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Solving aerosol dynamic models accurately to obtain the size distribution function is often computationally expensive. Conventional artificial neural network (ANN) models offer an alternative procedure to solve the aerosol dynamic equations. However, conventional ANN models can result in violation of aerosol mass conservation. To further enhance accuracy and reduce computational time, a hybrid ANN approach to solve the aerosol coagulation equation is developed, validated, and demonstrated. The methodology and assumptions for the development of the hybrid ANN model which provides an analytical closed form solution for aerosol coagulation is described. The ANN model is trained and validated using a dataset from an accurate sectional model. Following this, the hybrid ANN aerosol model is used to describe the evolution of aerosol in a furnace aerosol reactor. The hybrid ANN model results are compared to the accurate sectional and moment coagulation models. The hybrid ANN coagulation model prediction was found to accurately describe the evolution of the size distribution at a computational cost which is slightly more than the moment model but orders of magnitude less than the sectional model. Copyright © 2023 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Air quality is a global challenge issue, and many regions of the world, such as India, are experiencing daunting challenges. An important aspect is to identify and then control the emissions from major contributing sources. To advance this aspect, this paper describes an air quality network that has been set up in the National Capital Territory of Delhi (NCT-Delhi) to identify major contributing source categories in real-time. The various components include an innovative cloud-based dashboard to compile the data in real-time from a series of PM instruments (Beta Attenuation Monitors (BAM)) and a low-cost sensor network (22 APT- MAXIMA sensors). Furthermore, at one of the locations (urban site), three real-time chemical speciation monitors are installed to provide elemental speciation (30 elements), elemental carbon (EC), and organic carbon (OC) data. PM2.5 concentrations at different sites (urban, industrial, and background) were compared to the BAM measurements over an 8-month period from May 2019 to February 2020; spanning the summer, monsoon, autumn, and winter seasons in Delhi. The APT sensor measurements were well correlated to the BAM measurements, with R2 values ranging between 0.84 and 0.95 for all sites. This validated that the APT-MAXIMA low-cost sensors can be a useful tool for distributed monitoring of PM2.5 levels. The mean PM2.5 concentrations showed a trend with winter (Dec, Jan, Feb: 205.2 ± 95.1 µg m−3) and autumn (Oct, Nov: 171.7 ± 128.3 µg m−3) highs and summer (May, Jun: 64.6 ± 57.2 µg m−3) and monsoon (Jul, Aug, Sep: 27.6 ± 16.7 µg m−3) lows. The bivariate polar plot reveals high PM2.5 levels originated from local/regional combustion sources located east and south-west of the urban site, especially when high PM2.5 episodes are encountered during the festival season and other smog episodes. Implications: Low-cost sensors are useful for distributed monitoring under both low and high pollution conditions. A cloud-based dashboard system provided real-time, remote access to the data and in the visualization of air quality in the entire region. The real-time data availability on the cloud enabled establishing hot-spot regions of air pollution, spatial variation of PM2.5, real-time source apportionment, and health risk estimates to benefit both policy makers, and the general public. [ABSTRACT FROM AUTHOR]

While condensation particle counters (CPCs) are routinely used to measure particle number concentrations in the size range from 3 to 1000 nm, the detection efficiency for sub-3 nm particles remains relatively poor. In this study, the performance of an ultrafine butanol based CPC for the measurement of alkyl ammonium halide ions, flame-generated particles of titanium dioxide (TiO2) and soot is evaluated. Homogenous nucleation of butanol vapors, and detection efficiency of THAB ions are systematically evaluated for a range of saturator temperatures (39–45 °C) and capillary flow rates (30–70 sccm). The optimal operating conditions with minimal background interferences was found to be a saturator temperature of 45 °C and capillary flow rate of 70 sccm. Flame generated particles of TiO2 and soot were activated more readily than the alkyl ammonium halide salts of similar mobility diameters, especially in the below 1.6 nm mobility size range, whereas above 1.6 nm the detection efficiency is independent of particle material, but depends on particle size. The negative charge on the particles is found to promote activation with butanol vapors leading to higher activation efficiencies than positively charged particles. Finally, the importance of butanol as a working fluid, and its calibration for precise measurement of sub-3 nm particles is discussed. This will enable researchers to perform experiments using a 'conventional' CPC with boosted conditions for the understanding of early stages of particle formation and growth in different aerosol reactors. Copyright © 2021 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

© 2020 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

An open source software (Aerosol and Air Quality Research Lab-Aerosol Dynamics Model, AAQRL-ADM) used for aerosol dynamics simulations is developed by including four models: discrete, discrete-sectional, method of moments, and modal. First, the mathematical description of these models as well as the effects of aerosol dynamics available in the software are reviewed, and a modal model is developed to use multiple modes to represent particle size spectrum. Second, the design of a working principle and user graphical interface (GUI) of AAQRL-ADM is described. Third, the models in AAQRL-ADM are validated by investigating the evolution of particle size distribution (PSD) in considering the effects of coagulation, condensation, and nucleation. Next, the trade-off between simulation accuracy and numerical efficiency is discussed for all of the four models, and a guide to choosing the appropriate aerosol dynamic model in practical simulation is presented. Finally, discrete-sectional, moment, and modal models are used to investigate the particle size distribution in a furnace aerosol reactor along a streamline, coupled with the velocity and temperature profiles. AAQRL-ADM is provided free of charge for the use of public researchers. Copyright © 2020 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

This work introduces WUDESIM, an open-source C/C++ toolkit for modeling water quality in the dead-end branches of drinking water distribution networks. WUDESIM is linked to the programmers' toolkit of EPANET, a widely-used public-domain water network analysis model. In place of the advection-based water quality module in EPANET, WUDESIM allows the users to simulate water quality in the pipes of dead-end branches with dispersion as a constituent transport mechanism. In addition, WUDESIM corrects for the simulation errors that arise from the spatial aggregation of water demands due to network skeletonization, and enables the users to use stochastically-generated water demands at fine time-scales. The software comprises two components: a Windows® executable file and a C/C++ dynamic link library (DLL) toolkit. Examples of how the users can employ the different toolkit functions to run water quality analysis and obtain simulation results are provided. WUDESIM is available as a public-domain software. [ABSTRACT FROM AUTHOR]

The partitioning of semi-volatile organic compounds (SVOCs) between the gas and particle phase plays an important role in understanding the formation of secondary organic aerosols (SOAs) in the atmosphere. There are uncertainties and problems associated with measurements during the simultaneous sampling of both gas and particle phases. In recent studies, diffusion denuders have been used for separate sampling of gas and particle phases of organic compounds. The removal of the gaseous species in the denuder distorts the gas-particle equilibrium and leads to the dissociation of the particulate phase during the sampling. This phenomenon is particularly true for volatile organic species and leads to significant error in determining gas-to-particle phase partitioning of organic aerosols due to underestimation of the particle phase. In this study, a model for simultaneous gas diffusion and aerosol decomposition/evaporation in the parallel plate denuder was developed to investigate the effects of sampling artifacts on gas-particle partitioning measurements of SVOCs. The model equations were cast into dimensionless form for generalization, and the effects of governing dimensionless groups on the denuder sampling artifacts were evaluated by performing a sensitivity analysis. Also, regression correlations for denuder sampling artifacts as the function of governing dimensionless groups were obtained. It was observed that the sampling of SVOCs could result in substantial particulate phase loss due to evaporation in the denuder, resulting in significant errors in the phase partitioning measurements. Also, the operating conditions for the denuder, so that the denuder sampling artifacts lie within tolerable limits, were evaluated. Copyright © 2018 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

While there are several computational studies on differential mobility analyzers (DMA), there is none for high flow DMA to classify nanoparticles less than 3 nm. A specific design of a high flow DMA, a half mini DMA, is investigated to predict its performance through numerical modeling in the incompressible flow regime. The governing equations for flow field, electric field and aerosol transport are solved using COMSOL 5.3. The transfer function of the half mini DMA is compared with that of a nano DMA (TSI 3085). The results show that both the height of the transfer function and resolution (R) of the half mini DMA are much better than those of nano DMA in sub-2 nm particle size range. Finally, the transfer function of half mini DMA is evaluated for different values of aerosol flow rate to the sheath flow rate (q/Q). Comparison of the simulated transfer function with existing models from Knutson-Whitby and Stolzenburg is also elucidated. It is found that the former model overestimates the resolution; whereas the latter is close to the simulation results for q/Q above 0.067. This work provides a useful method to study the flow regimes and transfer function of a high flow DMA. Copyright © 2018 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The concentrations of fine particles and selected gas pollutants in the flue gas entering the stack were measured under several common operation modes in an operating coal power plant producing electricity. Particle size distributions in a diameter range from 10 nm to 20 μm were measured by a scanning mobility particle sizer (SMPS), and the flue gas temperature and concentrations of CO2 and SO2 were monitored by a continuous emission monitoring system (CEMS). During the test campaign, five plant operating modes were studied: soot blowing, bypass of flue-gas desulfurization (FGD), reheat burner operating at 0% (turned off), 27%, and 42% (normal condition) of its full capacity. For wet and dry aerosols, the measured mode sizes were both around 40 nm, but remarkable differences were observed in the number concentrations (#/cm3, count per square centimeter). A prototype photoionizer enhanced electrostatic precipitator (ESP) showed improved removal efficiency of wet particles at voltages above +11.0 kV. Soot blowing and FGD bypass both increased the total particle number concentration in the flue gas. The temperature was slightly increased by the FGD bypass mode and varied significantly as the rating of reheat burner changed. The variations of CO2 and SO2 emissions showed correlations with the trend of total particle number concentration possibly due to the transitions between gas and particle phases. The results are useful in developing coal-fired power plant operation strategies to control fine particle emissions and developing amine-based CO2 capture technologies without operating and environmental concerns associated with volatile amine emissions. Implications: The measurement of the fine particle size distributions in the exhaust gas under several common operating conditions of a coal-fired power plant revealed different response relations between aerosol number concentration and the operating condition. A photo-ionizer enhanced ESP was demonstrated to capture fine particles with higher efficiency compared to conventional ESPs, and the removal efficiency increased with the applied voltage. The characteristic information of aerosols and main gaseous pollutants in the exhaust gas is extremely important for developing and deploying CO2 scrubbers, whose amine emissions and operating effectiveness depends greatly on the upstream concentrations of fine particles, SO2, from the power plant. [ABSTRACT FROM AUTHOR]

Particle emissions from consumer-fused deposition modeling 3D printers have been reported previously; however, the complex processes leading to observed aerosols have not been investigated. We measured particle concentrations and size distributions between 7 nm and 25 μm emitted from a 3D printer under different conditions in an emission test chamber. The experimental data was combined with a moment lognormal aerosol dynamic model to better understand particle formation and subsequent evolution mechanisms. The model was based on particles being formed from nucleation of unknown semivolatile compounds emitted from the heated filament during printing, which evolve due to condensation of emitted vapors and coagulation, all within a small volume near the printer extruder nozzle. The model captured observed steady state particle number size distribution parameters (total number, geometric mean diameter and geometric standard deviation) with errors nominally within 20%. Model solutions provided a range of vapor generation rates, saturation vapor pressures and vapor condensation factors consistent with measured steady state particle concentrations and size distributions. Vapor generation rate was a crucial factor that was linked to printer extruder temperature and largely accounted for differences between filament material and brands. For the unknown condensing vapor species, saturation vapor pressures were in the range of 10−3 to 10−1 Pa. The model suggests particles could be removed by design of collection surfaces near the extruder tip. Copyright © 2018 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The ability to properly scale the synthesis of advanced materials through combustion synthesis routes is limited by our lack of knowledge regarding the initial stages of particle formation. In flame aerosol reactors, the high temperatures, fast reaction rates, and flame chemistry can all play a critical role in determining the properties of the resulting nanomaterials. In particular, multicomponent systems pose a unique challenge as most studies rely on empirical approaches toward designing advanced composite materials. The lack of predictive capabilities can be attributed to a lack of data on particle inception and growth below 2 nm. Measurements for the initial stages of particle formation during the combustion synthesis of SiO2and composite SiO2/TiO2using an atmospheric pressure inlet time-of-flight mass spectrometer are presented. Both positively and negatively charged clusters can be measured and results show the presence of silicic acid species which grow through dehydration, hydrogen abstraction, and interactions with hydroxyl radicals. In the case of composite SiO2/TiO2particle formation, new molecular species containing Ti atoms emerge. Tandem differential mobility analysis-mass spectrometry (DMA-MS) provided further insight into the size-resolved chemistry of particle formation to reveal that at each cluster size, further hydroxyl-driven reactions take place. From this we can conclude that previous assumptions on collisional growth from simple monomer species of SiO2and TiO2do not sufficiently describe the collisional growth mechanisms for particle growth below 2 nm. Copyright © 2018 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

Few studies reported the formation of Ti-containing clusters in the initial stages of TiO2flame synthesis. The conversion from synthesis precursor to TiO2monomers was commonly assumed to take place through global reaction such as thermal decomposition and/or hydrolysis at high temperatures. More recent studies have been able to identify stable intermediates of Ti-containing monomers, most commonly Ti(OH)4, as the final step before the formation of TiO2. However, no larger Ti-containing cluster formation mechanisms or interactions between these monomers have been tracked. To investigate cluster formation pathways of TiO2during flame synthesis, Charged clusters were measured in an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer. TiO2nanoparticles were synthesized by adding titanium tetraisopropoxide (TTIP) precursor to a premixed CH4/O2/N2flat flame aerosol reactor. Pure TiO2clusters were not detected by the APi-TOF. Results from measured mass spectra and mass defect plots show that for positively charged clusters, the abstraction of CH2groups occurs simultaneously with the clustering of larger intermediate organometallic species. For negatively charged clusters, NOxformation pathways in the flame may play a role during the initial stages of TiO2formation, since a lot of Ti-containing clusters were attached with nitrate-related species. These research findings provide insights on quantum dot synthesis and molecular doping where rapid dilution of the flame synthesized nanoparticles is needed to better control the particle size and chemical composition. The possible influences of and potential artifacts brought by the dilution system on observing the incipient particle formation in flames were also discussed. © 2017 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Flames generate a large amount of chemically and thermally ionized species, which are involved in the growth dynamics of particles formed in flames. However, existing models predicting particle formation and growth do not consider particle charging, which may lead to bias in the calculated size distribution of particles. In this study, Fuchs' charging theory was coupled with a monodisperse particle growth model to study the simultaneous charging and coagulation of nanoparticles during combustion. In order to quantify the charging characteristics of nanoparticles, a high-resolution DMA was used to measure the mobilities of ions generated from a premixed flat flame operated at various conditions. The effect of temperature on ion–particle and particle–particle combination coefficients was further examined. The proposed model showed that the influence of charging on particle growth dynamics was more prominent when the ion concentration was comparable to or higher than the particle concentrations, a condition that may be encountered in flame synthesis and solid fuel-burning. Simulated results also showed that unipolar ion environments strongly suppressed the coagulation of particles. In the end, a simplified analysis of the relative importance of particle charging and coagulation was proposed by comparing the characteristic time scales of these two mechanisms. © 2017 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Composite nanoparticles find application in catalysis, drug delivery, and energy storage and require increasingly fine control of their physical properties and composition. While composite nanoparticles have been widely synthesized and characterized, little work has systematically correlated the initial concentration of precursors and the final composition of flame synthesized composite nanoparticles. This relationship is explored in a diffusion flame aerosol reactor by coupling a scanning mobility particle sizer (SMPS) with an inductively coupled plasma optical emission spectrometer (ICP-OES). A framework for studying the relationship between the initial precursor concentrations of different elements and the final nanoparticle composition is explored. The size-resolved elemental composition was measured by directly injecting size-selected fractions of aggregated magnetite and silicon dioxide composite nanoparticles into the ICP-OES plasma. This work showed a correlation between precursor molar ratio and the measured elemental ratio in the mobility size range of 50 to 140 nm. Building on previous work studying size resolved elemental composition of engineered nanoparticles, the analysis is extended to flame synthesized composite nanoparticle aggregates in this work. Copyright © 2017 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

This study investigated the influence of gas pressure on the submicrometer particle capture performance of an electrostatic precipitator (ESP). Current-voltage characteristics and particle capture performance of the ESP were studied in air and in simulated flue gas (SFG) under 1, 2, and 3 atm. Using negative corona and air as the feed gas, the penetration of most particles of 40–400 nm in diameter decreased from 8 × 10−4− 2 × 10−2to 2 × 10−4− 1 × 10−2as pressure increased from 1 atm to 3 atm at constant current; and increased from 3 × 10−5− 1 × 10−3to 2 × 10−4− 1 × 10−2as pressure was elevated when the voltage was held roughly constant. Similar type of disparity under different pressures was also observed for positive corona and for SFG. Experiments set up to capture fly ash in the ESP showed that with constant current, higher pressure resulted in a higher initial charge fraction of the particles from the furnace, which could facilitate the penetration of fly ash particles. A semiempirical model was developed based on the Deutsch–Anderson equation and experimental data under 1, 2, and 3 atm to calculate the particle penetrations under high pressure. The total charge number on a particle (n') is calculated by incorporating the effects of current (I) and pressure (P) on relative weights of the diffusion charging number (ndiff) and field charging number (nfield), that is,n' = B1(I,P)ndiff+B2(I,P)nfield, whereB1(I,P) andB2(I,P) are both empirical coefficients dependent on current and pressure. Experimental penetrations under 1.5 and 2.5 atm validated this model over the particle diameter range in 100–400 nm. Copyright © 2016 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Aerosol gels are a novel class of materials with potential to serve in various energy and environmental applications. In this work, we demonstrate the synthesis of titanium dioxide (TiO2) aerosol gels using a methane-oxygen coflow diffusion flame reactor operated in down-fired configuration (fuel flow in the direction opposite to buoyancy forces). Titanium tetraisopropoxide was fed as a precursor to the flame under different operating conditions. Control of the monomer size and crystalline phase of TiO2gel particles was achieved by adjusting the flame operating conditions, specifically the flame temperature, which was shown to significantly influence the phase transformation and rate of particle growth and sintering. The resulting materials were characterized for their physical and optical properties. Results showed that the TiO2aerosol gels had effective densities in the range 0.021–0.025 g/cm3, which is 2 orders of magnitude less than the theoretical mass density of TiO2. The monomer size distribution, crystalline phase, and UV-Vis absorbance spectra of the gels showed distinct characteristics as a function of flame temperature. Copyright © 2015 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Particle sensors offer significant advantages of compact size and low cost, and have recently drawn great attention for usage as portable monitors measuring particulate matter mass concentrations. However, most sensor systems have not been thoroughly evaluated with standardized calibration protocols, and their data quality is not well documented. In this work, three low-cost particle sensors based on light scattering (Shinyei PPD42NS, Samyoung DSM501A, and Sharp GP2Y1010AU0F) were evaluated by calibration methods adapted from the US EPA 2013 Air Sensor Workshop recommendations. With a SidePak (TSI Inc., St. Paul, MN, USA), a scanning mobility particle sizer (TSI Inc.), and an AirAssure™ PM2.5Indoor Air Quality Monitor (TSI Inc.), which itself relies on a GP2Y1010AU0F sensor as reference instruments, six performance aspects were examined: linearity of response, precision of measurement, limit of detection, dependence on particle composition, dependence on particle size, and relative humidity and temperature influences. This work found that: (a) all three sensors demonstrated high linearity against SidePak measured concentrations, withR2values higher than 0.8914 in the particle concentration range of 0–1000 μg/m3, and the linearity depended on the studied range of particle concentrations; (b) the standard deviations of the sensors varied from 15 to 90 μg/m3for a concentration range of 0–1000 μg/m3; (c) the outputs of all three sensors depended highly on particle composition and size, resulting in as high as 10 times difference in the sensor outputs; and (d) humidity affected the sensor response. This article provides further recommendations for applications of the three tested sensors. Copyright 2015 American Association for Aerosol Research [ABSTRACT FROM PUBLISHER]

Aerosol emissions from toy cars with electric motors were characterized. Particle emission rates from the toy cars, as high as 7.47 × 107particles/s, were measured. This emission rate is lower than other indoor sources such as smoking and cooking. The particles emitted from toy cars are generated from spark discharges inside the electric motors that power the toy cars. Size distribution measurements indicated that most particles were below 100 nm in diameter. Copper was the dominant inorganic species in these particles. By deploying aerosol mass spectrometers, high concentrations of particulate organic matter were also detected and characterized in detail. Several organic compounds were identified using a thermal desorption aerosol gas chromatography. The mass size distribution of particulate organic matter was bimodal. The formation mechanism of particulate organic matter from toy cars was elucidated. Implications: A possible new source of indoor air pollution, particles from electric motors in toy cars, was identified. This study characterized aerosol emissions from toy cars in detail. Most of these particles have a diameter less than 100 nm. Copper and some organics are the major components of these particles. Conditions that minimize these emissions were determined. [ABSTRACT FROM PUBLISHER]

Corona discharge based techniques are promising approaches for oxidizing elemental mercury (Hg0) in flue gas from coal combustion. In this study, in-situ soft X-rays were coupled to a DC (direct current) corona-based electrostatic precipitator (ESP). The soft X-rays significantly enhanced Hg0oxidation, due to generation of electrons from photoionization of gas molecules and the ESP electrodes. This coupling technique worked better in the positive corona discharge mode because more electrons were in the high energy region near the electrode. Detailed mechanisms of Hg0oxidation are proposed and discussed based on ozone generation measurements and Hg0oxidation behavior observations in single gas environments (O2, N2, and CO2). The effect of O2concentration in flue gas, as well as the effects of particles (SiO2, TiO2, and KI) was also evaluated. In addition, the performance of a soft X-rays coupled ESP in Hg0oxidations was investigated in a lab-scale coal combustion system. With the ESP voltage at +10 kV, soft X-ray enhancement, and KI addition, mercury oxidation was maximized. Implications: Mercury is a significant-impact atmospheric pollutant due to its toxicity. Coal-fired power plants are the primary emission sources of anthropogenic releases of mercury; hence, mercury emission control from coal-fired power plant is important. This study provides an alternative mercury control technology for coal-fired power plants. The proposed electrostatic precipitator with in situ soft X-rays has high efficiency on elemental mercury conversion. Effects of flue gas conditions (gas compositions, particles, etc.) on performance of this technology were also evaluated, which provided guidance on the application of the technology for coal-fired power plant mercury control. [ABSTRACT FROM PUBLISHER]

Surface area in addition to mass concentration is increasingly being emphasized as an important metric representing potential adverse health effects from exposure to inhaled particles. Lung-deposited surface area (SA) concentrations for a variety of aerosols: coal, biomass, cigarette, incense, candle, and TiO2 were measured using an AeroTrak 9000 (TSI Incorporated) and compared with those calculated from number size distributions from a scanning mobility particle sizer (SMPS). Three methodologies to compute the SA concentrations using the International Commission on Radiological Protection's (ICRP) Lung Deposition model and an SMPS were compared. The first method calculated the SA from SMPS size distributions, while the second method used lognormal size distribution functions. A third method generated a closed-form equation using the method of moments. All calculated SMPS SA data against which the measured SA data were compared were gen-erated using the first method only; however, the SA concentrations calculated from each of the three methods demonstrated strong correlations with each other. Overall, results between measured and calculated lung-deposited SA indicated strong positive linear associations (R² 0.78 - >0.99), moderately dependent on the type of aerosol. In all cases, the measured SA concentrations slightly underestimated those calculated from the SMPS data, with the ex-ception of coal combustion particles. Although some dependency on aerosol material exists, the instrument measuring lung-deposited SA demonstrated consistent reliability across a range of concentra-tions for a range of materials. For optimal results however, applying a correction factor (CF) before taking the instrument to the field is recommended. [ABSTRACT FROM AUTHOR]

Nano-structured sorbent injection is a promising technique for heavy metal capture in combustion systems. The importance of sorbent injection strategies, including the form of the sorbent and its injection location for metal capture and removal is investigated in this study. A multi-component tri-modal aerosol dynamic model was employed to understand the evolution of heavy metals and sorbents, as well as their interactions in the incineration system. Experiments were conducted to assess the performance of in-situ generated SiO2, compared with bulk Ti-PICL sorbent, in capturing lead and cadmium from a demilitarization incineration system. Nano-structured SiO2 generated in-situ was found to be more efficient than the bulk Ti-PICL sorbent because it offers a higher external surface area for condensation. The sorbent injection location is important as it affects the physical properties of the sorbent and the pathway for heavy metal capture. Extensive sintering and reduction in the surface area were observed when sorbent was injected into high temperature flue gas, i.e., directly into the combustor. However, when injected into much lower temperature flue gas, the pathway for heavy metal capture was altered from condensation to inter-particle coagulation due to the nucleation of heavy metal species. This study further revealed that new emission standards can be readily met with an optimal sorbent injection strategy. [ABSTRACT FROM AUTHOR]

Engineered nanoparticles (NP) are being developed and incorporated in a number of commercial products, raising the potential of human exposure during manufacture, use, and disposal. Although data concerning the potential toxicity of some NP have been reported, validated simple assays are lacking for predicting their in vivo toxicity. The aim of this study was to evaluate new response metrics based on chemical and biological activity of NP for screening assays that can be used to predict NP toxicity in vivo. Two cell-free and two cell-based assays were evaluated for their power in predicting in vivo toxicity of eight distinct particle types with widely differing physicochemical characteristics. The cell-free systems comprised fluorescence- and electron spin resonance-based assays of oxidant activity. The cell-based systems also used electron spin resonance (ESR) as well as luciferase reporter activity to rank the different particle types in comparison to benchmark particles of low and high activity. In vivo experiments evaluated acute pulmonary inflammatory responses in rats. Endpoints in all assays were related to oxidative stress and responses were expressed per unit NP surface area to compare the results of different assays. Results indicated that NP are capable of producing reactive species, which in biological systems lead to oxidative stress. Copper NP had the greatest activity in all assays, while TiO2 and gold NP generally were the least reactive. Differences in the ranking of NP activity among the assays were found when comparisons were based on measured responses. However, expressing the chemical (cell-free) and biological (cells; in vivo) activity per unit particle surface area showed that all in vitro assays correlated significantly with in vivo results, with the cellular assays correlating the best. Data from this study indicate that it is possible to predict acute in vivo inflammatory potential of NP with cell-free and cellular assays by using NP surface area-based dose and response metrics, but that a cellular component is required to achieve a higher degree of predictive power. [ABSTRACT FROM AUTHOR]

Aerosolization of bacteriophage MS2 virions by nebulization and charge-reduced electrospray were compared during testing of three filter media. Sample swatches were taken from a surgical mask, N95 filtering-facepiece respirator (FFR), and N100 FFR for use in repeated, short-duration (15 min) penetration tests with bacteriophage MS2 aerosolized by nebulizer and electrospray. Evaluated were (1) the virus suspension preparation protocol, (2) resulting particle size distribution, count stability, and count variability, and (3) the ability to generate culturable MS2 virions. While preparation of the electrospray bacteriophage suspension required additional purification and concentration steps and took more time than the nebulization protocol, it resulted in a much higher titer suspension. The nebulizer produced a polydisperse aerosol; conversely, the electrospray produced a relatively monodisperse aerosol with a count peak at the mobility size of the single virion. The nebulized aerosol particle count was 2.8 times as variable as the electrosprayed aerosol particle count althoughneither aerosolization method maintained a constant count over repeated 15-minute filter tests. No differences in filter penetration were observed between nebulized and electrosprayed MS2 aerosol particles. Electrosprayed dextrose particles, used as an inert aerosol particle comparator, exhibited higher penetration than MS2 particles in two of the three filter samples, which can be attributed, atleast partially, to the difference in dielectric properties of dextrose and virus particles. Both aerosolization methods generated culturable MS2 virions with the electrospray producing an airborne concentration approximately 20-fold higher than the nebulizer. In general, the electrospray produced cleaner, more stable, and more viable bacteriophage aerosol particles compared to conventionalnebulization. The findings of this study are expected to assist researchers in selecting appropriate generation methods when using viable virus-based challenge aerosol particles. [ABSTRACT FROM AUTHOR]

A method to investigate the dependence of the physicochemical properties of nanoparticles (e.g., size, surface area and crystal phase) on their oxidant generating capacity is proposed and demonstrated for TiO2 nanoparticles. Gas phase synthesis methods that allow for strict control of size and crystal phase were used to prepare TiO2 nanoparticles. The reactive oxygen species (ROS) generating capacity of these particles was then measured. The size dependent ROS activity was established using TiO2 nanoparticles of nine different sizes (4-195 nm) but the same crystal phase. For a fixed total surface area, an S-shaped curve for ROS generation per unit surface area was observed as a function of particle size. The highest ROS activity per unit area was observed for 30 nm particles, and observed to be constant above 30 nm. There was a decrease in activity per unit area as size decreased from 30-10 nm; and again constant for particles smaller than 10 nm. The correlation between crystal phase and oxidant capacity was established using TiO2 nanoparticles of 11 different crystal phase combinations but similar size. The ability of different crystal phases of TiO2 nanoparticles to generate ROS was highest for amorphous, followed by anatase, and then anatase/rutile mixtures, and lowest for rutile samples. Based on evaluation of the entire dataset, important dose metrics for ROS generation are established. The implications of these ROS studies on biological and toxicological studies using nanomaterials are discussed. [ABSTRACT FROM AUTHOR]

Film deposition by electrohydrodynamic atomization of nanoparticle sols was studied experimentally using zinc oxide nanoparticles in ethanol and using sequential Monte Carlo simulations, in which proper statistics and particle transport to the substrate were accounted for. Experimentally produced and simulated films were in good agreement, and simulations were used to determine the influences of deposition time, nanoparticle concentration in the sol, mean droplet size, and droplet polydispersity on the film thickness, porosity, surface roughness, and lateral feature size. Film growth rates were non-constant due to decreases in the film porosity early in the deposition process. Over time, the thickness of films increased, while the porosity decreased. After sufficient deposition time, the porosity reached a constant value and consequently the film growth rate was constant. The use of high concentration sols or large droplets resulted in the deposition of agglomerated particles, which gave rise to thicker, more porous films. Control over film morphology using droplets from size distributions with geometric standard deviations greater than 2.0 was not possible and the film thickness and air to particle volume ratio for all films produced from polydisperse droplets were convergent regardless of the number concentration of nanoparticles in the sol. Film surface roughnesses were less than the volume equivalent diameter of the agglomerated particles deposited, indicating that films were relatively uniform in thickness. Radial distribution functions were calculated for both experimentally deposited and simulated films and were used to determine lateral feature sizes. Lateral feature sizes increased with increasing deposition time and deposited agglomerate size until the deposition surface was completely covered. This work provides the necessary link between electrohydrodynamic atomization parameters and the resulting morphology of deposited films. [ABSTRACT FROM AUTHOR]

Sintering rates of pristine and V-doped TiO 2 were obtained using a tandem DMA system. A range of experiments were conducted to first map out the variation of mobility size of a monodisperse (by mobility) agglomerate with time at three fixed temperatures. Using relationships of the surface area to the mobility size, the sintering equation was solved to determine the activation energy and pre-exponential factor. The value of the activation energy was 236 (± 46) kJ/mol for pristine TiO 2 and 363 (± 1) kJ/mol for V-doped TiO 2 . The corresponding pre-exponential factors were 7.22 × 10 19 and 2.22 × 10 12 s/m 4 K, respectively. These values were then used to predict changes in mobility diameter at different temperatures, and good agreement was obtained with measurements. Possible reasons for faster sintering rates of V-TiO 2 relative to pristine TiO 2 were conjectured. [ABSTRACT FROM AUTHOR]

As part of a larger study undertaken in the Greater Cincinnati area to determine if diesel truck emissions are adjuvant to naturally occurring bioaerosols in the initiation of allergies in children, a more detailed intensive measurement campaign was undertaken to elucidate the characteristics of the ambient aerosol and compare to the regular, integrated measurements being conducted. The mass concentration, total number concentration, size distributions, and morphologies were established at several locations including a residential area far from major traffic (Mernic), a suburban area on both sides of a major highway (I-275, Blue Ash), a site in the city center very close to the highway (I-75, Findlay), and an enclosed oval track at a Truck Driving School.Differences between real-time tapered element oscillating microbalance (TEOM) average mass concentrations and integrated Harvard impactor (HI) measurements were observed, with the magnitude of the difference being dependent on location and the organic compounds (OC) concentrations in the sample. Qualitative variation of the peaks in real-time PM 2.5 concentrations were observed with variation in truck traffic at the Findlay site; and no peaks in real-time PM 2.5 levels were observed at Mernic. Minimal variation in PM 2.5 was observed with distance from the highway at the Blue Ash site (fewer trucks). The site at Mernic had a smaller fraction of aggregated particles in comparison to the other sites. The two-dimensional fractal dimensions measured at the Findlay, Blue Ash, and Truck Driving School sites were statistically identical (1.58–1.61) but were higher than that measured at the Mernic site (1.41). Implications of the intensive measurement campaign vis-à-vis the epidemiological study are discussed briefly. [ABSTRACT FROM AUTHOR]

Nanoparticles synthesized in high temperature reactors provide a viable method for depositing nanostructured coatings. The morphology of the deposit is an important factor in many applications and cannot be predicted by continuum models. Computer simulation of nanoparticle deposition is used to relate operational conditions to the resulting morphology. Brownian dynamic simulation of nanoparticle deposition, accounting for the interparticle van der Waals and Coulomb interactions, is carried out. Influence of van der Waals interactions, gas temperature, and thermophoretic and electrophoretic interactions on deposit morphology is investigated. Fractal dimension, packing density, and coordination number and contact angle distribution for the nanoparticle deposits are reported. Results show that by suitably controlling the external electrical field, deposits with fractal dimensions ranging from 2.2 to 2.8 and packing density varying from 2 to 13% can be obtained. [ABSTRACT FROM AUTHOR]

The charge distribution of airborne MS2 bacteriophage nanoparticles and the efficiency of electrical-mobility-based capture mechanisms with bipolar charging were studied. MS2 virions form large agglomerated particles in a suspension. The average charge on airborne MS2 virions can be as high as one unit charge (negatively charged). The application of both soft X-ray irradiation and alpha rays from a Po-210 bipolar charger was shown to not only reduce the average charge on MS2 virion particles but also partially fragment the larger MS2 virion agglomerates, thereby increasing the number of ultrafine MS2 virion particles. A cylindrical electrostatic precipitator with a mounted soft X-ray emitter was used to determine the effectiveness of electrical capture methods for virus particles. At low applied voltages, it was found that the capture efficiency of ultrafine virus particles can be increased by applying in situ soft X-ray irradiation with electrostatic precipitation. It has also been shown that in the presence of both a positive and negative corona, virus particles are readily captured with log removal values exceeding 4. The unit developed and demonstrated in this work is a compact, low-pressure drop system that can be readily mounted in ventilation ducts or air supply systems to remove ultrafine particles such as viruses. [ABSTRACT FROM AUTHOR]

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[sub 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[sub 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 μg 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[sub pg] = 50 nm; 340 μg Ni/m[sup 3]) or 24, 48, or 72 hr of NiSO[sub 4] aerosol (d[sub pg] = 60 nm; 420 μg Ni/m[sup 3]; d[sub pg] = 250 nm; 480 μg Ni/m[sup 3]). Exposure to NiO produced no significant lung injury when either instilled or inhaled, whereas inhaled NiSO[sub 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. [ABSTRACT FROM AUTHOR]

A controlled laboratory scale burner was used to combust kerosene oil doped with varying concentrations of sulfur (organic form) and nickel (as an atomized 0.23 θm nickel nitrate aerosol). The resultant size distribution and speciation of the nickel aerosol was determined as a function of the distance from the burner outlet. In the high temperature region, nickel oxide was the dominant species formed, followed by a conversion to amorphous nickel sulfate at lower temperatures. The presence of sulfur in the fuel resulted in a greater degree of volatilization and formation of a higher concentration of smaller sized nickel species aerosol. Thermogravimetric analyzer tests were also used to establish the first order reaction rate constant for NiO formation. A mechanistic description for the formation of the submicrometer mode is proposed which includes volatilization/nucleation, direct conversion to NiO, and possible breakage. [ABSTRACT FROM AUTHOR]

Presents a laboratory furnace study conducted to aid understanding of the chemical and aerosol behavior of a self-fluxing brazing alloy used in welding operations. Nature of aerosols generated from the process; Thermodynamic equilibrium analysis; Potential formation of severe pulmonary irritants from heating; Importance of fluxing compounds in the formation of brazing fumes.

Editorial. Introduces several articles published in the December 2000 issue of the 'Aerosol Science and Technology' journal. Morphology of combustion aerosols; Plug flow model to simulate formation and growth of alkali metal species in combustor; Nucleation of particles in high alkali content flue gases; Effect of emissions of unvented, portable kerosene heaters in indoor environments.