UC Irvine

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.