Effect of Environmental Conditions on Composition and Photochemistry of Secondary Organic Aerosols PDF Download

Author: Mallory Lynn Hinks
Publisher:
ISBN: 9780355307016
Category :
Languages : en
Pages : 153

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Book Description
Atmospheric aerosols represent one of the greatest uncertainties in predicting the Earth's future climate. Secondary organic aerosols (SOA) are particularly complicated because they are highly susceptible to change upon exposure to different conditions, such as varying temperatures and relative humidities (RHs), sunlight, and different atmospheric pollutants. The goal of this work was to increase our understanding of the contribution of SOA to the Earth's radiation budget by exploring how different environmental conditions can affect aerosol properties and processes.The first project investigated the effect of viscosity on photochemical kinetics of probe molecules embedded in laboratory-generated SOA. Temperature and RH of the system were varied independently to adjust the viscosity of the SOA and the samples were irradiated. At lower temperatures and humidities both systems exhibited lower photoreaction rates, suggesting that increased viscosity hinders the motion of the molecules in the SOA slowing down their photochemical reactions. This means that molecules trapped inside SOA in cold, dry parts of the atmosphere will photodegrade slower than in warm and humid areas.The next stage of this work was to study the effect of RH on the mass loading and composition of SOA formed from toluene photooxidation. When the RH was increased from 0% to 75%, the yield of toluene SOA made under low NOx conditions decreased by an order of magnitude. High resolution mass spectrometry revealed a significant reduction in the fraction of oligomers present in the SOA made under humid conditions compared to dry conditions. These results suggest that water vapor suppresses oligomer formation in low NOx toluene SOA, reducing aerosol yield. This means that concentrations of toluene SOA in the atmosphere will be dependent on the RH and NOx concentrations.The last stage of this work investigated the interaction between SOA and ammonia. SOA made from toluene, n-hexadecane, or limonene in a chamber was exposed to gaseous ammonia while the mass loading and composition was monitored. These experiments indicated that ammonia could be taken up into SOA, leaving less ammonia in the atmosphere to neutralize atmospheric acids. This leads to a reduction of inorganic aerosols in the atmosphere.

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

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Book Description
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: Rachel Elizabeth Sellon
Publisher:
ISBN:
Category :
Languages : en
Pages : 274

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Book Description
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: Ian Colbeck
Publisher: Wiley-Blackwell
ISBN:
Category : Science
Languages : en
Pages : 282

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Book Description
Covering the most recent material, this text brings together all the information on atmospheric aerosols in one place, making it easily accessible to practitioners and students.

Author: Sherri W. Hunt
Publisher: ACS Symposium
ISBN: 9780841233638
Category : Science
Languages : en
Pages : 0

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Book Description
This book highlights new cross-disciplinary advances in aerosol chemistry that involve more than one phase, for example, unique chemical processes occurring on gas-solid and liquid-solid interfaces.

Author: Dian Elizabeth Romonosky
Publisher:
ISBN: 9781369227819
Category :
Languages : en
Pages : 199

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Book Description
A large fraction of organic aerosol particles are formed as secondary organic aerosol (SOA) resulting from the condensation of partially oxidized biogenic and anthropogenic volatile organic compounds (VOCs) with gas phase oxidants such as O3, OH, NOx, and NO3. An additional pathway for SOA formation is by the photochemical aqueous processing of VOC occurring inside cloud and fog droplets, followed by droplet evaporation. Once formed, SOA can age through heterogeneous oxidation and fog photochemical processes involving the hydroxyl radical (OH) as well as various other oxidants in the atmosphere. In addition to condensed phase oxidation, SOA can also age in the atmosphere upon exposure to radiation, for many of these organic compounds are photolabile and can degrade through direct photolysis, wherein the compounds absorb radiation and break into products, and indirect photolysis, wherein absorption of solar radiation initiates chemistry through the production of non-selective oxidants such as OH. These photochemical aging processes have the potential to be on time scales that are comparable to the typical lifetimes of droplets (hours) and particles (days), making them relevant to study further for both climate and health reasons. This dissertation presents a systematic investigation of the optical properties, molecular composition, and the extent of photochemical processing in different types of SOA from various biogenic and anthropogenic VOC precursors. Chamber- or flowtube-generated SOA is made and then analyzed using high-resolution mass spectrometry (HR-MS) to observe the extent of change in the molecular level composition of the material before and after aqueous photolysis. Significant differences in the molecular composition between biogenic and anthropogenic SOA were observed, while the composition further evolved during photolysis. To study the optical properties and lifetimes of organic aerosol, spectroscopy tools such as UV-Vis is utilized. Results of this study suggest that the condensed phase photolysis of SOA can occur with effective lifetimes ranging from minutes to hours, and therefore represents a potentially important aging mechanism for SOA. The outcome of this dissertation will be improved understanding of the role of condensed-phase photochemistry in chemical aging of aerosol particles and cloud droplets.

Author: Emma Quinn Walhout
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages :

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Book Description
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: Yue Zhang
Publisher: American Chemical Society
ISBN: 0841299293
Category : Science
Languages : en
Pages : 176

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Book Description
The uncertainties in the aerosol effects on radiative forcing limit our knowledge of climate change, presenting us with an important research challenge. Aerosols in Atmospheric Chemistry introduces basic concepts about the characterization, formation, and impacts of ambient aerosol particles as an introduction to graduate students new to the field. Each chapter also provides an up-to-date synopsis of the latest knowledge of aerosol particles in atmospheric chemistry.

Author: Adam Patrick Bateman
Publisher:
ISBN: 9781124668659
Category :
Languages : en
Pages : 189

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Book Description
Organic aerosols comprise hundreds, if not thousands, of distinct chemical compounds. Traditional analytical techniques for analysis of chemical composition lack the ability to completely characterize complex mixtures such as organic aerosol. Until recently, the best available methods could only provide information on selected aerosol compounds, on selected groups of compounds, or on sample-averaged elemental ratios. Such experimental limitations posed significant barriers to understanding the detailed chemical composition of organic aerosols and its atmospheric evolution. The unique HR ESI-MS methods developed in this research are able to not only characterize the organic aerosols average elemental ratios, but also simultaneously obtain information about hundreds or even thousands of individual compounds in organic aerosols. One of the key achievements of this work was the development of new methods for classification of individual compounds in organic aerosols by their functional groups using reactive HR ESI-MS. This contribution made it possible to track organic aerosols throughout their atmospheric evolution via functional group composition and average elemental ratios while still retaining the chemical composition of each individual compound. Other important scientific advances described in this thesis include: complete characterization of the chemical composition of limonene SOA as a function of particle size and reaction time; adaptation of PILS (particle-into-liquid sampler) to the HR ESI-MS platform; chemical characterization of the water soluble component of several types of organic aerosols; the effects of photochemical aging on the water soluble component of limonene SOA through characterization of the optical properties coupled with chemical composition; and investigation of photochemistry of carbonyls in model SOA matrices. The research included in this dissertation reviews the development of unique aerosol characterization tools utilizing the facilities at UCI and the Environmental Molecular Sciences Laboratory at the Pacific Northwest National Laboratory. The research project answered important questions regarding organic aerosol formation, evolution, and chemical composition that impact the direct and indirect influences of aerosols on Earth's climate.

Author: Barbara J. Finlayson-Pitts
Publisher: Elsevier
ISBN: 0080529070
Category : Science
Languages : en
Pages : 993

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Book Description
Here is the most comprehensive and up-to-date treatment of one of the hottest areas of chemical research. The treatment of fundamental kinetics and photochemistry will be highly useful to chemistry students and their instructors at the graduate level, as well as postdoctoral fellows entering this new, exciting, and well-funded field with a Ph.D. in a related discipline (e.g., analytical, organic, or physical chemistry, chemical physics, etc.). Chemistry of the Upper and Lower Atmosphere provides postgraduate researchers and teachers with a uniquely detailed, comprehensive, and authoritative resource. The text bridges the "gap" between the fundamental chemistry of the earth's atmosphere and "real world" examples of its application to the development of sound scientific risk assessments and associated risk management control strategies for both tropospheric and stratospheric pollutants. Serves as a graduate textbook and "must have" reference for all atmospheric scientists Provides more than 5000 references to the literature through the end of 1998 Presents tables of new actinic flux data for the troposphere and stratospher (0-40km) Summarizes kinetic and photochemical date for the troposphere and stratosphere Features problems at the end of most chapters to enhance the book's use in teaching Includes applications of the OZIPR box model with comprehensive chemistry for student use