Download or read book OH initiated Heterogeneous Oxidation of Atmospheric Organic Aerosols written by and published by . This book was released on 2003 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: PhD.

Download or read book OH initiated Heterogeneous Oxidation of Atmospheric Organic Aerosols written by Ingrid Jennifer George and published by . This book was released on 2009 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: The chemical aging of organic aerosols by OH-initiated heterogeneous oxidation was investigated using both model organic and ambient aerosol particles. Organic aerosol particles were exposed to OH radicals in an aerosol flow tube and the modification of their chemical composition and particle properties was studied. Overall, this work has shown that OH-initiated heterogeneous oxidation enhanced the degree of oxidation and the Cloud Condensation Nucleus (CCN) activity of organic aerosol particles for equivalent OH exposure timescales of a few days to a week. The modification of the hygroscopicity of model primary and secondary organic aerosols from chemical aging was investigated by measuring the CCN activity of organic aerosols exposed to OH radicals. Primary organic aerosols, initially CCN inactive, became as CCN active as secondary organic aerosols due to heterogeneous reaction, where surface tension reduction played a major role. The CCN activity for model secondary organic aerosols was also enhanced due to OH oxidation, but changes were less dramatic than for the model primary organic aerosols. Aerosol Mass Spectrometer (AMS) measurements showed that the heterogeneous uptake kinetics of OH radicals onto model primary organic aerosols was efficient. The heterogeneous reaction of organic aerosols with OH led to the production of high molecular weight particle-phase species with the addition of multiple oxygenated functional groups. These results were consistent with the observed increase in particle density with OH exposure. With the exception of solid organic aerosols, the particle volume and mass of organic particles were reduced by less than 20% from OH oxidation at high OH exposures due to volatilization of particle-phase reaction products. The degree of oxidation of the organic fraction of urban ambient aerosols was significantly enhanced for an equivalent atmospheric OH exposure time of 4 days for a daily average atmospheric OH concentration of 2x10 6 cm-3. Ambient aerosol particles sampled from a sparsely populated, forested region were initially more oxygenated than the urban aerosol particles and did not become more oxidized from reaction with OH radicals.

Download or read book OH initiated Heterogeneous Aging of Highly Oxidized Organic Aerosol written by and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The oxidative evolution (?aging?) of organic species in the atmosphere is thought to have a major influence on the composition and properties of organic particulate matter, but remains poorly understood, particularly for the most oxidized fraction of the aerosol. Here we measure the kinetics and products of the heterogeneous oxidation of highly oxidized organic aerosol, with an aim of better constraining such atmospheric aging processes. Submicron particles composed of model oxidized organics--1,2,3,4-butanetetracarboxylic acid (CH10O8), citric acid (C6H8O-- ), tartaric acid (C4H6O6), and Suwannee River fulvic acid--were oxidized by gas-phase OH in a flow reactor, and the masses and elemental composition of the particles were monitored as a function of OH exposure. In contrast to our previous studies of less-oxidized model systems (squalane, erythritol, and levoglucosan), particle mass did not decrease significantly with heterogeneous oxidation. Carbon content of the aerosol always decreased somewhat, but this mass loss was approximately balanced by an increase in oxygen content. The estimated reactive uptake coefficients of the reactions range from 0.37 to 0.51 and indicate that such transformations occur at rates corresponding to 1-2 weeks in the atmosphere, suggesting their importance in the atmospheric lifecycle of organic particulate matter.

Download or read book The Aging of Organic Aerosol in the Atmosphere written by Sean Herbert Kessler and published by . This book was released on 2013 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Investigating Sources and Sinks of Organic Aerosols written by Alan J.. Kwan and published by . This book was released on 2011 with total page 370 pages. Available in PDF, EPUB and Kindle. Book excerpt: Secondary organic aerosol (SOA) are important components in atmospheric processes and significantly impact human health. The complexity of SOA composition and formation processes has hampered efforts to fully characterize their impacts, and to predict how those impacts will be affected by changes in climate and human activity. Here, we explore SOA formation in the laboratory by coupling an environmental chamber with a suite of analytical tools, including a gas-phase mass spectrometry technique that is well suited for tracking the hydrocarbon oxidation processes that drive SOA formation. Focusing on the oxidation of isoprene by the nitrate radical, NO3, we find that reactions of peroxy radicals (RO2) to form ROOR dimers is an important process in SOA formation. The other gas-phase products of these RO2 reactions differ from what is expected from studies of simpler radicals, indicating that more studies are necessary to fully constrain RO2 chemistry. Finally, we examine the role of heterogeneous oxidation as a sink of organic aerosol and a source of oxygenated volatile organic compounds in the free troposphere.

Download or read book Elucidation of Mechanisms and Impacts of Oxidation on Organic Particulate Matter written by Katheryn Ruth Kolesar and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Laboratory Studies of the Multiday Oxidative Aging of Atmospheric Organic Aerosol written by Christopher Yung-Ta Lim and published by . This book was released on 2019 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Chemical Kinetics and Mechanisms of Unsaturated Organic Aerosol Oxidation written by Theodora Nah and published by . This book was released on 2014 with total page 137 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Quantifying the Reactive Uptake of OH by Organic Aerosols in AContinuous Flow Stirred Tank Reactor written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Here we report a new method for measuring the heterogeneous chemistry of submicron organic aerosol particles using a continuous flow stirred tank reactor. This approach is designed to quantify the real time heterogeneous kinetics, using a relative rate method, under conditions of low oxidant concentration and long reaction times that more closely mimic the real atmosphere. A general analytical expression, which couples the aerosol chemistry with the flow dynamics in the chamber is developed and applied to the heterogeneous oxidation of squalane particles by hydroxyl radicals (OH) in the presence of O2. The particle phase reaction is monitored via photoionization aerosol mass spectrometry and yields a reactive uptake coefficient of 0.51+-0.10, using OH concentrations of 1-7x108 molec cdot cm-3 and reaction times of 1.5+-3 hours. This uptake coefficient is larger than that found for the reaction carried out under high OH concentrations (~;;1x1010 molec cdot cm-3) and short reaction times in a flow tube reactor. This difference suggests that oxidant concentration and reaction time are not interchangeable quantities in reactions of organic aerosols with radicals. In general, this approach provides a new way to examine how the chemical aging of organic particles measured at short reaction times and high oxidant concentrations in flow tubes might differ from the long reaction times and low oxidant levels found in the real atmosphere.

Download or read book Chemistry of Carbonaceous Aerosols written by Kirsten Sue Johnson and published by . This book was released on 2007 with total page 151 pages. Available in PDF, EPUB and Kindle. Book excerpt: Carbonaceous aerosols are among the most prevalent yet least understood constituents of the atmosphere, particularly in urban environments. We have performed analyses of field samples and laboratory studies to probe the physico-chemical properties of soot and organic aerosols in a complimentary approach to obtain information essential for understanding their atmospheric evolution and environmental effects. Samples of particulate matter

Download or read book Fundamentals of Chemical Reaction Engineering written by Mark E. Davis and published by Courier Corporation. This book was released on 2013-05-27 with total page 385 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Measurement of Fragmentation and Functionalization Pathways in the Multistep Heterogeneous Oxidation of Organic Aerosol written by and published by . This book was released on 2009 with total page 33 pages. Available in PDF, EPUB and Kindle. Book excerpt: The competition between the addition of polar, oxygen-containing functional groups (functionalization) and the cleavage of C-C bonds (fragmentation) has a governing influence on the change in volatility of organic species upon atmospheric oxidation, and hence on the loading of tropospheric organic aerosol. However the branching between these two channels is generally poorly constrained for oxidized organics. Here we determine functionalization/fragmentation branching ratios for organics spanning a range of oxidation levels, using the heterogeneous oxidation of squalane (C30H62) as a model system. Squalane particles are exposed to high concentrations of OH in a flow reactor, and measurements of particle mass and elemental ratios enable the determination of absolute elemental composition (number of oxygen, carbon, and hydrogen atoms) of the oxidized particles. At low OH exposures, the oxygen content of the organics increases, indicating that functionalization dominates, whereas at higher exposures the amount of carbon in the particles decreases, indicating the increasing importance of fragmentation processes. Once the organics are moderately oxidized (O/C~;;0.4), fragmentation completely dominates, and the increase in O/C ratio upon further oxidation is due to the loss of carbon rather than the addition of oxygen. These results suggest that fragmentation reactions may be key steps in the atmospheric formation and evolution of oxygenated organic aerosol (OOA).

Download or read book Mechanisms of Atmospheric Oxidation of the Alkanes written by Jack G Calvert and published by Oxford University Press. This book was released on 2008-09-15 with total page 1005 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Atmospheric Multiphase Chemistry written by Hajime Akimoto and published by John Wiley & Sons. This book was released on 2020-06-02 with total page 539 pages. Available in PDF, EPUB and Kindle. Book excerpt: An important guide that highlights the multiphase chemical processes for students and professionals who want to learn more about aerosol chemistry Atmospheric Multiphase Reaction Chemistry provides the information and knowledge of multiphase chemical processes and offers a review of the fundamentals on gas-liquid equilibrium, gas phase reactions, bulk aqueous phase reactions, and gas-particle interface reactions related to formation of secondary aerosols. The authors—noted experts on the topic—also describe new particle formation, and cloud condensation nuclei activity. In addition, the text includes descriptions of field observations on secondary aerosols and PM2.5. Atmospheric aerosols play a critical role in air quality and climate change. There is growing evidence that the multiphase reactions involving heterogeneous reactions on the air-particle interface and the reactions in the bulk liquid phase of wet aerosol and cloud/fog droplets are important processes forming secondary aerosols in addition to gas-phase oxidation reactions to form low-volatile compounds. Comprehensive in scope, the book offers an understanding of the topic by providing a historical overview of secondary aerosols, the fundamentals of multiphase reactions, gas-phase reactions of volatile organic compounds, aqueous phase and air-particle interface reactions of organic compound. This important text: Provides knowledge on multiphase chemical processes for graduate students and research scientists Includes fundamentals on gas-liquid equilibrium, gas phase reactions, bulk aqueous phase reactions, and gas-particle interface reactions related to formation of secondary aerosols Covers in detail reaction chemistry of secondary organic aerosols Written for students and research scientists in atmospheric chemistry and aerosol science of environmental engineering, Atmospheric Multiphase Reaction Chemistry offers an essential guide to the fundamentals of multiphase chemical processes.

Download or read book Evolution of Secondary Organic Aerosol Composition Volatility and Absorption During Oxidation of Phenolic Compounds Under Conditions Relevant to Biomass Burning written by Carley Fredrickson and published by . This book was released on 2021 with total page 72 pages. Available in PDF, EPUB and Kindle. Book excerpt: Phenolic compounds emitted from wildfires and biomass burning (BB) are highly reactive and yield secondary organic aerosol (SOA) and brown carbon (BrC) upon oxidation initiated by the hydroxyl radical (OH) and nitrate radical (NO3). In high nitrogen dioxide (NO2) environments, such as BB plumes, phenolic oxidation is expected to form nitroaromatics in high yield which can explain in part the BrC content of associated SOA. We conducted a set of experiments as part of the Monoterpene and Oxygenated aromatics Oxidation at Night and under LIGHTs (MOONLIGHT) campaign to evaluate the chemical and physical drivers of phenolic compound evolution in high nitrogen oxide (NOx = NO + NO2) wildfire plumes, specifically investigating the composition, volatility, and absorption of the SOA components formed under OH and NO3 oxidation, with catechol as the focus of this thesis. Oxidation products in both the gas and particle phases were measured using an I- adduct high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF I- CIMS) coupled with the Filter Inlet for Gases and Aerosols (FIGAERO). Oxidation of catechol produced BrC, defined by light absorption at 405 nm, at the highest yields out of all the phenolics studied. Particle-phase nitrocatechol (C6H5NO4) was found to account for 28% and 79% of organic aerosol (OA) mass formed from OH-initiated or NO3-initiated oxidation, respectively, and was strongly associated with BrC. Effective molar yields, i.e., including chemical and physical losses, of nitrocatechol were measured to range from 0.65 to 1 for NO3-initiated oxidation, and 0.03 for OH oxidation conditions. Maximum SOA mass yields from catechol oxidation were strongly tied to formation of nitrocatechol, ranging from 0.38 to 1.63 for the different experiments, lower than previously reported values. Higher SOA mass yields from catechol oxidation were found for NO3 rather than OH oxidation. The effective volatility of the SOA measured with the FIGAERO thermograms decreased significantly with subsequent aging after formation. Gas-particle partitioning measurements imply the saturation vapor concentration of nitrocatechol to be roughly 5 [micrograms] m-3, while the FIGAERO thermogram model estimate is lower but in the same order of magnitude, implying that wildfire gas-particle partitioning of nitroaromatics is likely dynamic. Group contribution method estimates of nitrocatechol saturation concentration range across 8 orders of magnitude with 3 [micrograms] m-3 from the Nannoolal method paired with the Joback and Reid boiling point method being closest to our observational estimates. In extended photochemical aging experiments, BrC formed from catechol oxidation had a photochemical lifetime of ~12 hours, while that of particulate nitrocatechol ranged from 7 hours if formed by NO3 oxidation to 18 hours if formed by OH oxidation. Implications for atmospheric evolution of BrC in wildfire and mechanisms of particulate nitroaromatic losses are discussed.

Download or read book Chemical Processes in Atmospheric Oxidation written by Georges Le Bras and published by Springer Science & Business Media. This book was released on 2012-12-06 with total page 316 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Large Enhancement in the Heterogeneous Oxidation Rate of Organic Aerosols by Hydroxyl Radicals in the Presence of Nitric Oxide written by and published by . This book was released on 2015 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this paper we report an unexpectedly large acceleration in the effective heterogeneous OH reaction rate in the presence of NO. This 10-50 fold acceleration originates from free radical chain reactions, propagated by alkoxy radicals that form inside the aerosol by the reaction of NO with peroxy radicals, which do not appear to produce chain terminating products (e.g., alkyl nitrates), unlike gas phase mechanisms. Lastly, a kinetic model, constrained by experiments, suggests that in polluted regions heterogeneous oxidation plays a much more prominent role in the daily chemical evolution of organic aerosol than previously believed.