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Author: Anthony Joseph Carrasquillo Publisher: ISBN: Category : Languages : en Pages : 113
Book Description
Atmospheric particulate matter (or "aerosol") has important implications for public health, climate change, and visibility. Our ability to predict its formation and fate is hindered by uncertainties associated with one type in particular, organic aerosol (OA). The study of the chemistry underlying OA formation is complicated by the large number of reaction pathways and oxidation generations for a given precursor species. This thesis describes a series of experiments in which the chemistry is simplified to that of a single alkoxy radical (RO) isomer generated from the direct photolysis of alkyl nitrites (RONO). First, OA was generated from eleven different C10 RO isomers to determine the role of radical molecular structure in the formation of low-volatility species. Here, measured aerosol yields and chemical composition were explained by two major effects: (1) the relative importance of isomerization and fragmentation pathways, which control the distribution of products, and (2) differences in saturation vapor pressure of individual isomers. Next, we developed a method to investigate the reactivity of alkoxy radicals in the condensed phase. The long chain C20 RO radical was generated in hexane solvent to identify possible intermolecular (bimolecular) reactions with the condensed-phase. The lack of formation of the C20 alcohol, the expected product of the bimolecular reaction of RO with hexane indicates that these intermolecular reactions are unable to compete with available unimolecular isomerization processes. Finally, a molecular-level study of this same condensed-phase system with a soft ionization technique permitted the observation of molecular ions that are assigned to specific oxidation products. This approach enables the determination of the extent of branching for another important intermediate, the alkylperoxy radical. The results from this thesis highlight the role of radical structure in the formation of low-volatility products in the atmosphere, in addition to identifying the major reaction pathways responsible for particle-phase oxidative processing.
Author: Anthony Joseph Carrasquillo Publisher: ISBN: Category : Languages : en Pages : 113
Book Description
Atmospheric particulate matter (or "aerosol") has important implications for public health, climate change, and visibility. Our ability to predict its formation and fate is hindered by uncertainties associated with one type in particular, organic aerosol (OA). The study of the chemistry underlying OA formation is complicated by the large number of reaction pathways and oxidation generations for a given precursor species. This thesis describes a series of experiments in which the chemistry is simplified to that of a single alkoxy radical (RO) isomer generated from the direct photolysis of alkyl nitrites (RONO). First, OA was generated from eleven different C10 RO isomers to determine the role of radical molecular structure in the formation of low-volatility species. Here, measured aerosol yields and chemical composition were explained by two major effects: (1) the relative importance of isomerization and fragmentation pathways, which control the distribution of products, and (2) differences in saturation vapor pressure of individual isomers. Next, we developed a method to investigate the reactivity of alkoxy radicals in the condensed phase. The long chain C20 RO radical was generated in hexane solvent to identify possible intermolecular (bimolecular) reactions with the condensed-phase. The lack of formation of the C20 alcohol, the expected product of the bimolecular reaction of RO with hexane indicates that these intermolecular reactions are unable to compete with available unimolecular isomerization processes. Finally, a molecular-level study of this same condensed-phase system with a soft ionization technique permitted the observation of molecular ions that are assigned to specific oxidation products. This approach enables the determination of the extent of branching for another important intermediate, the alkylperoxy radical. The results from this thesis highlight the role of radical structure in the formation of low-volatility products in the atmosphere, in addition to identifying the major reaction pathways responsible for particle-phase oxidative processing.
Author: Lu Yu Publisher: ISBN: 9781339824093 Category : Languages : en Pages :
Book Description
Secondary organic aerosol (SOA) is formed and transformed in atmospheric aqueous phases (e.g., cloud and fog droplets and deliquesced airborne particles containing small amounts of water) through a multitude of chemical and physical processes. Understanding the formation and transformation processes of SOA via aqueous-phase reactions is important for properly presenting its atmospheric evolution pathways in models and for elucidating its climate and health effects. Phenolic compounds, which are emitted in significant amounts from biomass burning, can undergo fast reactions in atmospheric aqueous phases to form secondary organic aerosol (aqSOA). In this study, we investigate the formation and evolution of phenol (C6H6O), guaiacol (C7H8O2; 2-methoxyphenol) and syringol (C8H10O3; 2,6-dimethoxyphenol) and with two major aqueous phase oxidants -- the triplet excited state of an aromatic carbonyl (3C*) and hydroxyl radical (·OH) - and interpret the reaction mechanisms. In addition, given that dissolved organic matter (DOM) is an important component of fog and cloud water and that it can undergo aqueous reactions to form more oxidized, less volatile species, we further investigate the photochemical processing of DOM in fog water to gain insights into the aqueous-phase processing of organic aerosol (OA) in the atmosphere. In Chapter 2, we thoroughly characterize the bulk chemical and molecular compositions of phenolic aqSOA formed at half-life (t[subscript 1/2]), and interpret the formation mechanisms. We find that phenolic aqSOA formed at t[subscript 1/2] is highly oxygenated with atomic oxygen-to-carbon ratio (O/C) in the range of 0.85-1.23. Dimers, higher oligomers (up to hexamers), functionalized monomers and oligomers with carbonyl, carboxyl, and hydroxyl groups, and small organic acids are detected. Compared with ·OH-mediated reactions, reactions mediated by 3C* are faster and produce more oligomers and hydroxylated species at t[subscript1/2]. We also find that aqSOA shows enhanced light absorption in the UV-vis region, suggesting that aqueous-phase reactions of phenols are an important source of secondary brown carbon in the atmosphere, especially in regions impacted by biomass burning. In Chapter 3, we investigate the chemical evolution of phenolic aqSOA via aqueous-phase reactions on the molecular level and interpret the aging mechanisms. Our results indicate that oligomerization is an important aqueous reaction pathway for phenols, especially during the initial stage of photooxidation. Functionalization and fragmentation become dominant at later stages, forming a variety of functionalized aromatic and ring-opening products with higher carbon oxidation states. Fragmentation reactions eventually dominate the photochemical evolution of phenolic aqSOA, forming a large number of highly oxygenated ring-opening molecules. In addition, phenolic aqSOA has a wide range of saturation vapor pressures (C*), varying from 10−20 [mu]g m−3 for functionalized phenolic oligomers to 10 [mu]g m−3 for ring-opening species with number of carbon less than 6. The detection of abundant extremely low volatile organic compounds (ELVOC) indicates that aqueous reactions of phenolic compounds are likely an important source of ELVOC in the atmosphere. Chapter 3 investigates the molecular transformation with aging based on the characterization of three aqSOA filter samples collected at the defined time intervals of the photoreaction. However, the chemical evolution of aqSOA products with hours of illumination at a higher time resolution is largely unknown. In Chapter 4, we investigate the chemical evolution of aqSOA at a 1-min time resolution based on high-resolution aerosol mass spectrometer (AMS) analysis. This is important for understanding the continuous evolution of phenolic aqSOA with aging as well as for elucidating the formation and transformation of different generations of products. Our results suggest that dimer and higher-order oligomers (trimers, tetramers, etc.) are formed continuously during the first 1-2 hours of photoreaction but show a gradual decrease afterwards. Functionalized derivatives grow at a later time and then gradually decrease. Highly oxidized ring-opening species continuously increase over the course of reactions. Positive matrix factorization (PMF) analysis of the AMS spectra of phenolic aqSOA identifies multiple factors, representing different generations of products. The 1st-generation products include dimers, higher-order oligomers and their oxygenated derivatives. The 2nd-generation products include oxygenated monomeric derivatives. The 3rd-generation products include highly oxidized ring-opening species. In Chapter 5, we investigate the evolution of dissolved organic matter (DOM) in fog water. Our results show that the mass concentration of DOM[subscript OA] (i.e., low-volatility DOM in fog water) is enhanced over the course of illumination, with continuous increase of O/C and atomic nitrogen-to-carbon ratio (N/C). The increase of DOM[subscript OA] is due to the incorporation of oxygen- and nitrogen-containing functional groups into the molecules. The aqueous aging of DOM[subscript OA] can be modeled as a linear combination of the dynamic variations of 3 factors using PMF analysis. Factor 1 is chemically similar to the DOM[subscript OA] before illumination, which is quickly reacted away. Factor 2 is representative of an intermediate component, which is first formed and then transformed, and O/C of Factor 2 is intermediate between that of Factor 1 and Factor 3. Factor 3 represents highly oxidized final products, which is continuously formed during illumination. Fog DOM absorbs significantly in the tropospheric sunlight wavelengths, but this absorption behavior stays almost constant over the course of illumination, despite the significant change in chemical composition.
Author: Ronald E. Hester Publisher: Royal Society of Chemistry ISBN: 9780854042159 Category : Nature Languages : en Pages : 172
Book Description
This book describes techniques for the calculation of emissions inventories and strategies for control, and explores the many Government policy matters relating to these compounds. It gives readers in-depth coverage of the many issues involved.
Author: Sui So Publisher: ISBN: Category : Atmospheric chemistry Languages : en Pages : 346
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 G Calvert Publisher: Oxford University Press ISBN: 0199710880 Category : Science Languages : en Pages : 1005
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: James Freeman Hunter Publisher: ISBN: Category : Languages : en Pages : 110
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: David C. Catling Publisher: Cambridge University Press ISBN: 0521844126 Category : Science Languages : en Pages : 595
Book Description
A comprehensive and authoritative text on the formation and evolution of planetary atmospheres, for graduate-level students and researchers.
Author: John Oró Publisher: Springer Science & Business Media ISBN: 9401022828 Category : Science Languages : en Pages : 354
Book Description
Proceedings of the Fourth International Conference on the Origin of Life and the First Meeting of the International Society for the Study of the Origin of Life (ISSOL), Barcelona, June 25-28, 1973. Vol. II: Contributed Papers
Author: John Oró Publisher: Springer Science & Business Media ISBN: 9789027705181 Category : Science Languages : en Pages : 354
Book Description
Proceedings of the Fourth International Conference on the Origin of Life and the First Meeting of the International Society for the Study of the Origin of Life (ISSOL), Barcelona, June 25-28, 1973. Vol. II: Contributed Papers
Author: Anthony Joseph Carrasquillo
Author: Anthony Joseph Carrasquillo
Author: Lu Yu
Author: Ronald E. Hester
Author: Sui So
Author: Jack G Calvert
Author: Bernd Giese
Author: James Freeman Hunter
Author: David C. Catling
Author: John Oró
Author: John Oró