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Author: Publisher: ISBN: Category : Languages : en Pages : 306
Book Description
Secondary organic aerosol (SOA), formed from in-air oxidation of volatile organic compounds, greatly affects human health and climate. Although substantial research has been devoted to SOA formation and evolution, the modeled and lab-generated SOA are still low in mass and degree of oxidation compared to ambient measurements. In order to compensate for these discrepancies, the aqueous processing pathway has been brought to attention. The atmospheric waters serve as aqueous reaction media for dissolved organics to undergo further oxidation, oligomerization, or other functionalization reactions, which decreases the vapor pressure while increasing the oxidation state of carbon atoms. Field evidence for aqueous processing requires the identification of tracer products such as organosulfates. We synthesized the standards for two organosulfates, glycolic acid sulfate and lactic acid sulfate, in order to measure their aerosol-state concentration from five distinct locations via filter samples. The water-extracted filter samples were analyzed by LC-MS. Lactic acid sulfate and glycolic acid sulfate were detected in urban locations in the United States, Mexico City, and Pakistan with varied concentrations, indicating their potential as tracers. We studied the aqueous processing reaction between glyoxal and nitrogen-containing species such as ammonium and amines exclusively by NMR spectrometry. The reaction products formic acid and several imidazoles along with the quantified kinetics were reported. The brown carbon generated from these reactions were quantified optically by UV-Vis spectroscopy. The organic-phase reaction between oxygen molecule and alkenes photosensitized by [alpha]-dicarbonyls were studied in the same manner. We observed the fast kinetics transferring alkenes to epoxides under simulated sunlight. Statistical estimations indicate a very effective conversion of aerosol-phase alkenes to epoxides, potentially forming organosulfates in a deliquescence event and increasing aerosol mass. Finally, we built a containerless apparatus to study aqueous processing reactions using an acoustic levitator paired with a mass spectrometer. The levitator is capable of trapping droplets with the size of 80-500 [mu]m in diameter for over eight hours. The apparatus is also capable of drying and wetting the droplet in a controllable manner. We performed am example reaction between glyoxal and ammonium sulfate using this instrument, and showed that it could qualitatively monitor aqueous processing reactions.
Author: Publisher: ISBN: Category : Languages : en Pages : 306
Book Description
Secondary organic aerosol (SOA), formed from in-air oxidation of volatile organic compounds, greatly affects human health and climate. Although substantial research has been devoted to SOA formation and evolution, the modeled and lab-generated SOA are still low in mass and degree of oxidation compared to ambient measurements. In order to compensate for these discrepancies, the aqueous processing pathway has been brought to attention. The atmospheric waters serve as aqueous reaction media for dissolved organics to undergo further oxidation, oligomerization, or other functionalization reactions, which decreases the vapor pressure while increasing the oxidation state of carbon atoms. Field evidence for aqueous processing requires the identification of tracer products such as organosulfates. We synthesized the standards for two organosulfates, glycolic acid sulfate and lactic acid sulfate, in order to measure their aerosol-state concentration from five distinct locations via filter samples. The water-extracted filter samples were analyzed by LC-MS. Lactic acid sulfate and glycolic acid sulfate were detected in urban locations in the United States, Mexico City, and Pakistan with varied concentrations, indicating their potential as tracers. We studied the aqueous processing reaction between glyoxal and nitrogen-containing species such as ammonium and amines exclusively by NMR spectrometry. The reaction products formic acid and several imidazoles along with the quantified kinetics were reported. The brown carbon generated from these reactions were quantified optically by UV-Vis spectroscopy. The organic-phase reaction between oxygen molecule and alkenes photosensitized by [alpha]-dicarbonyls were studied in the same manner. We observed the fast kinetics transferring alkenes to epoxides under simulated sunlight. Statistical estimations indicate a very effective conversion of aerosol-phase alkenes to epoxides, potentially forming organosulfates in a deliquescence event and increasing aerosol mass. Finally, we built a containerless apparatus to study aqueous processing reactions using an acoustic levitator paired with a mass spectrometer. The levitator is capable of trapping droplets with the size of 80-500 [mu]m in diameter for over eight hours. The apparatus is also capable of drying and wetting the droplet in a controllable manner. We performed am example reaction between glyoxal and ammonium sulfate using this instrument, and showed that it could qualitatively monitor aqueous processing reactions.
Author: Felipe Daniel Lopez-Hilfiker Publisher: ISBN: Category : Languages : en Pages : 178
Book Description
The guiding question to this research is: To what extent and by what mechanisms do biogenic volatile organic compounds contribute to atmospheric aerosol mass? To address this question we need to understand the chemistry that produces condensable vapors which when in the presence of particles may partition onto the aerosol surface depending on their chemical and physical properties. I developed an insitu gas and aerosol sampling system, the FIGAERO (Filter Inlet for Gases and AEROsol) to speciate gas and particle phase organics derived from photochemical reactions with biogenic volatile organic compounds under both field and laboratory conditions. By coupling the FIGAERO to a High-Resolution Time-of-Flight Chemical Ionization Mass Spectrometer (HR-TOF-CIMS) I am able to elucidate chemical pathways by identifying elemental compositions and in some cases functional groups present in the detected molecular ions. The coupling of the FIGAERO to the HR-TOF-CIMS also allows the estimation of effective vapor pressures of the aerosol components and this information can be used to improve vapor pressure models and test associated partitioning theories and parameterizations. The approach also provides hundreds of speciated chemical tracers that can be correlated with traditional environmental and chemical measurements (e.g AMS, NOx, SO2, SMPS, VOC) to help derive sources and sinks and to constrain the mechanisms responsible for the formation and growth of organic aerosol. Measurements obtained across a wide range of conditions and locations allowing connections and contrasts between different chemical systems, providing insights into generally controlling factors of secondary organic aerosol (SOA) and its properties.
Author: Lindsay Diana Yee Publisher: ISBN: Category : Electronic dissertations Languages : en Pages : 466
Book Description
The photooxidation of volatile organic compounds (VOCs) in the atmosphere can lead to the formation of secondary organic aerosol (SOA), a major component of fine particulate matter. Improvements to air quality require insight into the many reactive intermediates that lead to SOA formation, of which only a small fraction have been measured at the molecular level. This thesis describes the chemistry of secondary organic aerosol (SOA) formation from several atmospherically relevant hydrocarbon precursors. Photooxidation experiments of methoxyphenol and phenolic compounds and C12 alkanes were conducted in the Caltech Environmental Chamber. These experiments include the first photooxidation studies of these precursors run under sufficiently low NOx levels, such that RO2 + HO2 chemistry dominates, an important chemical regime in the atmosphere. Using online Chemical Ionization Mass Spectrometery (CIMS), key gas-phase intermediates that lead to SOA formation in these systems were identified. With complementary particle-phase analyses, chemical mechanisms elucidating the SOA formation from these compounds are proposed. Three methoxyphenol species (phenol, guaiacol, and syringol) were studied to model potential photooxidation schemes of biomass burning intermediates. SOA yields (ratio of mass of SOA formed to mass of primary organic reacted) exceeding 25% are observed. Aerosol growth is rapid and linear with the organic conversion, consistent with the formation of essentially non-volatile products. Gas and aerosol-phase oxidation products from the guaiacol system show that the chemical mechanism consists of highly oxidized aromatic species in the particle phase. Syringol SOA yields are lower than that of phenol and guaiacol, likely due to unique chemistry dependent on methoxy group position. The photooxidation of several C12 alkanes of varying structure n-dodecane, 2-methylundecane, cyclododecane, and hexylcyclohexane) were run under extended OH exposure to investigate the effect of molecular structure on SOA yields and photochemical aging. Peroxyhemiacetal formation from the reactions of several multifunctional hydroperoxides and aldehyde intermediates was found to be central to organic growth in all systems, and SOA yields increased with cyclic character of the starting hydrocarbon. All of these studies provide direction for future experiments and modeling in order to lessen outstanding discrepancies between predicted and measured SOA.
Author: Murtaza Hyder Publisher: LAP Lambert Academic Publishing ISBN: 9783659222955 Category : Languages : en Pages : 76
Book Description
Airborne particulate matter is well known because of its adverse impacts on human health and its role in climate processes. The chemical composition of atmospheric aerosols is of basic importance. Chemical analysis of aerosols involves broadly two steps, extraction step and detection/quantification of chemical constituents. Generally aerosols are extracted using classical techniques which, have many disadvantages. This dissertation addresses the use of both classical extraction methods and liquid membrane based extraction as a sample preparation steps for aerosols analysis. Common techniques that are used for this purpose are not environmentally green as they involve a lot of organic solvent, they are not efficient and selective enough and do not serve the purpose of trace level analysis as they do not give sufficiently high enrichment. We have shown that hollow fiber liquid phase microextraction (HF-LPME), which is environmentally green is applicable to aerosol samples. Both two-phase and three phase HF-LPME are very helpful in pre-concentration of analytes from aerosol. The dissertation summarises the results of our research for the last four years.
Author: Ian Barnes Publisher: Springer ISBN: 940075034X Category : Science Languages : en Pages : 355
Book Description
Oxides and acids of nitrogen play an important role in regulating atmospheric radical levels, in particular, that of the OH radical the main initiator of the degradation of chemicals in the atmosphere. A comprehensive overview on the methods used to measure nitrogen oxides and acids in the troposphere is given and difficulties and artefacts associated with the use of the techniques for measurements in urban and mega city environments is illustrated. State-of-the-art methods for the measurement of OH and HO2 radicals are reviewed and recently recognised difficulties, in particular with the measurement of HO2 radicals, are highlighted. Other contributions to the book cover our present understanding of the gas, aqueous and particulate/aerosol phase atmospheric degradation chemistry of volatile organic compounds (VOCs) under NOx conditions typical of rural, urban and mega city environments. Examples of measurements of NOx and VOCs in the atmospheres of these environments are given, in particular for the megacities Cairo and Beijing, in conjunction with modelling studies which attempt to simulate the field observations using state-of-the art knowledge on the chemistry of the VOCs and radical levels.
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: Mark E. Davis Publisher: Courier Corporation ISBN: 0486291316 Category : Technology & Engineering Languages : en Pages : 385
Book Description
Appropriate for a one-semester undergraduate or first-year graduate course, this text introduces the quantitative treatment of chemical reaction engineering. It covers both homogeneous and heterogeneous reacting systems and examines chemical reaction engineering as well as chemical reactor engineering. Each chapter contains numerous worked-out problems and real-world vignettes involving commercial applications, a feature widely praised by reviewers and teachers. 2003 edition.
Author: Daniel J. Jacob Publisher: Princeton University Press ISBN: 0691001855 Category : Nature Languages : en Pages : 280
Book Description
Atmospheric chemistry is one of the fastest growing fields in the earth sciences. Until now, however, there has been no book designed to help students capture the essence of the subject in a brief course of study. Daniel Jacob, a leading researcher and teacher in the field, addresses that problem by presenting the first textbook on atmospheric chemistry for a one-semester course. Based on the approach he developed in his class at Harvard, Jacob introduces students in clear and concise chapters to the fundamentals as well as the latest ideas and findings in the field. Jacob's aim is to show students how to use basic principles of physics and chemistry to describe a complex system such as the atmosphere. He also seeks to give students an overview of the current state of research and the work that led to this point. Jacob begins with atmospheric structure, design of simple models, atmospheric transport, and the continuity equation, and continues with geochemical cycles, the greenhouse effect, aerosols, stratospheric ozone, the oxidizing power of the atmosphere, smog, and acid rain. Each chapter concludes with a problem set based on recent scientific literature. This is a novel approach to problem-set writing, and one that successfully introduces students to the prevailing issues. This is a major contribution to a growing area of study and will be welcomed enthusiastically by students and teachers alike.
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Author: Felipe Daniel Lopez-Hilfiker
Author: Lindsay Diana Yee
Author: Murtaza Hyder
Author: Ian Barnes
Author: Alla H. Falkovich
Author: Lu Yu
Author: Mark E. Davis
Author: Daniel J. Jacob
Author: Grish Chandra