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: Georges Le Bras Publisher: Springer Science & Business Media ISBN: 3642592163 Category : Science Languages : en Pages : 316
Book Description
Oxidation and removal of atmospheric constituents involve complex sequences of reactions which can lead to the production of photo-oxidants such as ozone. In order to understand and model these complex reaction sequences, it is necessary to have a comprehensive understanding of reaction mechanisms and accurate estimates of kinetic parameters for relevant gas-phase atmospheric reactions. This book presents recent advances in the field and includes the following topics: e.g. the oxidation of simple organic compounds, NOx kinetics and mechanisms, OH radical production and rate constants for the OH attack on more complex organic compounds, peroxy and alkoxy radical reactions, photo-oxidation of aromatic and biogenic compounds, and the interaction between radical species.
Author: N. M. Emanuel Publisher: Elsevier ISBN: 1483145115 Category : Science Languages : en Pages : 628
Book Description
Oxidation of Organic Compounds: Medium Effects in Radical Reactions explores the role of solvents and of the composition of phase states in radical-chain processes involved in the oxidation of organic compounds. Organized into 10 chapters, this book begins with a discussion of the basic concepts relating to the mechanism involved in the oxidation of hydrocarbons and other organic compounds in liquid-phase reactions. Subsequent chapters detail some methods for studying the mechanism of oxidation reactions; role of solvation in chemical reaction kinetics; role of the medium in chain-initiation reactions; role of non-specific and specific solvation in chain-propagation and chain-termination reactions; and the role of solvation in chain-termination reactions in inhibitors. The influence of the solvent and the phase state of substances undergoing oxidation on the rates and mechanisms of individual elementary processes are also addressed. The last chapter examines the problem of the influence of the solid state of the polymer on the reactivity of radicals. This monograph will be valuable to scientific research workers, engineers, and engineering technologists specializing in the field of radical reactions and in particular in the oxidation of organic compounds.
Author: Jack G. Calvert Publisher: Oxford University Press ISBN: 9780199771547 Category : Science Languages : en Pages : 570
Book Description
This text reviews many of the aspects of the chemistry of the aromatic hydrocarbons and a consensus evaluation of the data by seven of the leading atmospheric scientists. The book covers topics ranging from the relative importance of the compounds in ozone and haze development to methods of estimating elemantary rate coefficients based on structural features of the compounds to mechanisms of aerosol generation and atmostpheric reaction of the polycyclic compounds to photochemical processes. It identifies features of the aromatic hydrocarbons requiring further study and appendicies give the structural formulas and nomenclature of the compounds reviewed in the book.
Author: Jack Calvert Publisher: Oxford University Press ISBN: 0199877475 Category : Science Languages : en Pages : 1634
Book Description
Prepared by an international team of eminent atmospheric scientists, Mechanisms of Atmospheric Oxidation of the Oxygenates is an authoritative source of information on the role of oxygenates in the chemistry of the atmosphere. The oxygenates, including the many different alcohols, ethers, aldehydes, ketones, acids, esters, and nitrogen-atom containing oxygenates, are of special interest today due to their increased use as alternative fuels and fuel additives. This book describes the physical properties of oxygenates, as well as the chemical and photochemical parameters that determine their reaction pathways in the atmosphere. Quantitative descriptions of the pathways of the oxygenates from release or formation in the atmosphere to final products are provided, as is a comprehensive review and evaluation of the extensive kinetic literature on the atmospheric chemistry of the different oxygenates and their many halogen-atom substituted analogues. This book will be of interest to modelers of atmospheric chemistry, environmental scientists and engineers, and air quality planning agencies as a useful input for development of realistic modules designed to simulate the atmospheric chemistry of the oxygenates, their major oxidation products, and their influence on ozone and other trace gases within the troposhere.
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: Jeremy Daniel Smith Publisher: ISBN: 9781321609912 Category : Languages : en Pages :
Book Description
Organic aerosols (OA) are a dominant fraction of particulate mass in the atmosphere, and much is secondary in nature. Secondary organic aerosol (SOA) is formed in the atmosphere from volatile organic compound precursors. Traditional SOA formation pathways involve primarily gas-phase processes: Oxidation reactions of organic gases result in low-volatility products that condense to the particulate phase, increasing aerosol mass. However, in recent years heterogeneous processes, including aqueous reactions, have gained more attention as gas-phase processes often fail to accurately predict observed mass loadings of aerosol in the atmosphere. Aqueous SOA formation is the result of a volatile organic species partitioning to the aqueous phase (clouds, fogs, aqueous aerosols), where they are chemically converted into a non-volatile species that remains in the particulate phase upon water evaporation. In this work we explore the aqueous chemical reaction kinetics and the SOA formation potential of phenols, which are released in large quantities from biomass combustion. Phenols are a broad class of organic compounds with intermediate volatilities (102 - 106 [mu]g m−3 at 20°C) and moderate to high Henry's Law Constants (103 - 109M atm−1), indicating significant partitioning to atmospheric aqueous phases. We begin in chapters 2 and 3 by investigating the aqueous oxidation of the compounds phenol (compound with formula C6H5OH), guaiacol (2-methoxyphenol), syringol (2,6-dimethoxyphenol), and three dihydroxybenzenes (catechol, resorcinol, hydroquinone). For each phenol we examined reactions with two oxidants: hydroxyl radical (*OH) and the triplet excited state of 3,4-dimethoxybenzaldehyde, which is also emitted from biomass combustion. Triplet excited states (3C*) have been widely studied in surface waters (oceans and lakes) but are a novel oxidation pathway in atmospheric aqueous phases. The precursors for triplet excited states are essentially brown carbon: organic molecules high amoutns of conjugation (or nitrogen hetero atoms) that can absorb solar radiation, resulting in an excited molecule with a high oxidative potential. We find that the 3C*-mediated aqueous oxidations of phenols are rapid and can dominate over *OH at low pH (
Author: Slavtcho Rakovsky Publisher: ISBN: Category : Science Languages : en Pages : 366
Book Description
Two Bulgarian researchers summarize their contributions to the field of ozone chemistry, and outline future research trends. The monograph begins with the ozonolysis of hydrocarbons, oxygen containing organic compounds, and alkenes in liquid phase. The remaining chapters deal with ozone degradation and stabilization of real rubber systems; quantum chemical calculations of ozonolysis of organic compounds; properties, preparations, analysis, and decomposition of ozone; and ozone applications to ecology, industry, and medicine. Annotation copyrighted by Book News, Inc., Portland, OR
Author: Jack Calvert Publisher: OUP USA ISBN: 0199767076 Category : Science Languages : en Pages : 1634
Book Description
Prepared by an international team of eminent atmospheric scientists, Mechanisms of Atmospheric Oxidation of the Oxygenates is an authoritative source of information on the role of oxygenates in the chemistry of the atmosphere. The oxygenates, including the many different alcohols, ethers, aldehydes, ketones, acids, esters, and nitrogen-atom containing oxygenates, are of special interest today due to their increased use as alternative fuels and fuel additives. This book describes the physical properties of oxygenates, as well as the chemical and photochemical parameters that determine their reaction pathways in the atmosphere. Quantitative descriptions of the pathways of the oxygenates from release or formation in the atmosphere to final products are provided, as is a comprehensive review and evaluation of the extensive kinetic literature on the atmospheric chemistry of the different oxygenates and their many halogen-atom substituted analogues. This book will be of interest to modelers of atmospheric chemistry, environmental scientists and engineers, and air quality planning agencies as a useful input for development of realistic modules designed to simulate the atmospheric chemistry of the oxygenates, their major oxidation products, and their influence on ozone and other trace gases within the troposhere.
Author: Theodora Nah
Author: Lisa Viero
Author: Georges Le Bras
Author: N. M. Emanuel
Author: Jack G. Calvert
Author: Jack Calvert
Author: Sean Herbert Kessler
Author: Jeremy Daniel Smith
Author: Slavtcho Rakovsky
Author: Jack Calvert