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Author: Berk Oktem
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 278
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Author: Berk Oktem
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 278
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Author: Yuqian Gao
Publisher:
ISBN: 9781124611839
Category : Atmospheric aerosols
Languages : en
Pages :
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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.
Author: Katherine J. Heaton
Publisher:
ISBN: 9781124086231
Category : Atmospheric aerosols
Languages : en
Pages :
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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: Quentin Gerald James Malloy
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 414
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Author:
Publisher:
ISBN:
Category : Air
Languages : en
Pages : 64
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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: 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: Yun Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Fred Warren McLafferty (Chemiker, USA)
Publisher:
ISBN: 9780805370485
Category : Mass spectrometry
Languages : en
Pages : 278
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Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Aerosol particles are ubiquitous throughout the atmosphere and play an important role in human health, climate, and the chemistry of the atmosphere. A significant mass fraction of these particles is composed of organic species, which remain poorly characterized due to the number and diversity of species present. This thesis describes the development and characterization of two versions of a new single particle mass spectrometer with a 3D ion trap for organic aerosol studies. Version I combines CO2 laser desorption and electron impact ionization in an ion trap. Mass spectra obtained for four species are comparable to NIST EI spectra. Tandem mass spectrometry studies are also demonstrated. The effects of vaporization energy, ionization delay time, and electron pulse width on the mass spectra and fragmentation patterns are examined. The detection limit of the instrument is found to be ~1x108 molecules (350 nm diameter particle) for 2,4-dihydroxybenzoic acid. Version II integrates CO2 laser desorption and tunable VUV ionization in an ion trap and was used for a detailed study of oleyl alcohol, oleic acid and mixtures thereof. Both the degree of fragmentation in the mass spectra and the translational energy of the vaporized molecules are found to vary as a function of desorption energy in the pure particles and as a function of composition in the mixed particles. These changes can be described by the energy absorbed per particle during desorption. We show that these effects hinder the quantitative response of the instrument and have important implications for other two step laser desorption/ionization systems. The final part of this thesis presents preliminary results from atmospherically relevant particles. Mass spectra of cigarette sidestream smoke, fulvic acid, meat cooking, and ammonium bisulfate aerosols are collected using both versions of the instrument. The two step desorption/ionization process only worked for two types of aerosols, while CO2 only mass spectra w.
Author: Kai Wang
Publisher:
ISBN:
Category : Mass spectrometry
Languages : en
Pages :
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