As the second most populous urban area in the United States, the South Coast Air Basin (SoCAB) of California has long suffered threats from degraded air quality, which is harmful to human health. While regulation efforts have significantly improved air quality over the past six decades, the SoCAB remains in violation of both ozone (O3) and fine particulate matter (PM2.5) National Ambient Air Quality Standards. Moreover, the inequality of air pollutant exposure in disadvantaged communities has emerged as a prominent concern while there is a lack of robust community-scale air quality modeling for addressing the equality in prior studies. In this dissertation, the contribution of meteorological variability and anthropogenic emission changes to deteriorated O3 pollution are examined through state-wide CMAQ simulations (4×4 km). Further, a high-resolution (1×1 km) CMAQ model is developed to assess changes in air pollutant levels and exposure disparities for various racial/ethnic groups over the SoCAB between 2012 and 2018, aiming at revealing the effectiveness of regulation policies in reducing air pollution and improving environmental justice. A selected set of future deep decarbonization scenarios are adopted to examine local impacts of decarbonization on the SoCAB and disadvantaged communities, particularly for a community situated near the Ports of Long Beach. The results show that regulation efforts have achieved substantial decreases in nitrogen dioxide (NO2) and O3 concentrations over inland regions of SoCAB, while PM10, PM1, and ultrafine fine particles (UFPs) exhibited slight increases. Further analysis focused on exposure among different racial/ethnic groups pinpoints that, although absolute disparities of air pollution have fallen while relative disparities persist over time. The co-benefits of air quality and human health in future scenarios indicate that deep decarbonization could significantly diminish PM2.5 concentrations, subsequently leading to reduced mortality and considerable economic savings in 2035 and 2045. Nevertheless, the inequality of air pollution exposure remains a critical concern because most pollution-impacted communities still suffer from high levels of air pollution. This study underscores the urgent demand for targeted policies and programs designed to reduce air pollution exposure disparities within socially and economically disadvantaged groups towards improving environmental justice.

Initiatives to improve air quality in urban areas and to mitigate climate change through the reduction of greenhouse gas emissions have resulted in new mandates and legislation to implement zero emissions vehicles (ZEV). While several studies have focused on fueling infrastructure for light-duty fuel cell electric vehicles, there is a lack of knowledge regarding the nature of hydrogen supply chains for fuel cell electric buses. This thesis presents an analysis of hydrogen infrastructures to guide policymakers and transit agencies in the identification of preferable scenarios for the deployment of hydrogen fuel cell electric buses.

Based on research for light-duty vehicles conducted at the Advanced Power and Energy Program in the University of California, Irvine, two novel computer-based tools were developed to design and analyze environmentally sensitive hydrogen fueling infrastructure that addresses the wide range of requirements faced by transit agencies in the deployment of fuel cell buses. The first tool provides spatially-resolved allocation of hydrogen demand and identifies feedstocks for hydrogen production. The second tool provides a systematic evaluation of hydrogen supply chain scenarios through the analysis of well-to-wheel energy and water demand, and the emission of greenhouse gases and criteria pollutants. In addition, this evaluation includes a detailed analysis of the space requirements and operations modifications for the placement of hydrogen fueling infrastructure at transit agencies.

The tools were used to establish hydrogen fueling infrastructures scenarios at three levels of deployment: national, state and county. At the national level, the spatial allocation of hydrogen demand and potential environmental benefits of different hydrogen scenarios were developed for transit agencies in the U.S. At the state level, the hydrogen demand allocation and spatial rollout of possible feedstock sources were established for the state of California. At the local level, preferable hydrogen scenarios were developed for a large transit agency (the Orange County Transportation Authority) along with the quantification of emissions and resources and cost projections of hydrogen distribution pathways.

Residential water heating is the single most significant end-use for natural gas in California-- more than half of the net energy consumption for a typical Californian household goes into fulfilling hot water demands. Aided by cost-effective natural gas available in the state, about 90% of water heaters are natural gas-fueled storage tank systems, with 40-50-gallon capacity. In order to decarbonize residential spaces, a strong focus on water heating is essential.

This research focuses on the impact of renewable fuel (biogas and renewable hydrogen) injection into pipelines for gas-fired storage water heaters. Two representative models of storage water heaters were chosen for experiments. First, a conventional storage unit; meeting 40 ng/J NOx emission requirement, second, a low-NOx storage water heater meeting 10 ng/J NOx emission requirement. This research answers how much CO2/H2 content in natural gas can be tolerated without loss of critical performance parameters with reliable operation.

Characteristics like ignition delay, flashback, blow-off, ignition, flame structure, and emissions (NO2, N2O, NO, CO, CO2, UHC, and NH3) at different concentrations of CO2/H2 mixed with natural gas is investigated. The study found less than 10% H2 tolerance for both the water heaters, less than 15% CO2 tolerance for low-NOx water heater and no CO2 tolerance for the conventional storage model. NOx/NO emission reduction is achieved for both the water heaters with increased CO2/H2 and a simultaneous CO/UHC increase is observed. Further, both the water heater emission and stability performance were simulated using a chemical reactor network (CRN).