Modeling Global Secondary Organic Aerosol Formation and Processing with the Volatility Basis Set PDF Download

Author: Salvatore Farina
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Author: Wayne Li-wen Chang
Publisher:
ISBN: 9781124791869
Category :
Languages : en
Pages : 89

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Book Description
The detrimental impact on both human health and global climate of atmospheric particular matter (PM) is now well-established. Among the various classifications of PM, a significant portion is comprised of secondary organic aerosol (SOA). Despite its importance, there are still much uncertainty regarding the formation and evolution of SOA in the atmosphere, beginning with the oxidation of organic gases that leads to semi-volatile and low volatility products. The need to further improve the current knowledge SOA is made apparent by the observed large discrepancy between model predictions and field measurements of SOA. Proposed explanations behind the orders of magnitude underprediction of ambient SOA levels by state-of-the-art airshed models include: missing particle-forming oxidized organic products, unidentified SOA precursor emissions, and issues related to the fundamentals of current SOA partition theory, all of which are considered in this study to develop corresponding improvements to the latest airshed models. The model used in this study is the UCI-CIT airshed model, and the improvement scenario tests are set in the urban region of South Coast Air Basin of California. Recent chamber results have shown that the original implementation of alkane-derived SOA provided an underestimate for what was likely to be occurring in urban atmospheres. Thus, the original chemical mechanism is revised to include higher generation products of medium- and long-chain alkanes that can contribute to SOA in this study. Primary organic aerosol (POA) has been identified to be able to evaporate with dilution; therefore, test cases are developed that treat fractions of POA as semi-volatile, a source of SOA, rather than nonvolatile. While current atmospheric models assume that SOA are liquids into which semi-VOCs undergo equilibrium partitioning and grow the particles, recent laboratory and field experiments have shown otherwise. Hence, a new kinetics-driven partition theory is developed and analyzed against the original formulations. The results from the expanded chemical mechanism to include higher-generation products of alkane in the atmosphere shows that only the tetrahydrofurans will contribute to SOA and those contributions are only a small fraction compared to other SOA sources in the model, contrary to the prediction made based on chamber experiments and box models. In the tests for redistribution of POA as gas-phase parent VOCs sources, POA decreased with no commensurate increase in SOA. This is essentially due to the fact that the amount of mass that the POA can contribute is a small fraction of that already in the gas-phase parent VOC pool. Finally, using the newly developed kinetically determined SOA growth mechanism, to achieve the same level of predicted SOA levels as the original equilibrium approach requires 40-50% of SOA parent species to be allocated to the particle phase. The new formulation of SOA partition behavior based on kinetics will require the measurement of new input data and the corresponding parameterization for models in the future. The implication of this new approach should demand wider attention from the community.

Author: Emma Louise D'Ambro
Publisher:
ISBN:
Category :
Languages : en
Pages : 129

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Author: Mian Chin
Publisher: DIANE Publishing
ISBN: 1437912613
Category : Science
Languages : en
Pages : 128

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This Synthesis and Assessment Product (SAP) critically reviews current knowledge about global distributions and properties of atmospheric aerosols, as they relate to aerosol impacts on climate. It assesses possible next steps aimed at substantially reducing uncertainties in aerosol radiative forcing estimates. Current measurement techniques and modeling approaches are summarized, providing context. The objectives of this report are: (1) to promote a consensus about the knowledge base for climate change decision support; and (2) to provide a synthesis and integration of the current knowledge of the climate-relevant impacts of anthropogenic aerosols. Illustrations.

Author: Xuan Zhang
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages : 562

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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: Clemens Mensink
Publisher: Springer
ISBN: 3319576453
Category : Science
Languages : en
Pages : 612

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Book Description
Current developments in air pollution modelling are explored as a series of contributions from researchers at the forefront of their field. This newest contribution on air pollution modelling and its application is focused on local, urban, regional and intercontinental modelling; long term modelling and trend analysis; data assimilation and air quality forecasting; model assessment and evaluation; aerosol transformation. Additionally, this work also examines the relationship between air quality and human health and the effects of climate change on air quality. This Work is a collection of selected papers presented at the 35th International Technical Meeting on Air Pollution Modeling and its Application, held in Chania (Crete), Greece, Oct 3-7, 2016. The book is intended as reference material for students and professors interested in air pollution modelling at the graduate level as well as researchers and professionals involved in developing and utilizing air pollution models.

Author: Arthur W. H. Chan
Publisher:
ISBN:
Category : Atmospheric aerosols
Languages : en
Pages : 726

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Author: Bryan Edward Cummings
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 310

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Within residential buildings, organic aerosols (OA) often constitute the majority of particulate matter (PM) pollution, which is known to cause adverse cardiovascular and respiratory conditions. OA is composed of thousands of unique organic compounds, many of which are susceptible to partitioning between the aerosol and the gas phase. Until relatively recently, indoor air pollution models have largely neglected OA thermodynamic considerations, although certain organic thermodynamics modeling tools have been used with narrow applications to indoor PM studies over the past decade. Most of these cases have investigated particular processes, such as secondary organic aerosol (SOA) formation indoors or the repartitioning of outdoor OA. The need for the development of a comprehensive indoor OA thermodynamic model motivated the work done for this dissertation. Organic aerosol thermodynamics was modeled by the Indoor Model of Aerosols, Gases, Emissions, and Surfaces (IMAGES) using the volatility basis set (VBS). Explicitly representing indoor OA volatility allowed for errors associated with baseline, traditional particle models to be quantified across various model types and domains. For instance, traditional estimates of indoor particle emission rates for activities such as cooking may yield erroneous concentration predictions when used in other models. In such cases, error is driven by differences between model and experimental building conditions. Such errors were found to reach up to ~80% for typical stir-fry activities, associated with a magnitude of ~15-20 (microgram)/m3 depending on the particular emission strength. Epidemiological models that seek to predict indoor exposure to ambient pollution also have traditionally neglected volatility considerations. Such models fail to account for repartitioning driven by temperature and mass-loading gradients between the indoors and outdoors, leading to errors up to ~60% for total ambient PM, or about 3 (microgram)/m3 in the urban U.S. simulation domain that was considered. The two-dimensional volatility basis set (2D-VBS) was also incorporated into the underlying IMAGES model framework, representing its first known application to indoor air studies. Using the 2D-VBS to account for oxidation state in addition to volatility allowed OA aging transformations and water uptake to be modeled in addition to gas-to-particle partitioning. Simulation results showed that aging reactions are not likely to affect indoor OA composition and character from a day-averaged perspective, but may enhance peak OA concentrations under certain SOA-forming conditions on the order of ~10 (microgram)/m3. Also predicting the indoor humidity and aerosol water content in typical U.S. residences demonstrated that OA likely exists in a semisolid phase state indoors. Slow molecular diffusion within such particles challenges the implicit assumption often held by tradition indoor OA studies: that equilibrium thermodynamics holds, and that particles are typically liquid and well-mixed. A kinetic partitioning model of indoor organics was developed to more accurately represent the partitioning of material into and out of semisolid or glassy aerosols. This model was applied to a simulation of ambient aerosols that are transported into buildings and experience a temperature gradient that affects its effective volatility. Simulation results suggested that low diffusion inhibits repartitioning to at least some extent in the majority of simulated cases, representing residences in each of the 16 U.S. climate zones. Condensation may occur at equilibrium mostly in the southeastern U.S. in the summertime, where a hot and humid climate leads to a high indoor RH and therefore an indoor OA population in a liquid phase state. More northern locations along the east coast are typically associated with a drier indoor environment as the outdoor climate cools. In these cases, evaporation is often partially prohibited or fully prohibited. Dry climate zones from Arizona to Montana are more likely to experience limited or prohibited partitioning on hot outdoor days. And west coast marine climate zones are more likely to experience partial or equilibrium partitioning even in cooler regions.

Author: José Luis Jiménez
Publisher:
ISBN:
Category : Aerosols
Languages : en
Pages : 120

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Author: Shantanu Hemant Jathar
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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