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In the field of air quality measurement, low-cost sensors have been extensively used for capturing high-resolution spatial and temporal pollutant concentrations. However, data accuracy and the impact of environmental conditions particularly temperature and relative humidity, remain a significant issue. Careful sensor calibrations against reference instruments are necessary for ensuring data accuracy and validity. This study investigated the effectiveness of multiple calibration methodologies (linear calibration, 3rd order polynomial calibration, and Random Forest, RF) for low-cost air quality sensor calibration across six cities (Atlanta, Portland, Riverside, Sacramento, New York City, and Phoenix) in the United States. The data for this study is collected from April 2019 to April 2020 in the corresponding cities. The study showed that the local calibration provides better accuracy than adopting calibration equation developed for other regions across all the models tested. The potential reasons could be that different cities may have different pollution source combinations, which may result in varying types and concentration levels of interfering gas. Different weather conditions will also contribute to such results, as parameters especially temperature and relative humidity are known to impact the performance of low-cost sensors. Additionally, if included CO signal in the calibration models of NO2 and O3, model performances are found to increases across all the cities. Low-cost CO sensor is known to general perform better and has better long-term stability than their NO2 and O3 sensor counterparts. Results of this thesis contribute to better understanding on low-cost air pollutant sensor deployment and calibration techniques.

Air pollution is one of the most substantial challenges of our era. It is a major contributor to climate change and a significant health hazard contributing to increased mortality or severe illness. Environmental catalysis is one of the most sustainable and effective solutions for reducing the emissions of undesirable pollutants in the atmosphere. Nonetheless, the effectiveness of pollutant removal greatly hinges upon the catalyst employed, necessitating the urgent development of exceptionally efficient catalysts. In comparison to the commonly employed precious metal catalysts, there has been a notable surge of interest in non-noble transition metal catalysts, such as copper and nickel-based catalysts. This interest is primarily due to their abundant availability, lower cost, and their considerable activities in environmental related reactions that are comparable to those of noble metal catalysts. However, there is still a pressing need to significantly enhance their low-temperature activity to meet application requirements. Increasing the metal dispersion to create more active sites and establishing a strong interaction between metals and supports are effective strategies to improve the catalytic performance of supported metal catalysts. However, achieving these improvements using simple and scalable preparation methods has posed a considerable challenge in the material science and environmental catalysis field. In this work, using hydroxyl-rich (OH-rich) CeO2 and ZrO2 as supports and a facile incipient wetness impregnation (IWI) method, we report the successful preparation of three sets of catalysts, including CuO/CeO2, CuO/ZrO2, and Ni/CeO2, with high metal dispersion and enhanced metal-support interactions. Our findings show that these catalysts prepared using OH-rich supports exhibited superior catalytic performance in environmental-related reactions, including CO oxidation, NO reduction by CO, selective catalytic oxidation of NH3 (NH3-SCO), and dry reforming of methane (DRM), respectively. Using various experimental techniques, including X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), N2 physisorption, X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS), the effect of hydroxyls on Ce(OH)x and Zr(OH)x supports on the physicochemical properties of the catalysts was characterized in detail. Additionally, the structure-activity relationship and reaction mechanism on these newly developed catalysts were revealed. This study showcases the utilization of OH-rich supports to improve metal dispersion and strengthen the metal-support interaction, thereby improving the catalytic performance of supported transition metal catalysts. This research suggests that utilizing OH-rich supports holds great promise as an approach to designing highly efficient catalysts for important environmental catalysis applications.

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