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D.Phil. (Geography) / The Infrared Atmospheric Sounding Interferometer (lASI), operational in polar-orbit since 2006 on the European MetOp-A satellite, is the most advanced of its kind in space. It has been designed to provide soundings of the troposphere and lower stratosphere at nadir in a spectral interval of 0.25 em" across the range 645-2 760 em". Fine spectral sampling such as this is imperative in the sounding of trace gases. Since its launch, the routine retrievals of greenhouse, species from IASI measurements have made a valuable contribution to atmospheric chemistry studies at a global scale. The main contribution of this thesis is the development of a new trace gas retrieval scheme for IASI measurements. The goal was to improve on the global operational scheme in terms of the algorithm complexity, speed of calculation and spatial resolution achieved in the final solution. This schemedirectly retrieves column integrated trace gas densities at single field-of-view (FOV) from IASI measurements within a 10% accuracy limit. The scheme is built on the Bayesian framework of probability and based on the assumption that the inversion of total column values, as apposed to gas profiles, is a near-linear problem. Performance of the retrieval scheme is demonstrated on simulated noisy measurements for carbon monoxide (CO). Being a linear solution, the scheme is'highly dependent on the accuracy of the a priori. A statistical estimate of the a priori was computed using a principal component regression analysis with 50 eigenvectors. The corresponding root-mean-square (RMS) error of the a priori was calculated to be 9.3%. In general terms, the physical retrieval improved on the a priori, and sensitivity studies were performed to demonstrate the accuracy and stability of the retrieval scheme under a numberof perturbations. A full system characterization and error analysis is additionally preformed to elicidate the nature of this complex problem. The hyperspectral IASI measurements introduce a significant correlation error in the retrieval. The Absorption Line Cluster (ALC) channel selection method was developed in this thesis, to address the correlation error explicitly. When a first neighbour correlation factor of 0.71 is assumed in the measurement error covariance for the clusters of ALC channels, then most of the correlation error is removed in the retrieval. In conclusion, the total column trace gas retrieval scheme developed here is fast, simple, intuitive, transparent and robust. These characteristics together make it highly suitable for implementation in an operational environment intended for air quality monitoring on a regional scale.

The use of biomass as a renewable fuel source can help the United States reduce its dependence on fossil fuels, especially in providing affordable heat for many middle- and low-income households. However, residential wood combustion (RWC) releases pollutants that can negatively impact the environment and human health, especially for those living in the vicinity of wood-burning locations. Current compliance testing methods are insufficient in capturing the actual in-use emissions of residential wood heaters because they do not represent real-life use, leading to higher emissions during actual use. This thesis investigates emissions during realistic operations of wood-fired heaters to identify and quantify the majority of emissions and ways to minimize such emissions. The study focuses on investigating eight different woody biomass fired heaters, including three pellet stoves, a pellet boiler, two wood chip-fired hydronic heaters, and two outdoor cordwood fired hydronic heaters. This research contributes a new knowledge on the impact of combustion strategies, fuel type, and control strategies to minimize emissions. The obtained data can provide information to manufacturers, policy makers, and consumers, guiding low-emission and more efficient use of wood-fired heating devices. In all chapters, variability was evident due to burn phase, fuel type, and operation. The results from the pellet stoves showed that even while using a homogeneous fuel, different burn phases produce different emissions than the overall period. For the pellet boiler studies, the highest efficiencies were achieved during the high load, steady state tests. The burn phase also affects emissions from woodchip boilers, where low output periods are significantly higher in terms of emissions compared to high output periods. Each individual burn phase of the duty cycle produced different emissions in cordwood testing, with steady-state phases having the lowest emissions and highest efficiency. The variability in emissions from different burn phases is a crucial factor in evaluating the performance of wood-burning appliances. Lower moisture content fuels were found to have better performance in terms of PM emissions and efficiency. Fuel type can impact emissions, but it may be overshadowed by burn phase and technology. Relatively high emissions were often related to low or incorrect air-to-fuel ratios. Gasification techniques used in some woodchip boilers during low output periods significantly increased efficiency and reduced CO emissions. Additionally, gasification techniques used during high burn steady states with wet fuel chips resulted in a 77% reduction in PM emissions. Comparing all the primary heaters studied in this thesis, in terms of PM emission output, showed the units that used gasification, integrated catalysts, or thermal storage had the lowest emissions. The results of the study are compiled into data sets that give a more accurate picture of real-world operation of wood-fired heaters that will benefit air quality modelers and policy makers. Such emission data for various biomass heaters in EPA’s AP-42, under realistic operating conditions, currently either does not exist or is limited. Additionally, this research identifies the most important parameters that need to be included in the development of high-resolution models, optimizing the performance of wood-fired devices and supporting the transition from current compliance testing to more realistic testing. In conclusion, this work provides new insights into the performance and emissions of wood-fired heaters during realistic operation. The results of the study can help manufacturers optimize their products for real-life performance and help policy makers and consumers make informed decisions regarding low-emission and more efficient use of wood-fired heating devices. The study highlights the importance of capturing transient phases and the impact of fuel type and control strategies on minimizing emissions.

Excessive carbon dioxide (CO₂) emission into the atmosphere is the dominant factor in the global warming effect. The quick development in industries, anthropogenic activities, expansion of electric cars, and AI-Generated Content (AIGC) market significantly increase the energy demand. The emission of CO₂ gas into the atmosphere bounced back to a new high level after the economic recovery across the world following COVID-19. The zero-carbon policies were carried out by more countries to keep the temperature rise within 1.5 ℃ according to the Paris Agreement. However, fossil fuels still occupy the first place in emitting CO₂ into the air, though a lot of renewable appliances have started to run in recent years. Apart from controlling and diminishing the emission of CO2, capture and utilization technologies are the most significant strategy to achieve carbon neutrality before 2050. The utilization of CO₂ has become various, including direct CO2 electrolysis, two-step tandem CO₂ electrolysis, and hybrid process. Some technologies require concentrated CO₂, and the desorption of CO₂ is now becoming an unavoidable and energy-consuming process. In response to the excessive CO₂ emissions into the atmosphere, 2019 is the ninth year in a row that the global mean sea level has risen compared to the year before, setting a new record with a peak of 87.6 mm in the middle of the year. To meet the 1.5 ℃ objective, we should develop novel technologies to capture and convert CO₂ with new heating technology for tandem utilization or skip the specific desorption process to directly produce the value-added chemicals. Carbon materials are widely used in different industrial fields. Since graphene, graphene oxide, and carbon nanotubes have such remarkable properties, these three carbon-based materials have been highly interesting research subjects in recent years. Graphene stands out for its toughness, flexibility, lightness, high resistance, electrical conductivity, and heat conduction. The applications of graphene are very broad: they include electronics to improve the chip performance, flexible screens to enhance the user experience, construction materials to improve safety and save energy, and medical treatment for drug delivery. Thus, the process of producing premium graphene is the remaining problem blocking the development of graphene applications. Graphene is primarily made through two methods: chemical vapor deposition (CVD) and oxidation-reduction (Redox). The substance needed to make graphene using CVD is methane (CH4), and the temperature is around 1000℃, which makes this an energy-intensive method. The oxidation-reduction (Redox) method will need much stronger acids and oxidants to oxidize the graphite and then reduce the graphene oxide to get reduced graphene with defects, which also has a huge demand for energy. The proposed strategy is preparing the graphene by re-carbonization of asphaltene molecules extracted from crude oil or asphalt paving materials. This strategy saves a lot of energy and improves the use rate of abundant asphalt materials. During the synthesis process of graphene, we choose the natural montmorillonite as the substrate material to provide the designed space for re-carbonization reactions. Using this new method and these materials, we can get low-layer (< 3) graphene sheets with remarkable 2D scale. Using a scalable process to generate graphene of superior quality with neglectable defects, the applications of graphene in various fields would be largely enhanced and facilitated. Besides the above applications, graphene has become familiar as a composition of absorbent in the Carbon Capture Utilization and Storage (CCUS) field. To reach the goal of carbon-zero before 2050, the studies of CCUS have prevailed in the past years. The emission of CO2 comes from industry, agriculture, transportation, and other human activities. To overcome the challenge of removing the greenhouse effect, the CO₂ capture technologies are the most important part of the realm of CCUS. CO₂ capture technologies are primarily designed based on the main existing form, such as 3 to 8 % emitted by natural gas power plants, 10 to 18 % coal-fired plants, and 400 ppm (0.04%) in the atmosphere. Hence, a lot of sorbents were designed and produced for various CO₂ sources. Compared with the capture process, the demand for CO₂ desorption is becoming the most energy-intensive process. For example, the amine sorbents can only desorb the CO₂ at a high temperature around 100 to 120 ℃. The alkaline sorbents need protons to generate CO₂. With regard to the heating method, conventional heating, including vapor heating and induction heating, also consumes a lot of energy. To overcome the energy demand challenge, using microwave irradiation to desorb CO₂ becomes a potential solution to reduce the energy demand. Therefore, modified graphene-doped solvent-impregnated polymers (SIPs) were created to capture CO₂ and desorb CO₂ with a faster speed and lower energy consumption. Graphene is extraordinarily responsive to microwave irradiation. Carbon can be quickly heated to >1200℃ using a power of 1000 W at 2.45 GHz within 1 minute. Among the graphene (GN), graphene oxide (GO), and carbon nanotubes (CNTs), the low-layer graphene demonstrates a remarkable ability to absorb the microwave to generate heat to desorb CO₂ and a highly efficient ability to dissipate heat. The synthesized SIPs/GN absorbent can capture 400 ppm, 7%, 15%, and 100% CO₂ with great capacities and desorb the CO₂ with a power of 100 W microwave irradiation within 5 minutes at 50 ℃ for long-term use (50 cycles), accompanying no degradation of amine groups. With a fast and energy-saving heating method, the SIPs/GN sorbents would be one of the longest-lasting materials for industrial applications. In the tandem utilization of CO₂, the high concentration of CO₂ is a foundational reactant for following reactions to value-added products. So, the graphene-doped SIPs give a valuable strategy to lessen the energy demand. Except for the necessity of pure or high concentration of CO₂ for subsequent CO₂ utilizations, the direct conversion of CO₂ is also the other solution to convert the captured CO₂. The dual functional solid materials are one of the current feasible approaches to directly reduce CO₂ by introducing H₂ and catalyst at high temperatures to get CO or CH₄. With the rising trend of electrochemical electrolysis of CO₂, a dual functional liquid absorbent-based electrolyte can be the candidate to directly reduce CO₂. With a relatively slow CO₂ desorption rate compared to 2M MEA and 8 wt.% PEI solutions, the 10 wt.% NOHMs is made to serve as the electrolyte. This is an excellent electrolyte possessing a high conductivity to directly reduce the CO₂ to CO with 0.5 M NaCl and 83.3% less concentration than 2 M MEA + 3 M KCl. Thus, it realizes the same ∼ 20 % Faradaic Efficiency of CO and production rate of CO at 25 ℃. The study of direct reduction of 10 wt.% NOHMs gives inspiration for future large-scale continuous reduction in a flow cell. The high CO2 partial pressure in the reservoir and suitable pH value range would be adopted to convert the CO₂. In addition, the 10 wt.% NOHMs also saves at least 38.63% and 77.71% energy compared to 8 wt.% PEI and 2 M MEA solutions. When the adjusted cathode contact area and the stable current density of CO can give the same product rate of CO with the CO₂ desorption rate, the balance between the desorption rate and conversion rate would be achieved. In sum, the results of this thesis show the combined strategy to capture and convert various CO₂ sources efficiently. Due to the limitation of liquid NOHMs solution to capture and convert the 400 ppm CO₂, the 10 wt.% NOHMs solution is a good approach for 10 to 18 % CO₂ source. The solid SIPs/GN absorbent has a high capacity when capturing 400 ppm CO₂, which is one of the most effective ways for direct air capture (DAC). With the comprehensive capture technologies and excellent conversion rate to CO, the future CCUS technologies will be focused on the combinations of capture, conversion, and storage, with considerations of energy efficiency, process cost and production efficiency.

Tropospheric oxidation modulates pollution chemistry and greenhouse gas lifetimes. The hydroxyl radical (OH) is the primary oxidant and the main sink for methane, the second-most influential anthropogenic contributor to climate change. OH is produced following the photolysis of ozone, an oxidant, respiratory irritant and greenhouse gas. Trends in methane or ozone are frequently attributed to their sources, but sink-driven variability is less often considered. I investigate the influence of fluctuations in turbulent loss to the Earth’s surface, also known as deposition, on tropospheric ozone concentrations and chemistry over the relatively polluted eastern United States. I use idealized sensitivity simulations with the global chemistry-climate model AM3 to demonstrate that coherent shifts in deposition, on the order recently observed at a long-term measurement site, affect surface ozone concentrations as much as decreases in its precursor emissions have over the past decade. I conclude that a sub-regional deposition measurement network is needed to confidently attribute trends in tropospheric ozone. Next, I turn to the remote marine troposphere to evaluate two theoretical proxies for variability in the methane sink, OH, with observations from the NASA Atmospheric Tomography (ATom) aircraft campaign. The low concentration and short lifetime of OH preclude the development of a representative measurement network to track its fluctuations in space and time. This dearth of constraints has led to discrepancies in the methane lifetime across models that project atmospheric composition and climate. Observational and modeling studies suggest that few processes control OH fluctuations in relatively clean air masses, and the short OH lifetime implies that it is at steady-state (total production is equal to loss). I leverage this chemistry by evaluating a convolution of OH drivers, OH production scaled by the lifetime of OH against its sink with carbon monoxide, as a potential “steady-state” proxy. I also assess the predictive skill of formaldehyde (HCHO), an intermediate product of the methane and OH reaction. I find that both proxies broadly reflect OH on sub-hemispheric scales (2 km altitude by 20° zonal bins) relative to existing, well-mixed proxies that capture, at best, hemispheric OH variability. HCHO is produced following methane loss by reaction with OH and reflects the insolation influence on OH, while the steady-state proxy demonstrates a stronger relationship with OH and offers insight into its sensitivity to a wider array of drivers. Few components—water vapor, nitric oxide, and the photolysis rate of ozone to singlet-d atomic oxygen—dominate steady-state proxy variance in most regions of the remote troposphere, with water vapor controlling the largest spatial extent. Current satellite instruments measure water vapor directly, and other retrievals like nitrogen dioxide columns or aerosol optical depth or could be used to infer nitric acid or the rate of ozone photolysis. Thus satellite observations may be used to derive a steady-state proxy product to infer OH variability and sensitivity in the near-term. HCHO is also retrieved from satellite instruments, and an OH product using satellite-observed HCHO columns is already in development. The relatively high fluctuation frequency of HCHO or the steady-state proxy advances our insight into the connection between OH and its drivers. The observed steady-state proxy demonstrates a widespread sensitivity to water vapor along the ATom flight tracks, and I conclude that an improved and consistent representation of the water vapor distribution is a necessary step in constraining the methane lifetime across global chemistry-climate models.