Optical Properties and Chemical Composition of Secondary Organic Aerosol PDF Download

Author: Fathima Rifkha Kameel
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages : 86

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Book Description
Aerosol particles (APs) affect the Earth's energy balance directly by absorbing and scattering radiation, and indirectly by altering the reflectance and persistence of clouds. Both parameters are determined by the chemical composition, size and shape of APs. APs consist of complex organic and inorganic mixtures, which include black carbon/soot as well secondary organic matter (SOM) proceeding from the gas-phase. SOM, also known as humic-like substances (HULIS), plays a key role in determining the optical properties of APs due to its ability to absorb radiation in the visible region of the solar spectrum. The chemical characterization of SOM is a daunting task that involves comprehensive chemical analysis, largely via chromatography/high-resolution mass spectrometry (HRMS), one of the most powerful analytical techniques available. However, optical properties are associated with chromophores within specific chemical structures, rather than with molecular formulas. Simpler mixtures can mimic the optical properties of secondary organic aerosol (SOA). Optical properties of mixtures are not linear combinations of the optical properties of its components. Furthermore, optical properties are not intrinsic to APs, but depend on external parameters, such as insolation and relative humidity. Therefore full speciation is neither a necessary nor sufficient condition for characterizing the optical properties of SOA.

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

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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: Hwa Jin Kim
Publisher:
ISBN:
Category :
Languages : en
Pages : 193

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The refractive index is the fundamental property controlling aerosol optical properties. Secondary organic aerosols (SOA) constitute a large fraction of aerosols in the atmosphere, and yet the optical properties of this complex material are just beginning to be understood. They appear to be much more variable than expected. We explore the factors controlling the real refractive indices (mr) of SOA under conditions that are as close to atmospheric conditions as possible. SOA were generated from the alpha-pinene, beta-pinene, limonene and toluene using several oxidation chemistries including ozonolysis with and without scavenger and photooxidation at different HC/NOx ratios, different mass concentration and experimental temperatures. Mr were retrieved from polar nephelometer measurements using parallel and perpendicular polarized 532 or 670 nm light where there is no evidence of significant absorption by the particles investigated here. Retrievals were performed with a genetic algorithm method using Mie-Lorenz scattering theory and measured particle size distributions. Overall examination of the SOA data shows that SOA mr ranges from 1.34 to 1.62, reflecting the factors to control the chemical composition; decreases as the HC/NOx ratio increases, decrease at lower temperature (

Author:
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Category :
Languages : en
Pages :

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The objective of this workshop was to address the most urgent open science questions for improved quantification of sea spray aerosol-radiation-climate interactions. Sea spray emission and its influence on global climate remains one of the most uncertain components of the aerosol-radiation-climate problem, but has received less attention than other aerosol processes (e.g. production of terrestrial secondary organic aerosols). Thus, the special emphasis was placed on the production flux of sea spray aerosol particles, their number concentration and chemical composition and properties.

Author: Vanessa Selimovic
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages : 96

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"In this study, Fulvic Acid was used as a model to validate the experimental procedure for the analysis of several different samples of varying concentrations and compositions of SOA [secondary organic aerosols] generated by the oxidation of volatile organic compounds (VOC), specifically 1,2,4-trimethylbenzene." --

Author: Mariya M. Shcherbyna
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages : 350

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Author:
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ISBN:
Category :
Languages : en
Pages : 9

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The research conducted on this project aimed to improve our understanding of secondary organic aerosol (SOA) formation in the atmosphere, and how the properties of the SOA impact climate through its size, phase state, and optical properties. The goal of this project was to demonstrate that the use of molecular composition information to mechanistically connect source apportionment and climate properties can improve the physical basis for simulation of SOA formation and properties in climate models. The research involved developing and improving methods to provide online measurements of the molecular composition of SOA under atmospherically relevant conditions and to apply this technology to controlled simulation chamber experiments and field measurements. The science we have completed with the methodology will impact the simulation of aerosol particles in climate models.

Author: Jiumeng Liu
Publisher:
ISBN:
Category : Aerosols Optical properties
Languages : en
Pages :

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The chemical and optical properties of particulate organic compounds remain unclear, which leaves large uncertainties in the estimation of global radiative transfer balance. Gas and find particle (PM2.5) phase formic acid concentrations were measured with online instrumentation during separate one-month studies in the summer of 2010 in Los Angeles (LA), CA, and Atlanta, GA, and the gas-particle partitioning behavior was investigated and compared with that of water-soluble organic compounds (WSOC). The diurnal profiles clearly indicated that the photochemistry production serves as a strong source for the formation of organics, while the correlation between the gas and particle phase suggested that another partitioning route, the aqueous reactions, is also very important. Later, the optical properties of light-absorbing organic compounds were examined. Little is known about the optical importance of light absorbing particulate organic compounds (brown carbon), especially its extent and absorption relative to black carbon throughout the tropospheric column. Mie theory was applied to size-resolved spectrophotometric absorption measurements of methanol and water-extracts from cascade impactor substrates collected at three surface sites around Atlanta, GA, including both urban and rural. These results were applied to similar measurements of brown carbon in extracts from aircraft bulk filter samples collected over central USA. At the surface sites predicted light absorption by brown carbon relative to total absorption (brown carbon plus pure black carbon) was about 10% and 30% at 350 nm, versus 1 and 11% at 450 nm, for water and methanol extracts, respectively. The relative contribution of brown carbon was greater in the free troposphere and significantly increased with altitude. Although this approach has limitations, it demonstrates the ubiquity and significant potential contribution of brown carbon.

Author: Tran Bao Nguyen
Publisher:
ISBN: 9781267427212
Category :
Languages : en
Pages : 382

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Book Description
There are large gaps surrounding our understanding of secondary organic aerosols (SOA), which represent a significant fraction of fine particulate matter globally. One of the most difficult aspects of SOA to characterize is the molecular composition, because it is both complex and dynamic. However, the composition of SOA determines to a large extent the impact SOA has on climate, atmospheric chemistry, and human health. The main focus of this dissertation is the detailed composition analysis of SOA generated from important biogenic precursors and the characterization of chemistry induced by their simulated interaction with clouds, anthropogenic pollutants, and solar radiation. In particular, the gas- and aerosol-phase compounds associated with SOA from isoprene, the most abundant volatile organic compound emitted from the biosphere, are studied with the advanced technique of high-resolution mass spectrometry (HR MS). Many SOA compounds, particularly nitrogen-containing organics, are reported for the first time. Spectroscopy tools like UV-Vis, FT-IR and NMR are also used to characterize optical properties and molecular structures of SOA compounds. A secondary focus of this dissertation is to describe brown carbon formation from the ammonium- and amino acid-mediated aging of limonene SOA. Brown carbon changes the optical properties of SOA, but the sources are poorly understood. The experiments presented in this dissertation aim to elucidate the previously unknown precursors, kinetics and products of the reaction. The molecular detail gained from the HR-MS and spectroscopic analyses provides tremendous insight into the formation mechanism and further atmospheric reactions of SOA.

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.