Development of Numerical Models to Advance the Understanding of Air Quality in Los Angeles

Citation

Pennington, Elyse Ann (2023) Development of Numerical Models to Advance the Understanding of Air Quality in Los Angeles. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/cvzw-kt61. https://resolver.caltech.edu/CaltechTHESIS:09292022-204343735

Abstract

Atmospheric pollutants such as particulate matter (PM) and ozone (O₃) are harmful to human health and intensify climate change. Secondary organic aerosol (SOA) is a main component of PM and is formed via atmospheric oxidation reactions of thousands of gas- and aerosol-phase precursors. Regional-scale chemical transport models predict the formation of these pollutants by representing natural and human emissions of hundreds of species and their subsequent chemical and physical processing in the atmosphere. These models are useful in the absence of detailed measurements and allow researchers to investigate the impact of changing emissions and weather. Los Angeles has unique meteorology and anthropogenic emissions which lead to dangerous pollution events and make this region an important area to study SOA, PM, and O₃ formation. As vehicles have become cleaner and their emissions have declined, other sources of emissions have become increasingly important. One important category of emissions is volatile chemical products (VCPs), which are consumer and industrial products that have high volatile organic compound (VOC) emissions that have not been well-constrained or studied in relation to their SOA and O₃ formation potential. In this dissertation, I use the Community Multiscale Air Quality (CMAQ) model to represent the air quality of the Los Angeles Basin. First, a new chemical mechanism is developed to represent the formation of SOA from VCPs, implemented in the CMAQ model to simulate 2010 California, and the impact of VCPs on atmospheric pollutants is quantified. Next, we created contemporary inputs to CMAQ by simulating the meteorology, emissions, and land surface of the Los Angeles Basin in 2020. Lastly, the new inputs and chemistry are applied to CMAQ to understand current air quality issues in Los Angeles. We quantify the impact of VCPs on SOA, PM, O₃, and other pollutants in both 2010 and 2020. The apportionment of other emission sources and the impact of the COVID-19 pandemic are investigated, and pollutant concentrations are compared to measurements made throughout the Basin and specifically in Pasadena. This works demonstrates the importance of intentional policies to mitigate harmful air pollution events. Limiting NOₓ emissions is not sufficient to limit the formation of ozone and PM, and there must be a simultaneous reduction of VOC emissions.

Thesis Files