Implementing effective and environmentally responsible carbon capture technologies is one of the principle challenges of this century. Successful implementation requires a host of engineering advancements, but also a fundamental understanding of the underlying physics, chemistry, and materials science at play in these highly complex systems. A large body of scholarship examines both current technologies as well as future strategies, but to date little exploration of the surface behavior of these systems has been examined. As these carbon capture systems involve uptake of gaseous CO2 to either aqueous or solid substrates, understanding the chemistry and physics governing the boundary between the two reactant phases is critical. Yet probing the unique chemistry and physics of these interfacial systems is very difficult. This dissertation addresses this knowledge gap by examining the surface chemistry of monoethanolamine and CO2. Monoethanolamine is a simple organic amine currently used in small scale CO2 scrubbing, and acts as an industrial benchmark for CO2 capture efficiency. The studies presented throughout this dissertation employ surface selective techniques, including vibrational sum frequency spectroscopy, surface tensiometry, and computation methodologies, in order to determine the behavior governing aqueous amine interfaces. The adsorption behavior and surface orientation of aqueous monoethanolamine is examined first. The results show monoethanolamine is present at the surface, highly ordered, and solvated. Perturbations to this amine surface from gaseous CO2 and SO2, as well as from liquid HCl, are examined in the remainder of the dissertation. Reactions between the amine and acids are shown to cause immediate changes to the interface, but the interface then remains largely unaffected as further reaction evolves. The studies presented herein provide a needed exploration of the interfacial picture of these highly reactive systems, with implications for future carbon capture materials and design.

The focus of this work is the development and improvement of chemistry schemes in both 1D and 3D atmosphere models, applied to exoplanets. With an ever increasing number of known exoplanets, planets orbiting stars other than the Sun, the diversity in the physical and chemical nature of planets and their atmospheres is becoming more apparent. One of the prime targets, and the focus of many observational and theoretical studies, are the subclass of exoplanets termed hot Jupiters, Jovian sized planets on very short period orbits around their host star. Due to their close orbit, with orbital periods of just a few days, the atmospheres of such planets are heated to very high temperatures (~1000-2000 K) by the intense irradiation from the star. In addition, it is expected that these planets should have synchronised their rotation with their orbital period, a phenomenon called tidal-locking, that leads to a permanently illuminated dayside and a perpetually dark nightside. This combination of intense heating and tidal-locking leads to an exotic type of atmosphere that is without analogue in our own Solar system. Observational constraints suggest that some of these atmospheres may be clear whilst others may be cloudy or contain haze. Some hot Jupiters appear to be inflated with radii larger than is expected for their mass. For the warmest hot Jupiters optical absorbing species TiO and VO are expected to be present, due to the thermodynamical conditions, where they can strongly influence the thermal structure of the atmosphere, yet so far these species have remained elusive in observations. Theoretical simulations of these planets appear to provide poor matches to the observed emission flux from the nightside of the planet whilst providing a much better agreement with the observed dayside flux. These outstanding questions can be tackled in two complimentary ways. Firstly, the number of exoplanets subject to intense observational scrutiny must be increased to improve the statistical significance of observed trends. Secondly, and in tandem, the suite of available theoretical models applied to such atmospheres must be improved to allow for a more comprehensive understanding of the potential physical and chemical processes that occur in these atmospheres, as well as for better comparison of model predictions with observations. In this thesis we present the development and application of one-dimensional (1D) and three-dimensional (3D) models to the atmospheres of hot exoplanets, with a focus on improving the representation of chemistry. One of the concerns of this work is to couple the radiative transfer and chemistry calculations in a one-dimensional model to allow for a self-consistent model that includes feedback between the chemical composition and the thermal structure. We apply this model to the atmospheres of two typical hot Jupiters to quantify this effect. Implications for previous models that do not include this consistency are discussed. Another major focus is to improve the representation of chemistry in the Met Office Unified Model (UM) for exoplanet applications, a three-dimensional model with its heritage in modelling the Earth atmosphere that has recently been applied to exoplanets. We discuss the coupling of two new chemistry schemes that improve both the flexibility and capabilities of the UM applied to exoplanets. Ultimately these developments will allow for a consistent approach to calculate the 3D chemical composition of the atmosphere taking into account the effect of large scale advection, one of the processes currently hypothesised to cause the discrepancy between model predictions and observations of the nightside emission flux of many hot Jupiters.

abstract: The atmosphere contains a substantial amount of water soluble organic material, yet despite years of efforts, little is known on the structure, composition and properties of this organic matter. Aqueous phase processing by fogs and clouds of the gas and particulate organic material is poorly understood despite the importance for air pollution and climate. On one hand, gas phase species can be processed by fog/cloud droplets to form lower volatility species, which upon droplet evaporation lead to new aerosol mass, while on the other hand larger nonvolatile material can be degraded by in cloud oxidation to smaller molecular weight compounds and eventually CO2. In this work High Performance Size Exclusion Chromatography coupled with inline organic carbon detection (SEC-DOC), Diffusion-Ordered Nuclear Magnetic Resonance spectroscopy (DOSY-NMR) and Fluorescence Excitation-Emission Matrices (EEM) were used to characterize molecular weight distribution, functionality and optical properties of atmospheric organic matter. Fogs, aerosols and clouds were studied in a variety of environments including Central Valley of California (Fresno, Davis), Pennsylvania (Selinsgrove), British Columbia (Whistler) and three locations in Norway. The molecular weight distributions using SEC-DOC showed smaller molecular sizes for atmospheric organic matter compared to surface waters and a smaller material in fogs and clouds compared to aerosol particles, which is consistent with a substantial fraction of small volatile gases that partition into the aqueous phase. Both, cloud and aerosol samples presented a significant fraction (up to 21% of DOC) of biogenic nanoscale material. The results obtained by SEC-DOC were consistent with DOSY-NMR observations. Cloud processing of organic matter has also been investigated by combining field observations (sample time series) with laboratory experiments under controlled conditions. Observations revealed no significant effect of aqueous phase chemistry on molecular weight distributions overall although during cloud events, substantial differences were apparent between organic material activated into clouds compared to interstitial material. Optical properties on the other hand showed significant changes including photobleaching and an increased humidification of atmospheric material by photochemical aging. Overall any changes to atmospheric organic matter during cloud processing were small in terms of bulk carbon properties, consistent with recent reports suggesting fogs and clouds are too dilute to substantially impact composition. / Dissertation/Thesis / Doctoral Dissertation Chemistry 2014

No description available.

Biomass energy is the oldest form of energy harnessed by humans. Currently, processed biofuels, which are derived from biomass, are being pursued as a possi- ble route to decarbonize the transport sector - a particularly difficult task for both technological and sociological reasons. In this thesis I explore the impacts that large scale biofuel use could have on atmospheric chemistry. I review the current state of biofuels politically and technologically, focusing on ethanol and biodiesel. I discuss the salient features of tropospheric chemistry and in particular the oxidation of isoprene, an important biogenic volatile organic compound. I examine the impact that including isoprene oxidation has in a new chemistry-climate computer model, UKCA; the response of ozone turns out to depend on local chemical conditions. To evaluate the global model, I use data from the OP3 field campaign in Malaysia and compare it with output from the model chemical mechanism. The mechanism is able to reproduce NOx and ozone measurements well, though is more sensitive to representations of physical rather than chemical processes. I also perform a simple sensitivity study which examines crop changes in the region of Southeast Asia. In the final two chapters, I turn to two distinct phases of the biofuel life cycle. I characterize a potential future atmosphere through an ozone attribution study, then examine the impact of future cropland expansion (phase I of a biofuel life cycle) on tropospheric chemistry. I find that land use change has a large impact on ozone, and that it is more acute than another perturbation (CO2 suppression) to isoprene emissions. I then move to phase III of the life cycle - combustion - and look at the sensitivity of the model chemistry to surface transport emissions from biofuels as a replacement for conventional fuels. I find that biodiesel reduces surface ozone, while ethanol increases it, and that the response has both a linear and nonlinear component.

Much important work has been done to understand reaction pathways and identify products, yields, and reaction rates for atmospheric oxidation processes. Non-methane hydrocarbons (NMHCs) are the most significant of the organic compounds present in the atmosphere from a chemical perspective and are released into the atmosphere from both natural and anthropogenic sources. The oxidation of these hydrocarbons by hydroxyl radical HO generates products that may themselves be toxic, that play a major role in the formation of photochemical smog, and that to a lesser extent contribute to the formation of acid precipitation. NMHCs have chemical reactivities many times that of methane, the most abundant HC in the atmosphere. However, the atmospheric oxidation processes of less than 50% of atmospheric NMHCs are known. A new experimental technique is needed that can provide insight into atmospheric oxidation products, reaction intermediates, and the relative importance of secondary reaction pathways that follow the initial attack of HO upon a hydrocarbon. The technique should operate at atmospheric pressure to better represent natural reaction processes and conditions, and provide a rapid and direct measure of product identities and yields. In this study we will describe the development and application of a technique that we believe meets these requirements, a technique we call High Resolution Kinetic Atmospheric Pressure Ionization Mass Spectrometry (HRKAPIMS). We begin with the use of atmospheric pressure ionization mass spectrometry in studies of atmospheric oxidation processes. We first describe a potential pitfall in the use of APIMS for the analysis of smog chamber experiments, a common APIMS application, discussing methods to eliminate interference reactions that would otherwise make interpretation difficult. A new experimental approach to the use of APIMS for the analysis of oxidation processes is next described and its use demonstrated. The oxidation of toluene by API source-generated HO produces oxidation products that are protonated and detected by the mass spectrometer. With this approach, we observe all the products found in a variety of previous studies employing a large array of experimental setups and analytical instrumentation. This is significant because our experiments are carried out in a far simpler experimental environment. Toluene is chosen for these experiments because it is an important constituent in polluted urban atmospheres with a complex oxidation mechanism that remains poorly understood. We describe the development of HRKAPIMS, a powerful new approach that allows the simultaneous detection of stable products along with free radical intermediates. The use of nitric oxide to affect product yields is demonstrated, giving valuable insights into reaction kinetics and mechanisms. We also address the theoretical aspects of HRKAPIMS, describing semiempirical calculations to estimate gas-phase basicities for a wide variety of compounds and discuss the errors implicit in this approach. The use of gas-phase basicities is discussed in terms of mass spectrometric analysis and analyte response. Kinetic and thermodynamic modeling is used to address the issues of APIMS and HRKAPIMS sensitivity and response and gain insights into the conditions necessary for linear response and quantitative detection of analytes.

Given the role of HCN as a reactant in RNA building block production (e.g. nucleobases, ribose, and 2-aminooxazole), we propose that an atmosphere rich in hydrogen cyanide (HCN) is a distinguishing feature of what we term biogenic worlds. These are worlds that can produce key biomolecules for the emergence of life in situ rather than requiring they be delivered, e.g., by meteorites. To attack the question of whether early Earth was biogenic, we develop a series of new capabilities including the calculation of missing/unknown HCN reaction rate coefficients, the simulation of HCN chemistry in planetary atmospheres, and the coupling of atmospheric HCN chemistry and rain-out to the production and evolution of RNA building blocks in warm little ponds (WLPs). We make a major leap in understanding the origin of RNA on a biogenic early Earth by building a comprehensive model that couples terrestrial geochemistry, radiative transfer, atmospheric photochemistry, lightning chemistry, and aqueous pond chemistry. We begin by developing an accurate and feasible method to calculate missing reaction rate coefficients related to HCN chemistry in planetary atmospheres. We use density functional theory simulations to solve the transition states for various reactions, and use the simulated energies and partition functions to calculate the corresponding rate coefficients using the principles of statistical mechanics. We initially explore and calculate rate coefficients for a total of 110 reactions present in reducing atmospheres dominated by N2, CH4, and H2, including 48 reactions that were previously unknown in the literature. Our rate coefficients are most commonly within a factor of two of experimental values, and generally always within an order of magnitude of these values. This accuracy is consistent with the typical uncertainties assigned in large-scale kinetic data evaluations. Next, we develop a consistent reduced atmospheric hybrid chemical network (CRAHCN) containing experimental values when available (32%) and our calculated rate coefficients otherwise (68%). To validate our chemistry, we couple CRAHCN to a 1D disequilibrium chemical kinetic model (ChemKM) to compute HCN production in the reducing atmosphere of Saturn's moon Titan. Our calculated atmospheric HCN profile agrees very well with the measurements performed by instruments aboard the Cassini spacecraft, suggesting our chemical network is accurate for modeling HCN production in reducing environments. We also perform sensitivity analyses on this chemistry and find HCN production and destruction on Titan can be understood in terms of only 19 dominant reactions. The process begins with UV photodissociation of N2 and CH4 in the upper atmosphere, and galactic cosmic ray dissociation of these species in the lower atmosphere. The dissociation radicals then proceed to react along four main channels to produce HCN. It is of particular excitement that one of these channels was newly discovered in this work. Moving forward to modeling early Earth, we expand upon CRAHCN by exploring and calculating rate coefficients related to HCN and H2CO chemistry in atmospheres with oxidizing conditions. We calculate the rate coefficients for 126 new reactions, including 45 reactions that were first discovered in this work. We find the accuracy of our method continues to produce most commonly factor of two agreement with respect to experimental values. Next, we develop the oxygen extension to CRAHCN (CRAHCN-O), containing a total of 259 reactions for computing HCN and H2CO production in atmospheres dominated by N2, CO2, H2, CH4, and H2O. Again, experimental rate coefficients are used when available (43%), and our calculated values are used otherwise (57%). We then build a comprehensive model with a unique coupling of early Earth geochemistry, radiative transfer, atmospheric UV and lightning chemistry, and aqueous chemistry in WLPs. We calculate self-consistent pressure-temperature profiles using a 1D radiative transfer code called petitRADTRANS, and couple these to CRAHCN-O and ChemKM to simulate HCN and H2CO production on early Earth. We model two epochs, at 4.4 and 4.0 billion years ago (bya), which differ in atmospheric composition, luminosity, UV intensity, radical production from lightning, and impact bombardment rate. The respective reducing and oxidizing atmospheric compositions of the 4.4 and 4.0 bya epochs are mainly driven by the balance of H2 impact degassing and CO2 outgassing from volcanoes. We then couple the rain-out of HCN with a comprehensive WLP model to compute the in situ production of RNA building blocks for each epoch. HCN pond concentrations are multiplied by experimental yields to calculate biomolecule production, and there are various biomolecule sinks present including UV photodissociation, hydrolysis and seepage. At 4.4 bya, we find that HCN rain-out leads to peak adenine production of 2.8μM (378 ppb) for maximum lightning conditions. These concentrations are comparable to the peak adenine concentrations delivered by carbon-rich meteorites (10.6μM); however, the concentrations from in situ production persist for > 100 million years in contrast to ~days for meteoritic concentrations. Guanine, cytosine, uracil and thymine concentrations from in situ production at this time peak in the 0.19–3.2μM range, and ribose and 2-aminooxazole peak in the nM range. We note that cytosine and thymine are not present in meteorites, suggesting this biogenic pathway may be one of the only plausible origins of these RNA and DNA building blocks. We find that the high mixing ratio of HCN near the surface of our 4.4 bya model is mainly driven by lightning chemistry rather than UV chemistry. Our results show that HCN production at the surface is linearly dependent on lightning flash density. This result supports a lightning-based Miller-Urey scenario for the origin of RNA building blocks. At 4.0 bya, HCN production and rain-out is 2–3 orders of magnitude less abundant than it is at 4.4 bya, leading to negligible concentrations of RNA building blocks in WLPs during this late oxidizing phase. Similar to HCN production in Titan's atmosphere, HCN production in early Earth's atmosphere is strongly correlated with CH4 content. Reducing (H2-dominant) conditions sustain CH4 levels at a roughly constant ppm-level over 100 million years, which is favourable for HCN production. In oxidizing conditions, CH4 is readily oxidized into CO2, leading to less HCN. These results suggest that early Earth was biogenic at 4.4 bya, and remained so for at least ~100 million years, but was over by 4.0 bya due to oxidation of the atmosphere. This thesis provides a firm theoretical foundation for an origin of RNA in WLPs on a biogenic early Earth within about 200 million years after the Moon-forming impact and the cooling of the magma ocean. / Thesis / Doctor of Philosophy (PhD)

No description available.

Volatile organic compounds (VOCs) are those chemical species having sufficiently high vapor pressures to exist largely or entirely in the gaseous phase, whereas reactive organic carbon (ROC) encompasses all organics except methane. ROC can be emitted biogenically and anthropogenically, usually in a pure hydrocarbon form that is susceptible to reaction with common atmospheric oxidants such as hydroxyl and ozone in the initial steps to the formation of particulate matter, the criteria pollutant most strongly implicated in human mortality. The diversity of both the emitted VOCs and their possible atmospheric reactions yields countless different compounds existing in the atmosphere with a correspondingly wide range of volatility, solubility, reactivity, etc.. Moreover, the temporal and spatial variability of a given analyte is often large. Real-time chemical characterization of gaseous and particulate organic compounds can be achieved by instrumentation utilizing chromatographic and/or mass spectrometric techniques, but these methods are expensive, often logistically challenging, and require high levels of skills for both operation and data analysis. Conversely, filter-based measurements for organic particulates are inexpensive and straightforward, but do not give real-time data and analytes may be lost or transformed before analysis. There is a niche for robust, low-maintenance, moderate-cost instrumentation that offers chemical information on atmospheric carbon. Presented here are two projects that develop and validate instrumentation for measuring ROC. The first combines flame ionization detection (FID) with a CO2 detector to estimate the O/C ratios of sampled gases and particulates. O/C ratios are a particularly valuable piece of chemical information as higher ratios give lower volatility and higher solubility, meaning increased propensity to partition into the condensed phase. The second project utilizes portable VOC samplers with sorbent tubes that trap and protect analytes for detailed analysis. The samplers' portability and programmable microcontrollers offers the investigator great flexibility, both spatially and temporally. A third project analyzed the chemical composition of commercially available fragrance mixtures and modeled their emissions' impact on oxidant reactivity. It was observed that terpenes, despite their low mole fractions in the mixtures, represent the vast majority of emitted reactivity and are quantitatively evolved from the mixtures in a matter of hours. / Doctor of Philosophy / Organic (i.e., carbon-containing) compounds are emitted into the atmosphere from a variety of natural and anthropogenic sources. Respective examples would include the agreeable aroma of a pine forest (from terpene compounds) or the pungent smell of gasoline (from additives such as toluene). These emitted compounds are often pure hydrocarbons (molecules formed of carbon and hydrogen atoms), and the category VOCs (volatile organic compound) encompasses hydrocarbons and the products of their chemical reactions with atmospheric oxidants like the hydroxyl radical and ozone. In the presence of pollutant nitrogen oxides, oxidants modify these VOCs; adding oxygen lowers the VOCs' vapor pressure and increases aqueous solubility, resulting in higher likelihood of condensation from the gaseous phase into particulates (liquid or solid phases). "Smog" is a colloquial term for the entire suite of noxious chemical compounds produced in the air from reactions of largely anthropogenic organic precursors. Particulates, a.k.a. aerosols, are the most concerning atmospheric pollutant due to deleterious effects on respiratory and cardiovascular health and has shown strong correlations with increased mortality in exposed groups such city dwellers. Determining the chemical identities of the VOCs is useful for pollution forecasting and possibly identifying and quantifying VOC sources. Current methods for chemical identification are cumbersome, expensive, complex, and wholly unsuitable for many investigators. In this work, we introduce two new approaches to gathering chemical information about organic gases and particulates. The first instrument has been demonstrated to give accurate estimates of oxygen/carbon (O/C) ratios; higher O/C ratios represent higher propensities to condense into particulate forms. The second instrument developed is a portable VOC sampler, which traps (and prevents reaction of) a broad range of organics on a sorbent (such as activated charcoal) in a small metal tube. After sampling in remote locales, the tubes can be analyzed in the lab and the VOCs identified and quantified. The third study investigated the chemical composition of fragrance mixtures (present in perfumes, cleaning agents, etc.) and modeled (i.e., estimated) VOC emissions based on the fragrance components as well as the effects on atmospheric oxidant levels. Fragrance mixtures represent a significant source of atmospheric carbon, so a more thorough understanding of the fragrances' impacts on oxidant levels gives further insight into atmospheric processes and aerosol formation.

Trace gases and aerosols, or suspended liquid and solid material in the atmosphere, have significant climatological and societal impacts; consequently, accurate representation of their contribution to atmospheric composition is vital to predicting climate change and informing policy actions. Sensitivity analysis allows scientists and environmental decision makers alike to ascertain the role a specific component of the very complex system that is the atmosphere of the Earth. Anthropogenic and natural emissions of gases and aerosol are transported by winds and interact with sunlight, allowing significant transformation before these species reach the end of their atmospheric life on land or in water. The adjoint-based sensitivity method assesses the relative importance of each emissions source to selected results of interest, including aerosol and cloud droplet concentration. In this work, the adjoint of a comprehensive inorganic aerosol thermodynamic equilibrium model was produced to improve the representativeness of regional and global chemical transport modeling. Furthermore, a global chemical transport model adjoint equipped with the adjoint of a cloud droplet activation parameterization was used to explore the footprint of emissions contributing to current and potential future cloud droplet concentrations, which impact the radiative balance of the earth. In future work, these sensitivity relationships can be exploited in optimization frameworks for assimilation of observations of the system, such as satellite-based or in situ measurements of aerosol or precursor trace gas concentrations.