Size Dependent Morphology of Organic Aerosol PDF Download

Author: Muhammad Altaf
Publisher:
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Languages : en
Pages :

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The Earths atmosphere is composed of a wide variety of gas phase species and particulate matter that have a large impact on our climate. Though our understanding of the climate system has improved significantly over the past few decades, the impact of aerosol particles remains uncertain. Aerosol particles can affect climate through the absorption and scattering of radiation (aerosol direct effect) and by serving as cloud condensation nuclei (aerosol indirect effect). It is known that aerosol particles cause a net cooling effect on the planet, but the magnitude of cooling is unclear and remains under investigation. A large part of this uncertainty is due to an incomplete understanding of the complex physical and chemical properties of aerosol particles such as composition, morphology, and phase state.In this dissertation, we focus on investigating the role of particle size and composition in determining morphology. We have discovered that for some organic aerosol systems, particle morphology depends on size, where small particles are homogeneous and large particles are phase separated. To explore the origins of this size dependent behavior, we have worked with a model organic aerosol system, poly(ethylene glycol)-400 mixed with ammonium sulfate. We have used cryogenic-transmission electron microscopy to probe the effect of phase separation mechanism on particle morphology by varying the organic aerosol composition. Our results suggest that a size dependent morphology occurs due to an activated process, where the presence or absence of an activation barrier to phase separation controls the resulting morphology.We have also explored the kinetics and thermodynamics of the phase separation process that results in a size dependent morphology by varying the experimental drying rates. Drying rates that span over four orders of magnitude were investigated. We have observed that at the fastest drying rates, the size of the transition region where both phase separated and homogeneous morphologies exist is on the order of ~100 nm. At the slowest drying rates, the transition region shifts to smaller diameters and the width narrows to ~3 nm. Our results suggest that a size dependent morphology persists to the slowest drying rates. Thus, we conclude that an underlying thermodynamic effect results in this size dependent behavior, rather than solely a kinetic phenomenon.To determine the atmospheric implications of a size dependent morphology, we have used a cloud condensation nuclei counter to probe the effect of a homogeneous vs. a phase separated morphology on cloud condensation nuclei (CCN) activity. We have found that the activation diameters differ for particles which have the same composition, but varying morphology. Since aerosol optical properties are a sensitive measure of particle structure, we have studied the morphology-resolved optical properties of organic aerosol using cavity ring-down spectroscopy. Our spectroscopy data indicate that the optical properties of core-shell and partially engulfed particles are approximately equal, but different than the prediction for homogeneous particles. By accurately parametrizing aerosol particle morphology, optical properties, and CCN activity we will be able to better predict heterogeneous chemistry in the atmosphere, in addition to the aerosol direct and aerosol indirect effects which play a critical role in constraining climate forcing.

Author: Daniel Veghte
Publisher:
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Languages : en
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Major factors that affect climate change depend on gas and particulate phase components in the atmosphere. Gas phase species have been studied in great detail and are well understood, causing a warming effect on the atmosphere. The less understood major contributing factor in the atmosphere are aerosol particles, which range in size from nanometers up to microns. Aerosol particles can directly scatter and absorb light and also have secondary effects such as acting as a surface for gas phase reactions to occur or seed particles for cloud formation. Aerosol particles can cause health problems ranging from serious cardiovascular to respiratory effects. All Climate and health effects of aerosol particles are dependent on particle composition, morphology, concentration, and size. Since a large variety of particulate types exist in the atmosphere, we have focused on understanding the effect of mineral dust composition and morphology. Mineral dust is important because it is the second largest emission by mass. In order to study the optical properties of aerosol particles, we built a cavity ring-down spectrometer and developed methods to interpret the excinction cross section results for particles with a varied shape. We have studied the major components of mineral dust that include calcium carbonate, hematite, quartz, aluminosilicate clay minerals, and feldspars, along with a heterogeneous dust sample. We have found that non-absorbing species that have surface roughness and an aspect ratio close to one (such as calcite, quartz and feldspar) can be treated as spheres. Aerosol particles that are absorbing (hematite) that have an aspect ratio near one with a roughened surface need to be treated with more complex models; otherwise the extinction cross section will be underrepresented. For aerosol particles that are non-absorbing but have a high aspect ratio (aluminosilicate clay minerals), additional modeling parameters are also needed that will account for shape and orientation. We have used Arizona Test Dust to determine if the models we have developed can be used to model the optical properties of a heterogeneous mixture. We have shown that the extinction cross section of the Arizona Test Dust can be modeled as long as individual components are treated independently and significant error would be introduces if all species were treated as spheres.Organic aerosol particles are chemically complex species that originate from primary or secondary emissions. We have described mixed organic/ammonium sulfate particles in the submicron regime using TEM to understand phase separation. When the organic component has a high aqueous solubility, all particles exhibit a homogeneous morphology while at low aqueous solubility all particles exhibit a phase separated structure. Intermediate solubility organics show a size dependent morphology. For pimelic and succinic acid, small particles (under approximately 200 nm) have a homogeneous structure while the larger particles exhibit phase separated structures. We have studied samples collected in Ulaanbaatar, Mongolia to better understand the types of particles and the effect of aging on these particles in an urban environment. The majority of the particles are soot, small spheres, or mineral dust. When we compared the monthly particle composition, we saw that there was an increased aging of the particles during the winter months due to pollution and a lower boundary layer leading to reduced atmospheric mixing. By understanding the particle composition present in areas and modeling the optical properties of individual particle types, better models can be created to give insight into aerosol particles affects on the atmosphere.

Author: Kristin Di Monte
Publisher:
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Languages : en
Pages : 0

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Light extinction by atmospheric aerosol particles and their interactions with water are heavily dependent on their chemical composition, morphology, and mixing state. Both properties are crucial for determining the impact aerosol particles have on our climate. Since light extinction directly impacts visibility as well as climate, measurements of the extinction at varying relative humidities (RH) are needed in order to improve climate models. In this work we have measured the relative humidity dependence of aerosol light extinction and water uptake at 643 nm for particles of varying ammonium sulfate/organic compositions. Internal as well as external mixtures of levoglucosan, sucrose, and adipic acid with ammonium sulfate are investigated using cavity ring-down spectroscopy (CRDS). Optical growth factor (fRH) and hygroscopicity parameters ([kappa]) are reported for each aerosol system.

Author: Theresa M. Kucinski
Publisher:
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Languages : en
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Aerosols are suspended liquid or solid particles that are ubiquitous in the atmosphere. These particles can affect the climate directly by absorbing/scattering radiation or indirectly by helping the formation of clouds. Aerosol particles have an overall net cooling effect, however, there is a large uncertainty associated with the magnitude of cooling. A portion of this uncertainty is due to an incomplete understanding of the chemical and physical properties of particles. Aerosol particles also exist over a large range of sizes which can alter these properties due to size effects, that would require parameterization. Properties that need to be further explored include morphology, phase transitions, and their respective size dependence. This dissertation explores size effects associated with liquid-liquid phase separation (LLPS) and the development of a new method to study phase transitions in submicron particles. Previously, we found that LLPS is a size-dependent process in submicron particles consisting of an organic compound and a single salt component. The size-dependence produces large particles that phase separate while small particles remain homogeneous. Particles in the atmosphere are complex and can contain hundreds of organic compounds. To expand the size-dependence study to better mimic ambient aerosol, we studied particles consisting of complex organic mixtures and ammonium sulfate. The organic mixtures included: dicarboxylic acids (DCA), complex organic mixtures (COM), and [alpha]-pinene secondary organic matter (SOM). We imaged the particles with cryogenic- transmission electron microscopy (cryo-TEM) and all systems displayed size-dependent morphology. Additionally, we observed the presence of three-phase particles in addition to 'channel' morphology. Our results provide further evidence that size-dependent LLPS may be relevant for ambient aerosol. Studying phase transitions in individual submicron particles proves to be difficult with currently available techniques. We present a new method that flash freezes particles to create snapshots into the phase transition process for submicron particles. This method uses vitrification, which is a technique which cools the sample rapidly such that crystallization is avoided and the humidified properties are retained. A temperature controlled flow tube is use to vitrify the particles at several relative humidity (RH) points followed by imaging with cryo-TEM. The method was verified using efflorescence of potassium salts. Additionally, we demonstrate the ability to image the process of LLPS in submicron particles consisting of 2-methylglutaric acid (2-MGA) and ammonium sulfate. We applied the flash freeze technique to study the dynamics of LLPS in submicron particles. In particular, we studied separation relative humidity (SRH), which is defined as the RH that separation occurs, for 2-MGA/ammonium sulfate, 1,2,6-hexantriol/ammonium sulfate, and COM/ammonium sulfate. Particles were vitrified and imaged above phase separation, throughout the process of separation, and until LLPS reaches final maturation. We found that the onset of separation is lower for submicron particles than for particles several micrometers in diameter, indicating a potential shift in the phase diagrams. Additionally, the average SRH is significantly lower for submicron particles in the nucleation and growth regime compared to bulk systems. The decrease in SRH indicates a need for new parameterizations to accurately define particles in models. We also found that the dynamics of separation is a random process that is not dependent on size except for the smallest particles which remain homogeneous throughout. The onset of separation occurs over a large range of RH and our results suggest that this is a result of the energy barrier associated with nucleating a new phase.

Author: Emily Jean Ott
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Aerosol particles can have a variety of compositions which determines their origin and their phase transitions. They can exist in the atmosphere where they are emitted from a variety of natural and anthropogenic sources. Aerosol particles can impact the climate directly though interacting with radiation or indirectly by nucleating cloud droplets and the clouds interacting with the sun. Aerosols can also impact health through the respiratory system. Additionally, aerosols can be used for synthetic purposes where they are created purposely for pharmaceutical or material creation along with many other applications. Understanding the factors that influence phase transitions that a particle may undergo is a prerequisite to understanding both atmospheric aerosol and synthetic aerosol. Several of these factors are investigated. First, the impact of the average ratio of oxygen to carbon (O:C) atoms in the organic molecules through the addition of sucrose to aerosol particles is studied using optical microscopy. A variety of organic molecules and salts combinations which are able to undergo phase separation were studied. The organic/inorganic mixtures exhibit a mixture both high and low separation relative humidities. Then sucrose was added until the particles no longer exhibit phase separation. Particles with higher separation relative humidities in the absence of sucrose required larger quantities of sucrose in order to inhibit phase separation. Additionally, phase separation was seen at higher O:C values than published previously, showing that while average O:C is a good indicator of phase separation, the precise composition of the particles is more important. The morphology of polymer/polymer aerosol particles according to their size was determined. In agreement with previous work, large particles undergo liquid-liquid phase separation while small particles remain homogeneous. Polyethylene glycol with dextran was used as well as polystyrene sulfonate with polyvinyl alcohol. Both of these systems inhibited phase separation at small sizes. To understand the size dependent morphology of polymer/polymer systems, different molecular weight mixtures of the polymers were studied. As the molecular weight of the polymers increased, smaller and smaller aerosol particles were able to undergo phase separation. This was further confirmed with a simple model based on the equations of phase separation and Flory-Huggins theory of a binary system which also showed the decrease in the size of the smallest phase separated particle as the molecular weight of the polymers increase in the size regime studied. The project created novel polymer materials and investigated the phase separation of polymer/polymer systems in confinement. The phase separation of submicron aerosol particles with different salts was investigated to determine the influence of different anions on the size dependent morphology of aerosol particles. The ammonium, sodium, chloride and sulfate ions were used. TEM was used to determine that sodium salts transition to homogenous particles at smaller sizes than their comparable ammonium salt. This difference is likely due to the softness of the ammonium ion when compared to the hardness of the sodium ion. This study provides insights into the size dependent morphology of sea spray aerosol may differ from that of continental aerosol in addition to increasing our understanding of how cations and anions impact phase transitions under confinement. These studies combined increase knowledge of confined phase transitions. While the O:C ratio has been studied before, the importance of the actual composition over the average O:C ratio has now been shown which is useful in understanding atmospheric aerosol particles. The presence of a size dependent morphology for polymer-polymer systems has been shown and modeled in addition to the development of novel polymeric materials. The phase separation differences between ammonium containing aerosols and sodium containing aerosols provides key insights into the differences between continental aerosol and sea spray aerosol in addition to contributing new information about the importance of cations in liquid-liquid phase separation of confined systems. Through these studies both atmospheric aerosol and synthetic aerosol are now better understood.

Author: Emma Tackman
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Aerosol particles are a diverse class of materials that permeate the atmosphere with implications for global climate and human health. Atmospheric aerosols are released into the environment from many sources and continue to undergo atmospheric processing which introduces further variation into particle populations. This surfeit of sources and atmospheric trajectories leads to a wide variety in the properties in aerosol particles such as composition, shape, size, morphology, and reactivity. The methods measuring properties of aerosol particles is itself an important and developing field of study with direct applications in bettering our understanding of aerosol behaviors and atmospheric chemical systems. This work presents a critical analysis of existing microscopy-based measurements and provides new methods, applications, and recommendations for improving the assessment of aerosol properties. Chemical properties of aerosol particles include aqueous particle acidity and the O:C ratio of organic constituents. A new method for measuring the internal pH of aqueous aerosol microdroplets was developed and presented here using carbon quantum dots as a pH sensitive fluorophore. This technique was validated using a complex organic mixture representing various functional groups found in atmospheric organic material. The influence of organic O:C ratio on phase separation for proxy organic/inorganic mixed aerosol particles was assessed for microdroplets and nanoparticles. For optical microscope experiments, sucrose was added to organic/inorganic mixtures to systematically increase the O:C ratio of the system and was observed to suppress phase separation. Similarly, particles made up of combinations of carboxylic acids at particular O:C ratios and inorganic salts are analyzed using TEM for size dependence of phase separation at the nanoscale. Generally, large particles are able to phase separate while small particles remain homogeneous, or well mixed, and the transition region between the two regimes was examined. TEM is used in several studies to consider aerosol particle spreading and morphology at atmospherically relevant sizes. Inorganic particles were found to spread along the surface of a substrate. Particles with an organic coating also spread on the substrate but additionally lost volume, possibly due to outgassing of residual volatile species in storage or physical deformation during the impaction process. Results were compared to measurements of the same particles suspended in a gas flow and sizing discrepancies between the two methods were found, mostly attributed to the presence of a substrate in microscope assays. Further, the influence of generation parameters on the final morphologies of particles was determined for particles made under low and high relative humidity conditions with wet and dry seed particles. Wet seeds were found to restructure due to humidity cycling and spread less on the surface than dry seeds, while wet and dry coated particles were influenced similarly by the impaction process. Wet seeded organic particles also showed a new textured morphology, emphasizing the utility of microscope measurements of individual aerosol particles.

Author: Swarup China
Publisher: MDPI
ISBN: 3038971332
Category : Science
Languages : en
Pages : 215

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This book is a printed edition of the Special Issue "Morphology and Internal Mixing of Atmospheric Particles" that was published in Atmosphere

Author: Rekha Kale
Publisher: Scitus Academics LLC
ISBN: 9781681171326
Category : Aerosols
Languages : en
Pages : 0

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Book Description
Atmospheric Aerosols is a vital problem in current environmental research due to its importance in atmospheric optics, energetics, radiative transfer studies, chemistry, climate, biology and public health. Aerosols can influence the energy balance of the terrestrial atmosphere, the hydrological cycle, atmospheric dynamics and monsoon circulations. Because of the heterogeneous aerosol field with large spatial and temporal variability and reduction in uncertainties in aerosol quantification is a challenging task in atmospheric sciences. Keeping this in view the present study aims to assess the impact of aerosols on coastal Indian station Visakhapatnam and the adjoining Bay of Bengal. An aerosol is a colloid of fine solid particles or liquid droplets, in air or another gas. Aerosols can be natural or not. Examples of natural aerosols are fog, forest exudates and geyser steam.

Author: Claudio Tomasi
Publisher: John Wiley & Sons
ISBN: 3527336451
Category : Science
Languages : en
Pages : 706

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Book Description
Ein Blick auf die morphologischen, physikalischen und chemischen Eigenschaften von Aerosolen aus den unterschiedlichsten natürlichen und anthropogenen Quellen trägt zum besseren Verständnis der Rolle bei, die Aerosolpartikel bei der Streuung und Absorption kurz- und langwelliger Strahlung spielen. Dieses Fachbuch bietet Informationen, die sonst schwer zu finden sind, und vermittelt ausführlich die Kenntnisse, die erforderlich sind, um die mikrophysikalischen, chemischen und Strahlungsparameter zu charakterisieren, die bei der Wechselwirkung von Sonnen- und Erdstrahlen so überaus wichtig sind. Besonderes Augenmerk liegt auf den indirekten Auswirkungen von Aerosolen auf das Klima im Rahmen des komplexen Systems aus Aerosolen, Wolken und der Atmosphäre. Auch geht es vorrangig um die Wirkungen natürlicher und anthropogener Aerosole auf die Luftqualität und die Umwelt, auf die menschliche Gesundheit und unser kulturelles Erbe. Mit einem durchgängig lösungsorientierten Ansatz werden nicht nur die Probleme und Gefahren dieser Aerosole behandelt, sondern auch praktikable Lösungswege aufgezeigt.

Author: Yue Zhang
Publisher: American Chemical Society
ISBN: 0841299293
Category : Science
Languages : en
Pages : 176

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Book Description
The uncertainties in the aerosol effects on radiative forcing limit our knowledge of climate change, presenting us with an important research challenge. Aerosols in Atmospheric Chemistry introduces basic concepts about the characterization, formation, and impacts of ambient aerosol particles as an introduction to graduate students new to the field. Each chapter also provides an up-to-date synopsis of the latest knowledge of aerosol particles in atmospheric chemistry.