Secondary Organic Aerosol Formation from Radical-initiated Reactions of Alkenes
Secondary Organic Aerosol Formation from Radical-initiated Reactions of Alkenes

Author: Aiko Matsunaga

Publisher:

Published: 2009

Total Pages: 289

ISBN-13:

DOWNLOAD EBOOK

The products and mechanisms of secondary organic aerosol (SOA) formation from reactions of 1-alkenes, internal alkenes, and 2-methyl-1-alkenes with OH radicals in the presence of NO[subscript x] were investigated in an environmental chamber and the results used to develop quantitative models for SOA formation. Aerosol chemical composition was analyzed using a thermal desorption particle beam mass spectrometer (TDPBMS), and multifunctional organic nitrate products were quantified using a high-performance liquid chromatograph with UV-vis detector and identified using the TDPBMS and 1H NMR. The major products observed in reactions of linear alkenes were [beta]-hydroxynitrates, dihydroxynitrates, cyclic hemiacetals, dihydrofurans, and dimers formed from dihydroxycarbonyls. Trihydroxynitrates and trihydroxycarbonyls were observed in reactions of 2-methyl-1-alkenes, in addition to the products listed above. Dimers were not observed, apparently because electron donation by the additional methyl group (compared to linear 1-alkenes) reduces the driving force for hemiacetal formation. The measured yields of [beta]-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates were used to calculate relative ratios of 1.0:1.9:4.3 for forming primary, secondary, and tertiary [beta]-hydroxyalkyl radicals by OH radical addition to the C=C double bond, and branching ratios of 0.12, 0.15, and 0.25 for forming [beta]-hydroxynitrates from reactions of primary, secondary, and tertiary â-hydroxyperoxy radicals with NO. The trends are consistent with expected relative stabilities of [beta]-hydroxyalkyl radicals and ß-hydroxyperoxy radical-NO complexes. It should be possible to use these values to estimate product yields from similar reactions of other alkenes. Comparison of measured and model-calculated SOA yields showed that in some cases the models provide accurate predictions of SOA yields, but that uncertainties in gas- and particle-phase chemistry and gas-particle partitioning can lead to significant discrepancies. More limited environmental chamber studies were also carried out on SOA formation from reactions of linear alkenes with NO3 radicals. The major products were [beta]-hydroxynitrates, [beta]-carbonylnitrates, dihydroxynitrates, and hydroxy- and oxo- dinitrooxytetrahydrofurans, which had not been observed previously. It was observed that isomerization of [delta]-hydroxycarbonyls to cyclic hemiacetals, followed by dehydration to highly reactive dihydrofurans that can be further oxidized, can be important sources of SOA from reactions of alkenes with OH and NO3 radicals.

Chemistry of Secondary Organic Aerosol Formation from the Reaction of Hydroxyl Radicals with Aromatic Compounds
Chemistry of Secondary Organic Aerosol Formation from the Reaction of Hydroxyl Radicals with Aromatic Compounds

Author: Christen Michelle Strollo Gordon

Publisher:

Published: 2013

Total Pages: 185

ISBN-13: 9781303507403

DOWNLOAD EBOOK

Secondary Organic Aerosol (SOA) can have significant impacts on visibility, human health, and global climate, and a more detailed understanding of the roles of both gas-phase and heterogeneous/multiphase chemistry is needed to develop air quality models that accurately represent the formation of SOA from the oxidation of aromatic hydrocarbons. The objective of this dissertation is to investigate the mechanisms and products of SOA formation from the OH radical-initiated reaction of aromatics in an environmental chamber. This is done using a combination of thermal desorption particle beam mass spectrometry, functional group and CHON elemental analysis, and UV spectroscopy. Chapter 2 investigates the variability of SOA yields measured for reactions of m-xylene and other methylbenzenes as a function of humidity, seed particle, OH source, NO x concentration, light intensity, and mass loading. The most significant factor that determined SOA yields was the amount of m -xylene reacted. The chapter concludes with a discussion of a series of experiments conducted to isolate the contribution to SOA formation of specific primary gas-phase products of the m -xylene reaction. Chapter 3 examines the formation of SOA from the oxidation of 3-methylfuran, which produces among other compounds an [Alpha, Beta]-unsaturated dicarbonyl that is also a major product of the oxidation of m -xylene. We have determined that SOA forms from the heterogeneous/multiphase oligomerization of primary reaction products to form esters, hemiacetals, and acetals, and not through second-generation reactions. Chapter 4 discusses the chemical composition of SOA formed from the reaction of m -xylene and how the variables detailed in Chapter 2 affect the composition. Experiments were carried out with deuterated m-xylene to confirm that SOA is dominated by hemiacetals formed from C8 ring-opened primary products and their second-generation products. Finally, Chapter 5 shows that SOA formed from the oxidation of benzaldehyde in the absence of NOx is largely composed of oligomeric products formed through heterogeneous/multiphase reactions involving benzoic acid, peroxybenzoic acid, phenol, and benzaldehyde.

Mechanisms of Atmospheric Oxidation of the Alkanes
Mechanisms of Atmospheric Oxidation of the Alkanes

Author: Jack G Calvert

Publisher: Oxford University Press

Published: 2008-09-15

Total Pages: 1005

ISBN-13: 0199710880

DOWNLOAD EBOOK

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.

Secondary Organic Aerosol Formation Initiated by Îł-Terpineol Ozonolysis and Exposure Quantified by the Secondary Intake Fraction
Secondary Organic Aerosol Formation Initiated by Îł-Terpineol Ozonolysis and Exposure Quantified by the Secondary Intake Fraction

Author: Yanan Yang

Publisher:

Published: 2017

Total Pages: 338

ISBN-13:

DOWNLOAD EBOOK

Indoor air quality (IAQ) is associated with human health due to people spending most of their time indoors. Secondary organic aerosol (SOA) formation is an important source of fine airborne particles, which can cause acute airway effects and decreased lung function. SOA is a product of reactive organic gas (ROG) ozonolysis, which can be parameterized by the aerosol mass fraction (AMF). The AMF is the ratio of SOA formation mass to the reacted ROG mass, and it is positively correlated with the total organic aerosol mass concentration. Îł-Terpineol is a terpenoid that can have a strong emission rate indoors owing to consumer product usage. It reacts strongly with oxidants such as ozone, hydroxyl radical (OH), and nitrate radical (NO3), where those radicals are produced indoors due to ozone reaction with alkenes or nitrogen dioxide (NO2), respectively. Due to the fast reaction rates of Îł-terpineol with these oxidants, SOA formation has the potential to increase in-door fine particle concentrations. However, SOA formation from Îł-terpineol has not been systematically quantified. Therefore, the purpose of this work was to quantify SOA formation owing to Îł-terpineol ozonolysis, for two sets of experiments, one without and one with NO2 present. In the first set of 21 experiments, the SOA formation initiated by reacting 6.39 to 226 ppb Îł-terpineol with high ozone (~25 ppm) to ensure rapid and complete ozonolysis for high (0.84 h8́21), moderate (0.61 h8́21) and low (0.36 h8́21) air exchange rates (AER) was studied in a stainless steel chamber system. The resulting SOA mass formation was parameterized with the AMF for all experiments. The impact of reacted Îł-terpineol and AERs on AMFs as well as the SOA size distribution was investigated, and different AMF models (one-product, two-product, and volatility basis set) were fit to the AMF data. Predictive modeling investigated the impact of the SOA formation from Îł-terpineol ozonolysis in residential indoor air. Furthermore, a second set of 21 experiments in a Teflon bag operated as semi-batch reactor explored the impact of NO2 at 0 to 2000 ppb on SOA formation from Îł-terpineol ranging from 20 ppb to 200 ppb with excess ozone (~25ppm). In this system, ozone can either initiate reactions with Îł-terpineol to produce organic peroxy radicals (RO28́9) or react with NO2 to produce NO3, which can react with Îł-terpineol. For analysis of results, we classified experiments by logarithmic spacing into four groups according to the initial ratio of VOC/NO2 values. SOA mass was again parameterized by the AMF as a function of the organic aerosol concentration. The impact of VOC/NO2 on SOA mass as well as the SOA size distribution was investigated, and the SOA composition for each grouping of experiments was elucidated by the kinetic modeling. Finally, this SOA formation was put into context using the 'secondary intake fraction' (siF), which is a developed metric that evaluates SOA exposure during various human activities. The siF is defined as the up-taken mass of a secondary product for an exposed individual per unit mass of primary product emitted during human residential activities, over a given exposure time. The siF for individual intake was evaluated for SOA formation from d-limonene, Îł-terpineol, or Îł-pinene ozonolysis in five residential scenarios, including: I. Constant emission, II. Pulse emission, III. Surface cleaning, IV. Solution cleaning, and V. Skin cleaning. For a given input set, a transient model was used to predict SOA concentrations and the siF, using inputs cast as probability distributions within a Monte Carlo approach. Multiple linear regression techniques were applied to fit siF values for the five scenarios, for use in sensitivity analyses. Also, the multiple linear regression results can be used to predict the siF and the potential for human intake of SOA within exposure models.

Investigating Sources and Sinks of Organic Aerosols
Investigating Sources and Sinks of Organic Aerosols

Author: Alan J. Kwan

Publisher:

Published: 2011

Total Pages: 0

ISBN-13:

DOWNLOAD EBOOK

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.

The Aging of Organic Aerosol in the Atmosphere
The Aging of Organic Aerosol in the Atmosphere

Author: Sean Herbert Kessler

Publisher:

Published: 2013

Total Pages: 134

ISBN-13:

DOWNLOAD EBOOK

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.