Aerosol Science

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 SiO 2 , compared with bulk Ti-PICL sorbent, in capturing lead and cadmium from a demilitarization incineration system. Nano-structured SiO 2 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.

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 SiO 2 , compared with bulk Ti-PICL sorbent, in capturing lead and cadmium from a demilitarization incineration system. Nano-structured SiO 2 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.

The personal aeroallergen sampler (PAAS) with a structure resembling a gimbal to enable a particle collection surface continuously directed upward regardless of inclination of the sampler was developed. To evaluate the particle size-dependent collection characteristics by the PAAS, the particle size distributions obtained by the PAAS were compared with those by an existing reference active sampler for sampling durations of 5 h to 6 days. The results showed good correlations between the two methods, suggesting usability of the PAAS for long-term personal monitoring of airborne coarse particles such as aeroallergens. The effective particle deposition velocities experimentally obtained for the personal samplings by the PAAS were 0.17, 0.35, 0.66 and 1.6 cm s -1 for particles with projected area diameters of 10-20, 20-30, 30-50 and 50-100 m, respectively. Unlike existing active samplers, the PAAS is convenient for personal air sampling because of simplicity of handling. It can be easily used for epidemiological studies to investigate relationships between aeroallergen exposures and allergic airway diseases.

A computer-automated optical microscope combined with a line-sensing camera was used to capture the entire range of a particle deposit downstream of an individual acceleration nozzle in a hi-volume Andersen sampler. To investigate the particle bounce and reentrainment, particles collected on collocated greased and non-greased Te on plates on the inlet stage (d a ¿ 7 m) were observed by an automated particle counting, locating and sizing method. The result conÿrmed reproducible collection characteristics among nozzles even though application of the grease increased collection e ciency and altered the size distribution of collected particles to the larger side. In these experiments, assuming spherical particles with uniform density, approximately 65% of particle mass and 50% by number were lost from non-greased plates at 54% RH, while 45% by mass and 25% by number were underestimated at 84% RH. The spatial investigation showed that particles were densely deposited around the center of deposition on greased plates while on non-greased plates they were dispersedly distributed. Particle dispersions on the smooth impaction plate were due to bounce and/or reentrainment of small particles especially with d PA ¡ 10 m.

The time course change in particle penetration through capillary pore membrane ÿlters was investigated for relatively short ÿltration periods. In the laboratory experiments, penetration e ciencies of the 0.3 and 1:0 m standard particles through the 2:0 m capillary ÿlter were continuously monitored. While penetration e ciencies of both 0.3 and 1:0 m particles decreased, 1:0 m particles became selectively captured by the ÿlter. Furthermore, even small amount of collected particles (coverage fractions less than 1% of the ÿlter surface) was found to alter particle penetration characteristics possibly because of the intense accumulations around the rims of capillary pores due to signiÿcance of particle interception. No distinct e ect by addition of clogging particles of 2:0 m diameter was observed, indicating the change in particle penetration characteristics was initiated even when particle clogs became important. The present study showed the size distribution of collected particles by capillary pore membrane ÿlters could be biased with time even for short sampling duration.

A new hybrid analytical/numerical model that describes the formation of structured microparticles from evaporating microdroplets is presented. It is applicable when diffusion and surface recession are the main mechanisms of mass transport in the droplets. The model accounts for the transient nature of the solute concentration profiles during the evaporation process and thereby extends previously published models to particle formation processes in which the droplet surface recession rate is much faster than the diffusion in the droplets, i.e., in cases with large Péclet numbers. Furthermore, the model is useful when the initial concentration of solutes in the droplets is close to saturation. The model also predicts the dry particle diameter, assuming a spherical particle, particle density, and aerodynamic diameter. For hollow particles formed at large Péclet numbers the shell thickness can be approximated. The model is capable of predicting the radial distribution of the components in the final dry particle in the case of multi-component formulations. The results of the model were recast in a simple analytical form, which can be used in particle design without the need for numerical tools. Predictions of the model were found to be in good agreement with numerical and experimental results in the literature.

The influence of stimulated Raman scattering on the characterization of aqueous aerosols by linear Raman spectroscopy was studied experimentally. Raman scattering from a chain of microdroplets was excited by an argon ion laser. Holographic Raman filters, a spectrograph and a cryogenically cooled CCD detector were used to record the spectra. A procedure to estimate the detection limits of Raman instrumentation is presented. For the set-up used here, the detection limit for nitrogen in a gas mixture was 3 ppm. The detection limit for aqueous aerosol particles was limited to 100 mg mm3 by the occurrence of stimulated Raman scattering (SRS). The first measurement of SRS with continuous-wave excitation in water droplets is reported. The SRS thresholds for water droplets in the size range of 15-75 pm were 0.3 to 1 MW cm-*. For droplets, which consist of a 5 M NaNO, solution, the threshold was 0.2 MW cm 2. Continuous-wave excited four-wave mixing in microdroplets of NaNO, solution is reported.

Existing one-dimensional (1D) models of aerosol dosimetry often ignore mixing mechanisms of inhaled aerosols during their transport in the lung. This mixing or aerosol dispersion results from different physical mechanisms in different regions of the lung. It is a higher order effect, which cannot be directly captured in 1D modeling approaches, and thus is sometimes modeled as a diffusive process. In this study, we improved our recently developed alveolar mixing module incorporated in the multiple path particle dosimetry model (MPPD) to account for flow irreversibility and particle trapping in the alveolar spaces, as well as mixing occurring in the tracheobronchial region. This new version of MPPD was coupled with CFPD-based predictions of aerosol bolus dispersion in the oral airway. The model was used to predict the deposition, dispersion, and mode shift of aerosol bolus inhaled at different penetration depths within the lung for breathing patterns and particle size matching those used in a previous experimental study (Darquenne et al., 2016). Even though a quite simplified approach was used, the computations appear to describe subject-specific and test-specific experimental data reasonably well. The proposed combined dispersion-deposition model can be a useful tool for targeted drug delivery and also for exposure health risk assessment.

The present paper describes a comparison of the air quality and aerosols emission parameters around tea processing, coke oven and brick kiln industries that use high sulphur coals in their processes. The concentrations of gaseous species (SO 2 , NO 2 , and NH 3 ) and aerosols (PM 2.5, PM 10 and TSPM) along with the physico-chemical properties (Moisture, Ash, Volatile Matter, C, H, N, TS) of the feed coals are compared for these industries. The concentrations of the gases e.g. SO 2 , NO 2 and NH 3 emitted are observed to be higher in the coke oven and tea processing industries in comparison to the brick kiln industry. The mean PM 10 and PM 2.5 concentrations are found to be higher in the tea processing industry A, followed by the coke oven, tea processing industry B and lastly the brick industry. The Cytotoxicity (MTT) assay of the aerosols was performed for their risk assessment. Source apportionment was carried out by using Principal Component Analysis and a high factor loading was observed in Factor 1 with 58% total variance and was associated with the secondary aerosol sources.

Incoming and rebounding particle velocities were measured to within several particle diameters of the impaction surface using laser Doppler velocimetry. Impacts occurred normal to the surface and ranged from 1 m / s , near the threshold for particle hounce, to 100 m/s, well into the plastic damage regime. Monodisperse ammonium fluorescein spheres, 2.6-6.9 p m in diameter, impacted target surfaces including polished molybdenum and silicon, cleaved mica, and a fluorocarbon polymer. The incident kinetic energy recovered on rebound depended on particle size and target composition at low velocity ( < 20 m/s), where the adhesion surface energy is important. No dependence on target composition was found at higher velocities where up to half of the impact energy was lost to plastic deformation. Plastic deformation was a significant component of energy loss even at impact velocities near critical velocity. Critical velocities for the onset of hounce decreased with a stronger power-law dependence on particle diameter than expected from classical adhesion theory or the elastic flattening model proposed by Dahneke. This is consistent with kinetic energy loss contributions from both plastic deformation and surface forces. Auxiliary experiments conducted with and without continuous discharge of the impact surface indicated the absence of a significant electrostatic contribution to particle adhesion.

A pandemia da Covid-19 e a disseminação do vírus SARS-CoV-2 provocou uma emergência em saúde pública que o mundo não estava preparado para atender. Trouxe a necessidade de compreender as interações do meio ambiente com a saúde humana e animal. As interações ecológicas entre animais humanos e não humanos ocorrem em diversos ambientes, formas e são responsáveis pelas zoonoses. A abordagem &lt;em&gt;&quot;One Health&quot;&lt;/em&gt; ou saúde única apresenta uma visão holística e interdisciplinar colaborativa com objetivo de reduzir os riscos da disseminação de doenças infecciosas resultantes da interface saúde humana, animal e ambiental. Nesse momento de isolamento social, a atividade física tem se mostrado um recurso indispensável para mitigar os efeitos da Pandemia da Covid-19 na população, assim como auxilia na prevenção e tratamento das doenças crônicas não transmissíveis, há evidências científicas que asseguram os benefícios da atividade física na saúde humana. As informações cont...

Concerns regarding noxious emissions from internal combustion engines have increased over the years. There is a strong need to understand the nature of sub-23 nm particles and to develop measurement techniques to evaluate the feasibility of new regulations for particle number emissions in the sub-23 nm region (down to at least 10 nm). This paper presents the results of three EU-funded projects (DownToTen, PEMs4Nano and SUREAL-23) which supported the understanding, measurement and regulation of particle emissions below 23 nm and have successfully developed sub-23 nm particle measurement devices, specifically laboratory systems and mobile devices for RDE tests. The new technology was validated in chassis dyno tests and on the real road. The results show that sub-23 nm particles are mainly generated at the engine start and during acceleration phases. The innovations show that the technology is mature and robust enough to serve as a basis for regulating sub-23 nm particles.

In the past two decades, several experimental and simulation studies have proposed simple empirical relations between projected two-dimensional (2-D) and three-dimensional (3-D) structural properties of fractal-like aggregates in the cluster-dilute regime. These empirical relations have found extensive use in inferring the 3-D structural properties of aggregates from their projected (i.e., 2-D) properties-measurable from aggregate electron microscopy images. This study probes the limitations and nongeneralizability of these simple and straightforward empirical relationships and proposes replacing them with new empirical formulas. A straightforward empirical relationship for directly determining the 3-D fractal dimension (D f ) of an aggregate from the knowledge of its 2-D aspect ratio is also identified. These new relationships were derived by comparing the ratios of several 2-D and 3-D structural properties of a statistically significant number of simulated aggregates with point-contacting monomers as a function of their 3-D D f ranging from 1.0 to 3.0 in increments of 0.1.

This paper reports a study on the enlargement of particles, produced by a model ethylene/air flame, by heterogeneous condensation of water vapour. This was carried out in an instrumented lab-scale facility based on the use of a growth tube. Tests were performed by varying the temperature of the condensing vapour and the gas residence time in the growth tube. Particle enlargement was favoured by increasing the vapour temperature and the residence time. Experiments can be proficiently described using consolidated models for heterogeneous condensation, provided that the contact angle between the liquid embryo of condensing vapour and the particle surface is considered as an adjustable parameter, variable with temperature.

Una práctica ornamental en recintos defensivos de al-Andalus fue la aplicación reiterada de fragmentos cerámicos vidriados de uso
doméstico en los revestimientos de algunas torres. Se trata de un recurso del que prácticamente no se ha escrito nada; quizás porque
se ha considerado una práctica sin importancia, puntual, accidental o incluso de cronología posterior a la andalusí. Sin embargo, la
identificación de hasta cuatros ejemplos, que podemos fechar por ahora entre época almohade y nazarí, precisamente por el valor
cronológico reconocido en los tipos cerámicos, indica que fue un recurso no tan infrecuente.

Dispersion modelling is often used to estimate potentially contaminated areas in case of accidental release of microorganisms in the atmosphere. In the specific case of Legionella, accidental spread in the atmosphere due to contaminated cooling towers system may occur over distance larger than 10km. In addition, most cooling towers are located in urban areas where dispersion due to obstacles is complex. In this case, dispersion models have to take into account complex flows and microphysical processes that occur within the plume and may have an impact on the survival of the microorganisms. To estimate the concentration of microorganisms in these areas, a specific module has been developed within the lagrangian dispersion model Micro Swift Spray (MSS, Aria technologies). This module takes into account microorganisms outside or inside water liquid droplets and microphysical interaction inside the plume. A simple biological module governing the survival of airborne microorganisms has also been implemented in the dispersion model. In order to evaluate this model, a field campaign of biological aerosols dispersion was performed by CSTB (Champs-sur-Marne, France) on June 23 rd , 2009. Spores of bacillus atrophaeus (usually referred to as BG) initially contained in a water tank were disseminated in a suburban area from a source at 3 meters above ground level. Air was sampled by DGA MNRBC (Vert-Le-Petit, France) at 4 various locations from 50 to 300 meters from the source to monitor NG concentration. Direct impaction onto Petri dishes was performed with slit-samplers and sixstage Andersen impactors. Wetted-wall cyclones and SKC Biosamplers were also implemented in order to sample air and generate liquid samples. Dispersion modelling for this campaign has been carried out by INERIS using the microorganism module developed in MSS. The results show that predicted concentrations and in situ measurements are in agreement. MSS Model was implemented to simulate legionella airborne dispersion from a virtual cooling tower at the same location. The biological model has been activated. Results show that the impact of biological model on airborne concentration is significant.

Metal constituents of ÿlters collected from 1996 through 1998 from ÿve monitoring network stations of Mexico City, were identiÿed using ionization argon coupled plasma. Nine metals were quantiÿed: cadmium, chromium, copper, manganese, nickel, lead, titanium, iron and vanadium. The statistical analysis shows that in general the metal concentration diminished from 1996 to 1998 in total suspended particles and PM10 although there are some exceptions. The correlation between TSP and PM10 shows that there is a higher proportion of metals in the respirable fraction than in the particles with bigger diameter. Lead content did not exceed the standard concentration of 1:5 g=m 3 ; with an average value of 0.09 in PM10 and 0.17, in TSP and the highest values of this metal were 1.03 and 0.96 for PM10 and TSP, respectively, both in January of 1996. The study of size and shape by scanning electronic microscopy led us to identify particles from natural soils and clays, from combustion and from industrial processes.

Aerosol optical depth (AOD) provides a useful characterization of the total absorption and scattering effect of particles in direct or scattered sunlight, and can be derived from sun spectra measured directly by sun photometers. In this paper, atmospheric optical properties (e.g. AOD 440-1020 nm , α and β, the coefficients in Angstrom formula) and meteorological conditions are presented for: summer (July-August-September) and winter (December-January-February-March) of 2009 -2010 over Zanjan (36.411 N, 48 over Zanjan (36.411 N, 48.291 E) in northwestern Iran. The diurnal variation of AOD in Zanjan is approximately 15%. An exponential dependence of α on AOD in winter indicates that dust aerosols are major contributions of atmospheric turbidity in this region. AOD regressed against PM 10 to establish prediction models. The role of three meteorological parameters on the correlation of AOD and PM 10 are analyzed. Results show that there is a high correlation between AOD 440 and PM 10 in wintertime, and β is a better indicator of air quality in winter than in summer for the study region considered here. Hourly analysis shows that this correlation is highest in the afternoon when the atmospheric mixed layer is at its highest thickness. A similar behavior for AOD-PM 10 and a correlation between optical properties with NO 2 and PM 10 are detected. A sensitivity study was designed to quantify the role of meteorological properties, such as relative humidity, wind speed, and temperature, on the correlation between AOD and PM 10 concentration.

Aerosol optical depth (AOD) provides a useful characterization of the total absorption and scattering effect of particles in direct or scattered sunlight, and can be derived from sun spectra measured directly by sun photometers. In this paper, atmospheric optical properties (e.g. AOD 440-1020 nm , α and β, the coefficients in Angstrom formula) and meteorological conditions are presented for: summer (July-August-September) and winter (December-January-February-March) of 2009 -2010 over Zanjan (36.411 N, 48 over Zanjan (36.411 N, 48.291 E) in northwestern Iran. The diurnal variation of AOD in Zanjan is approximately 15%. An exponential dependence of α on AOD in winter indicates that dust aerosols are major contributions of atmospheric turbidity in this region. AOD regressed against PM 10 to establish prediction models. The role of three meteorological parameters on the correlation of AOD and PM 10 are analyzed. Results show that there is a high correlation between AOD 440 and PM 10 in wintertime, and β is a better indicator of air quality in winter than in summer for the study region considered here. Hourly analysis shows that this correlation is highest in the afternoon when the atmospheric mixed layer is at its highest thickness. A similar behavior for AOD-PM 10 and a correlation between optical properties with NO 2 and PM 10 are detected. A sensitivity study was designed to quantify the role of meteorological properties, such as relative humidity, wind speed, and temperature, on the correlation between AOD and PM 10 concentration.

The air-liquid interface (ALI) cell exposure system is a useful tool for assessing the toxicity of atmospheric aerosols and airborne engineered nanomaterials for in vitro studies. In order to evaluate dose-response relationships, it is necessary to determine the efficiency with which particles are deposited on cells in the ALI cell exposure chamber. In the present study, we determined the deposition efficiency for eight particle sizes between 30 and 1005 nm using two methods. Transmission electron microscopy was used to directly count the number of deposited particles, and particle trajectories were simulated using computational fluid dynamics, taking into account the drag, gravitational, and Brownian forces on the particle. The deposition efficiencies were validated separately and the results obtained by both methods were consistent. Both sets of results showed that the deposition efficiency was a minimum (below 1%) for 200-300 nm particles. A parametric study was also conducted, in particular to determine the influence of the distance (S) between the nozzle head and the bottom surface of the target cells on the deposition efficiency. For a particle size of 1005 nm, where the gravitational force dominates, the deposition efficiency was found to decrease linearly with increasing S. In contrast, for a particle size of 100 nm, where diffusion dominates, the decrease in deposition efficiency with increasing S followed a power law. It was shown that the deposition efficiency could be predicted for arbitrary particle properties, air flow conditions, and ALI cell exposure chamber geometry, based on the Stokes number, Froude number, Peclet number, and ratio of S to the inlet nozzle radius.

The reactions of ozone with a series of monoterpenes (a-pinene, sabinene, limonene and myrcene) were investigated in a novel flow reactor dedicated to the investigation of secondary organic aerosol (SOA) formation. Rate constants for the gas phase reactions and nucleation thresholds were determined at T $ 296 K, P $ 764 Torr under dry conditions (dew point r À 33 1C) and in absence of OH radicals scavenger and seed particles. Comparison with the literature as well as data from a simulation chamber showed good agreement. The experiments also show that the novel flow reactor improves the accuracy in evaluating the nucleation thresholds during the ozonolysis of monoterpenes and show that aerosol flow reactor is a useful tool to study the SOA nucleation step. Given as an upper limit, the nucleation thresholds obtained are (in molecule cm À 3 /ppb): a-pinene, 3.9 Â 10 10 /1.56; sabinene, 6.2 Â 10 9 /0.26; limonene, 1.1 Â 10 10 /0.43 and myrcene 2.1 Â 10 10 /0.83.

The feasibility of assessing the sampling efficiency of aerosol samplers for large windborne particles in the open air was determined in a pilot study. The experiments with 17 gm diameter monodisperse aerosols show the low sampling efficiency of widely used instruments such as the EPA high volume sampler and LIB sampler for a coarse aerosol. A new developed tunnel sampler shows a high sampling efficiency for this aerosol relative to the Rotorod as a reference sampler. Additional experiments with different aerosol sizes and under varying meteorological situations are planned.

Fine particulate matter (PM 2.5) concentrations associated with 202 24-hr samples collected at the National Energy Technology Laboratory (NETL) particulate matter (PM) characterization site in south Pittsburgh from October 1999 through September 2001 were used to apportion PM 2.5 into primary and secondary contributions using Positive Matrix Factorization (PMF2). Input included the concentrations of PM 2.5 mass determined with a Federal Reference Method (FRM) sampler, semi-volatile PM 2.5 organic material, elemental carbon (EC), and trace element components of PM 2.5. A total of 11 factors were identified. The results of potential source contributions function (PSCF) analysis using PMF2 factors and HYSPLIT-calculated back-trajectories were used to identify those factors associated with specific meteorological transport conditions. The 11 factors were identified as being associated with emissions from various specific regions and facilities including crustal material, gasoline combustion, diesel combustion, and three nearby sources high in trace metals. Three sources associated with transport from coalfired power plants to the southeast, a combination of point sources to the northwest, and a steel mill and associated sources to the west were identified. In addition, two secondary-material-dominated sources were identified, one was associated with secondary products of local emissions and one was dominated by secondary ammonium sulfate transported to the NETL site from the west and southwest. Of these 11 factors, the four largest contributors to PM 2.5 were the secondary transported material (dominated by ammonium sulfate) (47%), local secondary material (19%), diesel combustion emissions (10%), and gasoline combustion emissions (8%). The other seven factors accounted for the remaining 16% of the PM 2.5 mass. The findings are consistent with the major source of PM 2.5 in the Pittsburgh area being dominated by ammonium sulfate from distant transport and so decoupled from local activity emitting organic pollutants in the IMPLICATIONS Using PMF2 and PSCF analysis, particulate pollutant component concentrations, and HYSPLIT back-trajectory information obtained over a 2-yr study period, we determined sources of PM 2.5 at NETL, an urban Pittsburgh facility. The results indicate that the major pollutant in the Pittsburgh metropolitan area is secondary ammonium sulfate originating from distant sources in the Ohio River Valley and is decoupled from local activity involving organic pollutants in the metropolitan area. In contrast, the major local secondary sources were dominated by organic material, most of which may come from local mobile sources. Primary emissions from mobile sources were lower in concentration than these secondary sources. This study infers that effective state implementation plans for the Pittsburgh metropolitan area must consider reductions in PM and PM precursors from the Ohio River Valley, and more stringent controls on mobile emission sources.

The detection of atmospheric aerosol particles is becoming an important issue in many fields such as environmental science, occupational medicine, semiconductor industry and material science. In the present paper, we utilized the conductive polymer, polypyrrole (PPy), as a sensitive membrane for detecting aerosol particles optically. A polymer optical fiber reflectance probe is constructed by depositing the PPy nanofilm at the end face of the fiber. The sensor principle relies on the change in the refractive index of the PPy nanofilm upon its interaction with aerosol nanoparticles and on the electrostatic induction between aerosol particles and the PPy nanofilm, which leads to a change in the reflected intensity. For preliminary evaluation of optical aerosol detector, three types of aerosol particles, NaCl, black carbon (BC) and polystyrene latex (PSL), are selected. The fabricated fiber optic reflectance probe using the PPy nanofilm shows distinct variations in the reflected light intensity depending on the type of aerosol particle and its properties. The proposed sensing approach may promote the use of conductive polymers in optical techniques for the detection of atmospheric aerosols.

Concentrations of airborne continuous fine particulate matter or (PM 2.5), black carbon (BC), and ultrafine particles (UFP) were continuously measured over 5 days in winter and summer both indoors and outdoors at residences for forty-eight adults in 2005 and forty-seven asthmatic children in 2006. During 2006, personal concentrations of PM 2.5 were also measured continuously. All 4 continuous instruments employed performed well both in laboratory and field conditions. Mean outdoor concentrations of PM 2.5 , BC, and UFP were significantly higher than either indoor or personal concentrations. Air exchange rates were low (median value only 0.2/h), there was widespread use of central forced air and high-quality furnace filters. Outdoor concentrations of all particle-related pollutants showed overnight decreases followed by increases during the morning rush hours. Afternoon concentrations increased for UFP and decreased for BC, with PM 2.5 staying about the same. Between 5:00 pm and 7:00 pm, indoor UFP and PM 2.5 concentrations exceeded their mean daily values by 160% and 60%, respectively, suggesting that cooking is an extremely important source for these two pollutants. However, BC values did not increase at these hours. The highest indoor-outdoor ratios were observed for UFP suggesting that indoor sources were relatively more important for UFP than for other particle components. BC measurements in Windsor agreed moderately well (R 2 = 41%) with an independent measure of elemental carbon (EC) in Detroit. This large residential air pollution study has provided data making it possible to identify short-term variations and possible sources that can influence the relationships between pollutants and environments.

VUV spectra contain much less fragmentation than EI spectra and for many compounds the parent ion is the base peak in the VUV spectrum. Results for oleic acid are compared to experiments conducted using tunable VUV radiation from a synchrotron source and were shown to be comparable under similar conditions of photon energy and vaporizer temperature. Future technical modifications for improvements in sensitivity and its potential for ambient measurements will be discussed.

Solid or liquid particles within a carrier gas may be deposited on solid surfaces exposed to the gas stream and, in some practical applications, these aerosol deposits have deleterious effects. In order to mitigate these effects, particle repulsive fields may be applied near the surface to reduce the deposition rate. A current blowing through the exposed surface may play this repulsion role with such a forced stream pushing the aerosol particles away from the surface. The present paper develops a model to analyse and estimate the effect of blowing in reducing particle deposition for laminar flows with high Reynolds numbers over flat surfaces. A classical self-similarity analysis is used to solve the boundary layer equations for mass and momentum conservation. The solution of the particle transport problem provides the self-similarity mass fraction profile and the mass deposition rate in terms of two parameters: the Schmidt number Sc and the dimensionless blowing rate. Moreover, two approximate methods are implemented in two asymptotic limits: for large values of Sc and when the blowing parameter is sufficiently small.

In this work, 3-D structures resembling nanofiber (d f < 200 nm) filter media are simulated and challenged with nanoparticle aerosols at reduced operating pressures. For the range of fiber diameters considered in this paper, the free molecular flow regime is dominant. Therefore, the disturbances to the air flow field caused by the fibers are neglected. Nanoparticle capture efficiency of nanofiber webs, due to Brownian diffusion and interception, is calculated for particle diameters ranging from 50 to 500 nm. Our simulations show that by decreasing the fiber diameter, the minimum collection efficiency of filtration media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies-the most penetrating particle diameter. Moreover, it is demonstrated that increasing the flow temperature enhances the nanoparticle capture efficiency of nanofiber filters. Allowing the particles to deposit on the fibers as well as each other, the caking process of such nanofiber filters is simulated for different monodisperse and polydisperse aerosols at different temperatures. The statistical information regarding the composition of nanoparticle cakes formed at high and low temperatures is presented and discussed.

This paper describes different approaches for predicting collection efficiency of nonwoven fibrous filters. Traditionally, the flow field has been obtained by analytically solving the Navier- Stokes equations inside over-simplified geometries with the fibers placed in regular arrays perpendicular to the flow direction. Our approach, on the other hand, is to exploit a numerical method based on the finite -volume technique to solve the flow inside 3-D virtual webs generated based on the properties of real filters. Our results showed a good qualitative agreement with previous works.

This study reports on the effects of BaTiO 3-a high dielectric constant additive-addition on charging and filtration properties of meltblown polypropylene (PP) electret filters. Since electrostatic capture efficiency of electret filters is mainly dependent on electrical forces, surface potential and aerosol filtration properties were analyzed and compared. Due to quasipermanent nature of electret property, stability of charging and filtration performance was also investigated via following an isothermal charge decay procedure. Addition of BaTiO 3 did not alter fiber morphology significantly. Particularly, the stability of electrostatic filtration performance was found to be promising with the addition of BaTiO 3. Possible microstructural changes after addition of BaTiO 3 were investigated via wide angle X-ray diffraction. Changes in crystal structure of PP upon addition of BaTiO 3 did not deteriorate electrostatic properties.

In this work, 3-D structures resembling nanofiber (d f < 200 nm) filter media are simulated and challenged with nanoparticle aerosols at reduced operating pressures. For the range of fiber diameters considered in this paper, the free molecular flow regime is dominant. Therefore, the disturbances to the air flow field caused by the fibers are neglected. Nanoparticle capture efficiency of nanofiber webs, due to Brownian diffusion and interception, is calculated for particle diameters ranging from 50 to 500 nm. Our simulations show that by decreasing the fiber diameter, the minimum collection efficiency of filtration media having identical pressure drops increases. This effect is accompanied by a decrease in the particle diameter associated with these minimum efficiencies-the most penetrating particle diameter. Moreover, it is demonstrated that increasing the flow temperature enhances the nanoparticle capture efficiency of nanofiber filters. Allowing the particles to deposit on the fibers as well as each other, the caking process of such nanofiber filters is simulated for different monodisperse and polydisperse aerosols at different temperatures. The statistical information regarding the composition of nanoparticle cakes formed at high and low temperatures is presented and discussed.

Aerosol reactors pass through regimes where subsets of the population balance terms are dominant. Initially, mixing, reaction, nucleation and accretional growth dominate. This is generally followed by a regime in which coagulation and coalescence control evolution of the particle population into sintered aggregates. Conventionally, the boundary between regimes where coalescence is or is not important is assumed to be sharp and the collisioncoalescence regime is followed by a regime dominated by coagulation and breakup which controls the growth of loosely bonded agglomerates that grow large enough to be captured in conventional gas-solids separation equipment. When this boundary is not sharp, there can be a regime in which coagulation, coalescence and breakup all occur simultaneously. This paper describes the daughter distributions required to model breakup in a bivariate population, the moment models describing simultaneous collision, coalescence and breakage, and exhibits reconstructed steady-state distributions formed when the rate kernels are size independent.

A constant kernel collision and coalescence model in bivariate moment form is used to develop a criterion for when a bivariate formulation of the collision-coalescence problem is necessary. This analysis springs from a previous publication in which the more complex problem of simultaneous collision, coalescence and breakage is considered.

The properties of gas-borne aggregates are important in nano-technology and for potential health effects. Gold aggregates from three generators (one commercial and one custom built spark discharge generator and one high-temperature furnace) have been characterized. The aggregate surface areas were determined using five approachesbased on aggregation theory and/or measured aggregate properties. The characterization included massmobility relationships, effective densities (assessed by an Aerosol Particles Mass analyzer), primary particle analysis (based on Transmission Electron Microscopy), as well as total mass and number concentration outputs. The relationships between mass and mobility are well described by power-law functions with exponents of 2.18-2.35. For all generators, the primary particles of the aggregates were fused together by a bridge with a diameter typically~60-70% of the primary particle diameter (5-10 nm). The total mass outputs were 6.1-48.1 mg/m3 and the predicted surface area outputs in the range 0.9 Â 10-3-17 Â 10-3 cm 2 /cm 3. The aggregate effective densities differed considerably between generators. The difference could partly be explained by the differences in primary particle diameter, but not fully. This in turn may be explained either by a varying primary particle size with aggregate size, or by that there are slight differences in the morphology of the aggregates from the generators.