Browsing by Subject "Aerosols"

Now showing 1 - 7 of 7
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    Atmospheric nucleation: measurements, mechanisms, and dynamics.
    (2009-09) Kuang, Chongai
    New particle formation by nucleation of gas-phase species significantly influences the size distributions and number concentrations of atmospheric aerosols. These nucleated particles are formed at rates that are orders of magnitude higher than were predicted by early models and grow at rates that are typically ten times faster than can be explained by the condensation of sulfuric acid alone. The resultant aerosols exert a significant impact on global climate by affecting the earth's radiation balance directly through the scattering and absorption of incident solar radiation, and indirectly through their role as cloud condensation nuclei (CCN). High formation rates and fast growth to CCN sizes ensure that NPF contributes significantly to the global CCN population. It is the primary goal of the research described in this thesis to develop robust models, constrained by measurement, for the sequential formation of CCN from the nucleation of gas-phase precursors. To this end, my thesis focuses on four topics: the development of nucleation rate parameterizations from correlations between formation rates of 1 nm particles and gas-phase sulfuric acid concentrations in diverse environments; the development of a cluster formation mechanism incorporating energetic barriers at the smallest clusters; the derivation of a simple, dimensionless criterion determining whether or not NPF would occur on a particular day; and the determination of the survival probability of newly formed particles (3 nm) as they grow to a CCN-active size (100 nm).
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    Charge Distribution Inversion for Supermicrometer Particles via Differential Mobility Analysis and Optical Particle Spectrometry
    (2023) Ley, Sarah
    Charge control of particles has long been of use for applications in laser printing, electrophotography, and electrostatic powder coating. Effective charge control is difficult, however, without an accurate understanding of particle charge state distributions. Traditional methods of charge state characterization, including the use of an average charge value, or the employment of instruments like electrodynamic balances or spectrometers, fail to robustly capture a charge distribution.This work presents a novel approach to particle charge state characterization, using aerosol instrumentation to assess full charge state distributions for supermicrometer particles. While there are preexisting methods to discern aerosol charge state distributions, such as the Tandem Differential Mobility Analyzer approach, they are generally applied only for low charge, submicrometer particles. The method proposed here combines a Differential Mobility Analyzer (DMA) with a laser-based optical particle spectrometer capable of measuring supermicrometer-sized particle concentrations. Before selection based on electrical mobility by the DMA, particles collide with ions generated in a custom unipolar corona ionizer and become highly charged relative to what is achieved in an equilibrium charge distribution. The particles’ high charge state allows them to traverse the DMA despite their large diameter. The results of this work represent the possibility to expand the applications of aerosol instrumentation into additional fields, including for use with micropowder characterization in the printing industry.
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    Mass, momentum and energy transfer in aggregated particulate media
    (2013-12) Thajudeen, Thaseem
    Synthesis of nanoparticles in gas phase systems often results in the formation of non spherical particles which are commonly found as clusters of spherical particles, termed as aggregates. Prior studies have shown that these aggregates can be accurately modeled using statistical scaling law. While theories are available for determining the transport properties of spherical particles, the effect of the morphology of the particles has not been well studied. This dissertation focuses on studying how exactly the morphology of the aggregates arises in a given synthesis system and calculation of the transport properties of the formed aggregates. Given the particle morphology, this study also investigates the effect the aggregates have on altering the bulk properties of a system into which they are embedded. The study is computational, experimental and analytical in nature with specific emphasis on studying aggregate formation and transport properties of non spherical particles. An overview of the dissertation is given in Chapter 1. In Chapter 2, an expression is proposed for calculating the drag on non spherical particles (that determines their motion in gas phase systems) and is experimentally validated with a study on flame synthesized Titania aggregates. Chapter 3 looks at calculating collision rates between non spherical particles taking into account the morphology of both the colliding entities for all mass transfer regimes and in chapter 4; aerosol filtration process is studied as quintessentially a collision process. The proposed expressions are validated using a numerical study using Brownian Dynamics simulations. In chapter 5, aggregation process is studied in detail, with specific emphasis on aggregate formation and calculation of the transport properties of the formed aggregates, with the aggregation process occurring in different mass and momentum transfer regimes. Given the particle morphology, its effect in altering the bulk properties of the host medium into which they are embedded is dealt with in chapters 6 and 7, specifically looking into their effect on the thermal conductivity and convective heat transfer. The main conclusions from the study and suggestions for possible future studies based on this dissertation are explained in chapter 8.
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    Microfluidic studies of temperature dependent phase transitions in aerosol droplets
    (2021-06) Roy, Priyatanu
    Atmospheric aerosols are suspensions of microscopic chemically complex solid or liquid particles in the atmosphere. The composition and phase of aerosols play important roles in determining radiative forcing, cloud formation, atmospheric chemistry, visibility and human health. Temperature and relative humidity (RH) dependent aerosol particle phase states and phase transitions control interactions with the surrounding gas phase as well as with other particles, and the way the particles evolve with age. Due to acceleration of global warming, there is an urgent need to develop more accurate particle-resolved climate models to improve climate prediction. Aerosols remain the largest source of uncertainty in climate predictions. The main goal of this dissertation is to develop microfluidic instrumentation to measure aerosol droplet phase transitions such as liquid-liquid phase separation and ice nucleation as a function of temperature and relative humidity. First, liquid-liquid phase separation (LLPS) similar to that observed in atmospheric aerosol droplets is investigated with aqueous droplets containing organic and inorganic solutes in a static trap based microfluidic device. LLPS in an aerosol particle directly affects aerosol water uptake and formation of cloud drops. Temperature and RH dependence of LLPS and crystallization for model aerosol droplets with varying composition is explored. It is observed that temperature has a significant effect on some systems while having no effect on others depending on the organic to inorganic ratio (OIR) as well as the identity of the organic and inorganic phases. Second, a high-throughput droplet freezing counter based on flow-through droplet microfluidics was developed to estimate ice nucleation (IN) in liquid samples relevant to atmospheric cloud droplets. Automated detection and classification of frozen droplets from liquid drops was implemented through machine learning with a deep neural network. A case study with an ideal biological ice nucleating particle (INP), Snomax, was performed. Heating and aging of the sample were also performed to identify the molecular nature of ice nucleation. The device benchmarked well against literature data and provided the highest throughput of any existing INP counters. Finally, a large array based static trap microfluidic device was implemented to study both RH dependent phase and temperature dependent INP concentration of the same sample in situ using bulk sea water and sea surface microlayer (SSML) from a simulated waveflume experiment (SeaSCAPE). This study has implications in identifying origins of INPs in sea spray which make up a significant portion of atmospheric aerosols. Correlation between ice nucleation temperature and residual dry particle morphology showed that the bulk sample had lower INPs than SSML and the residual particles were significantly different between the samples. In this dissertation, instrumentation development and case studies have been performed to show the suitability of microfluidics as versatile, adaptable and highly customizable devices, which are applicable to studying phases of aerosols and has broad implications in climate science.
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    Predicting Influence of Relative Humidity (RH) on Low-Cost Particulate Matter Sensors (LCPMSs) with Empirically Derived Single-Parameter for Hygroscopicity based on K-Kohler Theory
    (2022-12) Tejada, Rayan
    Low-cost particulate matter sensors (LCPMSs) could provide significant insight into air quality data with their ability to be placed virtually anywhere, short sampling time, and cost to build. However, LCPMSs are also known to significantly overestimate particle counts when the relative humidity (RH) is above 65%. It is widely considered that the hygroscopic growth of aerosols is the cause. Hygroscopicity of PM can be described by a single parameter, symbolized as K, and was used in a previous study (Di Antonio et al., 2018) to correct LCPMS data with promising results. However, the study assumed ambient PM to be a pure substance, however, it is often found to be a complex mixture of organic and inorganic chemical species. This study tested if a statistically derived empirical value of K, referred to as “ambient K”, could improve representing the RH influence on LCPMSs. Ambient K is defined as the statistically best-fitting value for several experimental observations of hygroscopy and makes no assumptions on the number of species in ambient PM. Ambient K was graphically demonstrated to be more representative of the experimentally observed RH error compared to assuming K, while having the same statistical performance as conventionally assuming K. Varying observations of hygroscopic behavior among multiple sensors provided strong evidence of multiple chemical species in the observed ambient PM.
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    A simple, affordable, nature-enabled antiviral face covering for airborne coronavirus control
    (2023-05) Bastawisy, Tareq
    In response to the SARS-CoV-2 outbreak, citizens from around the world utilized common household fabrics to prevent infection or spread of the virus at the source. However, these common fabrics have an overall low filtration efficiency to remove viral-laden aerosols. This study aims to improve the performance of these common fabrics by applying antimicrobial proteins as a coating to enhance the capture of viral-laden aerosols. The antiviral proteins are a type of host defense peptide that carries positive charge, and naturally abundant from a tropical plant named Moringa Oleifera. The methods utilize common fabrics such as polyester material, to facilitate immobilization of the protein through simple electrostatic binding, verified by streaming potential. The protocols developed were simple enough to achieve at homes, such as the use of coffee grinders and filters to extract the protein serum, followed by dipping the textile to coat. This method was able to achieve an 85% increase in positive charge, suggesting that our simple dip coating procedure was successful and could be done by citizens at home. Finally, through Integrated Cell Culture-Reverse Transcription-quantitative Polymerase Chain Reaction (ICC-RT-qPCR), using murine hepatitis virus (MHV), as a surrogate to SARS-CoV-2, the serum coating results in a 5-log (99.999%) inactivation of virus in only 15 minutes of contact. Our work presents a new low-cost, natural, and highly effective coating to enhance viral capture of common household textiles that could be prepared by citizens at home to slow down the pandemic and possible future outbreaks.
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    Transition regime collisions in aerosols
    (2013-08) Gopalakrishnan, Ranganathan
    In most natural and engineered aerosol systems, particles fall in the "transition regime", intermediate to the free molecular and continuum ranges. Furthermore, while theories for transport properties of spherical particles in the free molecular and continuum ranges have been available for decades, theories that are applicable to particles of arbitrary shape are lacking. This thesis addresses the transport of neutral and charged molecules (ions) as well as coagulation with particles of arbitrary shape and size. Computational and experimental studies are performed to develop and validate models of collisional mass transfer onto aerosol particles. A broad overview of the thesis is presented in Chapter 1. Using dimensional analysis and Brownian Dynamics trajectory calculations, the collisions between spherical and nonspherical particles are analyzed in Chapters 2 & 3. This approach is extended to include the effect of Coulombic potential interactions in Chapter 4, along with a critical assessment of existing theories. Further, the unipolar charging of arbirary shaped aerosol particles is studied in Chapter 5. Different from previous chapters, an approach to directly calculate the steady state charge distribution of particles exposed to arbitrary bipolar ion populations is developed in Chapter 6. Experiments are conducted with spherical and cylindrical particles to better understand momentum transfer (Chapter 7) and bipolar charging (Chapter 8) in the transition regime. Finally, conclusions derived from this research and future directions are discussed in Chapter 9.