Characterization of Oligomers in Secondary Organic Aerosol Using Advanced Mass Spectrometry Techniques PDF Download
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Author: Wiley A. Hall
Publisher:
ISBN: 9781267214751
Category : Aerosols
Languages : en
Pages :
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Book Description
Biogenic secondary organic aerosol (SOA) forms from the reaction of gas phase organic molecules from biological sources with an atmospheric oxidant. Although biogenic SOA can comprise up to 80% of the particulate mass suspended in the atmosphere, the reactions that form SOA and the chemical identities of the compounds it contains are poorly understood, especially the oligomeric species that form the non-volatile core of SOA. In this dissertation, mass spectrometric techniques are used to characterize the oligomers found in SOA throughout their lifetime. Fresh aerosol was generated in a Tedlar bag and flow tube reactor (FTR) to determine: (1) the relevance of laboratory-generated oligomers to the atmosphere, and (2) the formation routes, and identity of the oligomers. Fresh SOA generated in the FTR was then reacted in a chamber designed to simulate photooxidation to (3) study the aging of SOA oligomers and determine if they are a source of highly oxidized atmospheric SOA. A scanning mobility particle sizer (SMPS) was found to accurately measure the concentration and size distribution of SOA. The SOA was then collected onto Teflon coated, glass fiber filters. Filter phase reactions were found to be minimal or non-existent. Various extraction solvents were tested, and acetonitrile was found to have high extraction efficiency without causing side reactions with the sample. Through the method of standard additions, the concentration of oligomeric species in the non-volatile core of the SOA collected and extracted was determined to be ~50% for laboratory SOA. SOA generated in the FTR was shown to have similar behavior as a class of organic aerosol found in the atmosphere. High resolution mass spectra revealed that oligomers undergo thermal degradation to volatile compounds when heated to high temperatures, so thermodenuders cannot be used to determine SOA volatility. High resolution tandem mass spectrometry (MSMS) was used to determine which compounds react to form oligomers and what their routes of formation are. By examining the product ions formed by dissociating oligomeric precursor ions, the monomers that are most likely to react were determined. Additionally, by searching precursor ions for the expected products of reported oligomerization reactions and examining their fragmentation spectra, several reported reactions were confirmed. These include the reactions of hydroperoxides, carbonyls and stabilized Criegee intermediates. Finally, an aerosol reaction chamber was constructed to test the theory that the oligomers found in SOA are sources of the highly oxidized class of organic aerosol found in the atmosphere after undergoing photo-oxidative aging. Freshly formed SOA was exposed to high levels of hydroxyl radical and then analyzed both online by the nanoaerosol mass (NAMS) spectrometer and off line by high resolution mass spectrometry. The average O:C and H:C ratios of the aged compounds were in the range reported for highly oxidized atmospheric SOA. Additionally, the extent of evaporation caused by the fragmentation of oligomers into smaller volatile species was not found to be significant enough to be a sink of atmospheric SOA, although the time scale of the experiment may not have been sufficient for evaporation to occur.
Author: Wiley A. Hall
Publisher:
ISBN: 9781267214751
Category : Aerosols
Languages : en
Pages :
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Book Description
Biogenic secondary organic aerosol (SOA) forms from the reaction of gas phase organic molecules from biological sources with an atmospheric oxidant. Although biogenic SOA can comprise up to 80% of the particulate mass suspended in the atmosphere, the reactions that form SOA and the chemical identities of the compounds it contains are poorly understood, especially the oligomeric species that form the non-volatile core of SOA. In this dissertation, mass spectrometric techniques are used to characterize the oligomers found in SOA throughout their lifetime. Fresh aerosol was generated in a Tedlar bag and flow tube reactor (FTR) to determine: (1) the relevance of laboratory-generated oligomers to the atmosphere, and (2) the formation routes, and identity of the oligomers. Fresh SOA generated in the FTR was then reacted in a chamber designed to simulate photooxidation to (3) study the aging of SOA oligomers and determine if they are a source of highly oxidized atmospheric SOA. A scanning mobility particle sizer (SMPS) was found to accurately measure the concentration and size distribution of SOA. The SOA was then collected onto Teflon coated, glass fiber filters. Filter phase reactions were found to be minimal or non-existent. Various extraction solvents were tested, and acetonitrile was found to have high extraction efficiency without causing side reactions with the sample. Through the method of standard additions, the concentration of oligomeric species in the non-volatile core of the SOA collected and extracted was determined to be ~50% for laboratory SOA. SOA generated in the FTR was shown to have similar behavior as a class of organic aerosol found in the atmosphere. High resolution mass spectra revealed that oligomers undergo thermal degradation to volatile compounds when heated to high temperatures, so thermodenuders cannot be used to determine SOA volatility. High resolution tandem mass spectrometry (MSMS) was used to determine which compounds react to form oligomers and what their routes of formation are. By examining the product ions formed by dissociating oligomeric precursor ions, the monomers that are most likely to react were determined. Additionally, by searching precursor ions for the expected products of reported oligomerization reactions and examining their fragmentation spectra, several reported reactions were confirmed. These include the reactions of hydroperoxides, carbonyls and stabilized Criegee intermediates. Finally, an aerosol reaction chamber was constructed to test the theory that the oligomers found in SOA are sources of the highly oxidized class of organic aerosol found in the atmosphere after undergoing photo-oxidative aging. Freshly formed SOA was exposed to high levels of hydroxyl radical and then analyzed both online by the nanoaerosol mass (NAMS) spectrometer and off line by high resolution mass spectrometry. The average O:C and H:C ratios of the aged compounds were in the range reported for highly oxidized atmospheric SOA. Additionally, the extent of evaporation caused by the fragmentation of oligomers into smaller volatile species was not found to be significant enough to be a sink of atmospheric SOA, although the time scale of the experiment may not have been sufficient for evaporation to occur.
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: Yongjie Li
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 121
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Author: Katye Elisabeth Altieri
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages : 163
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Atmospheric aerosols scatter and absorb light influencing the global radiation budget and climate, and are associated with adverse effects on human health. Precipitation is an important removal mechanism for atmospheric dissolved organic matter (DOM), and a potentially important input for receiving ecosystems. However, the sources, formation, and composition of atmospheric DOM in aerosols and precipitation are not well understood. This dissertation investigates the composition and formation mechanisms of secondary organic aerosol (SOA) formed through cloud processing reactions, elucidates the composition and sources of DOM in rainwater, and provides links connecting the two. Photochemical batch aqueous-phase reactions of organics with both biogenic and anthropogenic sources (i.e., methylglyoxal, pyruvic acid) and OH radical were performed to simulate cloud processing. The composition of products formed through cloud processing experiments and rainwater collected in New Jersey, USA was investigated using a combination of electrospray ionization mass spectrometry techniques, including ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry. This dissertation has resulted in the first evidence that oligomers form through cloud processing reactions, the first detailed chemical mechanism of aqueous phase oligomerization, the first identification of oligomers, organosulfates, and nitrooxy organosulfates in precipitation, and the first molecular level chemical characterization of organic nitrogen in precipitation. The formation of oligomers in SOA helps to explain the presence of large multifunctional compounds and humic like substances (HULIS) that dominate particulate organic mass. Oligomers have low vapor pressures and remain in the particle phase after cloud evaporation, enhancing SOA. The chemical properties of the oligomers suggest that they are less hygroscopic than the monomeric reaction products (i.e., organic acids). Their elemental ratios are consistent with the hypothesis that oligomers are a large contributor to aged organic aerosol mass. The majority of the compounds identified in rainwater samples by advanced mass spectrometry appear to be products of atmospheric reactions, including known contributors to SOA formed from gas phase, aerosol phase, and in-cloud reactions in the atmosphere. The similarities between the complex organic matter in rainwater and SOA suggest that the large uncharacterized component of SOA is the main contributor to the large uncharacterized component of rainwater DOM.
Author: Yadian Gómez González
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Christopher Holmes Clark
Publisher:
ISBN: 9781267729583
Category : Aerosols
Languages : en
Pages : 249
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This dissertation introduces and makes use of the Particle-into-Liquid-Sampler coupled to a Time-of-Flight mass spectrometer (PILS-ToF), a new instrumental method used here to provide new chemical characterization information on secondary organic aerosol (SOA). The PILS-ToF instrument improves upon drawbacks found in current state-of-the-art mass spectral chemical characterization methods to include lack of time resolution and ion fragmentation by electron impact ionization in the Aerodyne Aerosol Mass Spectrometer (AMS). The functionality of the PILS-ToF for collection and response to SOA particle formation is validated against a scanning mobility particle sizer (SMPS), a widely accepted and standardized physical chemical characterization instrument, for a well characterized SOA formation experiment, dark ozonolysis of [alpja]-pinene. The PILS-ToF is also used to lend insight into oligomer growth during the NO photo-oxidation of isoprene. It is of atmospheric importance to study SOA formation from isoprene as it is globally the most abundant non-methane hydrocarbon in the ambient. SOA from isoprene is further studied using the PILS-ToF as part of the suite instrumentation at the University of California, Riverside, College of Engineering, Center for Environmental Research and Technology (CE-CERT) atmospheric chamber providing a complete chemical and physical characterization of SOA formed by isoprene with various oxidants under a myriad of oxidant concentration conditions. In addition, the PILS-ToF is used, again in tandem with other chemical and physical characterization methods at CE-CERT, to probe temperature effects on SOA formation from isoprene under many different oxidizing conditions. Finally, the PILS-ToF is used to provide new mechanistic information on SOA formation from trimethylamine and tributylamine, two tertiary amines emitted from anthropogenic and animal husbandry processes. For these two teriary amines the PILS-ToF provides evidence of oligomerization giving a potential explanation to the high SOA yields from these parent compounds.
Author: Mohammad Safi Shalamzari
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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: Emma Quinn Walhout
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages :
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Complex organic mixtures in the environment can contain hundreds to thousands of different organic molecules, and their composition and reactivity can have important environmental implications. In addition to gases, the atmosphere is made of a variety of small liquids and solids called aerosols. These aerosols have large impacts on human health, climate, and atmospheric chemical reactions. Here, secondary organic aerosol (SOA) from the ozonolysis of [alpha]-pinene is characterized. The atmospheric lifetime of SOA is very uncertain, but recent laboratory and modeling studies have demonstrated that photolysis is potentially an important process for organic mass loss from aerosol particles.1-5 Photolysis modifies the molecular composition and properties of aerosols through photolytic cleaving and repartitioning of volatile products. Characterization of dry, irradiated SOA can provide insights into photolysis driven changes in absorption properties and chemical composition. These results illuminate aging mechanisms and chemical and physical properties of organic aerosols in order to improve atmospheric modeling and the understanding of atmospheric chemical reactions. However, the high chemical complexity and low atmospheric abundance presents a difficult analytical challenge. Milligrams, or more, of material may be needed for speciated spectroscopic analysis.6 This study used a suite of advanced analytical techniques, including a novel combination of action spectroscopy and mass spectrometry that provides more structural information on organic mixtures than mass spectrometry alone. This study also used tunable light from a free electron laser, infrared and UV/Vis absorption, and computational chemistry to characterize molecules in [alpha]-pinene SOA. In addition, complex organic mixtures are also found in particulate matter that has deposited onto Earth’s surface. The preliminary results of dew analysis, including a foundation method of analysis for future study, gives the first look at organic material deposited into dew water on natural surfaces. This offers insight into atmospheric organic deposition to better understand chemical transport, air quality, and carbon cycling in the atmosphere.
Author: Berk Oktem
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 278
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