Browsing by Subject "Aerosol"
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Item Aerosol particle electroscavenging by droplets.(2012-06) Zhang, MengWhen water droplets precipitate under the action of gravity and frictional forces, they will collide with smaller aerosol particles and fall to the ground. Usually, either droplets or aerosol particles carry some electric charges, and some may be highly charged. Therefore, the electrostatic effect is a very important factor in particle scavenging. Wet scrubbers as air pollution control devices use the same theory as scavenging to remove both particulate and gas contaminants from the industrial exhaust streams. Electrostatic wet scrubbers were developed in an attempt to improve collection efficiency by raising the attraction force between droplets and particles. Very few numerical models have been developed to describe the phenomenon of particle collection by highly charged droplets when electrostatic force is dominant. In an attempt to understand the physics of scavenging, a new three-dimensional model has been developed to simulate neutral or charged particles collected by a group of neutral or charged droplets. The model can simulate the particle traveling through a matrix of droplets. Both the inertial effect and the electrostatic effect on particle scavenging have been considered. The collection efficiency can be estimated by utilizing this developed model. The effect on the collection efficiency by the size of the particle and of the droplet, the charges of the particle the droplet, and droplet distance have been investigated. A validation approach has also been developed and the study results have achieved good agreement with published data.Item Aerosol printing of colloidal nanocrystals by aerodynamic focusing.(2010-07) Qi, LejunColloidal synthesized semiconductor nanocrystals, or quantum dots, have shown promise as the active material in electronic and optoelectronic applications, because of their high quantum yield, narrow spectral emission band, size-tunable bandgap, chemical stability, and easy processibility. Meanwhile, it is still challenging to print patterns of nanocrystal films with desired linewidth and thickness, which is a critical step in fabrication of nanocrystal-based devices. In this thesis, a direct-write method of colloidal semiconductor nanocrystals has been developed. Like other direct-write techniques, this aerosol printing method also simplifies printing process and reduces the manufacturing cost, as it avoids mask screening, lithography, and pre-patterning of the substrate. Moreover, the aerosol printing with aerodynamic lenses needs neither microscale nozzles nor sheath gases, and is able to incorporate with the vacuum systems currently used in microelectronic fabrication. First, the synthesized colloidal nanocrystals in hexane were nebulized into compact and spherical agglomerates suspending in the carrier gas. The details about the impact dynamics of individual aerosolized nanocrystal agglomerates were investigated. As building blocks of printed nanocrystal films, the agglomerate exhibited cohesive and granular behaviors during impact deformation on the substrate. The strength of cohesion between nanocrystals in the agglomerates was adjustable by tuning the number concentration of colloidal nanocrystal dispersion. Second, ultrathin films of nanocrystals were obtained by printing monodisperse nanocrystal agglomerates. As the result of the granular property of nanocrystal agglomerates, it was found that the thickness of deposited agglomerates strongly depended on the size of agglomerates. A single monolayer film of nanocrystals was attained by aerodynamically focusing 40-nm nanocrystal agglomerates and translating the carbon substrate at a velocity of 10 µm/s. The formation of nanocrystal films during printing was found strongly influenced by the substrate surface wettability. Third, microscale towers, lines, and patterns were obtained by printing polydisperse nanocrystal agglomerates. The thickness and line width of the patterns were adjustable by altering experimental conditions. Micropatterns of linewidth of less than 10 µm were demonstrated. Upon exposure to near-UV illumination, the printed nanocrystals exhibited robust fluorescence in the visual, with the color depending on the diameter of the individual nanocrystals.Item Biofuel combustion: a single particle approach including new tandem measurements.(2011-10) Dutcher, Dabrina DThe physicochemical properties of aerosol particles are complex. They are often irregular in shape, and can contain complex mixtures of liquids and solids. By measuring multiple properties of a particle, it is possible to describe it more completely than is possible if only one property is evaluated. This is the principle behind the theme of this chapter: tandem aerosol measurements. The Aerosol Time-of-Flight Mass Spectrometer carries out tandem measurements of a particle's vacuum aerodynamic diameter and its composition. I describe here the use of the ATOFMS in series with instruments that measure other properties so as to provide still more information. These additional properties include particle mobility, mass, and "brightness" (i.e., the amount of light that it scatters when illuminated by a laser). In addition, we show that when the ATOFMS is used downstream of tandem differential mobility analyzer systems (TDMA), new information can be gained about species that affect a particle's hygroscopicity (HTDMA) or volatility (VTDMA). These novel instrument combinations yield information regarding the dependence of particle effective density, volatility, and hygroscopicity on particle composition. Additional information is presented about the relationship between particle mobility size and vacuum aerodynamic size for assorted particle types and about the unanticipated difficulties that I encountered when using the ATOFMS for tandem measurements. I discovered that the rotating seals in the aerosol particle mass analyzer (APM) contain compounds that volatilize and react with acidic particles. The ATOFMS is exceedingly sensitive to these reaction products, so much so that it is not possible to obtain meaningful information about the composition of the particles under investigation. This sensitivity may provide a sensitive means, however, to assess the particle acidity.Item Epidemiology of influenza A viruses of swine: surveilance, airborne detection and dissemination(2012-08) Corzo, Cesar AgustinChapter 2: Swine Influenza Active Surveillance in the United States Influenza A virus (IAV) in swine continues to be an important swine respiratory agent along with being a source of concern to public health authorities. While veterinary diagnostic laboratories are a valuable source of information with regards to the identification and genetic characterization of newly emerged virus through passive surveillance, there is still a need for additional surveillance programs that can aid in detecting new viruses in a timely manner. An active surveillance program was performed in 32 pig farms throughout the Midwestern United States between June 2009 and December 2011. Thirty nasal swabs were collected from growing pigs on a monthly basis and tested for IAV by RRT-PCR. During sample collection, data on sample collection date, pig age, pig group respiratory signs, clinical status and vaccination history were recorded. A total of 16,170 nasal swabs from 540 groups of growing pigs were collected from which 746 (4.6 %) nasal swabs and 117 (21.7 %) groups tested positive for IAV, respectively. Throughout the study, IAV was consistently detected in at least one farm except in two months. From the positive groups of pigs, H1N1, H1N2, H3N2, 2009 pandemic H1N1were detected in 18%, 16%, 7.6% and 14.5% of the groups, respectively. In seven groups, H1N2 or H3N2 reassortants containing genes from 2009 pandemic H1N1 were found. There were eight groups in which an H1N2 and the 2009 pandemic H1N1 were identified simultaneously. Groups of pigs were more likely to test positive for IAV during the spring and summer seasons compared to the fall. Age and group respiratory clinical signs were not predictors of group IAV status. This active IAV surveillance program provided quality data and increased the understanding of the current situation of circulating viruses in the U.S. pig population. Further studies in swine should be conducted to increase our knowledge regarding the characteristics of IAV. Chapter 3: Swine influenza virus risk factors in growing pigs Influenza A virus (IAV) is an important cause of respiratory disease in swine. Understanding the epidemiology of the disease is in its early stages and is needed to develop effective control and prevention strategies. A study was conducted to assess the relationship between the presence of IAV in growing pig farms and farm level risk factors. Twenty-six pig farms participated in the study from which 30 nasal swabs from growing pigs were collected on a monthly basis for 12 or 24 consecutive months between 2009 and 2011. Nasal swabs were tested for IAV by RRT-PCR. Weather stations were located at every participating farm for monitoring temperature, relative humidity, light intensity, wind speed and wind gusts. Farm level data was obtained through a questionnaire to assess the relationship between the presence of IAV and farm level characteristics. At the individual level, 4.6% of the nasal swabs from growing pigs tested positive for IAV. Of the monthly groups of pigs from which nasal swabs were collected, 20.8% had at least one positive nasal swab. Positive nasal swabs originated from 23 of the 26 participating farms. Farm type, pig flow and gilt source were associated with the presence of IAV. Environmental temperature and wind speed were associated with the presence of IAV. Overall, this study provides insights into the ecology of IAV which can aid in the development of control and prevention strategies. Chapter 4: Prevalence and risk factors for H1N1 and H3N2 influenza A virus infections in Minnesota turkey premisesInfluenza virus infections can cause respiratory and systemic disease of variable severity and also result in economic losses for the turkey industry. Several subtypes of influenza can infect turkeys causing diverse clinical signs. Influenza subtypes of swine origin have been diagnosed in turkey premises. However, it is not known how common these infections are nor the likely routes of transmission. We conducted a cross-sectional study to estimate the seroprevalence of influenza viruses in turkeys and examine factors associated with infection on Minnesota turkey premises. Results for influenza diagnostic tests and turkey and pig premises location data were obtained from the Minnesota Poultry Testing Laboratory (MPTL) and the Minnesota Board of Animal Health (MBAH) respectively from January 2007 to September 2008. Diagnostic data from 356 premises were obtained, of which 17 premises tested positive for antibodies to influenza A virus by agar gel immunodiffusion (AGID) assay and were confirmed as either H1N1 or H3N2 influenza viruses by hemagglutination and neuraminidase inhibition assays. Influenza infection status was associated with proximity to pig premises and flock size. The latter had a sparing effect on influenza status. This study suggests that H1N1 and H3N2 influenza virus infections of turkey premises in Minnesota are an uncommon event. The route of influenza virus transmission could not be determined, however, the findings suggest that airborne transmission should be considered in future studies. Chapter 5: Characterization of the temporal dynamics of airborne influenza A virus detection in acutely infected pigs Influenza A viruses infect many species including avians, mammals and humans. Aerosol transmission is one route that enables the virus to infect populations. This study explored the relationship between number of infected pigs and the probability of detecting influenza virus RNA in bioaerosols through the course of an acute infection. Bioaerosols were collected using a cyclonic collector in two groups of seven week-old pigs that were experimentally infected upon exposure with a contact infected pig (seeder pig). After contact exposure, individual pig nasal swab samples were collected daily and air samples were collected three times per day for eight days. All samples were tested for influenza by RRT-PCR targeting the influenza virus matrix gene. All pigs' nasal swabs became influenza virus RRT-PCR positive upon exposure to the infected seeder pig. Airborne influenza was detected in 58% (25/43) of the air samples collected. Temporal dynamics of influenza virus detection in air samples were in close agreement with the nasal shedding pattern in the infected pigs. First detection of positive bioaerosols occurred 2 days post contact (DPC). Positive bioaerosols were consistently detected between 3 and 6 DPC, a time when most pigs were also shedding virus in nasal secretions. Overall, the odds of detecting a positive air sample increased 2.2 times with every additional nasal swab positive pig in the group. In summary, there was a strong relationship between the number of pigs shedding influenza virus in nasal secretions and the detection of bioaerosols during the course of an acute infection in non-immune population. Chapter 6: Detection of airborne influenza A virus in experimentally infected pigs with maternally derived antibodies.This study assessed whether recently weaned piglets with maternally derived antibodies were able to generate infectious influenza aerosols. Three groups of piglets were assembled based on the vaccination status of the dam. Sows were either non vaccinated (CTRL) or vaccinated with the same (VAC-HOM) strain or a different (VAC-HET) strain than the one used for challenge. Piglets acquired the maternally derived antibodies by directly suckling colostrum from their respective dams. At weaning, pigs were challenged with influenza virus by direct contact with an infected pig (seeder pig) and clinical signs were evaluated. Air samples, collected using a liquid cyclonic air collector, and individual nasal swabs were collected daily for 10 days from each group and tested by matrix real-time reverse transcriptase polymerase chain reaction (RRT-PCR) assay. Virus isolation and titration were attempted for air samples on Madin-Darby canine kidney (MDCK) cells. All individual pigs from both VAC-HET and CTRL groups tested positive during the study but only one pig in the VAC-HOM group was positive by nasal swab RRT-PCR. Influenza virus could not be detected or isolated from air samples from the VAC-HOM group. Influenza A virus was isolated from 3.2% and 6.4% air samples from both the VAC-HET and CTRL groups, respectively. Positive RRT-PCR air samples were only detected in VAC-HET and CTRL groups on day 7 post-exposure. Overall, this study provides evidence that recently weaned pigs with maternally derived immunity without obvious clinical signs of influenza infection can generate influenza infectious aerosols which is relevant to the transmission and the ecology of influenza virus in pigs. Chapter 7: Detection of airborne swine influenza A virus in air samples collected inside, outside and downwind from swine barns Airborne transmission of influenza A virus (IAV) in swine is speculated to be an important route of virus dissemination, but data are scarce. This study attempted to detect airborne IAV by virus isolation and RRT-PCR in air samples under field conditions. This was accomplished by collecting air samples from four acutely infected pig farms and locating air samplers inside the barns, at the external exhaust fans and downwind from the farms and at distances up to 2.1 km. Weather data was also collected to explore the relationship between detection of IAV and temperature, relative humidity and sunlight intensity. IAV was detected in air samples collected in all the farms included in the study. On average, 96% and 85% of the air samples collected inside and at the exhaust fans from positive farms tested positive through RRT-PCR, respectively. Isolation of IAV was possible from air samples collected inside the barn at two of the farms and in one farm from the exhausted air. Influenza virus RNA was detected in air samples collected between 1.5 and 2.1 Km away from the farms. The odds of detecting IAV decreased with distance from the farm and greater levels of sunlight intensity. The results from this study prove evidence of the risk of aerosol transmission in pigs under field conditions and perhaps to other species as well.Item Evaluation and development of methods for measurement of penetration of filtering facepiece respirators(2015-07) Satish, SwathiElevated concentrations of diesel exhaust have been linked to adverse health effects. Filtering facepiece respirators (FFRs) are widely used as a form of respiratory protection against diesel particulate matter (DPM) in occupational settings. The objective of this study was to evaluate NIOSH-certified R95 and P95 electret respirators challenged with Diesel exhaust and get a better understanding of the factors that influence penetration. Two techniques were employed for the measurement of penetration: (a) particle counting technique using a Scanning Mobility Particle Sizer (SMPS, TSI Inc.) which measures particle size distribution, and (b) Gravimetric analysis using polyfluortetraethylene (PTFE) and polypropylene (PP) filters. Gravimetric measurements using PP filters were variable compared to SMPS measurements and biased high as a result of the adsorption of gas-phase semi-volatile material. Relatively inert PTFE filters adsorbed less semi-volatile material resulting in more accurate measurements. To attempt to correct for these artifacts associated with adsorption of semi-volatile material, primary and secondary filters were used in series upstream and downstream of the FFR. Correcting for adsorption by subtracting the secondary mass from the primary mass improved the result for both PTFE and PP filters but this correction is subject to “equilibrium” conditions that depend on sampling time and the concentration of particles and semi-volatile material. Overall, the results demonstrate that great care must be taken when using filters to determine filtration efficiency of FFRs challenged with diesel exhaust. Pure PTFE or other filters that minimize adsorption of semi-volatile artifacts and two filters should be used in tandem to allow correction for adsorbed artifacts. Analysis of SMPS measurements indicated that the respirators behave differently for Diesel exhaust generated at light and heavy load on engine. At light load, the penetration of the R-95 and P-95 respirators showed a steep increase with time, exceeding the maximum allowed penetration of 5% after about 40 minutes. Whereas at heavy load, the respirators were found to have a relatively unchanging penetration (less than 5%) throughout the 90-minute test duration. This difference was attributed to the presence of a high concentration of organic carbon (OC) in Diesel exhaust which has a tendency to degrade the electric charges on the respirators, thus reducing the filtration enhancement from electrostatic attraction forces. To account for the complex nature of DPM and its varying properties with changes in operating and sampling condition, an oxidation-dilution tunnel was designed to produce Diesel exhaust with a controlled set of properties: elemental carbon (EC) concentration, OC concentration, EC/OC ratio and volume flow rate. This device was used to evaluate R-95 and P-95 respirators for solid Diesel exhaust aerosol. The methodology proved to be effective in controlling the EC concentration and total volume flow rate. Results showed that the R-95 and P-95 respirators were more than 95% efficient for solid Diesel exhaust aerosol. This thesis is divided into two parts. The first focuses on the measurement of penetration of FFRs for Diesel exhaust, the second on the development of a standard DPM generator for testing filtration systems.Item New Instrumentation and Methods for Studying Heterogeneous Vapor Uptake by Aerosol Particles Ranging In Size From One Molecule to 10nm(2013-10) Oberreit, DerekAerosol particles in the presence of a vapor will often change in size and composition due to heterogeneous vapor uptake. The physics and thermodynamics of this phenomenon are not well understood for particles less than ~10 nm where traditional models using bulk properties begin to break down. Further, existing methods for measuring/quantifying vapor uptake by particles are not effective for examining particles below 5 nm in size, and at relatively high vapor saturation ratios. This dissertation presents two new methods for measuring vapor uptake by aerosol particles in this size range. Each system measures the change in electrical mobility (which can be related to size) of aerosol particles when they are introduced to a vapor of known concentration. The first system consists of a tandem High Resolution Differential Mobility Analyzer - Drift Tube Ion Mobility Analyzer (HRDMA-DTIMS) for measuring uptake by particles ranging from ~2nm to >12nm, and the second system is a tandem HRDMA-Mass Spectrometer for measuring uptake by particles ranging from a single molecule to ~2nm. For the HRDMA-DTIMS system a new drift tube ion mobility spectrometer was developed and is described, with the goal of high resolution and fast measurement times. The device is capable of sub second mobility distribution scans and resolving powers similar to DMAs currently used in similar vapor uptake experiments. Measurement of water vapor uptake by hygroscopic salts of lithium iodide and sodium iodide particles compared to theoretical calculations exposes the flaws in existing vapor uptake models. The precision of the growth factor (wet diameter / dry diameter) measured using this system is shown to be ~0.2% for the presented data. For the HRDMA-MS system we are able to identify electrospray generated ions of a specific composition and then measure their change in electrical mobility as a function of relative humidity. Using this system we measured vapor uptake by alkyl halide salt cluster ions ranging from one to 27 molecules. We also describe how structures determined using density functional theory can be used to estimate the change in electrical mobility due to additions of vapor molecules. In addition to describing new instrumentation and systems, a model for estimating mobility changes based on collision mechanics as well as thermodynamics of individual molecule uptake is presented. This model can be applied to any vapor uptake measurement systems.Item Synthesis and aerosol-phase treatments of environmental and materials nanoparticles(2011-09) Winters, Brandon JamesThe synthesis of silicon nanoparticles using a non-thermal RF plasma system is explored followed by in-air oxidation of these particles. The oxidation process is monitored over a period of 1 month using FTIR, XPS and EELS. The results show a complex relationship between the rate of oxidation and the degree to which the surface bound hydrogen has been desorbed. Additionally, the synthesis of natural gas soot followed by aerosol-phase heating under various system pressures with different oxygen partial pressures is explored. The pressure of the synthesis system in tandem with the furnace temperature are shown to affect the growth of the graphene crystallites contained within the synthesized particles. FTIR, Raman, and TEM are used in this analysis.Item Zinc aerosol hydrolysis in a transverse jet reactor.(2011-12) Haltiwanger, Julia FrancesSome of the major challenges---both technical and economic---of the Zn/ZnO two-step thermochemical hydrogen production cycle are investigated in this study. Technically, complete hydrolysis of Zn in the hydrogen production step remains a major barrier to implementation, and much attention has been given to Zn nano-scale reacting aerosols as a solution. Smaller particles favor faster reaction kinetics, and because they can be entrained and reacted in a gas flow, a continuous controllable process is possible. However, success of this continuous process depends on achieving high particle yields and high conversions in the aerosol, neither of which have yet been achieved in laboratory reactors. The ability of a new reactor concept based on transverse jet fluid dynamics to control the flow field and rapidly cool the Zn vapor is investigated. In the transverse jet reactor, evaporated Zn entrained in an Ar carrier gas issues vertically into the horizontal tubular reactor through which cooler H2O and Ar flow. Particles are formed in the presence of steam at ~450 K. The objective of controlling the flow field is to keep Zn away from the walls, thereby reducing particle deposition in the reactor and increasing particle yields on the filter. A computational fluid dynamics (CFD) model indicates that the trajectory of the jet can be controlled so that the majority of the Zn mass is directed down the center of the reactor, not near the reactor walls. Furthermore, the model shows that quench rates of 2x10^4 K/s are achieved and reactants are well mixed. Experimentally, maximum particle yields of 93% of the mass entering the reactor are obtained. Hydrolysis experiments are conducted in the transverse jet reactor at 418 K, 573 K, 603 K, and 713 K to assess the mechanisms of particle growth and hydrolysis. Experiments are conducted with and without steam to assess the effect of the reacting gas on particle morphology. SEM images of particles collected on a filter downstream from the reaction zone indicate that particle growth is dominated by condensation, resulting in hexagonal particles generally with lengths across their hexagonal face of 300 nm to 1micron in experiments with stream, and 1 to 3 micron in experiments without steam. Furthermore, the SEM images indicate that in hydrolysis experiments, ZnO forms on the surface of particles early on, protecting them from re-evaporation. Particle yield on the filter, Y, is defined as the fraction of the total mass entering the reactor that is collected on a filter placed downstream of the reaction zone. Overall conversion, X, is measured by monitoring the H2 content of the effluent gas throughout experiments with a gas chromatograph. Conversion of aerosol particles, Z, is the ZnO content (by mole) of particles collected from the downstream filter; it is measured by x-ray diffractometry with the internal standard calibration method. At all temperatures, particle yield remains high---generally 70 to 80% in hydrolysis experiments---and particle deposition on the walls of the reaction zone is eliminated for temperatures of 573 K and above. However, the conversion in the aerosol is <7% and decreases with reaction zone temperature. The overall conversion ranges from 11% at 418 K to 49% at 713 K. The higher overall conversion than conversion in the aerosol is attributed to heterogeneous Zn vapor hydrolysis. Visual observation proves heterogeneous hydrolysis occurs on the reactor walls; it is inferred that the heterogeneous Zn vapor reaction also occurs on the surface of aerosol particles. In this study, high particle yields are achieved for the first time---an important step forward for the continuous aerosol process. However, complete conversion of the aerosol particles remains a major challenge. In an economic and policy study of the Zn/ZnO cycle, the time frame for economic viability is assessed through the use of experience curves under minimal input, mid-range, and aggressive incentive policy scenarios. For the technology to become cost competitive, incentive policies that lead to early implementation of solar hydrogen plants will be necessary to allow the experience effect to draw down the price. Under such policies, a learning curve analysis suggests that hydrogen produced via the Zn/ZnO cycle could become economically viable between 2032 and 2069, depending on how aggressively the policies encourage the emerging technology. Thus, if the technical challenges are resolved, the Zn/ZnO cycle has the potential to be economically viable by mid-century if incentive policies--such as direct financial support, purchase guarantees, low interest rate loans, and tax breaks--are used to support initial projects.