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Author: Chen Wang
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
A sound parameterization of the gas-particle partitioning process is essential for understanding and quantifying secondary organic aerosol (SOA) formation. This thesis aimed to improve the understanding and description of phase partitioning during SOA formation through a combination of both laboratory and modeling studies. Partitioning of organic compounds between gas and particle phase is influenced by the presence of a large quantity of inorganic salts in aerosol, which is known as the salt effect. The salt effects of atmospherically relevant inorganic salts for a large number of organic compounds with various functional groups were measured in this study. The results revealed the importance of both salt species and organic compound identities on the salt effect, with the former as the dominant determinant. Models in predicting salt effect were calibrated and evaluated using the experimental data. Salt effect in mixtures was also investigated, which assists the understanding of salt effect in mixture salt solutions, including aerosols. A new approach for predicting gas-particle partitioning during SOA formation based on quantum chemical calculations was presented, which considers the partitioning species explicitly and captures the dynamic aspects of the aerosol formation processes. The role of different atmospheric parameters and chemical properties (organic loading, liquid water content, salinity, chemical ageing, etc.) was investigated and compared. Performance of the model was found to be comparable to the best currently used group contribution methods. SOA formation from constant emission and oxidation of precursor compounds was simulated to resemble the realistic scenario in the ambient atmosphere. The differential yield that describes the amount of SOA formed from a certain amount of added oxidation products was introduced, which is more relevant for SOA formation in the ambient atmosphere. The necessity of considering kinetic processes in addition to the thermodynamic equilibrium process was also discussed.
Author: Chen Wang
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
A sound parameterization of the gas-particle partitioning process is essential for understanding and quantifying secondary organic aerosol (SOA) formation. This thesis aimed to improve the understanding and description of phase partitioning during SOA formation through a combination of both laboratory and modeling studies. Partitioning of organic compounds between gas and particle phase is influenced by the presence of a large quantity of inorganic salts in aerosol, which is known as the salt effect. The salt effects of atmospherically relevant inorganic salts for a large number of organic compounds with various functional groups were measured in this study. The results revealed the importance of both salt species and organic compound identities on the salt effect, with the former as the dominant determinant. Models in predicting salt effect were calibrated and evaluated using the experimental data. Salt effect in mixtures was also investigated, which assists the understanding of salt effect in mixture salt solutions, including aerosols. A new approach for predicting gas-particle partitioning during SOA formation based on quantum chemical calculations was presented, which considers the partitioning species explicitly and captures the dynamic aspects of the aerosol formation processes. The role of different atmospheric parameters and chemical properties (organic loading, liquid water content, salinity, chemical ageing, etc.) was investigated and compared. Performance of the model was found to be comparable to the best currently used group contribution methods. SOA formation from constant emission and oxidation of precursor compounds was simulated to resemble the realistic scenario in the ambient atmosphere. The differential yield that describes the amount of SOA formed from a certain amount of added oxidation products was introduced, which is more relevant for SOA formation in the ambient atmosphere. The necessity of considering kinetic processes in addition to the thermodynamic equilibrium process was also discussed.
Author: Wayne Li-wen Chang
Publisher:
ISBN: 9781124262932
Category :
Languages : en
Pages : 44
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Book Description
Secondary organic aerosol (SOA) comprises a significant portion of atmospheric particular matter (PM). The impact of PM on both human health and global climate has long been recognized. Despite its importance, there are still many unanswered questions regarding the formation and evolution of SOA in the atmosphere. This study uses a modeling approach to understand the preferred partitioning behavior of SOA species into aqueous or organic condensed phases. More specifically, this work uses statistical analyses of approximately 24,000 data values for each variable from a state-of-the-art 3-D airshed model. Spatial and temporal distributions of fractions of SOA residing in the aqueous phase (fAQ) in the South Coast Air Basin of California are presented. Typical values of fAQ within the basin near the surface range from 5 to 80%. Results show that the distribution of fAQ values is inversely proportional to the total SOA loading. Further analysis accounting for various meteorological parameters indicates that large fAQ values are the results of aqueous-phase SOA insensitivity to the ambient conditions; while organic-phase SOA concentrations are dramatically reduced under unfavorable SOA formation conditions, aqueous-phase SOA level remains relatively unchanged, thus increasing fAQ at low SOA loading. Diurnal variations of fAQ near the surface are also observed: it tends to be larger during daytime hours than nighttime hours. When examining the vertical gradient of fAQ, largest values are found at heights above the surface layer. In summary, one must consider SOA in both organic and aqueous phases for proper regional and global SOA budget estimation.
Author: Mark E. Davis
Publisher: Courier Corporation
ISBN: 0486291316
Category : Technology & Engineering
Languages : en
Pages : 385
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Book Description
Appropriate for a one-semester undergraduate or first-year graduate course, this text introduces the quantitative treatment of chemical reaction engineering. It covers both homogeneous and heterogeneous reacting systems and examines chemical reaction engineering as well as chemical reactor engineering. Each chapter contains numerous worked-out problems and real-world vignettes involving commercial applications, a feature widely praised by reviewers and teachers. 2003 edition.
Author: Bethany A. Warren
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 414
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Book Description
Author: Christopher James Hennigan
Publisher:
ISBN:
Category : Air
Languages : en
Pages :
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Book Description
This thesis characterizes properties of ambient secondary organic aerosol (SOA), an important and abundant component of particulate matter. The findings presented in this thesis are significant because they represent the results from ambient measurements, which are relatively scarce, and because they report on properties of SOA that, until now, were highly uncertain. The analyses utilized the fraction of particulate organic carbon that was soluble in water (WSOCp) to approximate SOA concentrations in two largely different urban environments, Mexico City and Atlanta. In Mexico City, measurements of atmospheric gases and fine particle chemistry were made at a site ~ 30 km down wind of the city center. Using box model analyses and a comparison to ammonium nitrate aerosol, a species whose thermodynamic properties are generally understood, the morning formation and mid-day evaporation of SOA are investigated. In Atlanta, simultaneous measurements of WSOCp and water-soluble organic carbon in the gas phase (WSOCg) were carried out for an entire summer to investigate the sources and partitioning of WSOC. The results suggest that both WSOCp and WSOCg were secondary and biogenic, except possibly in several strong biomass burning events. The gas/particle partitioning of WSOC in Atlanta was investigated through the parameter, Fp, which represented the fraction of WSOC in the particle phase. Factors that appear to influence WSOC partitioning in Atlanta include ambient relative humidity and the WSOCp mass concentration. There was also a relationship between the NOx concentration and Fp, though this was not likely related to the partitioning process. Temperature did not appear to impact Fp, though this may have been due to positive relationships WSOCp and WSOCg each exhibited with temperature. Neither the total Organic Carbon aerosol mass concentration nor the ozone concentration impacted WSOC partitioning.
Author: Xuan Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Our understanding of the processes and mechanisms by which secondary organic aerosol (SOA) is formed is derived from laboratory chamber studies. In the atmosphere, SOA formation is primarily driven by progressive photooxidation of SOA precursors, coupled with their gas-particle partitioning. In the chamber environment, SOA-forming vapors undergo multiple chemical and physical processes that involve production and removal via gas-phase reactions; partitioning onto suspended particles vs. particles deposited on the chamber wall; and direct deposition on the chamber wall. The main focus of this dissertation is to characterize the interactions of organic vapors with suspended particles and the chamber wall and explore how these intertwined processes in laboratory chambers govern SOA formation and evolution. A Functional Group Oxidation Model (FGOM) that represents SOA formation and evolution in terms of the competition between functionalization and fragmentation, the extent of oxygen atom addition, and the change of volatility, is developed. The FGOM contains a set of parameters that are to be determined by fitting of the model to laboratory chamber data. The sensitivity of the model prediction to variation of the adjustable parameters allows one to assess the relative importance of various pathways involved in SOA formation. A critical aspect of the environmental chamber is the presence of the wall, which can induce deposition of SOA-forming vapors and promote heterogeneous reactions. An experimental protocol and model framework are first developed to constrain the vapor-wall interactions. By optimal fitting the model predictions to the observed wall-induced decay profiles of 25 oxidized organic compounds, the dominant parameter governing the extent of wall deposition of a compound is identified, i.e., wall accommodation coefficient. By correlating this parameter with the molecular properties of a compound via its volatility, the wall-induced deposition rate of an organic compound can be predicted based on its carbon and oxygen numbers in the molecule. Heterogeneous transformation of delta-hydroxycarbonyl, a major first-generation product from long-chain alkane photochemistry, is observed on the surface of particles and walls. The uniqueness of this reaction scheme is the production of substituted dihydrofuran, which is highly reactive towards ozone, OH, and NO3, thereby opening a reaction pathway that is not usually accessible to alkanes. A spectrum of highly-oxygenated products with carboxylic acid, ester, and ether functional groups is produced from the substituted dihydrofuran chemistry, thereby affecting the average oxidation state of the alkane-derived SOA. The vapor wall loss correction is applied to several chamber-derived SOA systems generated from both anthropogenic and biogenic sources. Experimental and modeling approaches are employed to constrain the partitioning behavior of SOA-forming vapors onto suspended particles vs. chamber walls. It is demonstrated that deposition of SOA-forming vapors to the chamber wall during photooxidation experiments can lead to substantial and systematic underestimation of SOA. Therefore, it is likely that a lack of proper accounting for vapor wall losses that suppress chamber-derived SOA yields contribute substantially to the underprediction of ambient SOA concentrations in atmospheric models.
Author: Jay Russell Odum
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 246
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Author: Chunyi Wang
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 372
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Book Description
People in developed countries spend about 90% of their time indoors, so controlling in-door air quality (IAQ) is of primary importance for not harming public health. Airborne particu-late matter (PM) is one of the most problematic pollutants indoors, since exposure to particles with aerodynamic diameters smaller than 2.5 Îơm (i.e, PM2.5) is associated with respiratory dis-eases, as well as morbidity and mortality outcomes. Organic aerosol components, so called organic aerosol (OA), generally comprise the ma-jor portion of indoor PM, owing to its large indoor emission. One important component of OA indoors is secondary organic aerosol (SOA), which are condensed phase particles composed of semi- and low-volatility compounds. Most research has focused on SOA generated by terpene ozonolysis occurring in the gas phase. This work, however, explores a lesser researched for-mation mechanism, which is the possibility of airborne SOA generated by ozone surface reac-tions with sorbed squalene (C30H50), which is a nonvolatile constituent of skin oil. As such, thirteen steady state chamber experiments were performed to measure the SOA formation en-tirely initiated by ozone reactions with squalene sorbed to glass at two RH conditions of 21% and 51%, in the absence of seed particles. SOA was initiated from these surface reactions, and all experiments but one exhibited nucleation and mass formation. Mass formation increased with ozone concentration at RH = 51% while nucleation was more obvious at RH = 21%. Additionally, most indoor OA, either emitted or generated (i.e., not only SOA), is at composed of semivolatile compounds (SVOCs) in a state of dynamic equilibrium between gas and particle phases. Filters might have a reduced efficiency on removing these kinds of particles since they coexist in gas and condensed aerosol phases. The preferential filtration of particle phase material of the OA system could disrupt the equilibrium, and the removed aerosols might be enhanced by desorption from surfaces and repartitioning from gas phase. To explore this phenomenon, three types of particles, including non-volatile ammonium sulfate ((NH4)2SO4) aerosol, incense aerosol (which might be partly semi-volatile), and SOA derived from ozone + d-limonene reactions (the majority of which are SVOCs), were characterized and compared in terms of their effective removal by a portable air cleaner. For this comparison, the metric of the Clean Air Delivery Rate, CADR (m3/h), was used, which is the volumetric flow of pollutant-free air produced by an air cleaner. Results demonstrated that the lowest effective CADR was for SOA, followed by the incense, and then the ammonium sulfate particles, indicating a repar-titioning processes reduced the filter efficiency. Then a model based on the principles of desorp-tion and repartition process was developed, to quantify the reduced CADR as a function of par-ticle concentration and distribution, in terms of parameter ATSP, which is the ratio of particle surface area to mass. Finally, the influence of the above two parameters on amount of CADR reduction was discussed. Using some details gleaned from the above two experimental studies, a thermodynamic equilibrium model was developed using the volatile basis set (VBS), to predict indoor organic aerosol concentrations and behavior. The model outcomes are the total organic mass indoors (gas + condensed phase), and the fraction of it that partitions to the aerosol phase, including that existing as SOA formed by ozone + d-limonene reactions. With this model, the total OA concentration was simulated at key locations in an indoor environment, such as in the occupied space and different positions in a building mechanical system. The impacts of different condi-tions were compared, including commercial against residential buildings, surface against gas reactions, and winter against summer, within a Monte Carlo framework. Indoor OA concentra-tion indoors were higher when reactions were involved, and gas phase reactions had much more influence on SOA than surface reactions. Finally, the result dataset was used to evaluate the influence of key factors on the indoor OA concentrations, using multiple linear regression sen-sitivity methods. The most important factor that enhanced indoor particles was d-limonene emission rate with average SRC of 0.73, while the negative related factors were filtration effi-ciency with SRC of -0.33 for commercial and surface deposition rate with SRC of -0.22 for resi-dential buildings. Beyond the three SOA studies discussed above, humidifiers used indoors might be strong PM emitters. So, as a supplementary piece, this work also investigated the influence of three humidifier types (ultrasonic, evaporative, and steam humidifiers), and water type used (tap water, de-ionized (DI) water or distilled water), on indoor aerosol number/mass concentra-tions by performing 16 experiments. Particle size distribution during emission periods and size-resolved emission rates were explored to compare the emission ability of humidifiers. Two lung deposition models were also applied to simulate the deposition percentage of particles breathed in on three lung regions (HA, TB, and AL), and total percentage on varying age groups. Results showed that two year-old group was most vulnerable, with number deposition fractions of 0.36, compared with 0.25 for adults. Furthermore, roughly 70% of the total emitted particles pene-trates into the AL region of the lung.
Author: Chen Song
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 532
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Author: Jack G Calvert
Publisher: Oxford University Press
ISBN: 0199710880
Category : Science
Languages : en
Pages : 1005
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Book Description
An international team of eminent atmospheric scientists have prepared Mechanisms of Atmospheric Oxidation of the Alkanes as an authoritative source of information on the role of alkanes in the chemistry of the atmosphere. The book includes the properties of the alkanes and haloalkanes, as well as a comprehensive review and evaluation of the existing literature on the atmospheric chemistry of the alkanes and their major atmospheric oxidation products, and the various approaches now used to model the alkane atmospheric chemistry. Comprehensive coverage is given of both the unsubstituted alkanes and the many haloalkanes. All the existing quality measurements of the rate coefficients for the reactions of OH, Cl, O(3P), NO3, and O3 with the alkanes, the haloalkanes, and their major oxidation products have been reviewed and evaluated. The expert authors then give recommendations of the most reliable kinetic data. They also review the extensive literature on the mechanisms and rates and modes of photodecomposition of the haloalkanes and the products of atmospheric oxidation of the alkanes and the haloalkanes, and make recommendations for future use by atmospheric scientists. The evaluations presented allow an extrapolation of the existing kinetic and photochemical data to those alkanes and haloalkanes that are as yet unstudied. The current book should be of special interest and value to the modelers of atmospheric chemistry as a useful input for development of realistic modules designed to simulate the atmospheric chemistry of the alkanes, their major oxidation products, and their influence on ozone and other trace gases within the troposphere.
