Elucidation of Mechanisms and Impacts of Oxidation on Organic Particulate Matter PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download Elucidation of Mechanisms and Impacts of Oxidation on Organic Particulate Matter PDF full book. Access full book title Elucidation of Mechanisms and Impacts of Oxidation on Organic Particulate Matter by Katheryn Ruth Kolesar. Download full books in PDF and EPUB format.
Author: Katheryn Ruth Kolesar Publisher: ISBN: 9781339261232 Category : Languages : en Pages :
Book Description
Atmospheric particulate matter (PM) is a component of air pollution that negatively impacts human health and welfare and has strong impacts on global climate. The organic fraction of PM, organic aerosol (OA), is often a dominant fraction of PM mass. Organic aerosol can be emitted directly into the atmosphere as primary OA (POA) or can be produced in the atmosphere from processes such as gas phase reactions of volatile organic compounds (VOCs) with oxidants or aqueous phase reactions of dissolved organics both of which form secondary OA (SOA). The formation and evolution of SOA, as well as the interaction between SOA and POA, are poorly characterized, which leads to uncertainties in the prediction of their concentrations and impacts in the atmosphere. This dissertation addresses processes associated with gas phase SOA formation as well as chemical and physical processing of SOA and POA through experimental studies investigating: 1) the volatility of SOA, 2) the influence of SOA on the heterogeneous oxidation of POA, and 3) the chemical mechanisms of POA oxidation. In the first set of studies (Chapters 2-3), it is experimentally demonstrated that there has been a fundamental disconnect between the properties of SOA as derived from SOA formation and growth experiments and those derived from evaporation experiments, which has implications for the representation of SOA within air quality and climate models. Specifically, SOA is experimentally determined to be less volatile than predicted based on formation studies through the measurement of the extent of evaporation with temperature change along with concurrent measurement of the particle composition. Volatility measurements were made as a function of mass concentration for [alpha]pinene+O3 SOA and with accompanying particle composition measurements for different SOA types. It was found that SOA volatility was independent of mass concentration and that nine types of SOA had similar volatilities. Furthermore, SOA composition remained constant as particles evaporated. When compared to results from a detailed, physically based model of evaporation, these observations suggest that there are condensed-phase chemical reactions that rapidly produce oligomers and that oligomers are likely the majority of the SOA mass. In a second study (Chapter 4), a detailed experimental and model assessment of the chemical pathways associated with OH-driven heterogeneous chemistry of two model POA compounds is discussed. The chemical pathways for oxidation of POA are often assumed to be the same as gas phase reactions, yet the higher density of molecules in the condensed phase may increase the dominance of alternate mechanisms. The heterogeneous oxidation of squalane and BES are used as model POA compounds to investigate structure-dependent chemical mechanisms of oxidation. The oxidation of squalane is dominated by the formation of products with added ketone or alcohol functionality whereas the oxidation of BES is dominated by the addition of ketone moieties with minor contributions from pathways forming alcohol substituted products. These differences are shown to be linked directly to differences in the dominant chemical pathways available to the different precursor molecules that result from structural differences in the molecules. In Chapter 5, the influence of an SOA "coating" on the OH initiated heterogeneous oxidation of model POA particles, comprised of squalane, is considered. Previous studies have shown that SOA can protect buried compounds from reaction with O3 but the extent to which such protection extends to other oxidants had not been established. Here, it is shown that when OH is the oxidant SOA does not block squalane from oxidation and, in fact, the rate of oxidation with OH exposure is enhanced. Although it is clear that an enhancement occurs, the exact extent of enhancement is dependent on the assumed particle morphology, i.e. whether the particle is well mixed, partially engulfed or there is an SOA coating on the squalane core.
Author: Katheryn Ruth Kolesar Publisher: ISBN: 9781339261232 Category : Languages : en Pages :
Book Description
Atmospheric particulate matter (PM) is a component of air pollution that negatively impacts human health and welfare and has strong impacts on global climate. The organic fraction of PM, organic aerosol (OA), is often a dominant fraction of PM mass. Organic aerosol can be emitted directly into the atmosphere as primary OA (POA) or can be produced in the atmosphere from processes such as gas phase reactions of volatile organic compounds (VOCs) with oxidants or aqueous phase reactions of dissolved organics both of which form secondary OA (SOA). The formation and evolution of SOA, as well as the interaction between SOA and POA, are poorly characterized, which leads to uncertainties in the prediction of their concentrations and impacts in the atmosphere. This dissertation addresses processes associated with gas phase SOA formation as well as chemical and physical processing of SOA and POA through experimental studies investigating: 1) the volatility of SOA, 2) the influence of SOA on the heterogeneous oxidation of POA, and 3) the chemical mechanisms of POA oxidation. In the first set of studies (Chapters 2-3), it is experimentally demonstrated that there has been a fundamental disconnect between the properties of SOA as derived from SOA formation and growth experiments and those derived from evaporation experiments, which has implications for the representation of SOA within air quality and climate models. Specifically, SOA is experimentally determined to be less volatile than predicted based on formation studies through the measurement of the extent of evaporation with temperature change along with concurrent measurement of the particle composition. Volatility measurements were made as a function of mass concentration for [alpha]pinene+O3 SOA and with accompanying particle composition measurements for different SOA types. It was found that SOA volatility was independent of mass concentration and that nine types of SOA had similar volatilities. Furthermore, SOA composition remained constant as particles evaporated. When compared to results from a detailed, physically based model of evaporation, these observations suggest that there are condensed-phase chemical reactions that rapidly produce oligomers and that oligomers are likely the majority of the SOA mass. In a second study (Chapter 4), a detailed experimental and model assessment of the chemical pathways associated with OH-driven heterogeneous chemistry of two model POA compounds is discussed. The chemical pathways for oxidation of POA are often assumed to be the same as gas phase reactions, yet the higher density of molecules in the condensed phase may increase the dominance of alternate mechanisms. The heterogeneous oxidation of squalane and BES are used as model POA compounds to investigate structure-dependent chemical mechanisms of oxidation. The oxidation of squalane is dominated by the formation of products with added ketone or alcohol functionality whereas the oxidation of BES is dominated by the addition of ketone moieties with minor contributions from pathways forming alcohol substituted products. These differences are shown to be linked directly to differences in the dominant chemical pathways available to the different precursor molecules that result from structural differences in the molecules. In Chapter 5, the influence of an SOA "coating" on the OH initiated heterogeneous oxidation of model POA particles, comprised of squalane, is considered. Previous studies have shown that SOA can protect buried compounds from reaction with O3 but the extent to which such protection extends to other oxidants had not been established. Here, it is shown that when OH is the oxidant SOA does not block squalane from oxidation and, in fact, the rate of oxidation with OH exposure is enhanced. Although it is clear that an enhancement occurs, the exact extent of enhancement is dependent on the assumed particle morphology, i.e. whether the particle is well mixed, partially engulfed or there is an SOA coating on the squalane core.
Author: Theodora Nah Publisher: ISBN: Category : Languages : en Pages : 137
Book Description
Understanding the heterogeneous oxidation of organic particulate matter ("aerosol") is an active area of current research in atmospheric and combustion chemistry. The chemical evolution of organic aerosol is complex and dynamic since it can undergo multiple oxidation reactions with gas phase oxidants to form a mixture of different generations of oxidation products that control the average aerosol mass and volatility. In many of these systems, hydrocarbon free radicals, formed by reaction with gas phase oxidants, play key roles as initiators, propagators and terminators of surface reactions. This dissertation presents a detailed study of the reaction kinetics and mechanisms of the heterogeneous oxidation of unsaturated organic aerosol, and aims to provide new molecular and mechanistic insights into the reaction pathways in heterogeneous organic aerosol oxidation. The heterogeneous oxidation of unsaturated fatty acid (oleic acid C18H34O2, linoleic acid C18H32O2 and linolenic acid C18H30O2) aerosol by hydroxyl (OH) radicals is first studied in Chapter 2 to explore how surface OH addition reactions initiate chain reactions that rapidly transform the chemical composition of unsaturated organic aerosol. Oleic acid, linoleic acid and linolenic acid have the same linear C18 carbon backbone structure with one, two and three C=C double bonds, respectively. By studying carboxylic acids with different numbers of C=C double bonds, the role that multiple reactive sites plays in controlling reaction rates can be observed. The kinetic parameter of interest in these studies is the effective uptake coefficient, defined as the number of particle phase unsaturated fatty acid molecules reacted per OH-particle collision. The effective uptake coefficients for the unsaturated fatty acids are larger than unity, providing clear evidence for particle-phase secondary chain chemistry. The effective uptake coefficients for the unsaturated fatty acids decrease with increasing O2 concentration, indicating that O2 promotes chain termination in the unsaturated fatty acid reactions. The kinetics and products of squalene (a C30 branched alkene with 6 C=C double bonds) oxidation are compared to that of the unsaturated fatty acids in Chapters 3 and 4 to understand how molecular structure and chemical functionality influence reaction rates and mechanisms. The squalene effective uptake coefficient, which is also larger than one, is smaller than that of linoleic acid and linolenic acid despite the larger number of C=C double bonds in squalene. In contrast to the unsaturated fatty acids, the squalene effective uptake coefficient increases with O2 concentration, indicating that O2 promotes chain propagation in the squalene reaction. Elemental and product analysis of squalene aerosol shows that O2 promotes particle volatilization in the squalene reaction, suggesting that fragmentation reactions are important when O2 is present in the OH oxidation of branched unsaturated organic aerosol. In contrast, elemental and product analysis of linoleic acid aerosol shows that O2 does not influence the rate of particle volatilization in the linoleic acid reaction, suggesting that O2 does not alter the relative importance of fragmentation reactions in the OH oxidation of linear unsaturated organic aerosol. Lastly, depending on the aerosol phase (e.g. solid and semi-solid) and the timescale for homogeneous mixing within the aerosol particle, the chemical composition may vary spatially within an aerosol particle. This necessitates the need for new techniques to characterize the interfacial chemical composition of aerosol particles. In the last portion of the dissertation, direct analysis in real time mass spectrometry (DART-MS) is used to analyze the surface chemical composition of nanometer-sized organic aerosol particles in real time at atmospheric pressure. By introducing a stream of aerosol particles in between the DART ionization source and the atmospheric pressure inlet of the mass spectrometer, the aerosol particles are exposed to a thermal flow of helium or nitrogen gas containing some fraction of metastable helium atoms or nitrogen molecules. In this configuration, the molecular constituents of organic aerosol particles are desorbed, ionized and detected with reduced molecular ion fragmentation, allowing for compositional identification. The reaction of ozone with sub-micron oleic acid particles is also measured to demonstrate the ability of DART-MS to identify products and quantify reaction rates in a heterogeneous reaction.
Author: Christopher Yung-Ta Lim Publisher: ISBN: Category : Languages : en Pages : 101
Book Description
Fine particulate matter (PM, or "aerosol") in the atmosphere affects the Earth's radiative balance and is one of the most important risk factors leading to premature mortality worldwide. Thus, understanding the processes that control the loading and chemical composition of PM in the atmosphere is key to understanding air quality and climate. However, the chemistry of organic aerosol (OA), which comprises a significant fraction of submicron atmospheric PM, is immensely complex due to the vast number of organic compounds in the atmosphere and their numerous reaction pathways. Laboratory experiments have generally focused on the initial formation of OA from volatile organic compounds (VOCs), but have neglected processes that can change the composition and loading of OA over longer timescales ("aging"). This thesis describes several laboratory studies that better constrain the effect of two important aging processes over timescales of several days, the oxidation of gas phase species to form secondary OA (condensation) and the reaction of gas phase radicals with organic molecules in the particle phase (heterogeneous oxidation). First, the oxidation of biomass burning emissions is studied by exposing particles and gases present in smoke to hydroxyl radicals (OH). Increases in organic aerosol mass are observed for all fuels burned, and the amount of OA formed is explained well by the extent of aging and the total concentration of measured organic gases. Second, the effect of particle morphology on the rate of heterogeneous oxidation is examined by comparing the oxidation of particles with thin organic coatings to the oxidation of pure organic particles. Results show that morphology can have a strong impact on oxidation kinetics and that particles with high organic surface area to volume ratios can be rapidly oxidized. Third, the molecular products from the heterogeneous OH oxidation of a single model compound (squalane) are measured. Formation of a range of gas-phase oxygenated VOCs is observed, indicating the importance of fragmentation reactions that decrease OA mass, and providing insight into heterogeneous reaction mechanisms. The results from this work emphasize that the concentration and composition of OA can change dramatically over multiple days of atmospheric oxidation.
Author: Clemens von Sonntag Publisher: IWA Publishing ISBN: 1843393131 Category : Science Languages : en Pages : 306
Book Description
Even though ozone has been applied for a long time for disinfection and oxidation in water treatment, there is lack of critical information related to transformation of organic compounds. This has become more important in recent years, because there is considerable concern about the formation of potentially harmful degradation products as well as oxidation products from the reaction with the matrix components. In recent years, a wealth of information on the products that are formed has accumulated, and substantial progress in understanding mechanistic details of ozone reactions in aqueous solution has been made. Based on the latter, this may allow us to predict the products of as yet not studied systems and assist in evaluating toxic potentials in case certain classes are known to show such effects. Keeping this in mind, Chemistry of Ozone in Water and Wastewater Treatment: From Basic Principles to Applications discusses mechanistic details of ozone reactions as much as they are known to date and applies them to the large body of studies on micropollutant degradation (such as pharmaceuticals and endocrine disruptors) that is already available. Extensively quoting the literature and updating the available compilation of ozone rate constants gives the reader a text at hand on which his research can be based. Moreover, those that are responsible for planning or operation of ozonation steps in drinking water and wastewater treatment plants will find salient information in a compact form that otherwise is quite disperse. A critical compilation of rate constants for the various classes of compounds is given in each chapter, including all the recent publications. This is a very useful source of information for researchers and practitioners who need kinetic information on emerging contaminants. Furthermore, each chapter contains a large selection of examples of reaction mechanisms for the transformation of micropollutants such as pharmaceuticals, pesticides, fuel additives, solvents, taste and odor compounds, cyanotoxins. Authors: Prof. Dr. Clemens von Sonntag, Max-Planck-Institut für Bioanorganische Chemie, Mülheim an der Ruhr, and Instrumentelle Analytische Chemie, Universität Duisburg-Essen, Essen, Germany and Prof. Dr. Urs von Gunten, Eawag, Swiss Federal Institute of Aquatic Science and Technology, Dübendorf, and Ecole Polytechnique Federal de Lausanne, Lausanne, Switzerland.
Author: Sean Herbert Kessler Publisher: ISBN: Category : Languages : en Pages : 134
Book Description
The immense chemical complexity of atmospheric organic particulate matter ("aerosol") has left the general field of condensed-phase atmospheric organic chemistry relatively under-developed when compared with either gas-phase chemistry or the formation of inorganic compounds. In this work, we endeavor to improve the general understanding of the narrow class of oxidation reactions that occur at the interface between the particle surface and the gas-phase. The heterogeneous oxidation of pure erythritol (C4H1 00 4 ) and levoglucosan (C6H1 00 5) particles by hydroxyl radical (OH) was studied first in order to evaluate the effects of atmospheric aging on the mass and chemical composition of atmospheric organic aerosol, particularly that resembling fresh secondary organic aerosol (SOA) and biomass-burning organic aerosol (BBOA). In contrast to what is generally observed for the heterogeneous oxidation of reduced organics, substantial volatilization is observed in both systems. As a continuation of the heterogeneous oxidation experiments, we also measure the kinetics and products of the aging of highly oxidized organic aerosol, in which submicron particles composed of model oxidized organics -- 1,2,3,4-butanetetracarboxylic acid (C8H100 8), citric acid (C6 H8 0 7), tartaric acid (C4H6 0 6 ), and Suwannee River fulvic acid -- were oxidized by gas-phase OH in the same flow reactor, and the masses and elemental composition of the particles were monitored as a function of OH exposure. In contrast to studies of the less-oxidized model systems, particle mass did not decrease significantly with heterogeneous oxidation, although substantial chemical transformations were observed and characterized. Lastly, the immense complexity inherent in the formation of SOA -- due primarily to the large number of oxidation steps and reaction pathways involved -- has limited the detailed understanding of its underlying chemistry. In order to simplify this inherent complexity, we give over the last portion of this thesis to a novel technique for the formation of SOA through the photolysis of gas-phase alkyl iodides, which generates organic peroxy radicals of known structure. In contrast to standard OH-initiated oxidation experiments, photolytically initiated oxidation forms a limited number of products via a single reactive step. The system in which the photolytic SOA is formed is also repurposed as a generator of organic aerosol for input into a secondary reaction chamber, where the organic particles undergo additional aging by the heterogeneous oxidation mechanism already discussed. Particles exiting this reactor are observed to have become more dramatically oxidized than comparable systems containing SOA formed by gas-phase alkanes undergoing "normal" photo-oxidation by OH, suggesting simultaneously the utility of gas-phase precursor photolysis as an effective experimental platform for studying directly the chemistry involved in atmospheric aerosol formation and also the possibility that heterogeneous processes may play a more significant role in the atmosphere than what is predicted from chamber experiments. Consideration is given for the application of these results to larger-scale experiments, models, and conceptual frameworks.
Author: Kelly Elizabeth Daumit Publisher: ISBN: Category : Languages : en Pages : 118
Book Description
Atmospheric particulate matter (or "aerosol") is known to have important implications for climate change, air quality, and human health. Our ability to predict its formation and fate is hindered by uncertainties associated with one type in particular, organic aerosol (OA). Ambient OA measurements indicate that it can become highly oxidized in short timescales, but this is generally not reproduced well in laboratory studies or models, suggesting the importance of formation processes that are not fully understood at present. In this thesis, I focus on the potential for chemistry within aqueous aerosol to produce highly oxidized OA. I first use a retrosynthetic modeling approach to constrain the viable precursors and formation pathways of highly oxidized OA, starting with a target oxidized product and considering possible reverse reactions. Results suggest three general formation mechanisms are possible: (1) functionalization reactions that add multiple functional groups per oxidation step, (2) oligomerization of highly oxidized precursors, or (3) fast aging within the condensed phase, such as oxidation within aqueous particles. The focus of the remainder of the thesis involves experiments designed to study this third pathway. To examine the importance of the formation of highly oxidized OA in the aqueous phase (wet particles or cloud droplets), I investigate aqueous oxidation of polyols within submicron particles in an environmental chamber, allowing for significant gas-particle partitioning of reactants, intermediates, and products. Results are compared to those from analogous oxidation reactions carried out in bulk solution (the phase in which most previous studies were carried out). Both sets of experiments result in rapid oxidation, but substantially more carbon is lost from the submicron particles, likely due to differences in partitioning of early-generation products. Finally, OA is formed from the gas-phase ozonolysis of biogenic precursors in the presence of reactive aqueous particles, showing that oxidation within the condensed phase can generate highly oxidized products. The overall results of this thesis demonstrate that aqueous-phase oxidation can contribute to the rapid formation of highly oxidized OA and therefore its inclusion in atmospheric models should be considered, but that experiments to constrain such pathways must be carried out under atmospherically relevant conditions.
Author: Katheryn Ruth Kolesar
Author: Katheryn Ruth Kolesar
Author: Leo Aloysius Wall
Author: Theodora Nah
Author: Christopher Yung-Ta Lim
Author: Clemens von Sonntag
Author: E.K. Duursma
Author: Sean Herbert Kessler
Author: Shabana Naz Anwar
Author: M. A. Waters
Author: Kelly Elizabeth Daumit