The Atmospheric Oxidation of Volatile Organic Compounds Through Hydrogen Shift Reactions PDF Download
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Author: Hasse Christian Knap
Publisher:
ISBN:
Category :
Languages : en
Pages : 145
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Book Description
Author: Hasse Christian Knap
Publisher:
ISBN:
Category :
Languages : en
Pages : 145
Get Book Here
Book Description
Author: Hasse Christian Knap
Publisher:
ISBN: 9788791963704
Category :
Languages : en
Pages :
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Book Description
Author: Ralf Koppmann
Publisher: John Wiley & Sons
ISBN: 0470994150
Category : Science
Languages : en
Pages : 512
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Book Description
Every day, large quantities of volatile organic compounds (VOCs) are emitted into the atmosphere from both anthropogenic and natural sources. The formation of gaseous and particulate secondary products caused by oxidation of VOCs is one of the largest unknowns in the quantitative prediction of the earth’s climate on a regional and global scale, and on the understanding of local air quality. To be able to model and control their impact, it is essential to understand the sources of VOCs, their distribution in the atmosphere and the chemical transformations which remove these compounds from the atmosphere. In recent years techniques for the analysis of organic compounds in the atmosphere have been developed to increase the spectrum of detectable compounds and their detection limits. New methods have been introduced to increase the time resolution of those measurements and to resolve more complex mixtures of organic compounds. Volatile Organic Compounds in the Atmosphere describes the current state of knowledge of the chemistry of VOCs as well as the methods and techniques to analyse gaseous and particulate organic compounds in the atmosphere. The aim is to provide an authoritative review to address the needs of both graduate students and active researchers in the field of atmospheric chemistry research.
Author: Sui So
Publisher:
ISBN:
Category : Atmospheric chemistry
Languages : en
Pages : 346
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Book Description
[Beta]-Hydroxyperoxyl radicals are formed during atmospheric oxidation of unsaturated volatile organic compounds (VOCs) such as isoprene. They are also important intermediates in the combustion of alcohols. In these environments the unimolecular isomerisation and decomposition of [beta]-hydroxyperoxyl radicals may be of importance. Results of ion-trap mass spectrometry generating a prototypical distonic charge-tagged [beta]-hydroxyalkyl radical anion •CH2C(OH)(CH3)CH2C(O)O- have been obtained by a collaborating research group. The subsequent reaction of the radical anion with O2 in the gas phase has been investigated under conditions that are devoid of complicating radical-radical reactions. In this thesis, quantum chemical calculations and master equation/RRKM theory modelling are used to rationalise the results and discern a reaction mechanism. Reaction is found to proceed via initial hydrogen abstraction from the [gamma]-methylene group and [beta]-hydroxyl group, with both reaction channels eventually forming isobaric product ions due to loss of either •OH + HCHO or •OH + CO2. Isotope labelling studies confirm that a 1,5-hydrogen shift from the [beta]-hydroxyl functionality results in a hydroperoxyalkoxyl radical intermediate that can undergo further unimolecular dissociation. Furthermore, facile decomposition of [beta]-hydroxyperoxyl radicals has been confirmed to yield •OH in the gas phase. Moreover, the influence of an anionic charge on the reaction chemistry of [beta]-hydroxyperoxyl radicals has been investigated by examining the molecular orbitals of a distonic [beta]-hydroxyperoxyl radical anion analogue •OOCH2CH(OH)CH2C(O)O-. Instead of following the conventional Aufbau principle, the radical anion exhibits a peculiar electronic arrangement, where the singly occupied molecular orbital (SOMO) is no longer the frontier orbital and carries energy lower than other doubly occupied molecular orbitals (HOMOs). This phenomenon is manifested as SOMO-HOMO conversion and is caused by the through space stabilisation between the interaction of the anion and radical site. Further investigation of the other C4H6O5•- isomers involved in the unimolecular reaction mechanisms of the hydroxyperoxyl radical anion •OOCH2CH(OH)CH2C(O)O- revealed that these radical anion isomers exhibit different extent of orbital conversion. As a result, the reaction chemistry of this radical anion is influenced by various additional stabilities associated with the unconventional electron arrangement, switching the dominant reaction pathway from [beta]-OH abstraction in the relevant neutral radical to C-H abstraction at the [beta]-carbon in the radical anion analogue. Despite the change in product distribution, all reaction pathways remain the same in both the neutral radical and radical anion analogues. Enols are emerging as trace atmospheric components that may play a significant role in the formation of organic acids in the atmosphere. They are unsaturated VOCs and their oxidation involves hydroxyperoxyl radicals as key intermediates. It has recently been discovered that acetaldehyde can undergo UV-induced isomerisation to vinyl alcohol (the enol counterparts) under atmospheric conditions. The •OH-initiated oxidation chemistry of vinyl alcohol has been investigated in this thesis, using quantum chemical calculations and energy-grained master equation simulations. The reaction proceeds by •OH addition at both the [alpha]-carbon (66%) and [beta]-carbon (33%) of the [pi] system, yielding the C-centred radicals •CH2CH(OH)2 and HOCH2C•HOH respectively. Subsequent trapping by O2 leads to the respective peroxyl radicals. About 90% of the chemically activated population of the major peroxyl radical adduct •O2CH2CH(OH)2 is predicted to undergo fragmentation to produce formic acid and formaldehyde, with regeneration of •OH. The minor peroxyl radical CH2(OH)CH(OH)O2• is even less stable and almost exclusively undergoes HO2• elimination to form glycolaldehyde. The •OH-initiated oxidation of vinyl alcohol ultimately leads to three main product channels, being (i) •O2CH2CH(OH)2 (8%), (ii) HC(O)OH + HCHO + •OH (56%) and (iii) HOCH2CHO + HO2• (37%). This study supports previous findings that vinyl alcohol should be rapidly removed from the atmosphere by reaction with •OH and O2, with glycolaldehyde being identified as a previously unconsidered product. Moreover, it is also shown that direct chemically activated reactions can lead to •OH and HO2• (HOx) recycling. Following the study on the acetaldehyde-vinyl alcohol pair, the photo-isomerisation of glycolaldehyde to 1,2-ethenediol has been studied. The keto-enol isomerisation is associated with a barrier of 66 kcal mol-1 and involves a double hydrogen shift mechanism to give the lower energy Z isomer. This barrier lies below the energy of the UV/Vis absorption band of glycolaldehyde and is also considerably below the energy of the products resulting from photolytic decomposition. The atmospheric oxidation of 1,2-ethenediol by •OH is initiated by radical addition to the [pi] system to give the •CH(OH)CH(OH)2 radical, which is subsequently trapped by O2 to form the peroxyl radical •O2CH(OH)CH(OH)2. According to kinetic simulations, collisional deactivation of the latter is negligible and cannot compete with rapid fragmentation reactions, which lead to (i) formation of glyoxal hydrate and HO2• through an [alpha]-hydroxyl mechanism (96%) and (ii) two molecules of formic acid with release of •OH through a [beta]-hydroxyl pathway (4%). The lifetime of the two enols in the presence of tropospheric levels of •OH is determined to be around 4 hours and 68 hours respectively. Phenomenological rate coefficients for these two oxidation reactions are obtained for use in atmospheric chemical modelling. Finally, photo-induced dissociation and isomerisation of other common tropospheric carbonyl compounds, namely methyl vinyl ketone (MVK) and methacrolein (MACR), has been reinvestigated. The reaction of both molecules proceeds through dissociation, cyclisation and hydrogen shift (including keto-enol isomerisation) pathways. From the simulation of reaction dynamics, MACR photolysis is significantly less efficient than MVK photolysis, which is consistent with the experimental data in the literature. Isomerisation dominates dissociation in the actinic spectrum at longer wavelengths for both MVK and MACR photolysis. The total photolysis rate of MVK and MACR is calculated to be 3.8 x 10-5 s-1 and 8.6 x 10-7 s-1 respectively. The study reveals that MVK and MACR photolysis may lead to formation of new atmospheric VOCs such as hydroxylbutadiene from MVK and dimethylketene from MACR.
Author: Jack Calvert
Publisher: OUP USA
ISBN: 0199767076
Category : Science
Languages : en
Pages : 1634
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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: Georges Le Bras
Publisher: Springer Science & Business Media
ISBN:
Category : Science
Languages : en
Pages : 348
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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:
Publisher:
ISBN:
Category :
Languages : en
Pages : 9
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Book Description
To be able to understand and predict the concentration of a target compound in the atmosphere one must understand the atmospheric chemistry involved. The transformation of volatile organic compounds (VOCs) in the troposphere is predominantly driven by the interaction with the hydroxyl and nitrate radicals. The hydroxyl radical exists in daylight conditions and its reaction rate constant with an organic compound is typically very fast. The nitrate radical drives the nighttime chemistry. These radicals can scavenge hydrogen from an organic molecule generating secondary products that are often overlooked in detection schemes. Secondary products can be more stable and serve as a better target compound in detection schemes. The gas-phase reaction of the hydroxyl radical (OH) with cyclohexanol (COL) has been studied. The rate coefficient was determined to be (19.0+4.8) x 10-12cm3 molecule-1 s-1 (at 297+3 oK and 1 atmosphere total pressure) using the relative rate technique with pentanal, decane, and tridecane as the reference compounds. Assuming an average OH concentration of 1 x 106 molecules cm-3, an atmospheric lifetime of 15 h is calculated for cyclohexanol. Products of the OH + COL reaction were determined to more clearly define cyclohexanol's atmospheric degradation mechanism. The observed products were: cyclohexanone, hexanedial, 3-hydroxycyclohexanone, and 4-hydroxycyclohexanone. Consideration of the potential reaction pathways suggests that each of these products is formed via hydrogen abstraction at a different site on the cyclohexanol ring.
Author: James Freeman Hunter
Publisher:
ISBN:
Category :
Languages : en
Pages : 110
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Book Description
.Organic molecules have many important roles in the atmosphere, acting as climate and biogeochemical forcers, and in some cases as toxic pollutants. The lifecycle of atmospheric organic carbon is extremely complex, with reaction in multiple phases (gas, particle, aqueous) and at multiple timescales. The details of the lifecycle chemistry (especially the amount and properties of particles) have important implications for air quality, climate, and human and ecosystem health, and need to be understood better. Much of the chemical complexity and uncertainty lies in the reactions and properties of low-volatility oxidized intermediates that result from the oxidation of volatile organic precursors, and which have received comparatively little study thus far. This thesis describes three projects that link together the entire chain of oxidation (volatile to intermediate to condensed) in an effort to improve our understanding of carbon lifecycle and aerosol production. Laboratory studies of atmospherically relevant aerosol precursors show that the slow oxidation of intermediates is critical to explaining the yield and properties of aerosol under highly oxidized ("aged") conditions, and that the production of organic particles is significantly increased when intermediates are fully oxidized. This aging process is a strong function of molecular structure, and depends on aerosol concentration through the phenomenon of condensational trapping. Further laboratory studies of a series of (poly)cyclic 10 carbon alkanes show that structural effects are largely explained through fragmentation reactions, and that more generally, carbon-carbon bond scission is a ubiquitous and important reaction channel for oxidized intermediates. Finally, direct measurement of oxidized intermediate compounds in field studies shows that these compounds are abundant and important in the ambient atmosphere, with concentrations and properties in between those of volatile and particulate organic compounds. Together with other co-located measurements and complementary techniques, this enables estimates of emission, oxidation, and deposition to be constructed. The results from this thesis can be used to inform more sophisticated models of atmospheric organic carbon cycling, and to improve prediction of organic particulate matter concentrations.
Author: Jack G Calvert
Publisher: Oxford University Press
ISBN: 0199710880
Category : Science
Languages : en
Pages : 1005
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Book Description
An international team of eminent atmospheric scientists have prepared Mechanisms of Atmospheric Oxidation of the Alkanes as an authoritative source of information on the role of alkanes in the chemistry of the atmosphere. The book includes the properties of the alkanes and haloalkanes, as well as a comprehensive review and evaluation of the existing literature on the atmospheric chemistry of the alkanes and their major atmospheric oxidation products, and the various approaches now used to model the alkane atmospheric chemistry. Comprehensive coverage is given of both the unsubstituted alkanes and the many haloalkanes. All the existing quality measurements of the rate coefficients for the reactions of OH, Cl, O(3P), NO3, and O3 with the alkanes, the haloalkanes, and their major oxidation products have been reviewed and evaluated. The expert authors then give recommendations of the most reliable kinetic data. They also review the extensive literature on the mechanisms and rates and modes of photodecomposition of the haloalkanes and the products of atmospheric oxidation of the alkanes and the haloalkanes, and make recommendations for future use by atmospheric scientists. The evaluations presented allow an extrapolation of the existing kinetic and photochemical data to those alkanes and haloalkanes that are as yet unstudied. The current book should be of special interest and value to the modelers of atmospheric chemistry as a useful input for development of realistic modules designed to simulate the atmospheric chemistry of the alkanes, their major oxidation products, and their influence on ozone and other trace gases within the troposphere.
Author: R M Harrison
Publisher: Royal Society of Chemistry
ISBN: 1847552315
Category : Science
Languages : en
Pages : 156
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Book Description
Interest in volatile organic compounds (VOCs) as air pollutants has increased dramatically in recent years. This book covers a number of very topical issues concerning VOCs, including stratospheric ozone depletion due to CFCs, and the properties of alternative substances; the role of VOCs in the photochemical formation of lower atmosphere (tropospheric) ozone; and the problem of the direct toxicity of VOCs such as benzene and formaldehyde. This Issue reviews our current knowledge of VOCs, drawing upon the expertise of renowned experts and major national and international research programmes. It examines man-made and natural sources, as well as pathways and chemical reactions in the atmosphere. It also looks closely at the sources and concentrations of VOCs indoors, where humans are most likely to be exposed to them. Volatile Organic Compounds in the Atmosphere describes techniques used for the calculation of emissions inventories and strategies for control, and explores the many Government policy matters relating to VOCs. It provides readers with in-depth, clearly explained coverage of the many complex scientific and policy issues surrounding VOCs in the atmosphere.
