions. It is the first comprehensive attempt to compute micron-particle transport in a (Weibel Type A) 16-generation model with realistic inlet conditions. The CFD modeling predictions are compared to experimental observations as well as analytical modeling results. Based on the findings with the validated computer simulation model, the following conclusions can be drawn:
Journal literature on nucleation problems is listed for the period January 1972–July 1973. Homogeneous and heterogeneous nucleation processes between gaseous, liquid, and solid phases are discussed, including thin film deposition, decomposition of alloys, glasses, polymers and atmospheric applications.
The present study analyses in-situ aircraft measurements of aerosol particles and ozone in the higher troposphere during one flight in 1992. The results reveal strong fluxes of stratospheric air masses into the troposphere (tropopause folds) in the Arctic. This is demonstrated by increasing concentrations of particles (in the size range 0.25 to 0.50 μm optical diameter) and ozone, which are furthermore highly correlated. The number size distributions obtained during such events show a predominant mode centred at 0.35 μm optical diameter.
Observations of Polar Stratospheric Clouds (PSCs) were carried out with an airborne lidar on the stratospheric M55 Geophysica aircraft during a flight from Rovaniemi, Finland, on 9 January, 1997. The clouds were observed at the zenith, downwind from the Norwegian Alps: three PSCs, of somewhat different characteristics, were detected at heights between 23 and . In two of the clouds, different types of particles seem to coexist: echoes attributable to types I and II PSCs are found in different portions of the clouds. The formation of the PSCs is related to an orographic lee-wave, whose development was forecast by a mesoscale dynamical model used to plan the flight path. The largest observed PSC displays a complex structure, that appears to be influenced by waves of different wavelengths. In particular, lidar and in situ data suggest the presence of a wave having a relatively short length (about ) that overlaps on the main lee-wave. The short wavelength oscillation is thought to play a major role in the cloud development, determining the rapid formation and evaporation of particles and therefore the non-stationary character of the PSC.
The mixture state of individual aerosol particles collected at altitudes of 1– on 23 and 25 October 1997, from an aircraft flying over southern Kalimantan during the 1997 Indonesian forest fires, has been examined using the dialyses of water-soluble material with water, and organic material with benzene in conjunction with electron microscopy. Individual aerosol particles in the radius range of 0.1– were mainly present as an internal mixture of water-soluble organic material and inorganic salt (mainly ammonium sulfate). Although material comprised of chain aggregations of electron-opaque spherules (elemental carbon) was also found, the proportion of these was small.
Optical properties of aerosol particles were characterized during two field campaigns at a remote rainforest site in Rondônia, Brazil, as part of the project European Studies on Trace Gases and Atmospheric Chemistry, a contribution to the Large-Scale Biosphere-Atmosphere Experiment in Amazonia (LBA-EUSTACH). The measurements included background (wet season), biomass burning (dry season), and transition period conditions. Optical measurements of light scattering and absorption were combined with data on number/size distributions in a new iterative method, which retrieves the effective imaginary refractive index of the particles at a wavelength of . For ambient relative humidities lower than 80%, background aerosols exhibited an average refractive index of 1.42−0.006i. Biomass burning aerosols displayed a much larger imaginary part, with an average refractive index of 1.41−0.013i. Other climate-relevant parameters were estimated from Mie calculations. These include single-scattering albedos of 0.93±0.03 and 0.90±0.03 (at ambient humidity), asymmetry parameters of 0.63±0.02 and 0.70±0.03, and backscatter ratios of 0.12±0.01 and 0.08±0.01 for background and biomass burning aerosols, respectively.
An intensive soot aerosol characterisation campaign was organised in October 1999 at the large aerosol chamber facility AIDA in Karlsruhe, with the participation of scientists from nine Austrian, German, Russian, and Swiss Research Centres and Universities who contributed special equipment and expertise. The main goal was a comprehensive physical and chemical characterisation of soot aerosol from a modern turbo Diesel passenger car equipped with an oxidation catalyst, in comparison with artificial soot aerosol (“Palas” soot) from a commercial spark discharge generator which is often used as a surrogate for combustion soot in laboratory studies. Included were experiments with pure ammonium sulphate aerosol as well as its external mixtures with soot aerosols, and their evolution to partially internal mixtures on time scales up to . Effects of organic coatings on various aerosol properties, generated in situ by heterogeneous nucleation of products from the reaction of α-pinene with ozone were also investigated. The purpose of this paper is to present an overview of the whole campaign. This includes the description of technical and modelling tools, standard procedures, and the presentation of experimental parameters in tabular form, as a common background for a series of companion papers which focus on selected scientific issues. Included is a comparison between Diesel and spark generated soot in terms of their Raman and ESR spectra. The most remarkable difference is the large spin density in spark generated soot, which exceeds that of Diesel soot by an order of magnitude. However, the spin densities in both materials are too small to affect the surface properties of soot aerosols to a significant extent.
During the soot aerosol campaign particle carbon mass concentrations of Diesel soot, spark generated “Palas” soot, external and internal mixtures of Diesel soot with (NH4)2SO4, and particles coated with secondary organic aerosol material were determined by several different methods. Two methods were based on thermochemical filter analysis with coulometric and NDIR detection of evolved CO2 (total carbon, TC and elemental carbon, EC) and four methods employed optical techniques: aethalometry (black carbon, BC), photoacoustic soot detection (BC), photoelectron emission, and extinction measurement at . Furthermore, β-attenuation (total particulate mass), FTIR spectroscopy (sulphate), and COSIMA model calculations were used to determine particle mass concentrations. The general agreement between most methods was good although some methods did not reach their usual performance. TC determined by coulometric filter analysis showed good correlations with optical extinction, photoacoustic BC signal, and photoelectron emission data. However, the evolution of the photoelectron emission signal correlated with changes in accessible surface area rather than mass concentration and was very sensitive to surface conditions. The BC content as measured by the aethalometers approximately equal to less than 70% of the EC content for Diesel soot and amounts to less than 25% of the EC content of “Palas” soot.
The total (TSP), PM10, and PM2.5 aerosol samples have been collected simultaneously in indoor and outdoor air of three residences in the Taipei area. The samples were analyzed by X-ray fluorescence for up to 20 elements (Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Se, Br, and Pb). The dominant elements in TSP, PM10, and PM2.5 particulate matter were observed to be aluminum, silicon, sulfur, chloride, potassium, calcium, titanium, iron, zinc, and lead. In addition, their individual concentrations were even higher than 1 μg/m3, in some cases. For most of the measured elements, the Indoor/Outdoor ratios were found to be smaller than 1, which suggested most of indoor particles appeared to be mainly influenced by the infiltration of outdoor air. Moreover, the observed high enrichment factors indicated that man-made sources are a great contributor to indoor air quality.
Atmospheric aerosols were collected in separate fine (<2.5 μm) and coarse (>2.5 μm) size fractions in the period December 2006–March 2007 at Amsterdam Island in the southern Indian Ocean. A major objective of the study was to assess biogenic impact on the marine aerosol. The samples were analysed for organic carbon, water-soluble organic carbon, major inorganic ionic species, and organic species, including methanesulphonate (MSA), dicarboxylic acids, and organosulphates. The concentrations of sea salt, non-sea-salt sulphate, and water-soluble and water-insoluble organic matter (WSOM and WIOM) were estimated. Sea salt dominated the composition of the aerosol and accounted for 83% and 91% of the sum of the mass of the four aerosol types in the fine and coarse size fractions, respectively. WSOM, which can serve as a proxy for biogenic secondary organic aerosol (SOA), accounted for only 2.8% of the sum of the mass of the four aerosol types in the fine size fraction. MSA was the dominating organic compound with a median concentration of 47 ng m−3. The organosulphates were characterised as sulphate esters of hydroxyl acids and a dihydroxylaldehyde, which may originate from the oxidation of algal/bacterial unsaturated fatty acid residues. No evidence was found for isoprene SOA.
To investigate the contribution of ions to gas nucleation, we have performed experiments on the formation of water droplets in H2O/N2 and H2O/Ar gas mixtures by irradiation with a 20 MeV proton beam and by positive corona discharge. The size of the formed nanoparticles was measured using a differential mobility analyzer equipped with a Faraday cup electrometer. Using the proton beam, droplets around 10 nm in diameter were observed for both positively and negatively charged particles, but none were found when the corona discharge was used. This implies the importance of the presence of both positive and negative ions for the formation of nanosize droplets, which attract each other by Coulomb interactions, enhancing the collision frequency and leading to the formation of the 10 nm droplets.
This paper reports the measurements of the single fiber efficiency for a screen mesh at elevated temperatures up to 500 K for silver nanoparticles in the size range from 3 to 20 nm. Thermal rebound of particles from a filter surface is predicted to occur at 500 K for 3 nm diameter particles based on a theory by Wang and Kasper [(1991). Filtration efficiency of nanometer-size aerosol particles. Journal of Aerosol Science, 22, 31–41]; however, rebound was not detected in our study. A small change in the single fiber efficiency with temperature was observed for a fixed mass flow as is predicted by classical filtration theory. The measured increase of 8%±5% for particles of size 3, 4, and 5 nm is less than the 19% predicted by classical filtration theory. Measurements of particle penetration at a temperature of about 600 K were not possible because of particle production within the filter/holder.
Concentrations of radioactive 210Pb and 210Bi were measured in surface air after chemical separation and radiochemical analysis in an annual cycle and were used to determine aerosol residence times in the lower atmosphere. It was concluded that residence times of 8 days would apply to aerosols of 0.3 μm activity median aerodynamic diameter (AMAD). Cascade impactor data are also presented in relating the residence times and the AMAD of atmospheric aerosols.
Pollutants from mid-latitudes (mainly from Eurasia) reach the polar region through long-range atmospheric transport during winter. Due to very low precipitation in the arctic region, the pollutant-laden aerosols in the stable, and dark polar atmosphere are believed to have relatively longer residence times. The disequilibrium between the daughter products of 222Rn, in conjunction with the concentrations of 7Be in arctic aerosols can be utilized to obtain information on the residence times and sources of the arctic haze. We have carried out a pilot study to explore the feasibility of determining the residence time of aerosols from the arctic haze. Towards this, we have analyzed 10 aerosol samples from two stations, Poker Flat and Eagle, Alaska for the concentrations and activity ratios of 7Be, 210Po, and 210Pb. The activity ratios of 210Po/210Pb varied between 0 and 0.177. The corresponding residence time obtained using the disequilibrium between the 210Po and 210Pb, varied between 0 and 39 days. This is the first time an estimate on the residence time of aerosols from the arctic haze is determined. The 7Be/210Pb activity ratios varied between 2.2 and 14.0, possibly suggesting varying inputs of 7Be from the upper atmosphere to the arctic atmosphere. Since long-range atmospheric transport is one of the major pathways of arctic pollution, this study has potential significance on the fate and transport of inorganic and organic atmospheric pollutants in the arctic region.
The majority of the atoms (the first progeny of radon) are attached to natural aerosols in the air. After their alpha decay, the newly formed nuclei of may detach from the carrier aerosol due to recoil. The average fraction of the nuclei detached in this manner is called the “recoil factor”. It is an important parameter in the calculation of the radon-progeny concentration and the related radiation dose in lungs. We determine this parameter for eight common aerosol types and show that it cannot be treated as a fixed constant since it varies strongly with the aerosol particle size, shape, material, and surface/volume type of contamination. The range of values that the recoil factor can take broadens with the hygroscopic growth of the aerosol particles, to the maximum range between approximately 0.1 and 0.8.
A new method is presented to estimate mean activity concentration and mean size distribution of nanometer 218Po over long time, i.e. several weeks in indoor atmospheres. It uses an annular channel, equipped with an LR 115 solid-state alpha-track detector, as diffusion sampler. Design, experimental characterisation and analytical methods are described. The calibration was carried out in a 0.35 m3 test radon chamber without aerosol particles by comparing the number of tracks registered on the film detector with the nanometer 218Po particle concentrations measured in parallel with a classical single screen-filter method. A calibration factor of 0.107 tracks cm-2 h-1 was established. The size distribution of these nanometer radioactive particles in the range of 0.5–5 nm was reconstructed from the track density recorded on the detector film with non-linear inversion techniques.
Experimental studies of nasal passage deposition were performed in three adult human subjects with ultrafine 218Po aerosols to determine the inspiratory deposition efficiency of such aerosols. Constant flow rates in the range 5.9–17.51 min−1 were employed with aerosols whose diameters ranged from 0.53 to 0.62 nm. The deposition efficiency was found to range from 93.7 to 98.7%, showing a weak dependence on flow rate. These results are compared to previously published nasal deposition measurements in replicate nasal airway casts and in human subjects and found to be in good agreement. It is concluded that the nasal passage is a highly efficient collector for unattached radon progeny aerosols whose particle diameter is of the order 1 nm, and that measurements in replicate nasal models accurately predict overall deposition at this size. These in vivo experiments extend the range of measured deposition of ultrafine aerosols to < 1 nm.
Determining the diffusion coefficient of 218Po is an important application of the two-filter method (Thomas and LeClare, 1970, Hlth Phys.18, 113). Air containing a known concentration of 222Rn is drawn through a cylindrical tube with filters at both ends. The 218Po activity on the downstream filter relative to the 222Rn concentration in air is interpreted to determine the diffusivity of 218Po. Previously, the interpretation scheme was based on a theoretical analysis of 218Po transport and production in a tube by Tan (1969, Int. J. Heat Mass Trans.12, 471), and Tan and Hsu (1970, Int. J. Heat Mass Trans.13, 1887). Their analysis did not account for radioactive decay of airborne 218Po within the apparatus nor for the perturbation of the fluid flow caused by the flow resistance of the downstream filter. Also, simplified analytical air flow profiles were assumed in that analysis. In this paper, the two-filter method is re-analyzed numerically, by solving the continuity equation, the Navier-Stokes equations and the species conservation equation for a tube. Full account is taken of the effects of radioactive decay of 218Po, and the flow resistance of the downstream filter. The results of the new analysis lead to a downward correction of reported diffusivities of 218Po by about 10–20%.
Condensation in the continuum regime is investigated. The effects of the Stephan flow and the thermal diffusion on the mass flux have been considered. The correction factor, which takes into account the temperature dependence of the diffusion coefficient, is derived. Four different temperature profiles have been compared with each other to evaluate the temperature at the droplet surface. Also the Dufour effect has been studied. The importance of different effects has been studied numerically. They are significant if the vapour mole fraction is high enough and the temperature difference between droplet surface and medium is large (some tens of Kelvins) or if the absolute value of the thermal diffusion factor is over 0.1.
The deposition velocities of 222Rn (radon) and 220Rn (thoron) progeny species have been measured in a chamber, in a test house, and in dwellings by relating the atom deposition fluxes of these species to their atom concentrations in air. These measurements were carried out using absorber-mounted nuclear track detectors (LR-115) which selectively register the tracks due to alpha emissions from 212Po and 214Po from the deposited atoms of 220Rn and 222Rn progeny species, respectively. These are termed as DRPS (direct radon progeny sensor) and DTPS (direct thoron progeny sensor). Measurement of parameters such as ventilation rate, particle size distribution and unattached fractions were also carried out along with deposition velocity. The experimental data on deposition velocity in test house and chamber were compared with the predictions based on the indoor progeny dynamics model and particle deposition models. These showed excellent agreement with experimental values although the data on radon progeny showed slightly higher dispersion. The progeny deposition velocities were also measured in living rooms of dwellings in Mumbai and were found to be close to the model results which in turn imply that in the long term, the average environmental conditions are similar to that in the test house. These results point at a plausible constancy of long time averaged indoor deposition velocities. From these studies, we are inclined to assign summary values of deposition velocities of 0.075 m h−1 for 220Rn progeny and 0.132 m h−1 for 222Rn progeny, for indoor conditions.
Airborne fungi were collected using the N6 Andersen sampler at 1-month intervals for I yr inside and outside of six apartments in Taipei. It was shown that seasonal variations of indoor and outdoor fungus number concentrations were remarkable and indoor and outdoor air spore counts varied considerably from residence to residence. The geometric mean concentrations of indoor and outdoor fungi were found to be higher than 1000 CFU m−3 during the summer months and abruptly decreased to below 100 CFU m−3 in the winter. A high correlation coefficient was found between fungus concentrations in living rooms and outdoors. Moreover, the ratios of indoor to outdoor fungus concentrations (0.21–3.81) were too low to indicate the presence of any indoor fungus sources. A large variety of mold genera was isolated, and Aspergillus, Penicillium, Cladosporium, and yeast were observed to be predominant. Indoors, Penicillium showed the highest concentrations in the summer and autumn months, while Asperyillus and Cladosporium were also observed frequently. The outside air was dominated by Asperyillus, Penicillium, and Cladosporium in spring, summer, and autumn, but by Penicillium and yeast during winter months. In addition, Cladosporium was found to be absent indoors and outdoors in the winter.
The diffusion coefficient of WOx, Pt, and NaCl particles in the diameter range from 3 to 84 nm, determined from the penetration through a set of wire screens in the temperature range 295–600 K were recalculated with account for polydispersity of the used particles. Neglecting of polydispersity in Rudyak, Dubtsov, and Baklanov (2009) resulted in overestimation in the reported diffusion coefficient values by 10–15%. This difference, however, does not depend on the temperature in the range 300–600 K. However this decrease does not exceed the experimental error and, most importantly, the exponent of the T dependence remains almost unchanged.
A mole fraction-based multicomponent thermodynamic model, previously applied to the system H2OH2SO4, is here extended to mixtures with (NH4)2SO4 at 298.15 K. Model parameters are determined by fitting to vapour pressure data (from isopiestic and electrodynamic balance studies), together with degrees of dissociation of the bisulphate ion and salt solubilities (solid phases (NH4)2SO4, (NH4)3H(SO4)2 and NH4HSO4). The model successfully represents the thermodynamic properties of the system to high supersaturation over the full range of composition from (NH4)2SO4H2O to H2SO4H2O. Equilibrium vapour pressures of NH3 have been calculated for mixtures of various compositions.
Top-cited authors
Markku Kulmala
  • University of Helsinki
Veli-Matti Kerminen
  • University of Helsinki
William C Hinds
  • University of California, Los Angeles
Heinz Johannes Fissan
  • Institute of Energy and Environmental Technology e.V. (IUTA)
Urs Baltensperger
  • Paul Scherrer Institut