A Molecular Characterization of Biogenic Secondary Organic Aerosol by High-resolution Time-of-flight Mass Spectrometry PDF Download

Author: Felipe Daniel Lopez-Hilfiker
Publisher:
ISBN:
Category :
Languages : en
Pages : 178

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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: Peijun Tu
Publisher:
ISBN: 9780355733846
Category :
Languages : en
Pages : 154

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Secondary organic aerosol (SOA), which is produced by the oxidation of volatile organic compounds (VOCs) emitted from biogenic and anthropogenic sources, has great impact on the environment and human health. In this dissertation, SOA particles derived from biogenic precursors were characterized with various mass spectrometry techniques for molecular level analysis. Differences in the chemical compositions of these particles at different formation stages were used to gain insight into the formation and fate of SOA in the atmosphere. While not pursued in this dissertation, the changes studied here may also provide significant information about SOA toxicity and harm to human health. ☐ SOA derived from ozonolysis of biogenic precursors was generated in a flow tube reactor and then sent into a photo chamber where the OH radicals could be produced to simulate further aging (fresh SOA oxidation with OH radicals to produce aged SOA). The molecular compositions of both fresh and aged SOA were studied with high resolution ESI-MS, and thousands of unique molecular formulas were characterized. Among these, a class of highly oxidized multifunctional (HOM) components, which are believed to contribute significantly to the formation of SOA, were identified and compared with previously reported Extremely Low-Volatility Organic Compounds (ELVOC) detected in the gas phase and Low Volatility Organic Oxygenated Aerosol (LV-OOA) measurements of the particle phase. HOMs in fresh SOA consisted mostly of monomers and dimers, which are consistent with condensation of ELVOCs reported from a separate study. Aging caused an increase in the average number of carbon atoms per molecule of the HOMs, which is consistent with particle phase oxidation of (less oxidized) oligomers already existing in fresh SOA. For the biogenic precursors and experimental conditions studied, HOMs in fresh biogenic SOA have molecular formulas more closely resembling LVOOA than HOMs in aged SOA, suggesting that aging of biogenic SOA is not a good surrogate for ambient LVOOA. ☐ In a separate set of experiments, SOA particles were size-selected in the 30-100 nm range with a Differential Mobility Analyzer (DMA) and analyzed by both on- and off-line mass spectrometry techniques. The chemical composition was found to change significantly with particle size. Both the average oxygen-to-carbon (O/C) ratio and carbon oxidation state (OSc) were found to decrease with increasing particle size, while the change of relative abundance of oligomers was opposite as the particle size increases. These changes allowed the relative contributions of condensation, partitioning, and particle phase oligomerization to be determined at various stages of particle formation and growth. Condensation of non-/low- volatility, highly oxidized species dominates the formation/growth of smaller SOA particles, while the partitioning of semi-volatile, less oxidized species tends to play an important role in the growth of larger SOA particles. The formation of oligomers that primarily takes place in the particle phase (accretion reactions) becomes more favored as the volume to surface area ratio of the particle increases. ☐ Additionally, due to the complex molecular components of atmospheric nanoparticles, Reverse Phase Liquid Chromatography (RPLC) and Ion-Mobility Separation (IMS)- Mass Spectrometry were employed for molecular separation. Compositions partially separated based on their size, shape and polarity were subjected to tandem mass spectrometry for structure elucidation. In some cases, isomers/ isobars were identified and separated with the help of HPLC using gradient elution method.

Author: Sandra Louise Blair
Publisher:
ISBN: 9781339820262
Category :
Languages : en
Pages : 228

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Aerosols can substantially impact human health, atmospheric chemistry, and climate. The composition and photochemistry of a variety of anthropogenic and biogenic primary and secondary organic aerosols (POA and SOA) have yet to be fully characterized. The composition of organic aerosols is extremely complex - they contain a variety of highly oxidized, multifunctional, low vapor pressure organic compounds. The primary focus of this thesis is on the molecular characterization of organic aerosols that are not well understood or have not been studied before, such as primary emissions from electronic cigarettes, iron (III) mediated SOA, and photooxidized biodiesel and diesel fuel SOA. Another focus of this dissertation is the effect of direct photochemical aging on the composition of organic aerosol. Direct photolysis experiments were first applied to a system that is known to have a photolabile composition, alpha-pinene ozonolysis SOA, such that characterization of a photochemical effect would be possible to quantify. Photolysis of more complex SOA that have not been studied before, photooxidized biodiesel and diesel fuel SOA, were also investigated in this thesis. Advanced high resolution mass spectrometry techniques were used in the molecular characterization of organic aerosols, including nano-Desorption Electrospray Ionization Mass Spectrometry (nano-DESI) and Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR). An additional suite of online instrumentation was used to measure gas-phase composition, particle-phase composition, particle size and concentration, and absorption properties: Proton Transfer Reaction Time-of-Flight Mass Spectrometry (PTR-ToF-MS), Aerosol Mass Spectrometry (ToF-AMS), Scanning Mobility Particle Sizing (SMPS), and UV-vis spectroscopy. The molecular analysis of these aerosols provides valuable insight to the formation and photochemical behavior of unexpected, polymeric, light absorbing, and unique organosulfur species.

Author: Katherine J. Heaton
Publisher:
ISBN: 9781124086231
Category : Atmospheric aerosols
Languages : en
Pages :

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Book Description
Secondary Organic Aerosol (SOA) forms in the atmosphere from the oxidation of biogenic emissions. Even though SOA has been linked to health and climate effects, the chemical mechanism of SOA formation is not well understood. Through the use of mass spectrometry, this work characterizes SOA during the early stages of growth from the reaction of ozone with monoterpenes, a major biogenic emission. In this thesis, three types of studies are described for analyzing SOA formation: (1) the molecular composition of SOA is studied using the photoionization aerosol mass spectrometer, (2) the atomic composition is studied with the nanometer aerosol mass spectrometer and (3) high resolution mass spectrometry is used to help reconcile atomic and molecular composition data. The monoterpene ozonolysis reactions were performed in a flow tube reactor, where the reaction period could vary from 3s to 22s. The Photoionization Aerosol Mass Spectrometer (PIAMS) detected the formation of oligomers within seconds of the onset of the reaction. Ions that were detected were mapped to dimers that could form via the stabilized Criegee intermediate channel or the hydroperoxy channel. The Nanometer Aerosol Mass Spectrometer (NAMS) analyzed the elemental composition of the SOA which showed the formation of highly polar compounds during the early stages of SOA growth. NAMS also analyzed the changes in the composition of SOA when it formed in the presence of atmospheric species (water vapor, nitric acid vapor and sodium chloride seed particles). The data collected indicated that there is not as much change for endocyclic compounds as there is for exocyclic compounds. Finally, a new off-line analysis technique was created to micro-extract SOA deposited on a plate from the flow tube reactor. The samples were analyzed with the Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTICR-MS). The FTICR-MS was used to collect molecular and elemental data simultaneously. The FTICR-MS produced accurate mass data that could be used to calculate molecular formulas. This provided a direct comparison of the data acquired with PIAMS and NAMS.

Author: Yunzhu Zhao
Publisher:
ISBN:
Category : Atmospheric chemistry
Languages : en
Pages : 256

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Atmospheric aerosol affects the Earth's energy budget, reduces visibility and influences human health. The organic composition of aerosol is quite complex and continuously evolves through various atmospheric processes. To gain a deeper understanding of the molecular composition of atmospheric organic matter (AOM), chamber-generated biogenic secondary organic aerosol (SOA), ambient aerosol and cloud water samples were studied. Ultrahigh resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry was used to provide detailed molecular characterization of the atmospheric samples. Due to the extremely high mass resolution and mass accuracy, thousands of individual molecular formulas were identified in all of the samples studied. Multivariate statistical analysis methods were evaluated to compare the similarities and differences of the sample compositions. The biogenic SOA from three individual monoterpene precursors and a sesquiterpene precursor have clusters of peaks in their mass spectra, indicating that high molecular weight oligomers are a major component of the SOA. The monoterpene SOA have similar molecular compositions, which are different from the sesquiterpene SOA composition. The indicator species of SOA were identified using multivariate statistical analysis. Daily 24-hour water-soluble organic carbon samples from ambient aerosol collected at the Storm Peak Laboratory (SPL) show similar bulk chemical properties regarding their average elemental ratios and double bond equivalents. Using multivariate statistical analysis, the site meteorological conditions were found to affect the aerosol molecular composition. Days with strong UV radiation and high temperature were found to contain large numbers of biogenic SOA molecular formulas. Days with high relative humidity and high sulfate ion concentrations were found to contain many sulfur-containing compounds, suggesting their aqueous phase formation. The collection of cloud samples at the SPL provided an opportunity to study aqueous processing of AOM. The cloud composition was affected by biomass burning and SOA. Comparisons of the sample compositions indicate biogenic SOA components are commonly observed in ambient aerosol and cloud samples collected at the SPL. Thus, the ambient samples were used to confirm the biogenic SOA indicator species identified in chamber-generated SOA. This study of the three types of atmospheric samples helps to understand the composition of AOM with respect to atmospheric processes.

Author: Yadian Gómez González
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Rachel Elizabeth Sellon
Publisher:
ISBN:
Category :
Languages : en
Pages : 274

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Atmospheric aerosols can affect visibility and the Earth's climate by scattering and absorbing light and they also can have adverse effects on human health. The organic portion of atmospheric aerosols is very complex and is a major fraction of fine particulate matter. High molecular weight (high-MW)/oligomeric organic compounds can make up a large part of this organic fraction and the composition, sources, and formation mechanisms for these compounds are not well understood. This knowledge and understanding is necessary to decrease the uncertainty in the climate affects of aerosols and to improve climate models. This dissertation investigates the composition and formation mechanisms for the high-MW/oligomeric fraction of secondary organic aerosols (SOA) collected in Bakersfield, CA and presents a comparative analysis of chamber and ambient SOA, from both Los Angeles (LA) and Bakersfield, to investigate sources at both locations. A novel sampling technique, nanospray-Desorption Electrospray Ionization (nano-DESI), was used with high resolution mass spectrometry (HR-MS) to determine the molecular formulas of the high molecular weight (HMW)/oligomeric fraction of SOA. Nano-DESI involves direct desorption from the sample surface and was used to limit reactions that can take place with extraction and storage in solvent. The samples were collected in Bakersfield and LA during CalNex 2010. Both Bakersfield and LA are out of compliance with EPA standards of ozone and particulate matter and provide opportunities to examine air masses affected by both anthropogenic and biogenic sources. This dissertation has provided the first evidence of observable changes in the composition of high-MW/oligomeric compounds throughout the day. Using positive mode nano-DESI, afternoon increases in the number of compounds that contain carbon, hydrogen and oxygen (CHO) were observed consistent with photochemistry/ozonolysis as a major source for these compounds. Compounds containing reduced nitrogen groups were dominant at night and had precursors consistent with imine formation products from the reaction of carbonyls and ammonia. In the negative mode, organonitrates (CHON) and nitroxy organosulfates (CHONS) had larger numbers of compounds in the night/morning samples consistent with nitrate radical formation reactions. A subset of the CHONS compounds and compounds containing sulfur (CHOS) had the same composition as known biogenic organosulfates and nitroxy organosulfates indicating contributions from both biogenic and anthropogenic sources to the SOA. This dissertation also provides the first analysis of the high-MW/oligomeric fraction in size resolved samples; the majority of the compounds were found in aerosol diameters between 0.18-1.0 micrometers and the CHON were bimodal with size. Finally, this dissertation presents the first comparative analysis of the overlap in the composition of this fraction of SOA between ambient and chamber samples. Samples collected in Pasadena, LA and Bakersfield were compared with samples collected in a smog chamber using diesel and isoprene sources. The results indicate that diesel had the highest overlap at both sites, Bakersfield samples were more oxidized, and LA showed evidence of a SOA plume arriving from downtown LA. The addition of ammonia to the diesel chamber experiment was necessary to form many of the 2N compounds found in Bakersfield. These results increase our understanding of the types of compounds found in urban environments and give evidence for the timescales of formation reactions in an ambient environment. They show that the majority of the high-MW oligomeric compounds are found in submicron size particles and that the composition of this fraction of SOA varies with aerosol size. Results from the chamber comparisons show that both diesel and isoprene are important sources for these compounds and also that there other sources are present. Future work that combines this type of analysis, in other ambient environments, with studies of the optical properties of aerosols could be used to help improve climate models and to start to close the gap in our understanding of the climate effects of atmospheric aerosols.

Author: Gabriel Avram Isaacman
Publisher:
ISBN:
Category :
Languages : en
Pages : 167

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Particles in the atmosphere are known to have negative health effects and important but highly uncertain impacts on global and regional climate. A majority of this particulate matter is formed through atmospheric oxidation of naturally and anthropogenically emitted gases to yield highly oxygenated secondary organic aerosol (SOA), an amalgamation of thousands of individual chemical compounds. However, comprehensive analysis of SOA composition has been stymied by its complexity and lack of available measurement techniques. In this work, novel instrumentation, analysis methods, and conceptual frameworks are introduced for chemically characterizing atmospherically relevant mixtures and ambient aerosols, providing a fundamentally new level of detailed knowledge on their structures, chemical properties, and identification of their components. This chemical information is used to gain insights into the formation, transformation and oxidation of organic aerosols. Biogenic and anthropogenic mixtures are observed in this work to yield incredible complexity upon oxidation, producing over 100 separable compounds from a single precursor. As a first step toward unraveling this complexity, a method was developed for measuring the polarity and volatility of individual compounds in a complex mixture using two-dimensional gas chromatography, which is demonstrated in Chapter 2 for describing the oxidation of SOA formed from a biogenic compound (longifolene: C15H24). Several major products and tens of substantial minor products were produced, but none could be identified by traditional methods or have ever been isolated and studied in the laboratory. A major realization of this work was that soft ionization mass spectrometry could be used to identify the molecular mass and formula of these unidentified compounds, a major step toward a comprehensive description of complex mixtures. This was achieved by coupling gas chromatography to high resolution time-of-flight mass spectrometry with vacuum ultraviolet (VUV) photo-ionization. Chapters 3 and 4 describe this new analytical technique and its initial application to determine the structures of unknown compounds and formerly unresolvable mixtures, including a complete description of the chemical composition of two common petroleum products related to anthropogenic emissions: diesel fuel and motor oil. The distribution of hydrocarbon isomers in these mixtures - found to be mostly of branched, cyclic, and saturated - is described with unprecedented detail. Instead of measuring average bulk aerosol properties, the methods developed and applied in this work directly measure the polarity, volatility, and structure of individual components to allow a mechanistic understanding of oxidation processes. Novel characterizations of these complex mixtures are used to elucidate the role of structure and functionality in particle-phase oxidation, including in Chapter 4 the first measurements of relative reaction rates in a complex hydrocarbon particle. Molecular structure is observed to influence particle-phase oxidation in unexpected and important ways, with cyclization decreasing reaction rates by ~30% and branching increasing reaction rates by ~20-50%. The observed structural dependence is proposed to result in compositional changes in anthropogenic organic aerosol downwind of urban areas, which has been confirmed in subsequent work by applying the techniques described here. Measurement of organic aerosol components is extended to ambient environments through the development of instrumentation with the unprecedented capability to measure hourly concentrations and gas/particle partitioning of individual highly oxygenated organic compounds in the atmosphere. Chapters 5 and 6 describe development of new procedures and hardware for the calibration and analysis of oxygenates using the Semi-Volatile Thermal desorption Aerosol Gas chromatograph (SV-TAG), a custom instrument for in situ quantification of gas- and particle-phase organic compounds in the atmosphere. High time resolution measurement of oxygenated compounds is achieved through a reproducible and quantitative methodology for in situ "derivatization"--Replacing highly polar functional groups that cannot be analyzed by traditional gas chromatography with less polar groups. Implementation of a two-channel sampling system for the simultaneous collection of particle-phase and total gas-plus-particle phase samples allows for the first direct measurements of gas/particle partitioning in the atmosphere, significantly advancing the study of atmospheric composition and variability, as well as the processes governing condensation and re-volatilization. This work presents the first in situ measurements of a large suite of highly oxygenated biogenic oxidation products in both the gas- and particle-phase. Isoprene, the most ubiquitous biogenic emission, oxidizes to form 2-methyltetrols and C5 alkene triols, while [alpha]-pinene, the most common monoterpene, forms pinic, pinonic, hydroxyglutaric, and other acids. These compounds are reported in Chapter 7 with unprecedented time resolution and are shown for the first time to have a large gas-phase component, contrary to typical assumptions. Hourly comparisons of these products with anthropogenic aerosol components elucidate the interaction of human and natural emissions at two rural sites: the southeastern, U.S. and Amazonia, Brazil. Anthropogenic influence on SOA formation is proposed to occur through the increase in liquid water caused by anthropogenic sulfate. Furthermore, these unparalleled observations of gas/particle partitioning of biogenic oxidation products demonstrate that partitioning of oxygenates is unexpectedly independent of volatility: many volatile, highly oxygenated compounds have a large particle-phase component that is poorly described by traditional models. These novel conclusions are reached in part by applying the new frameworks developed in previous chapters to understand the properties of unidentified compounds, demonstrating the importance of detailed characterization of atmospheric organic mixtures. Comprehensive analysis of anthropogenic and biogenic emissions and oxidation product mixtures is coupled in this work with high time-resolution measurement of individual organic components to yield significant insights into the transformations of organic aerosols. Oxidation chemistry is observed in both laboratory and field settings to depend on molecular properties, volatility, and atmospheric composition. However, this work demonstrates that these complex processes can be understood through the quantification of individual known and unidentified compounds, combined with their classification into descriptive frameworks.

Author:
Publisher:
ISBN:
Category : Air
Languages : en
Pages : 64

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Book Description
The oxidation of volatile organic compounds (VOCs) plays a role in both regional and global air quality through the formation of secondary organic aerosols (SOA). More than 1000TgC/yr of non-methane VOCs are emitted from biogenic sources (significantly greater than from anthropogenic sources). Despite this magnitude and potential importance for air quality, the body of knowledge around the identities, quantities and oxidation processes of these compounds is still incomplete (e.g., Goldstein & Galbally, 2007; Robinson et al., 2009). Two-dimensional gas chromatography paired with time-of-flight mass spectrometry (GC×GC/TOFMS) is a powerful analytical technique which is explored here for its role in better characterizing biogenic VOCs (BVOCs) and thus SOA precursors.

Author: Yuqian Gao
Publisher:
ISBN: 9781124611839
Category : Atmospheric aerosols
Languages : en
Pages :

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Book Description
Organic aerosol is a major constituent of atmospheric fine particles, especially over continental regions. These particles adversely affect human health and global climate. A significant fraction of organic aerosol is considered to be from the oxidation products of ozone and volatile organic compounds, which are called secondary organic aerosol (SOA). To study the formation mechanisms of secondary organic aerosol, it is important to characterize their molecular composition. The composition of secondary organic aerosol is very complex including thousands of species with molecular weight up to over a thousand Dalton. Methods utilized for the identification of these oxidation products involve advanced mass spectrometry techniques. In this dissertation, three mass spectrometry techniques were developed to study the molecular composition of organic aerosol. Firstly, online nano-aerosol sample deposition methods for matrix-assisted laser desorption/ionization (MALDI) mass spectrometry was developed to incorporate matrix particles directly with analyte particles onto a conventional MALDI plate. Secondly, a microsampling and analysis technique was developed in order to collect microgram samples and analyze them with high performance mass spectrometry. With this technique, the molecular composition of particle phase SOA at a low mass loading can be elucidated, which provides information about SOA formation at the early stages. A species with the (neutral molecule) formula C 17 H 26 O 8 (MW 358) increased substantially in intensity relative to other products as the mass loading decreased. Tandem mass spectrometry (MS n) of this species showed it to be a dimer of C 9 H 14 O 4 and C 8 H 12 O 4, most likely pinic acid and terpenylic acid, respectively. This species is likely to be critical at the early stages of SOA formation. Thirdly, ambient secondary electrospray ionization (ESI) source was designed to characterize the molecular composition of both gas and particle phases SOA online. This ion source was demonstrated to be applicable to a wide range of mass spectrometers having an ambient inlet. This technique provides a tool to acquire detailed information about possible SOA nucleation agents. A species with the (neutral molecule) formula C 20 H 36 O 6 (MW 372) was found in the gas-phase products of SOA, which could be critical for the new particle formation of SOA. Tandem mass spectrometry (MS n) of this species showed it to be a dimer of an organic hydroperoxide C 10 H 18 O 3, which is likely formed via OH-initiated oxidation pathway.