Browsing by Author "Ravishankara, A. R., committee member"
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Item Open Access Climate and health impacts of particulate matter from residential combustion sources in developing countries(Colorado State University. Libraries, 2018) Kodros, John K., author; Pierce, Jeffrey R., advisor; Volckens, John, committee member; Kreidenweis, Sonia, committee member; Ravishankara, A. R., committee memberGlobally, close to 2.8 billion people lack access to clean cooking technology, while 1.8 billion people lack access to electricity altogether. As a means to generate energy for residential tasks, it is common in many developing countries to rely on combustion of solid fuels (wood, dung, charcoal, trash, etc.). Solid fuel use (SFU) can emit substantial amounts of fine particulate matter (PM2.5), often in or in close proximity to residences, creating concerns for human health and climate; however, large uncertainties exist in indoor and outdoor concentrations and properties, limiting our ability to estimate these climate and health impacts. This work explores the uncertainty space in estimates of premature mortality attributed to exposure to PM2.5 from residential SFU (e.g., cooking, heating, lighting) and makes the first estimates of health and radiative effects from combustion of domestic waste (i.e., trash burning). Next, we investigate key uncertain parameters (emission size distribution, black carbon mixing state, and size-resolved respiratory deposition) that drive uncertainties in health and radiative impacts from SFU, in order to improve model estimates of aerosol impacts from all sources. In many developing regions, combustion of solid fuels for cooking and heating is not the only aerosol source impacting air quality and climate. While uncontrolled combustion of domestic waste has been observed in many countries, this aerosol source is not generally included in many global emissions inventories. Using a global chemical-transport model, we estimate exposure to ambient PM2.5 from domestic-waste combustion to cause 270,000 (5th-95th percentile: 213,000 to 328,000) adult mortalities per year, most of which occur in developing countries. Regarding aerosol radiative effects, we estimate the globally averaged direct radiative effect (DRE) to range from -40 mW m-2 to +4 mW m-2 and the aerosol indirect effect (AIE) to range from -4 mW m-2 to -49 mW m-2. In some regions with significant waste combustion, such as India and China, the aerosol radiative effects exceed −0.4 W m−2.The sign and magnitude of the global-mean DRE is strongly sensitive to assumptions on how black carbon (BC) is mixed with scattering particles, while the AIE is strongly sensitive to the emission size distribution. To determine what factors dominate the uncertainty space in mortality estimates from SFU, we perform a variance-based sensitivity analysis on premature mortality attributed to the combined exposure to ambient and household PM2.5 from SFU. We find that uncertainty in the percent of the population using solid fuels for energy contributes the most to the uncertainty in mortality (53-56% of uncertainty across Asia and South America) with the concentration-response function the next largest contributor (40-50%). In the second half of this dissertation, we explore several key uncertainties in climate and health estimates of aerosol from residential sources in order to reduce overall model uncertainty of aerosol impacts from any source. To test the sensitivity of the AIE to treatment of aerosol size distributions in global models, we estimate the AIE due to anthropogenic emissions with prognostic sectional aerosol microphysics and compare this to the AIE calculated when the simulated aerosol mass of each species is remapped onto a prescribed size distribution. Simulations using the prognostic scheme yield a global mean anthropogenic AIE of −0.87 W m−2, while the simulations with the prescribed scheme predict −0.66 W m−2. These differences suggest that simulations with prescribed size‐distribution mapping are unable to capture regional and temporal variability in size‐resolved aerosol number and thus may lead to biases in estimates of the AIE.Item Open Access Daytime evolution of oxidized reactive nitrogen in western U.S. wildfire smoke plumes: in situ and satellite observations(Colorado State University. Libraries, 2020) Juncosa Calahorrano, Julieta Fernanda, author; Fischer, Emily V., advisor; Bond, Tami, committee member; Pierce, Jeffrey R., committee member; Ravishankara, A. R., committee memberThe Western Wildfire Experiment for Cloud Chemistry, Aerosol Absorption, and Nitrogen (WE-CAN) deployed the NSF/NCAR C-130 aircraft in summer 2018 across the western U.S. to sample wildfire smoke during its first day of atmospheric evolution. We present a summary of a subset of oxidized nitrogen species (NOy) in plumes sampled in a pseudo-lagrangian fashion. Emissions of nitrogen oxides (NOx = NO + NO2) and nitrous acid (HONO) are rapidly converted to more oxidized forms. Within 4 hours, ∼86% of the measured NOy (∑ NOy) is in the form of peroxy acyl nitrates (PANs) (∼37%), particulate nitrate (pNO3) (∼26%) and gas-phase organic nitrates (∼23%). The average e-folding time and distance for NOx are ∼90 minutes and ∼40 km, respectively. Nearly no enhancements in nitric acid (HNO3) were observed in plumes sampled in a pseudo-lagrangian fashion, implying HNO3-limited ammonium nitrate (NH4NO3) formation, with one notable exception that we highlight as a case study. We also summarize the observed partitioning of ∑ NOy in all the smoke-impacted samples intercepted during WE-CAN. In the smoke-impacted samples intercepted below 3 km above sea level (ASL), HNO3 is the dominant form of ∑ NOy and its relative contribution increases with smoke age. Above 3 km ASL, the contributions of PANs and pNO3 to ∑ NOy increase with altitude. WE-CAN also sampled smoke from multiple fires mixed with anthropogenic emissions over the California Central Valley. We distinguish samples where anthropogenic NOx emissions appear to lead to an increase in NOx abundances by a factor of 4 and contribute to additional PAN formation. We utilize data from the Cross-Track Infrared Sounder (CrIS) on the Suomi National Polar-orbiting Partnership (Suomi-NPP) satellite, which continues the thermal infrared peroxyacetyl nitrate (PAN) satellite record established by the Tropospheric Emission Spectrometer (TES) onboard the Aura satellite. CrIS provides improved spatial resolution, allowing for improved analysis opportunities. Here we present an analysis of CrIS PAN retrievals over the western US during the summer 2018 wildfire season. The analysis period coincides with WE-CAN. CrIS is capable of detecting PAN and CO enhancements from smoke plumes sampled during WE-CAN, especially those that became active before the satellite overpass or burned for several days (e.g., Carr Fire, Mendocino Complex Fire). The analysis show that ∼40 - 70% of PAN over the western U.S. can be attributed to smoke from wildfires. The contribution of smoke from wildfires to free tropospheric PAN generally increases with latitude. We calculate peroxyacetyl nitrate (PAN) excess mixing ratios normalized by CO (NEMRs) in fresh smoke plumes from fires and follow the evolution as these plumes are transported several hours to days downwind. This analysis shows that elevated PAN within smoke plumes can be detected several states downwind from the fire source. The combination of high CrIS spatial resolution and favorable background conditions on 13 September 2018 permits detecting chemical changes within the Pole Creek smoke plume in Utah. In this plume, CrIS PAN NEMRs increase from < 1% to 3.5% within 3 - 4 hours of physical aging. These results are within the range observed in fresh plumes sampled during WE-CAN, where PAN NEMRs increased from 1.5% to 4% within 4 hours of physical aging.Item Open Access Developing paper-based devices for mapping agricultural pesticides and environmental contaminants(Colorado State University. Libraries, 2021) Menger, Ruth F., author; Henry, Charles S., advisor; Borch, Thomas, advisor; Ravishankara, A. R., committee member; Neilson, James R., committee member; Trivedi, Pankaj, committee memberThe detection of environmental contaminants is important to ensure the health of both humans and the environment. Currently, detection is done by instrumentation like liquid or gas chromatography coupled with mass spectrometry. While sensitive and selective for multiple analytes, these instruments suffer from disadvantages like large size, high sample cost, and the need for a trained analyst to run the samples. As an alternative, microfluidic paper-based analytical devices (µPADs) are becoming more common as inexpensive, fast, easy to use devices to detect and quantify a variety of analytes. My research has been focused on developing µPADs for three different analytes: pesticides, PFAS, and heavy metals. In order to ensure proper crop protection and pest management, it is important to manage and optimize pesticide application. Currently, this is done by water-sensitive papers, which often inaccurately portray the presence of pesticide due to humidity and extraneous water droplets that are not pesticide. In Chapter 2, I have developed a method that uses filter paper to capture a fluorescent tracer dye that has been mixed with the pesticide and then sprayed over the crop. The filter papers are imaged with a lightbox and Raspberry Pi camera system and then analyzed to determine percent coverage. After optimization and validation of the method to WSP, the filter paper method was used to evaluate pesticide distribution in a citrus grove in Florida (Chapter 3). The data from these field studies was used to make recommendations for which application method is best for the different types of pesticides. Paper-based devices are inherently limited by the inability to control fluid properties like mixing. In order to incorporate mixing but also retain a small device that does not require external power to initial flow, a microfluidic device was fabricated out of two glass slides. A staggered herringbone pattern is laser ablated into the slides, and a channel is formed by double-sided adhesive (Chapter 4). Mixing was quantified using blue and yellow dyes. A reaction between horseradish peroxidase and hydrogen peroxide was used as a representative enzymatic reaction and also to determine enzyme kinetics. Since the microfluidic device is made of glass, it is also compatible with non-aqueous solvents. Paper-based devices do not work well with organic solvents because the hydrophobic wax on the paper is dissolved by the solvent. In Chapter 5, the dissertation returns to traditional µPADs for environmental contaminants. Per- and polyfluoroalkyl substances (PFAS) are class of compounds that are highly persistent, toxic, bioaccumulative, and ubiquitous. While multiple instrument-based methods exist for sensitive and selective detection in a variety of matrices, there is a huge need for a fast, inexpensive, and easy-to-use sensor for PFAS detection. This would enable widespread testing of drinking water supplies, ensuring human health. A µPAD was developed for the detection of perfluorooctane sulfonate (PFOS) where the ion-pairing of PFOS and methylene green forms a purple circle. The diameter of the purple circle can be measured by the naked eye with a ruler or with the help of a smartphone to correlate the diameter back to PFOS concentration. At a cost of cents per sample, this µPAD enables fast and inexpensive detection of PFOS to ensure safe drinking water. A common issue with environmental µPADs is the relatively high limits of detection compared to what is needed for regulatory purposes. It can be challenging to lower the limits of detection without incorporating an external pretreatment and/or preconcentration step. As µPADs are small and handle only a small volume of sample (<120 µL), there is the possibility of increasing the sample capacity of the device but without significantly increasing the device size or analysis time. By adding multiple layers of absorbent filter paper underneath radial device for heavy metal detection, the sample volume increased to 1 mL, decreasing the limit of detection for a radial copper detection card from 100 ppb to 5 ppb (Chapter 6). The research presented here achieves the goal of developing µPADs for environmental contaminants. They can be used in different ways to visualize the presence of the contaminant for monitoring and management purposes, ultimately ensuring human and environmental health.Item Open Access Fundamental investigations of hydrocarbon plasma chemistry: mechanistic studies of gas-phase processes and plasma-surface interactions(Colorado State University. Libraries, 2020) Van Surksum, Tara, author; Fisher, Ellen R., advisor; Van Orden, Alan K., committee member; Ravishankara, A. R., committee member; Weinberger, Christopher R., committee memberTo view the abstract, please see the full text of the document.Item Open Access Investigating contributions to elevated surface ozone in the Colorado Front Range during summer 2015(Colorado State University. Libraries, 2018) Lindaas, Jakob, author; Fischer, Emily V., advisor; Farmer, Delphine K., committee member; Ravishankara, A. R., committee memberTropospheric ozone (O3) is a significant pollutant in the Colorado Front Range. The northern Front Range metropolitan area (NFRMA) has exceeded the U.S. EPA national ambient air quality standard for O3 since 2008. While many regions in the country have experienced downward trends in ground-level O3, the NFRMA O3 mixing ratios have remained stagnant despite efforts to reduce precursor emissions. Rapid population growth and a boom in oil and natural gas development over the past 15 years have changed the quantity and spatial distributions of many important O3 precursors. O3 precursors may also be transported into the NFRMA, such as during wildfire smoke events. Here I use in situ measurements of O3, a suite of volatile organic compounds (VOCs), and reactive oxidized nitrogen species collected during summer 2015 at the Boulder Atmospheric Observatory (BAO) in Erie, CO, to investigate the contribution of different VOC sources to elevated surface O3 in the NFRMA. The first analysis combines observations of acyl peroxy nitrates (APN) and a previously described positive matrix factorization of the VOCs to investigate the contribution of different VOC sources to high O3 abundances at BAO. Based on the ratio of PPN to PAN, I find that anthropogenic VOC precursors dominate APN production when O3 is most elevated. Propane and higher alkanes, primarily from oil and natural gas emissions in the Colorado Front Range, drive elevated PPN to PAN ratios during high O3 events. The percentage of OH reactivity associated with oil and gas emissions is also positively correlated with O3 and PPN/PAN. Lastly, idealized box model simulations are used to probe the chemical mechanisms for these observations. I find that VOC precursor mixtures dominated by oil and gas emissions create abundant and more efficient peroxy radical intermediates compared to mixtures dominated by traffic or biogenic emissions. This work may help guide efforts to control O3 precursors in the NFRMA. The second analysis examines the impact of wildfire smoke on O3 abundances via a case study. Aged wildfire smoke impacted BAO during two distinct time periods during summer 2015: 6 – 10 July and 16 – 30 August. The smoke was transported from the Pacific Northwest and Canada across much of the continental U.S. Carbon monoxide and particulate matter increased during the smoke-impacted periods, along with acyl peroxy nitrates and several VOCs that have atmospheric lifetimes longer than the transport timescale of the smoke. During the August smoke-impacted period, nitrogen dioxide was also elevated during the morning and evening compared to the smoke-free periods. There were nine empirically defined high O3 days during our study period at BAO, and two of these days were smoke-impacted. I examined the relationship between O3 and temperature at BAO and found that for a given temperature, O3 mixing ratios were greater (~10 ppbv) during the smoke-impacted periods. Enhancements in O3 during the August smoke-impacted period were also observed at two long-term monitoring sites in Colorado: Rocky Mountain National Park and the Arapahoe National Wildlife Refuge near Walden, CO. Given that the relative importance of wildfire smoke for air quality over the western U.S. is expected to increase as the climate warms and anthropogenic emissions decline, this case study offers important insights into how aged wildfire smoke can influence atmospheric composition at an urban site.Item Open Access Investigating emissions and evolution of reactive nitrogen in western U.S. wildfire smoke plumes(Colorado State University. Libraries, 2020) Lindaas, Jakob, author; Fischer, Emily, advisor; Ravishankara, A. R., committee member; Collett, Jeffrey, Jr., committee member; Jathar, Shantanu, committee memberWildfires are an important source of reactive nitrogen (Nr) to the atmosphere. Large wildfires are becoming more frequent in the western U.S. and smoke from large western U.S. wildfires is becoming a proportionately larger driver of poor air quality in certain U.S. regions. Nr in smoke contributes to the production of ozone (O3), the formation of secondary inorganic and organic aerosol, and nitrogen deposition to downwind ecosystems, with attendant negative impacts on human and ecosystem health and important consequences for the earth's radiative budget. Smoke from wildfires is difficult to sample though, since it is hard to predict exactly where fires will start and which fires will grow larger across the western U.S. Scientific aircraft are able to sample smoke where and when it occurs, making them ideal platforms from which to gather observations of gases and particles in smoke. This dissertation presents results from three analyses investigating the emissions and evolution of reactive nitrogen in wildfire smoke using data from the Western wildfires Experiment on Cloud chemistry, Aerosol absorption, and Nitrogen (WE-CAN). The WE-CAN field intensive sampled fresh smoke from 23 identified large wildfires in the western U.S. during August and September 2018. Pseudo-Lagrangian ("lawn-mower pattern") sampling was accomplished for about half of these fires, meaning that the plane was able to intercept the same smoke multiple times as it was transported downwind. Additionally, mixed and older smoke from indeterminate sources was sampled in the free troposphere as well as in the California Central Valley where it mixed with anthropogenic emissions. These data represent a large increase in the number of western wildfire smoke plumes intercepted by research aircraft in a systematic fashion. First, I present a general overview of Nr emissions from 16 wildfires using a large cross section of the suite of chemical and physical measurements made onboard the National Science Foundation/National Center for Atmospheric Research (NSF/NCAR) C-130 aircraft. I find that reduced N compounds generally make up more than half of the total measured Nr (∑Nr) (39 - 80%, median = 66%). This was not necessarily expected since we sampled plumes from fires at their most active time of day, with assumed burning conditions that favored emission of oxidized forms of Nr. I observe evidence of rapid chemistry in the minutes between emission and the first sampling periods in all fires via significant abundances of peroxyacetic nitric anhydride (PAN) even in these youngest plume samples. I find evidence for the influence of both combustion conditions and fuel N content influencing the ratio of the sum of measured ammonia (NH3) plus particulate ammonium (pNH4) and the sum of oxidized nitrogen (∑NHx/∑NOy). Finally, estimated emission factors (EF) from these fires can be compared with previous literature for similar fuel types, with NH3 EFs similar to or higher than previous lab and field observations, and NOx EFs generally lower than previous estimates. Next I explore the evolution of NH3 in fresh and aged smoke. Focusing on 8 pseudo-Lagrangian sampled plumes, I observe e-folding loss timescales for NH3 with respect to gas-particle partitioning on the order of minutes to hours, similar to previous estimates in fresh smoke. I find empirical evidence for the association of NH3 and nitric acid (HNO3) to form ammonium nitrate (NH4NO3), though not all plumes contain conditions favorable to NH4NO3 formation. Fresh, dense plumes injected at higher altitudes (and lower temperatures) are more likely to favor NH4NO3 formation, a conclusion consistent with previous model simulations in the literature. Measured organic acid ions also suggest the presence of NH4-organic salts in the plumes sampled. Finally, I also use observations collected in medium and old aged smoke to find additional evidence for the formation of NH4NO3 in plumes injected higher in the atmosphere with larger oxidized N to NH3 ratios. Lastly, I investigate the production of PAN and peroxypropionic nitric anhydride (PPN) in the same set of pseudo-Lagrangian sampled plumes. Increases in dilution-corrected PAN and PPN mixing ratios in all plumes suggest that PAN and PPN are produced in all smoke plumes sampled, with the rate of increase similar to the handful of previous observations. I then use a simple observation-based model to determine the dominant precursors of PAN and PPN in fresh smoke plumes. From the model I infer that acetaldehyde is the dominant immediate PAN precursor in large western wildfire smoke plumes, with biacetyl also serving as an important precursor. To my knowledge this is the first time these conclusions have been drawn for smoke from an observational framework and it suggests that biacetyl should be included in models of smoke plume evolution. With respect to PPN, I find that propanal is an important immediate PPN precursor in fresh wildfire smoke. Unexpectedly, I also find that at least one other immediate PPN precursor is likely needed to explain PPN production, and suggest that this precursor may be ethylglyoxal. However, very few in situ measurements of ethylglyoxal exist to test this hypothesis.Item Open Access Nitric oxide generation from S-nitrosothiols via interactivity with polymer-supported metal-organic frameworks(Colorado State University. Libraries, 2018) Neufeld, Megan J., author; Reynolds, Melissa, advisor; Chen, Eugene, committee member; Finke, Richard, committee member; Kipper, Matthew, committee member; Ravishankara, A. R., committee memberCatheters, extracorporeal systems, stents, and artificial heart valves are all common blood-contacting medical devices. Due to the differences in the chemical and physical properties of the polymeric materials used to construct medical devices and biological tissues in the cardiovascular system, complications such as thrombus formation arise from the resulting incompatibilities. Introduction of foreign materials that lack critical biological cues can result in disruption of the delicate balance maintained within the circulatory system. This disruption of homeostasis initiates a complex cascade of events such as platelet adhesion and protein deposition that ultimately result in thrombus formation. As such, the propensity of blood to clot upon contact with a foreign surface represents a challenge unique to devices intended for vascular applications. The current clinical use of devices such as vascular catheters includes the administration of anticoagulants, however their associated complications such as internal hemorrhaging renders this practice undesirable as a long-lasting solution. A general limitation of existing devices made from synthetic polymers is their inability to integrate with their environment through biological cues (natural regulators). Materials that lack this behavior are often described as passive towards their environment. In comparison, active materials that can simulate natural molecules used to maintain biological responses may result in enhanced integration of medical devices. In the natural, healthy endothelium, the prevention of thrombus formation occurs through the release of anticoagulants and platelet inhibitors such as gaseous nitric oxide (NO). While the use of NO for medicinal purposes began indirectly in the late 1800s, the significance of its endogenous production was not known until the 1970s. In particular, NO is a key factor in the prevention of thrombus formation. While its remedial potential has led to its use as an exogenous therapeutic agent, its high reactivity limits its applicability as a localized therapeutic. This limitation is addressed by mimicking the natural endothelium and using small molecules in the bloodstream known as S-nitrosothiols (RSNOs) to produce NO directly from this physiological source. Biological RSNOs are theorized to aid in the stabilization and transport of NO and undergo an NO-forming decomposition in the presence of heat, light, and certain metals such as copper. Prior strategies have evaluated exploiting the physiological supply of RSNOs through the incorporation of copper complexes into polymeric materials. While these copper-based materials demonstrate the production of NO from RSNO decomposition, limitations arise due to the gradual loss of the catalytic material and toxicity from copper leaching. In order for this type of approach to be feasible, the active metal species must remain immobilized within the structural framework. Metal–organic frameworks (MOFs) are a class of crystalline materials that consist of organic ligands coordinated to metal centers. Certain copper-based MOFs have demonstrated the ability to enhance the generation of NO from RSNOs without the gradual loss of the active species. Through integration of certain copper-based MOFs with medically relevant polymers, materials can be prepared that promote the localized generation of NO at their surfaces. However, the feasibility of utilizing copper-based MOFs for such applications depends on effective incorporation within a supporting polymeric matrix and the retention of useful activity thereafter. As such, it is necessary to assess different MOF/polymer composites for their ability to promote NO generation from RSNOs prior to use in medical applications. This dissertation investigates the incorporation of two distinct copper-based MOFs into a selection of medically-relevant polymeric materials including cotton, poly(vinyl chloride), chitosan, and poly(vinyl alcohol). These MOF/polymer materials were subsequently tested for their ability to promote NO generation from RSNOs in an effort to assess the impact of incorporation within a polymer matrix. Overall, this work demonstrates the potential for blood-contacting MOF-containing materials in biomedical settings by identifying ideal characteristics that MOF/polymer composites should exhibit for optimization and translation to a clinical setting.Item Open Access Quantifying internal climate variability and its changes using large-ensembles of climate change simulations(Colorado State University. Libraries, 2020) Li, Jingyuan, author; Thompson, David W. J., advisor; Barnes, Elizabeth A., committee member; Ravishankara, A. R., committee member; Cooley, Daniel, committee memberIncreasing temperatures over the last 50 years have led to a multitude of studies on observed and future impacts on surface climate. However, any changes on the mean need to be placed in the context of its variability to be understood and quantified. This allows us to: 1) understand the relative impact of the mean change on the subsequent environment, and 2) detect and attribute the external change from the underlying "noise" of internal variability. One way to quantify internal variability is through the use of large ensemble models. Each ensemble member is run on the same model and with the same external forcings, but with slight differences in the initial conditions. Differences between ensemble members are due solely to internal variability. This research exploits one such large ensemble of climate change simulations (CESM-LE) to better understand and evaluate surface temperature variability and its effects under external forcing. One large contribution to monthly and annual surface temperature variability is the atmospheric circulation, especially in the extratropics. Dynamical adjustment seeks to determine and remove the effects of circulation on temperature variability in order to narrow the range of uncertainty in the temperature response. The first part of this work compares several commonly used dynamical adjustment methods in both a pre-industrial control run and the CESM-LE. Because there are no external forcings in the control run, it is used to provide a quantitative metric by which the methods are evaluated. We compare and assess these dynamical adjustment methods on the basis of 2 attributes: 1) the method should remove a maximum amount of internal variability while 2) preserving the true forced signal. While the control run is excellent for assessing the methods in an "ideal" environment, results from the CESM-LE show biases in the dynamically-adjusted trends due to a forced response in the circulation fields themselves. This work provides a template from which to assess the various dynamical adjustment methods available to the community. A less studied question is how internal variability itself will respond to climate change. Past studies have found regional changes in surface temperature variance and skewness. This research also investigates the impacts of climate change on day-to-day persistence of surface temperature. Results from the CESM-LE suggest that external warming generally increases surface temperature persistence, with the largest changes over the Arctic and ocean regions. The results are robust and distinct from internal variability. We suggest that persistence changes are mostly due to an increase in the optical thickness of the atmosphere due to increases in both carbon dioxide and water vapor. This increased optical thickness reduces the thermal damping of surface temperatures, increasing their persistence. Model results from idealized aquaplanet simulations with different radiation schemes support this hypothesis. The results thus reflect a robust thermodynamic and radiative constraint on surface temperature variability.Item Open Access The role of Earth system interactions in large-scale atmospheric circulation and climate(Colorado State University. Libraries, 2023) Yook, Simchan, author; Thompson, David W. J., advisor; Ravishankara, A. R., committee member; Hurrell, James, committee member; Ebert-Uphoff, Imme, committee memberThe complex interactions among different components of the Earth system play a key role in governing the climate variability through various physical processes. For example, an interaction between the fluctuations in one component of the Earth system and associated variations in another component of the Earth system can either amplify or dampen the climate variability depending on the nature of their two-way feedback mechanisms. Thus, understanding the role of various physical interactions among components of the Earth system is critical to understand the changes in climate as well as to reduce the uncertainty in future climate projections. This dissertation focuses on discovering the key processes and interactions among different components of the Earth system on the climate variability using observations and model hierarchies. In Part 1, the interactions between the atmospheric circulation and western North Pacific SST anomalies are explored in two sets of simulations: 1) a simulation run on a coupled atmosphere-ocean general circulation model (GCM), and 2) a simulation forced with prescribed, time-evolving SST anomalies over the western North Pacific. The results support the interpretation of the observed lead/lag relationships between western North Pacific Sea Surface Temperature (SST) anomalies and the atmospheric circulation, and provide numerical evidence that SST variability over the western North Pacific has a demonstrable effect on the large-scale atmospheric circulation throughout the North Pacific sector. In Part 2, the role of moist lapse rate in altering the temperature variability under climate change is explored. To reduce the complexity of the problem, the changes in the temperature variance under global warming are first analyzed in the simplest version of model hierarchy: a single column Rapid Radiative Transfer Model with a simplified convective adjustment. Similar analyses were repeated with varying model hierarchies with additional complexities: a global general circulation model in global Radiative Convective Equilibrium (RCE) setting with fixed SST, and fully coupled Earth system models. The results highlight the role of moist lapse rate as a potential constraint for climate variability in the tropical atmosphere simulated by different model hierarchies. In Part 3, the effects of coupled chemistry-climate interactions on the amplitude and structure of stratospheric temperature variability are quantified in two numerical simulations: A "free running" simulation that includes fully coupled chemistry-climate interactions; and a "specified chemistry" version of the model forced with prescribed chemical composition. The results indicate that the inclusion of coupled chemistry-climate interactions increases the internal variability of temperature by a factor of ~two in the lower tropical stratosphere through dynamically driven ozone-temperature feedbacks. The results highlight the fundamental role of two-way feedbacks between the atmospheric circulation and chemistry in driving climate variability in the lower stratosphere. In Part 4, the effects of coupled chemistry-climate interactions on the large-scale atmospheric circulation are further explored based on two observational case studies of the Antarctic ozone holes of 2020 and 2021. The 2020 and 2021 were marked by two of the largest Antarctic ozone holes on record. It has been demonstrated that the ozone holes of 2020 and 2021 were associated with large changes in the atmospheric circulation consistent with the climate impacts of Antarctic ozone depletion. The ozone holes were also unusual for their associations with aerosol burdens due to two extraordinary events: the Australian wildfires of early 2020 and the eruption of La Soufriere in 2021. The results provide suggestive evidence that injections of both wildfire smoke and volcanic emissions into the stratosphere can lead to hemispheric-scale changes in surface climate. This dissertation provides a detailed look at the complex aspects of the coupled interactions among different components of the Earth system and their roles on climate variability and large-scale dynamics. To clarify the role of the different physical processes contributing to the climate responses, this study performed a comprehensive analysis based on observations as well as a series of numerical experiments run on different configurations of climate model hierarchies. The findings herein improve our understanding of different Earth system interactions and their influences on global climate and large-scale atmospheric dynamics.Item Open Access Transport-radiation feedbacks of ozone in the tropical tropopause layer(Colorado State University. Libraries, 2017) Charlesworth, Edward, author; Birner, Thomas, advisor; Ravishankara, A. R., committee member; Oprea, Iuliana, committee memberThe tropical tropopause layer (TTL) is a region in the atmosphere that shows an interesting combination of tropospheric and stratospheric characteristics over the extent of several kilometers. For example, the TTL shows both convectively-driven tropospheric dynamics and the beginning of the mechanically-driven Brewer-Dobson circulation. The TTL is also important for climate due to its role as the gateway for most air that enters the stratosphere. In this work, a single-column model is used to investigate why a tropical tropopause layer of the observed vertical extent exists. This is done through computations of radiative convective equilibrium temperatures and interactive photochemical equilibrium ozone concentrations. The model uses only a basic simulation of ozone chemistry, convection, and stratospheric upwelling, but the results show that such a simplified expression of critical processes can produce temperature and ozone profiles that are very similar to observations. It is found that vertical transport of ozone by the Brewer-Dobson circulation and its associated effects on radiative heating rates is of first-order importance in producing the observed temperature structure of the tropical tropopause layer, within this simple modeling context. Adiabatic cooling due to stratospheric upwelling is found to be equally important to generate the tropical tropopause layer. With these combined processes, it is suggested that the even the lowest upwelling velocities on the order of observed upwelling can produce a TTL. With regards to climate change through the strengthening Brewer-Dobson circulation, this model suggests that an increase in upwelling from 0.5 to 0.6 mm/s should cool the cold point tropopause by 3.5 K and loft it by half a kilometer.